Let's see. All right, welcome, everyone, to today's Webmaster Central Office Hours Hangouts. My name is John Mueller. I'm a webmaster trends analyst here at Google in Switzerland. And part of what we do are these Office Hour Hangouts, where webmasters can jump in and ask us any question that's kind of on their mind with regards to websites and web search. Let's see. A bunch of things were already submitted, so we can go through some of those. But as always, you're welcome to get started here if you want to ask the first couple of questions. If not, that's also fine. OK, I'll just jump through the questions that came in already because there are a ton of them this time. I think everyone dropped their questions into this Hangout rather than the other ones last time, but that's fine too. Let's see. The viewport tag on responsive sites. So this is a fairly complicated question. It took me a couple of times to try to understand what exactly is going on. I think what it comes down to is this is a website that has separate mobile URLs. And at the same time, they're using the viewport meta tag on some of the pages. And they're wondering, does the viewport tag tell Google this is a mobile page and block the separate mobile URLs from being used? And the viewport tag is essentially something that we use to try to understand the mobile friendliness of a page. So it's a way of scaling things for the viewport, which is usually used on mobile devices, but it's not only for mobile devices. So just because you have a viewport meta tag doesn't mean that we will see this as the mobile version and we won't look for the other versions that are available. So in particular, if you have separate mobile URLs, what we recommend is, on the one hand, having the link between the two versions. So from the desktop version, you have a link rel alternate to the mobile version. From the mobile version, you have the link rel canonical back to the desktop version. That's one thing. And the other thing that I strongly recommend is setting up redirects so that when desktop users go to the mobile site, they get redirected to the desktop site. And when mobile users go to the desktop site, they get redirected to the mobile site. And with both of those mechanisms, you're really making it clear to us that this is the mobile version, this is the desktop version. And we can connect the two, so we can use them properly for indexing. But you're giving us a clear definition like what these versions are. And with that clear definition, it doesn't matter if you have a viewport meta tag or if the desktop version is also kind of usable on mobile or not. So that's kind of the direction I would get there. In general, though, we've stopped recommending using separate mobile URLs mostly because they just add a lot of complexity. And they make things like understanding which one is canonical, which one you should track and search console, which one you should focus on, make all of that a lot harder. And you add more complexity on your side as well with regards to keeping track of all those redirects, making sure that all of those links between those versions are correct, all of that. So if you can move to a single URL setup, which could be either responsive or dynamic serving, where you're serving a mobile version specifically for mobile users, if you do need to use separate mobile URLs, then the links and the redirects are the way to go. A client's Google My Business listing isn't showing up. I can't help with Google My Business issues. I don't really have any insight there, so I'd recommend going to their help forum. I work with a large health fitness publisher that took a huge hit after the March update, getting back our results slowly, is Google experimenting with health related search terms and preference they receive in rankings, with some of the health partnerships where curious also if more approved terminology is being evaluated or elevated. So I don't think we have any specific algorithms that look out for these kind of sites, but our general ranking algorithms do try to make sure that we treat sites in a way that we think is appropriate in search in terms of trying to understand the intent of the queries that people have and trying to show relevant search results that we can kind of trust. And some of the ideas behind that are visible in the quality radar guidelines that we publish regularly. There are various sites that go through these, because these guidelines are quite comprehensive in the meantime. So my recommendation there would be to look through these guidelines and to try to understand how Google tries to evaluate the quality, especially in four sites that kind of go into this health medical area. Then second part is a question with regards to Google News were being denied while competitors with less research content are being included. I also don't have any insight into Google News. I know they have made, I believe they've made the application process a little bit more strict. So that's something where I think it's kind of OK to have a high bar for something that's included in a new service like Google News. If you're unsure about why you're not being accepted there when you're applying, I would also make sure to post in the Google News Publisher Help Forum. There are lots of folks there who have experience with these kinds of issues and who can help you to figure out what you could do to improve there. How to correctly implement pagination on an e-commerce site? The links inside each page will be found and indexed. So that's kind of a short question on a really big topic. So it's kind of hard for me to package that into a really short answer. We do have some guidelines on how to deal with pagination. I think in our Help Center, as well as a blog post that we did a couple years back, I'm currently trying to look into creating some more specific guidelines for e-commerce sites just to make it a little bit easier for them to implement things like pagination and filtering, category pages, all of that. A customer is closing their business site, but it has a lot of useful articles. Is it safe to use the content on a different domain name? Yes, of course. If this is content that you're allowed to publish and it's otherwise not published anymore, then I think that's a good way to make this kind of content available. Our website has a growing commerce strategy. And some members of our team believe affiliate links are detrimental to our website ranking for other terms. Do we need to no follow all affiliate links? If we don't, we'll just hurt our organic traffic. So this is something that I think comes up every now and then. From our point of view, affiliate links are links that are placed with a commercial background there in that you're obviously trying to earn some money by having these affiliate links and pointing to a distributor that you trust and where you have some arrangement with them. From our point of view, that's perfectly fine. That's a way of monetizing your website. You're welcome to do that. We do expect that these kind of links are marked appropriately so that we understand that these are affiliate links. One way to do that is just to use a no follow. A newer way to do that to let us know about this kind of situation is to use the sponsored rel link attribute. That link attribute specifically tells us that this is something that has to do with an advertising relationship. We treat that essentially the same as a no follow. A lot of the affiliate links out there follow really clear patterns, and we can recognize those. So we try to take care of those on our side when we can. But to be safe, usually we recommend just using a no follow or the rel sponsored link attribute, I guess. But in general, this isn't something that would really harm your website if you don't do it. It's something that makes it a little bit clearer for us what these links are for. And if we see, for example, that a website is engaging in large scale link selling, then that's something where we might take manual action. But for the most part, if our algorithms just recognize that these are links that we don't want to count, then we just won't count them. Add a new site map slowly or all at once. I have a directory that generates 30 million URLs. And I was advised to submit 10 site maps every five to seven days to show these in the search console. That means 600 site maps to submit. So I guess, first of all, from a more general point of view, if you have a website that generates 30 million URLs, I'd be kind of cautious about the overall quality that you're creating there. So it's obviously possible for a website to come up and say, well, I have 30 million new URLs and they're all fantastic. I digitize the archive of my city. And it's like a lot of content. And I want to put it all online. And that might be perfectly fine. But on the other hand, we often also see sites that generate 30 million URLs based on a database or where they enumerate all phone numbers that are available worldwide. And they start putting up pages for each phone number individually. And that's the kind of thing where it's easy to generate a ton of pages, but you're not generating a ton of quality. And that's something when our algorithms look at it, they'll be like, well, we don't really know what to do with this website. We spent a lot of time trying to crawl all of this, but there's no really fantastic content here. Why are we spending so much time on this site? Well, we could be spending time on sites that do provide really good content. So instead of worrying about whether or not the site maps is the problem, I would primarily worry about the quality of your content overall. And if you're sure that the quality of your content is really high, if this is really fantastic content that we've been missing, then just submit it all directly. It's like, let us know as quickly as possible so that we can crawl and index all of this content as quickly as possible. And if you're unsure about the quality of the content, then maybe double check the quality of the content first and not worry so much about how you can sneak this through with site map files. I have one question. I just want to know if it's the right practice to add two authors to one content piece. Sometimes an article requires technical expertise about a subject. And the main writer is, I guess, there are two people behind the article. Sure, I don't see any problem with that. I mean, we don't have any authorship markup. So how you put information about who wrote your content on your pages is totally up to you. Some people put the names directly. Some people just have it as a part of their normal website. Ultimately, that's totally up to you. Just a little bit of background noise somewhere. Let me see. The new snippet tags that Google has recently added is mandatory for every website to implement these. If I add max snippet number 350 to 400 characters, is Google going to show that? Is it required to news and media sites where their story appears in the latest post section in mobile? So no, it's definitely not required for every site to use these new meta tags, robots meta tags that we have available. It's totally up to you. So what you can do with these new meta tags is on the one hand saying, this is the number of characters I want you to show at most as a snippet for my website. If you don't care, then just don't specify that. If you do care, then you can specify that. You can specify the size of an image preview, which is something that may make sense if you have images on your pages that you want to have shown in a large way. Or it may make sense if you don't want to have these images shown as a preview for your web pages. So in particular, there are four AMP pages because the AMP article markup includes a large image by default. For AMP pages, we would default to large image for you. And for normal HTML pages, we would default to the standard image preview. I think it's called standard or default or something like that. And then there's something similar for video where you can also specify the number of seconds that you would like to have a video preview shown. For most websites, these defaults are the same as before. For European press publishers, when their content is shown in France, the default is slightly different. So I would double check the recent blog post we did on that topic to see what the exact defaults are for European press publishers when the sites are shown in France. For all other websites, for other locations, for non-press publications, you can use them however you want. The defaults are essentially the same as they've been before. One thing I would shy away from is just going in there and saying, well, I will specify 5 million characters as a maximum snippet and always large and the maximum of everything. I don't think you'd get any value out of that. And I think it just makes things confusing for you because afterwards you're like, why do I specify 5 million? What was I thinking of specifically there? It doesn't really make that much sense. So that's kind of something where I'd say unless you have a reason for wanting a change in the way that your pages are shown in the search results as a preview, then I would just leave the defaults there. What's the correct way to add schema markup to a website? For example, an article schema that also includes breadcrumbs or a web page that also includes is part of a website and so on complex schemas. If incorrect, does every schema have to be separate? Also, if the schema is being found by schema tester and rich snippet scanner by URL, does it mean that crawlers can find a two? Or is there any other technical aspect to consider to make them easier to read for crawlers? Wow, that's a lot of questions. Let's see. So in general, we recommend using JSON-LD to add structured data to pages. There are different ways that you can do it. It seems like JSON-LD is the one that's easiest to implement because it doesn't rely on the actual HTML elements within your page's content. So you don't have to wrap it around the right pieces of text. You can just include that snippet of markup anywhere on the page, and that can be picked up. And if it can be picked up by the usual testing tools, then it can be picked up by search as well. If you're doing something fancy like injecting that structured data with other JavaScript, for example, if you're using the Google Tank Manager to inject the structured data, then you might need to watch out how you test that to make sure that you're actually testing the JavaScript side, not just the static HTML version of the page. If you have multiple kind of complex pieces of schema, then there are multiple ways that you can implement that. On the one hand, you can include them separately. On the other hand, you can embed that, how's it called, like one within the other, depending on the type of structured data that it is. That's something that's essentially up to you. We should be able to pick that up either way, provided, of course, the testing tools show that information. The two other things, I guess, to watch out for using structured data in a way that matches our guidelines doesn't guarantee that we will show it as rich results in the search results. So it might, on the one hand, take some time. It might be something where algorithms say, well, we don't know if we can actually show this in search. That's one thing. And the other thing is that there's a lot of schema types out there that are not used at all by our systems. So that's something where you wouldn't see any visible effect of applying that kind of structured data. So I believe, for example, there are some types for different types of cheese, for example. And we don't have a cheese feature in search, which is kind of sad, I guess. But it's something where you can specify these things on your pages. And search engines can look at that. They can understand that this markup is here. But they don't necessarily do anything visible with that. And from our point of view, that means you're providing information. It's nice that you're providing this information. But we don't actually do anything without information. So if you're kind of time limited or resource limited and can't do everything on your website, then I would concentrate my efforts on using structured data for the elements that are actually visible in search, or that you have some other kind of direct return from. So if there's something specific that you won't have shown, like you have events on your page and you also have a lot of cheese on your page, then mark up the events so that you can be shown in the events feature in search. And if you have extra time or you feel like it's fun, then marking up the cheese elements is also fine. But that's not something where you would see any direct effect from. Our company is changing our website from CMS to a custom solution. And this change will include design, some content, and some architecture. What are some tips that you can give us to do this while losing as little traffic as possible? So kind of in general, if you make really big changes across your website, then you should expect some changes in search. Sometimes those are positive changes. Sometimes those are negative changes. So that's something where if you significantly improve your website, if you improve your site's architecture, if you improve the way that search engines can pull out information from your pages, then that's all fantastic. That's a big change on your website. And that's something that likely you'll see some positive effects from. On the other hand, if you change your website's architecture, and it's essentially all the same, but it's all set up in a different way, then probably it'll take a bit of time for us to understand the new setup and to understand that, oh, this is actually the same. And you'll see most likely kind of a significant drop in visibility over the time where we're confused. We're like, how do these pages belong together? How do they connect together? And over time, that will settle down again. So I guess with regards to tips how to avoid any kind of fluctuations over this time, I would start with the assumption that you will see fluctuations and that they will be in place for a couple of months, even if you improve things overall afterwards. I think going with that assumption prevents you from kind of being, I don't know, surprised by these fluctuations. Because it's very common that if you make significant changes across your website, if you change the URL structure, if you change the design, the internal linking, then you will see changes in search over the time where it takes search engines to kind of get reconnected with your website and to understand how these pages all belong together. So going with that assumption, it might help you to figure out when would be a good time to make this kind of change. That might be a period where you're saying, well, traditionally, people don't search for my business during this time of the year. So I'll make this change during that time of the year so that the practical effect on my site is minimal. You could also go the other way around and say, well, during this time of the year, we're doing lots of TV advertising or lots of offline advertising anyway. So we don't really need to have the direct traffic from search during that time because we're compensating with all of this other sources of traffic, which might be another approach. That's kind of one thing to watch out for. The other is we generally try to recommend doing these changes incrementally so that you make one change and then you move to the next so that you're able to determine if something in between goes wrong, what that change was, and to make changes and fix that before you go to the next step. Sometimes that's possible. Sometimes that's not easily possible. So that's something where it depends a little bit on your site, on the kind of changes that you're making if you're moving to another domain and changing site architecture or if you're changing your design and changing all of the internal URLs. Sometimes it's possible to decouple those. Sometimes that's not so easily possible. If you can decouple those, I think that generally makes sense because, like I said, it's easier to recognize where problems come from and to fix them before you move on. But if you can't decouple those, then my main recommendation there would be to really make it absolutely clear a map of the starting state and the final state that you're aiming for so that you can monitor everything that's happening over that period of time so that you can check for things like redirects and make sure that all of the content is correct by crawling your website and checking it like that. It's a lot harder to try to figure that out afterwards. So if you're coming afterwards and you're seeing, well, I lost a lot of traffic, but I don't know why. And you don't know what the old URLs exactly were, then you're kind of digging for information at a time when everything is falling apart. Anyway, I hope this move goes well and that it doesn't all fall apart. Let's see. Next question we have here. I know Google ignores relnext in previous annotation. And the best practice, if you have two more pages, was to canonicalize each page like this. So you have link rel canonical to page equals 2, for example. I worry if Google can't recognize the relevance between page equals 1 and page equals 2. The pages are thought to be duplicate to each other and the value is not unified. So we do recognize URL parameters and we can crawl URLs with URL parameters and index them like that. So in general, that's not something you'd need to worry about that we wouldn't be able to recognize URL parameters. However, there's a URL handling tool in Search Console where you can specify which URL parameters we should ignore. And if you're seeing that we can't pick up your page equals 2 annotations or URLs, then I would double check there to make sure that you're not accidentally marking these as URL parameters that we should ignore. Then a question about short-lived pages, like product pages that are sold out within a few days. Is it better to let Googlebot crawl these and index them or to add product markup or what should we do? It's totally up to you. If you know ahead of time that something will be short-lived, you can make the decision to say, well, I'll just no index it from the start so that Googlebot doesn't have to spend a lot of time on it. There's also the unavailable after-robots meta tag where you can explicitly tell us that the content on this page is only valid for a certain period of time. And we can drop it after that date. So with products that you just have a limited amount from, you probably don't know the date when it's finished. But if it's an auction or if it's some kind of a classified ad that is only available for a couple of weeks or a week or so, then you can use that robots meta tag to tell us about that. So that might be an idea. With regards to product markup, in general, if it's an e-commerce site and you have products on there, I would use product markup. I think that's a good match. I think that's independent of whether or not this is a page that will be longer term on your site or more short-lived. I found some directory links from a previous SEO pointing to my client's website, but they use branded anchor text or URL. Is it safe to assume that these aren't, whoops, now I clicked the wrong button, is it safe to assume that these aren't hurting my website as you would discount the bad anchor text rather than demoting? Probably. So if these are just random links that you found to your website and you feel they're kind of irrelevant, then it's possible that we're ignoring them. In general, if you find a bigger section of links going to your website where when you look at them, you're like, well, someone might assume that if they're looking at this manually that these are paid links or that there's some kind of a link scheme happening behind these links, then that might be something where you could go to the disavow tool and say, well, I want to make sure that you don't take these into account. On the other hand, if you just find random links to your website and some of them are a bit spammy and some of them a little bit low quality, I wouldn't lose any sleep over that. That's something that happens to all websites across the web and we ignore a lot of those kind of crazy links that just happen everywhere. Google did a core update this June, July, and many websites that got hit. My website, too, can you please tell us some details regarding this core update and what we should do to get our traffic back? So we did a blog post on core updates maybe, I think, like two or three months ago. I would definitely check that out. It's a pretty long blog post. There's a lot of information there. So a little bit of the thoughts behind these bigger algorithm changes that we make. So I would kind of check that out. And with regards to getting our rankings back, sometimes it's not a matter of getting rankings back, essentially by fixing a bug or something on your website. Essentially, these core ranking algorithm changes are kind of different ways that we look at the relevance for search results. So that's not something where we would say, a website has done something wrong and therefore if they fix that issue, then they will be ranking normally again. Essentially, we're saying, well, we think relevance should be determined slightly differently for these kinds of queries. And that means we would show a slightly different websites. So instead of thinking about it as something that you've been doing wrong, think about it more of like, how can I make sure that my website is seen as something that is relevant for these queries when you look at it based on these criteria that Google was looking at here. In a sector, I work a large amount of sites participate in the nefarious link schemes to manipulate page rank. These sites often rank extremely well for high value terms because of this. As recommended by Google and standard SEO practices, I have reported these activities, how often and how seriously does Google treat these reports? Yeah, there are definitely some areas where we see more issues with regards to links or with regards to other kinds of activities that go against our webmaster guidelines. That's definitely the case. However, I wouldn't necessarily assume that these sites are ranking because of those activities. Sometimes what we see is that sites rank fairly well just in general. And it's something that they're almost ranking despite doing a lot of these crazy things. So that's one thing to keep in mind. What generally doesn't happen is that when we recognize that a site is, for example, participating in link schemes, that we would remove the whole site from search because often they're doing other things which are fairly well. And on a balance, that's something where maybe we should still show them in search based on the other things that they're doing really well. So it's not that we would remove them completely from search just because they're doing one thing wrong. One of the big reasons why I think that's important is that a lot of sites do things badly accidentally. They don't know that this is something that they shouldn't be doing. They heard about it, I don't know, in some SEO blog or from some SEO consultant that's working with them or that used to work with them. And they did all of this crazy stuff. And they didn't realize that this was actually something that they shouldn't be doing. This is something I see a lot when it comes to smaller businesses in particular. They don't have time to invest to understand all of the details of SEO and all of the details of what you should and shouldn't be doing. They worry about their business primarily. So they'll do weird things like in the past, they would do a lot of hidden texts or kind of stuff things into the footer of their pages because they heard that that works. And our algorithms, when they run across these kinds of issues, one of the things we try to do is to ignore this kind of activity and say, well, we don't know for sure that they did this on purpose. So we'll try to ignore it and we'll try to evaluate the site based on the other factors that we have there. So that might be playing a role there. I know there are probably some niches where people are doing everything to push the boundaries. So that might be something where, in particular, where you're active, maybe that's slightly different. If you do find situations where there are really larger schemes, larger level schemes at play, where you think that maybe the web spam report isn't a good way to specify that, you can also send that to me directly. And I'll take a look at that with the web spam team to make sure that we're really covering that properly. In general, they do look at the web spam reports and they do try to take appropriate action where they think that's necessary. So kind of going back to the starting point, if we recognize or if the web spam team recognizes that our algorithms are already ignoring these, then maybe there's nothing extra that they need to do. On the other hand, if they recognize that our algorithms are picking these up in a way that they shouldn't be picking it up, then maybe they will take manual action to make sure that those kind of links are neutralized. We have a page which downloads certain content with JavaScript calls to the server on page load. If the Ajax requests that we do are blocked by RobotSex, will Googlebot be able to see this content on the second wave of indexing? No. We need to be able to access the JavaScript files and the server endpoints that you're using for these kind of Ajax requests if there's content that you're pulling in that way that you won't have indexed. So we kind of need to be able to access those things if that's something that you want to have indexed. When keeping URL simple, is it OK to have a URL to be longer with the top level page, for example, slash services category slash service type name, or should it be kept short with just slash service type name? That's totally up to you. You can have longer URLs or shorter URLs. You can have multiple folders or slashes in between those URLs. That's totally up to you. It's not something that you need to artificially shorten or artificially make longer. The limit that we have, I think, is something like 2,000 characters. So that's something that pretty much no site runs into accidentally when they're just creating URLs manually. Then, let's see, there's a fairly long question about a specific medical site and also with regards to the algorithm updates that we had there. So I haven't been able to take a look at the site specifically, but I would really take a look at the blog post that we did on the core algorithm updates a while back and look at the kind of things that we try to keep in mind when it comes to medical sites or when it comes to sites in general. Also, the quality radar guidelines are a good thing to go through specifically with regards to medical sites to kind of understand a little bit better what we're looking at or what we recommend our quality raiders look at. So just to clarify, the quality raiders don't make the rankings. They help us to improve our algorithm so. Two niche questions about country restricted websites due to legal purposes. When using tools like page feed insights or structured data testing tool, both seem to be coming from external country IPs and are restricted from accessing the site. Is there a list of IP addresses that we could whitelist? I'm not aware of any list of IP addresses specifically for those tools. So with Googlebot, you can confirm the IP address using the reverse DNS lookup. But specifically for those tools, I don't think they would use the same Googlebot IP addresses. So that's kind of tricky. Now, how could you test those? I guess one way to test that is to create separate test pages that are accessible and to see what IP addresses those requests are coming from. There are hreflang tags that redirect each user to the appropriate TLD website based on their country to avoid restrictions. There's also a single page.com website. The website is the X default hreflang of all websites, but only in their home page. Is this the right way, or should this be X default for all pages? I would try it out. I think it'll be kind of tricky in general when you're restricting access on a per country basis. On the one hand, for Googlebot, it might be tricky because if you're blocking users from the US, then that would include blocking Googlebot. So it would limit the number of pages or the exact pages that we could actually look at there. But I would try this out. I think, in general, having the hreflang across different country versions, different TLDs, that's a perfectly fine accepted approach. Having the hreflang only on the home page is also perfectly fine, acceptable. Using the X default to have a default page that is valid for all users that are not within the countries that you're specifically showing individual pages for is also acceptable. We're a news website, and we use News XML sitemap for discoverability and indexing. But as a news organization, we have to update our stories with more facts and information as the story develops. And I think it kind of goes in a direction of how do we make sure that these updates are also processed as quickly as possible. So I'm not aware of anything specific that you could do to make it so that we pick up these updates faster. Essentially, using a second file with the last modification date, that's a great way to do it. Using a RSS atom feed with the last modification date is really useful. Both the News sitemap and the atom feed are useful because they're just focused on the new URLs for your website, or the new and changed URLs on your website. We don't have anything like an indexing API where you can push changes to us. Why does the website's rankings bounce back? I don't know. It really kind of depends on the website. So there are different things that can play a role there. On the one hand, our ranking algorithms can change. So it's something where it's possible that our algorithms will say that one site, we don't really trust that much or we don't know if we can trust it that much. It will be a little bit more critical. And the next time around when our algorithms look at it again, they might say, well, actually it's a good site. We should trust it a lot more and show it more in search. And then you might see some fluctuations like that. On the other hand, it might be that within your website, things change. And that could be a sign for us that, oh, there's something different here. We should perhaps reconsider how we were showing it in search. And of course, there are the situations where something changes in the rest of the web, where suddenly we look at other websites and say, well, actually they weren't as great as we originally thought. We'll show them a bit lower. And then suddenly those that were below those start showing up a little bit higher. And all of these things are essentially a normal part of search. We're constantly working on our algorithms to try to improve them. We constantly work to try to understand websites better. And because of that, you will almost certainly see fluctuations across different things in search. Is there any means to request Google crawling from another country other than the US? No. We primarily crawl from the US. There are very few exceptions. And for those exceptions, it's a very small number of countries. And it's something that would be essentially limited to websites in those countries. So for the most part, we do crawl websites from the US. Please remove YouTube from Google search. Let each of us compete with each other. And let websites compete with websites. It's not fair when I write a 4,000-word article covering every aspect of a topic and then get overranked by a 500-word article just because this website has more authority. So I think, first of all, I'm quite happy with having different kinds of search results in Google search. And that includes sites like YouTube. That includes other video sites. That includes image sites. All of these things bring diversity into the search results. They bring a diverse set of view-pouring points to users in search. And there are different ways of finding relevant content. So some people like to find content on video. Some people like to find content in text forms. Some people don't know what they're looking for for a specific query. And then they get surprised by one or the other. I think all of that is essentially fine. The other thing is, with regards to the number of words in your article, the number of words on a page are not a factor that we would use for ranking. So just because you have 4,000 words and someone has 500 words doesn't mean that your page is automatically more relevant than another page. So instead of kind of focusing on word count, I would really try to focus on the quality of the content that you're providing and the consistent quality. So if you're working on a website and you're creating one article after another, make sure that you're really hitting the bar that you want to reach. And maybe instead of writing one extra article, think about ways that you can make sure that anything that you create on your website is of the highest quality possible and is, in a way, something that clearly should be ranking number one by far for the things that you're targeting. So not just like, am I kind of doing the same thing as other people, but really making sure that when someone objectively looks at these search results, they say, well, this article is fantastic. And it should clearly rank above all of the other ones. And that's kind of the level that you should be aiming for. And at that point, that sometimes also means like maybe you should be including video content. Maybe you should be including more images. Maybe sometimes articles need fewer words. Sometimes they need more words. That's something where just purely the word count alone is not really the measure that you should be aiming for. I have a website in Angular where previously I had URLs getting indexed through the escape fragment version of the page. However, due to some technical issues, escape fragment version was removed. And now the same page is not getting indexed, though I tried submitting the same using search console. What's an alternative to getting my page indexed? So there are a few things going on in this question. And I think instead of trying to answer all of the different things here, I would double check kind of the technical setup that you have there to make sure that things can actually get indexed. So you can use things like the inspect URL tool to double check. Make sure that you have actual URLs on the page and not just hash fragments that you're trying to index. And most of all, especially for JavaScript sites, I would recommend taking a look at our documentation. We have fairly extensive documentation on JavaScript sites now. We have a set of videos on YouTube for JavaScript sites. So I would kind of make sure that you have all of the technical basics set up there properly. It's easy to say, well, it kind of worked in the past or if I just wanted to work again. But especially with JavaScript sites, you need to make sure that you're doing things properly so that we can actually render and index the content there accordingly. And if you are doing things properly, then that's something where these sites can show up in search normally, too. Wow, OK. Running out of voice almost. What kind of questions are on your minds? What am I missing? Oh, wow. Lots of stuff happening in the chat. Long questions, at least. We're facing an issue for one of our clients where two similar pages were made live and submitted for indexing at the same time. One got crawled and indexed, and now is ranking well. The other is still unindexed, so no matter what we tried. We checked robot sex, metarobots, no issues submitted in sitemaps, submitted feedback in Search Console, but in vain. Can you help to understand what might be the issue? So I would double check in the Inspect URL tool to see what the status is there. Oftentimes, it'll tell you what is happening, why a page is not being indexed. So that's something where maybe you can find more information there. It's kind of hard to say without looking at the URLs what exactly is going on there. If you have a bit of time afterwards, we can take a quick look. I have a bit more time. Afterwards, I'll pause the recording at some point, but we can double check that afterwards if you want. Any other questions from any of you in the meantime? No more questions. OK. Actually, I do have a question. OK. So some of the backlinks to our website are not showing up in the Search Console, in the links section. And I wanted to know if that means that they're not passing any signals if they don't show up in that list. And they're from big, authoritative sites. Yeah. We try to show a relevant sample in Search Console, but we don't show all of the links that we have there. So if these are normal links that you know exist to your website, then I would assume that we can pick those up. Similarly, what's also sometimes confusing is if a link has a nofollow or is in a disavow file, we'll still show that in Search Console if we think it's like one of these sample links that we should show. OK. Now, do links expire after a while? I mean, the signals that they're passing? No, no. They don't expire. What does happen, though, is that especially if you're talking about a large website that's growing regularly, then the pages that links are on, over time they get even deeper and deeper within this website. So for example, if you have a link from CNN and it's in an article that's linked on the home page, then that's something that's really important for us. On the other hand, if this article is maybe a year or two later is somewhere in the archive at CNN, then that article itself is not something that we will find that important anymore. So it's not that the link expires after a certain period of time, but just often that the page where that link is on that becomes less and less relevant over time. If it's on a site that is growing fairly regularly. OK, but given that the page doesn't change or if it's on an important page in a website, then it shouldn't have any different effects over time. Exactly, yeah. OK, and I have another quick question. So we've been getting some new backlinks recently and we have seen our ranking increase in search in the console. But we haven't seen any difference in actual SERP. And there hasn't been any change in, we haven't seen any increase in traffic to their website. So we were wondering why is that happening? That's hard to say offhand. But in general, one thing to keep in mind is that the ranking that we show in Search Console is on the one hand based on what was actually shown to users. And on the other hand, it's essentially based on that search results page that we would show to users. And sometimes what you'll see is that a site goes maybe from number 10 to number 8 or something like that. And that might be something that's a little bit more visible to users in Search, but it's still not something where you would immediately get a lot more traffic from. But yeah, sorry. And the other thing is that sometimes the title and the snippet that we show in the search results doesn't match what the user is exactly looking for. So it might be ranking higher for certain queries, but if users are looking for something different for those queries, then it wouldn't necessarily mean that you'd see more traffic. I see. OK, thank you. Sure. Thank you. Hi. Hi. Question here about Search Console. So really, would like to understand a bit more about your take on Google Fakes in general. Because you know, whilst using the search analytics, more often than not, by filtering for queries, pages, or whatever, right? If I say, I want to include the terms x, y, z, and then I get some kind of numbers, then if I say, OK, give me all the numbers without the terms A, B, Z, or whatever it was in the previous example, the numbers never match. So I totally appreciate that you say, OK, we do normalize data. We do certain times exclude the x because of whatever reason, privacy, blah, blah, blah. But my question in reality is, OK, if you do that kind of discrepancy, and I can see discrepancy up to 60%, 70% of the numbers, how would you expect us working into the industry taking the tool seriously for measurement? Because we can't really rely on such a data if you skew too much. I can understand that for privacy, you can say, OK, well, let's take out 2%, 3%, 5%, because a certain condition for ourself doesn't really make sense for you to be seen. Fair enough, 5%, 6% is OK. 70% or 60%, 70%, it's a bit too much. I guess it all depends on the kind of site and the kind of queries and the level of queries that you're looking at there. So that's something for some sites, depending on what you're searching for, you might see bigger changes if you start doing things like including and excluding things. For other sites, you'll see smaller changes. So what I would recommend doing there, instead of using the filters to kind of try to tweak things like this is just to export the list and work with the list of queries or the list of URLs and the clicks, impressions, and position that you have there and work with those directly. So doing something in a spreadsheet or database, pulling them out with the API, for example, and focusing on the data there. That's something that makes it a little bit more deterministic what you're working with, because then you know what the default set is. Well, yeah, OK, yeah. It makes sense just using the raw data at that point in time, which is something that I have been doing in any case. I was just a bit more concerned about the general average of users or even when it comes to some stakeholders that they just don't really have time, patience to wait for you to elaborate the data with the database or whatever the tools you may think about. And they just jump straight on. The Google Search Console says, OK, let's have a look on how we've been playing balls over here. And the numbers didn't really play well. So then you have double challenge. Not only finishing the job as in data structure and computation, but also demonstrating to them that the Google Search Console is actually wrong. Because it's such a kind of level of discrepancy who's going to be then on the right side. You elaborating on the API or Google telling the truth. You know what I mean? But I guess it all depends on the site and what you're looking at there. Well, it's not on the side. Try to put in, say, whatever I have, boss shoes, right? You are the employee. I am the boss. And I'm jumping on the Google Search Console this morning. I say, OK, give me query x minus x, traffic six. And you employee, you have been telling me for, say, a week or a month that you've been playing against the optimization of a certain page or a certain set of pages to optimize them, right? Great. And you have told me, oh, boss, I've done such a magnificent job over here. And I got so great results. And then I'm jumping on the Search Console. And it says, oh, don't worry, it says that you just brought me, I don't know, 10K traffic, right? You respect the websites. And I don't know if that's really reasonable comparison. Because on the one hand, if you're doing all of these kind of crazy comparisons with plus and minus, then that's a fairly advanced usage. On the other hand, if you're looking at changes, then those trends would be visible regardless. So that's something where it's like, sure, the absolute number might be different if you're doing this kind of complex query. But if you're looking at it over time, that's something where I totally expect to see reasonable results there. And I don't see this changing at any point in the future. So it's not like we wouldn't be able to show the queries that we're filtering out for privacy reasons. That's not going to happen. All right. Well, thank you. Sure. All right. Let's take a break here. I'll pause the recording. And if any of you want to stick around, and I think that one URL, I'm happy to take a look at that, too. And otherwise, I wish you all a great weekend and hope to see you all again in one of the future Hangouts. Bye, everyone.


Hi, I'm Sandy Allnog, and today I am painting a full crocus garden on a long skinny card. The stamp sets I'm using are both from Pretty Pink Posh. One is crocus flowers, has lots of different variations on a crocus, and Courage, which has some simple sentiments. And I'm going to use the Inspiration set from Daniel Smith. This is one of the little sets that I've talked about recently. There is a video about them all, but it has these purples in it. It's got a little bit of yellow and a little opera pink. So I'm going to use some of these colors to paint the the crocuses. I'm keeping it off screen there, but I've listed the colors up above. And when I paint really loose flowers like this, and I encourage that you try it, a lot of us try to color in all the things.  So I'm just kind of slapping some colors into different flowers. Notice one thing that light purple that I just painted on that very top flower, that one has some opacity to it. So I'm going to have to be careful with that color because it's not fully transparent like all the others are. But I'm kind of playing around with what happens if I throw some opera pink into some of these other colors and what do they do? What do those colors do when they mix? And then spray it with water. Holy cow. Sandy's crazy. She's gone nuts. And I noticed I like that orangey color off in the right hand side that's mixed with the Indian yellow and the rose of ultramarine. Kind of a neat color. It makes this really interesting brownish purple color. Going to have to figure out how to use that on something in the future on purpose. But this kind of an exercise while making a really beautiful background for my flowers is also teaching me things. I'm noticing how the colors react to each other when they're next to each other. Do they blend right into each other or do they push away from each other? There's a lot of different things, different pigments will do, and you can't guarantee what's going to happen until you try it. You can have somebody tell you that nickel azo is amazing, which is not in this video by the way, but until you actually use it and see it right in front of you, it's not really going to teach you so that you know internally what color to pick. So I'm just taking an almost dry baby wipe to wipe off some of the color and then I let it dry because I wanted that background to be super soft. And that allows me to have all this space now to paint just a couple of petals here and there. I'm not painting them all. I'm not painting them consistently. Some of the flowers are going to be orangey yellowy pink. Some of them are going to have more of the darker purple, some will have more of the lighter, and it really depends on which flower you feel like focusing on. The one that I've just removed color from had a little bit too much of that wisteria. The wisteria is the one that has a little too much of that opacity for me. I'll use that deliberately sometimes to make a highlight on something maybe in a dark color because it has opacity but here it's just going to cover up my stamp lines. So I just want it in there very light and if I use it with a lot of water and just let it mix in a little bit with some other colors then it's not going to be a problem that it's partially opaque. So I'm just kind of throwing some colors in here and there and playing around with my brush. This is a great time to learn your brush strokes and mess around with them. See look at me I used my finger on something because I have this loose soft background. If I mess up and my brush goes outside the lines it doesn't matter because I've got this beautiful loose background anyway. It's very forgiving this kind of painting and just helps to loosen you up.  So even if you practice this way and then go to your tight painting afterwards sometimes I find just letting it out helps me just feel more relaxed in my next painting session. So sometimes I'll start off with something like this and then go do something else entirely different. Back when I still used brush oh which I don't haven't really used a whole lot lately but when I did that was one of my favorite things to do until now I've kind of learned how to do that same thing but with regular watercolors and just kind of letting the watercolor do what the watercolor feels like doing. I did do this card in a long skinny format because I wanted something to use all the flowers on. I just wanted to paint all the flowers because you know that's what we like to do. We like to paint them all. So using a format that's going to fit in a business envelope instead is going to allow me to have more of a crocus garden. I've loaded up my brush with a couple of the colors that are in here and dabbed some of them off so that they wouldn't be super bright and strong but they would be just little splatters of color here and there just add a little bit more interest. So there is my finished card. I hope you enjoyed this video. If you did click the like button etc and make sure you go see the blog hop because Pretty Pink Posh is celebrating this new release. They're having a big old blog hop and you want to see what everybody else has been creating as well. I will see you guys again another time. Have a lovely lovely day. Go create something beautiful yourself. Bye bye.


All right in this lecture 4 we will talk about measurement of spreading cohesion through the sessile drop method which is used for negative spreading cohesion and then we will think about the measurement of positive spreading cohesion. One will have to think of a clever way of doing a measurement in case the spreading cohesion is positive and the background for that is already known to you, but before we do that we will have a quick recap of the weighting balance method of finding the work of addition and spreading cohesion. This method proposed by Guastalla is known as weighting balance method using willyme plate where we obtain the work of addition or the work of weighting without measuring the contact angle directly and as expected this would correspond to the work of addition related to a monolayer of water or surfactant on the solid in adsorb form. A thin slide of perimeter 1 centimeter is used it is immersed in the liquid and then raised to the surface till the external vertical pull f becomes constant. After buoyancy correction that force should be equal to gamma L a cos theta. Work done is now of withdrawing the slide and that is further equal to work of devating the slide. If the slide is hydrophobic then cos theta is negative and the work is gained when the slide is withdrawn. If the plate is immersed then work will have to be done. I tried to explain this through a mnemonic analog of a plastic ball being dipped in water if it were to contain a hole. In the process of immersing this ball in water you will have to overcome the buoyancy force if the ball contains a tiny hole through which water can enter the ball then it will help in immersing this solid object inside water. In the real practice that corresponds to filling of crevices in the surface by water and also involves the work of leaving a thin film of water on top of solid. As we had seen earlier in systems of this kind hysteresis will be observed because the advancing and receding contact angles would not be same and we tried to assign significance to the area of hysteresis loop that would correspond to the work lost in removing adsorbed gas from the surface cracks. Sometimes that involves also the work of leaving this thin film in the cracks or scratches after withdrawal of the slide. So, to get a feel for numbers if we take a paraffin wax slide of perimeter 1 centimeter F would be obtained as about minus 24 dynes and that means gamma LA cos theta when equated to minus 24 dynes per centimeter gives a contact angle of 110 degrees nearly equal to the measured value. Should you have a surfactant like meristille tri-methyl ammonium bromide dissolved in water then this wax solid surface can be made weightable. This will immediately give you F of 15 dynes per centimeter 15 dynes this is for unit perimeter. So, 1 centimeter is already there incorporated and if we equate that to the gamma LA cos theta we will find that here the contact angle necessarily will correspond to the weightable situation. The positive F shows that after the adsorption of the surfactant monolayer the wax slide will be immerse spontaneously unless the restraining external pull F can prevent that. Waiting will be complete if F tends to gamma LA that is theta will be then less than or equal to 0 and this is attained at higher concentrations of MTMAB greater than very small value of 1 milli normal and together with the concentration of a solid surface like a glass we would see that the glass will get de-weighted. So, what can weight paraffin surface will be de-weighting glass and it could leave the surface dry. So, by measuring gamma LA as well as F 1 can obtain the magnitude of contact angle. So, that is the first thing that is the result of the weighting balance method we can measure the contact angle from the measured vertical pull F and the measured surface tension and accidentally one would do this experiment for two kinds of solid surfaces one for which the liquid shows a weighting behavior in which case theta will be 0. In other case theta is non-zero by measuring the vertical pull in the two cases F 1 and F 2 and using equality of F 1 2 gamma L cos theta 1 and F 2 equal to gamma LA cos theta 2 where cos theta 2 will become 1 because theta 2 is 0 we should be able to get gamma LA and therefore, cos theta and therefore, theta. Once we know the contact angle then by using this pair of equations S equal to gamma LA cos theta minus 1 and W S L equal to gamma LA cos theta plus 1 for theta greater than 0 we can obtain the spreading cohesion and the work of addition. Remember this is the spreading cohesion which is negative. So, with that quick recap we move on to the main topic of discussion here one. This one is first to address the Caesile drop method. Once again the Caesile drop method yields you a negative spreading cohesion. So, the situation is one of equilibrium. This method involves measurement of the height of a large Caesile drop lying in equilibrium on a smooth solid surface. Before we go any further I would like you to look at some lighter side of this word Caesile. The dictionary meaning of Caesile drop the adjective Caesile has come from the life sciences. We will take two versions the botanical version is that is something attached by the base or without any distinct projecting support. So, in the context of leaves it would be a leaf directly issuing from the stem alright. So, that is the first interpretation. The zoological meaning of this is it is something permanently attached and not freely moving ok. We may not go into the origin of this word, but rather look at the next slide. Incidentally this picture is taken from a promotional still from 1937 feature film of Laurel and Hardy way out waste. What is the connection of the two gentlemen here to the Caesile drop? What I wanted to indicate was here you do not see any neck. In a sense this head could be described as Caesile head it is directly supported by the base. Coming back to our measurement in our experiment this is an exaggerated figure of a liquid drop placed on a horizontal smooth solid surface. So, we have a drop with radius r and height h. This density this liquid L has density rho L and we presume the volume of the drop capital V to be constant. Now we could imagine for a large drop of this sort a differential infinite symbol change in the equilibrium position of the drop. For instance one could imagine that this drop is let us say spread slightly onto the solid surface. It is an equilibrium drop, but we allow it to spread infinite similarly in which case the radius r will increase by an amount delta r. Because the volume of the drop is constant the height of the drop h will diminish by a magnitude delta h alright. It is here that we propose to make the energy balance. You may want to reflect on this figure a little more. What all things can come into consideration? What all factors merit accounting here? First let us say we look at what happens to the potential energy of this drop when it is spread slightly so that the center of gravity moves. Original location of the center of gravity should be at h by 2 from the base, but since the height has dropped by delta h the center of gravity would have moved a small distance downwards. So, there will be loss of potential energy that is the first consideration. The second consideration is we will have some additional area on the solid which was originally in contact with air here. I am not indicated, but the rest of the space here is air. That additional area which was in contact with air would now be in contact with this given liquid. So, there should be a change in free energy from the initial surface energy of the solid to the final interfacial energy between the solid and liquid. Is that all or would there be anything else? That is the question I can pose before you. Solid liquid interfacial area we said what was already there that has become slightly larger. So, we are taking care of that, but do you suspect there is something else operative here? Remember in all analysis it is important to know what is your relevance list, what all factors relevant in your problem must not be missed out rate of increase of r. We are talking of let us say just the differential increase and it is an it is a differential change in an equilibrium system. So, by very tenets of thermodynamics we know that time is not to be worried about here, but there is something else perhaps what is it? Total surface area of the drop changes. Total surface area of the drop changes. So, what would that bring in? How would one account for surface energy of the liquid if it changes? Let me give you a hint besides energies may be it is worthwhile to always keep in mind as far as we deal with liquids its surface tension and already large drop when it is flattened a bit little more we would have to do certain work and if it is an equilibrium system which is not receiving external work then that work will come at the cost of the energy of the system itself. So, that should account for it with that question prompting you to think perhaps it will be easier for you to grasp the next equation. We are looking at the total change in energy in this equilibrium system that must be equal to 0. So, right hand side is clear. The first factor that I talked about is the loss in potential energy. So, if there is a differential change in the height h by dh it will mean the loss in potential energy corresponding to lowering of the center of gravity from h by 2 to h minus delta h by 2 right. So, total height is decreased by delta h. So, center of gravity will have shifted by this amount h minus delta h the total height of I mean the height of the CG will be h minus delta h by 2 initially it is h by 2 finally, it is h minus delta h by 2. So, the displacement of CG is by delta h by 2. So, loss in potential energy can be given as minus delta h by 2 and the product of this rho L V times G M G delta h by 2 V is constant. So, rho L V is the mass of the drop times G is the weight of the drop M G h M G delta h by 2 is the loss in potential energy clear. When we have allowed the drop to spread a bit the increase in the area will be 2 pi r is the perimeter of the drop in the beginning times delta r is here I think I must clarify a bit more here. Please remember that this drop is relatively large and in our simpler analysis we are taking an approximation that this can be represented as a cylinder. So, the curvature at the edge of the drop is neglected in a more precise analysis we can allow for the actual shape, but supposing it is a drop which you can regard as a cylinder then the perimeter will be 2 pi r and when the radius increases by delta r then 2 pi r delta r will be the additional area. It is that additional area that we have to worry about in estimating the change in energy. Since we are looking at the change in energy free energy we can look at it this way this is a loss term. So, we have put a negative sign loss in potential energy.  Finally, it will be f s l s. So, f s a s minus f s l s is the decrease in the free energy of the solid when it has been invaded by the liquid ok. So, these terms I think were obvious to you from the beginning at least the factors responsible for these 3 terms. Potential energy loss change in the free energy when the solid was initially in contact with air later in contact with liquid right. The other thing is when this drop has expanded a bit you can look at work done against the surface tension. The surface tension force was operative over a perimeter 2 pi r. So, when the perimeter has increased we would have equivalent energy loss where this force is 2 pi r gamma l a and the action of this force is through distance delta r or d r. So, because it is an expansion that has to come at the cost of energy this will correspond to the loss of energy in having this infinite simile expansion of the drop against the restraining action of the surface tension ok. So, once that is noted then I think this equation is self-explanatory. Once we have this in this slide I think I may add this additional part the first term is the product of additional area which is this term and the energy change in spreading over the additional area which comes principally from the solid being now exposed to liquid from initial exposure to air and the loss of energy due to the expansion against action of surface tension and the second one is already explained to you. Now comes the approximation that this very flat large drop can be taken as a cylinder. So, if it is a cylinder then the volume of the drop V which is constant is going to be pi r square pi r square into H where H is the height of the drop. So, area times height that is the volume for you. Since V is constant we could differentiate this equation and write it as 2 pi r d r times H plus pi r square d H that is equal to 0. First differentiate this so you get 2 pi r d r times H and next plus pi r square times d H V is constant so this should be equal to 0. Now here we can replace for pi r square V by H pi r square is V by H. So, if you substitute for pi r square V by H then we get 2 pi r d r is equal to minus V by H by this H.  So, substituting for 2 pi r d r as minus V by H square d H and cancelling V d H we obtain s equal to minus half rho l g H square clear. We have V d H cancelling from here only H square is left in the denominator. So, that goes on this side and therefore, s is equal to minus rho l g H square look at the right hand side density acceleration due to gravity and the height of the drop all are positive quantities. So, this is a negative s as has to be there for the equilibrium non-spreading drop to begin with. Question now is what are the precautions one has to take while making use of this analysis or the method of sysile drop for estimating this negative spreading question. We only need this height of the drop density of the liquid can be easily measured. To measure the height of the drop we have some options we will come to those options, but even before that I would like to tell you something more about how large this drop can be or should be. Obviously, it cannot be such a small drop that we cannot take the cylindrical approximation for its shape ok. So, sysile drop typically is a large drop yeah. So, according to that equation how will we accounting for the change in the solid like if we change the solid will be estimate the same. Interesting question the spreading question the spreading question is if you recall a difference of the work of addition of the liquid to the solid and the work of cohesion of the liquid right. So, whatever is the interaction between the liquid and solid and whatever is the intramolecular interaction for the molecules of liquid would all be reflected in this single entity H. So, if we were to take a different solid you would expect a change here. Correspondingly the spreading question the difference of work of addition of work of and work of cohesion will be different. So, experimental is very simple you do not really actually measure the contact angle you do not need to measure the contact angle you straight away measure only the height of the drop. Provided the approximations made are complied with bio precautions this would give a very quick reliable way of estimating negative spreading question. So, what does one experimental do one places a drop of liquid on a clean horizontal solid surface and just waits for equilibrium to be established. Then the height of the drop is measured in two ways you could use a spirometer or a long focus cathetometer. So, very quick introduction to spirometer and long focus cathetometer can be provided by the next few slides. This is just a schematic of a spirometer you see here there are three legs third one is not visible that is behind here there is a central one here. And we have this capable of rotating in the process the vertical displacement can be measured two turns of this disc will correspond to about tenth of a centimeter on this centimeter scale. So, this is going to move up and down because it is supported with a screw here. So, when you rotate this it will correspond to upward movement and that is measured related to this. So, in typical measurement of the radius of curvature what one does this is a rough photograph of the apparatus here these three legs visible this is the central one that is the disc and this is the vertical centimeter scale. This schematic diagram will tell you that here we are looking at the two legs over here this is the central one and this circle is supposed to be what is circumscribing the three legs this one this one then one behind radius of that is to be read as R this is written E here it should be R. And the difference between the heights of the central leg and these three other legs which are in the same plane that will be H radius of curvature then can be found out as R equal to R square by 2 H plus H by 2. Once you know this the height of the drop can be found out or simpler still will be a method that most of you might have come across in the experiments that you might have done in the mass transfer laboratory while determining the gas phase diffusivity of volatile liquids. What you do is you contain the liquid in a thin capillary the liquid should be volatile and it is laid vertically and a stream of air which does not contain any vapour of this liquid flows past the top of the tube. In the process the liquid evaporates at the interface between air and the meniscus of the liquid and the evaporated liquid then makes its way through the diffusional path between the interface and the top of the tube. If one measures the drop in level of the liquid with time one would be able to use a steady state diffusion analysis to calculate the diffusivity. And to measure the change in the height one uses the long focus cathetometer or a microscope cathetometer which is shown here. So, it allows you to focus on the meniscus at a distance and any change in the level of the meniscus can be measured accurately with this cathetometer. So, you could use the same thing for measuring the height of the drop. Once the height of drop is then known then minus rho L gh square gives you that spreading cohesion. So, this is the only thing which is necessary to measure density of liquid of course, is of course, straight forward. Now how do we comply to the approximation that this drop can be taken as a cylinder? We have to ensure that the radius is large compared to the height of the drop or should be much greater than h. For most liquids if you take a drop volume of about 1 ml this should be a safe choice. And for measurements to be reproducible of course, with the same requirements that the solid should be smooth and clean. So, what kind of values do we get and what is the accuracy of this method? For paraffin wax water system from the height measurement we obtain the spreading cohesion as minus 100 dyns per centimeter by this method. If we were to use the wetting balance method we would get values from minus 99 to minus 100 dyns per centimeter. And if we take the help of a goniometer to measure the contact angle and thereby measure the spreading cohesion from that gamma L e cos theta minus 1 kind of equation we get minus 99 dyns per centimeter. So, this should be pretty much convincing that societal drop actually offers a useful direct method of measuring the negative spreading cohesions. That kind of concludes all the major discussion about negative spreading cohesions that I intended to do in this lecture. That brings us then to the bigger question how do we how do we make measurement of positive spreading cohesion? How do we get the positive s values directly? In the backdrop of what we have seen so far I would like you to think now. How do we measure a positive s for a given spreading liquid on solid? If we take that solid and place the liquid just spreads all over forming a very flat film leads to no measurement. Even societal drop method is not adequate now that was only for negative values. I will like you to connect this problem with at least two earlier notions. We did have two or three occasions in which we needed to talk about a liquid spreading on solid. Because in this system theta will be equal to 0 we had difficulties. I am just trying to connect this question with as many things as possible that you already know so that you get a good hangout what this idea is all about. May be the first to come to your mind could be when we talked about an adsorb monolayer on surface of pure water. We know that if there is a surfactant monolayer on top of water the surface tension drops and it drops by a magnitude which corresponds to the surface pressure or film pressure of the monolayer. So, if the pure water has surface tension gamma 0 and the surface pressure of the monolayer is pi then the actual surface tension that you get to measure is gamma equal to gamma 0 minus pi. It is a diminished value below gamma 0 by magnitude pi right. So, this is the first point of contact second point of contact was in relation to the spreading. We talked about different liquid drops being placed on water and that was the discussion when we are trying to get started with exposure to contact angles. You take a heavy paraffinic oil drop it rests on water giving you equilibrium shape. If you take a lower boiling paraffin oil we might be able to just manage spreading. If you take a small chain associated with alcoholic group we will have a very large spreading question. So, the liquid can spread quickly on the solid surface and when you have that strong positive spreading tendency even if there is there is contamination on the surface this spreading liquid highly spreading liquid will just push out the impurities and occupy the position on the liquid surface. So, this is second point that I want you to recollect. If these things are clear then many things become integral in your mind. Third thing what you should you should be thinking of will be about the piston oils and indicator oils. Once again that was the concept to characterize the contamination of on water bodies. So, they were two different approaches. In the indicator oil you could think of spreading liquids which which have different spreading pressures. So, that you can you can have a thick enough film to yield interference pattern which can be related to thickness. In case of piston oil it should have sufficient surface pressure to be able to overcome the surface pressure of the contamination. So, while taking different piston oils with different spreading pressures you could be able to bracket the existing pressure right. Yet another point which will be a relevant to this discussion conceptually is when we talked about determining the work of addition of a given liquid with respect to a given solid when this liquid spreads spreads on the solid. So, we talked of let us say a liquid L which is capable of weighting a solid S. There is no hope of measuring the contact angle here. So, we would not be able to use the Laplace Young equation. But then a little reflection revealed that we could always think of a two liquid system where the second liquid M is chosen such that it does not weight the solid. And now looking at the measurable contact angle for the given solid between these two liquids we could establish an energy balance which allowed us to extract WSL from all other measurements right. We also said that the liquid L which weights a solid will be capable of pushing the liquid M from the surface although it can take time. All these have one generic principle that is operational here that is given a strongly spreading tendency of a liquid we might be able to offset it by the action of opposing surface pressure of another entity. It could be a layer of another liquid or it could be a surface layer. Here in particular we will look into the action of a monolayer. So, now I think we are in a position to go further and understand this method quickly. The spreading cohesion S is positive and we try to restrain it with the help of surface pressure of a monolayer at air water surface. So, what we do is maybe I can show you the diagram first and then come back to this slide. In this schematic diagram we see water, air, solid and this liquid L ok. It has not been indicated by any line here, but there is a thin layer of water on the solid even to begin with before we place the drop over here. Once the drop is placed the drop will squeeze out this thin film of water push it out because it has affinity for the solid and in the process that pushed out water will get accumulated around its periphery. What we do is to offset the spreading tendency of this drop over the solid we do not start with water, but an aqueous solution of a surfactant whose molecules are indicated here as these chains coupled to heads right. So, there is a surface pressure associated with this monolayer of surfactant on water. So, when this drop tries to spread it will push out this surfactant solution and it will pile up around this drop. In order to spread further it will push this layer of surfactant solution further it may happen to an extent, but after certain extent of spreading it would reach an equilibrium situation provided the surface pressure here is sufficient to counteract the spreading pressure of this drop. So, we have few notations to contain here with as usual air, water and solid are indicated by AWS liquid L by this liquid is L, the surface tension acts along this direction gamma L A, the surface tension of the surfactant solution is gamma which acts as a tangent to this surface and then the contact angle here that is theta 1 other notations are FSLS for the interfacial energy between solid and liquid and between water and solid FSWS. So, what we done is we started with the solid surface kept just below the surface of this aqueous solution of surfactant in a Langmuir trough and then the oil drop could be prevented from spreading with the help of a monolayer which could be steric acid or satil alcohol. Now, this is the situation that we need to analyze, there could be some criticism for this method, one of the strong ones could be is there no possibility of contamination after all you are using a surfactant or a surface activity like steric acid or satil alcohol, would it not contaminate the solid and would it not change its interfacial energy with the liquid? It turns out the experiments reveal that other monolayers than steric acid also give you the same values, accidental values. So, that effectively counters the criticism that they may be contamination of the solid surface altering its interfacial energy. How do we analyze this? First, the basic definition of spreading cohesion for the given liquid on the solid S is FSAS minus gamma LA plus FSLS. In your mind you can replace FSAS by gamma SA FSLS by gamma SL and it is the definition of spreading cohesion of one liquid on another. For solids we replace the surface tension interfacial tension by the surface and interfacial free energy per area. This we know is positive, we need to measure it. So, we look at our equilibrium situation when our drop is in contact with this monolayer covered water all around it. At this point how would we set up the force balance? You know that there will be surface tension between solid and liquid operative. There will be surface energy between solid and liquid operative, surface tension of liquid, surface interfacial energy between the solid and water, surface tension of this aqueous solution, contact angle and one more entity which you might not foresee is the hydrostatic head of this water layer which will be trying to restrain the drop here. So, if we take all these factors together, keep this in mind with this diagram in mind we should be able to understand this equation. G is the hydrostatic spreading force of water layer that is helping the attempt of the liquid to keep to itself in vicinity of the solid FSLS plus gamma LA. Some of you might think why is there no contact angle associated with gamma LA. Remember that this was a kind of highly spreading liquid on solid. So, even when you have this restraining monolayer the drop will still exhibit considerable spreading tendency. It will just be overcome by the surface pressure of the monolayer. So, that angle we take as quite small close to 0. So, we have gamma LA. This is what is trying to help the drop keep to itself the left hand side. The right hand side on the other hand is gamma cos theta 1 in the opposite direction here component of gamma operating in this direction plus FSWS right. There should be 2 things in the gamma water layer and gamma water solid. Why is not why is there. No, no hold on. I while I try to help you to make the force balance and the vectorial concepts visualize the equations never let go the fact that solid is ultimately different from liquid ok. So, we have 2 liquids here L which has surface tension of gamma LA. Another liquid which is the surfactant solution in water which has the surface tension gamma and then there are 2 interfaces with the solid of L with S and of W with S. Those should be expressed in terms of the surface energies. So, free and this will be interfacial energy FSLS and FSWS. What you are trying to think of is why is there no interfacial tension between solid and water that is represented here by the energy right. Instead of dynes per centimeter we are talking of urges per centimeter square. So, we have this action trying to restrain the drop and this is what is trying to pull it apart. So, the factors which are trying to pull it apart are the interfacial energy between solid and water and the surface tension of the surfactant solution with this component. And then these 2 plus the hydrostatic pressure of this water layer over here. Now, how do we go further? Maybe we have to think of yet another situation. This oil L has a positive spreading tendency for this solid over this solid which means we could think of a pure water drop resting on the solid that would give you equilibrium shape ok. So, let see what is the consequence of that. If we place a pure water drop on the solid surface same solid surface surface tension of water is gamma 0 acting along the tangent. F s a s is the free energy of the solid in contact with air. F s w s is the free energy of the solid in contact with water and now that the oil spreads on the solid water would not spread. So, equilibrium contact angle is theta 2 this should be measurable right. So, we repeat gamma 0 is now for pure water theta 2 is the contact angle for water drop placed on the same solid surface in absence of any monolayer. In principle then we should be able to make a force balance here. So, that is the next thing. This equation 17 is the force balance for system of pure water drop resting at equilibrium on the same solid. Here the hydrostatic pressure is trying to help the spreading. F s a s is the free is trying to pull the drop outward. The hydrostatic pressure of this drop is trying to help it. Gamma 0 and F s w s act in the opposite direction counteracting. So, we have gamma 0 cos theta 2 plus F s w s ok. Now, this is all we require. We have the definition for spreading cohesion. We have the balance of the surface energy and surface tension acting. For the drop trying to spread on a monolayer covered water on the solid and the last one is just the drop of water pure water on solid. All we need to do is combine these three equations. For F s a s we substitute from equation 17 from pure water drop. For F s l s we substitute from water drop or like oil drop, l drop resting on monolayer covered water surface trying to push it. So, once you substitute for F s a s and F s l s from equation 17 and 16 in this spreading cohesion, the result you get is this.   So, that is our result s is now gamma 0 cos theta 2 minus gamma cos theta 1. In principle this is the equation which one can use for measuring the spreading cohesion because gamma 0 is known surface tension for the monolayer covered surfactant solution is also known and the two contact angles. Maybe we will just take a logical break here and resume from here. In principle this is to be simplified for different materials and we have to check how good the predictions of this equation is prediction of this equation is in the face of external values.