(c) The kindhng temperature.
(d) The results as shown by the lime wa-

ter test. [Refer to XI, 16, experi-
ments (d)* (e) and (f ).]

Note. — Read in any chemistry what is said upon
the subjects of combustion, carbon, oxygen and carbon
dioxide.
NUMBER WORK.
1. Prom the results obtained with the coal in
the clay pipe, calculate the amount of gas, that,
at the same rate, could be made from a ton of
coal.
2. At the gas-works they can make about
10,000 cubic feet of gas from a ton of soft coal.
Find out from your gas meter how much gas is
consumed in one month and calculate the
amount of coal needed to make it.
3. Compare the price paid for the gas with
the market value of the coal ; the cost of the
coal is what per cent, of the cost of the gas?

4. Whatbecomes of the difference between the
cost of the coal and the cost of the gas ? Consider :

• (a) The cost of manufacture.
THE GEAMMAE GEADBS. 121

(b) The cost of transmitting.
(c) The interest on the money invested in

the gas plant send pipes.
Note. — The gas is not tlie only thing of value

obtained by the gas companies from the coal ; read an

account of gas manufacture in any chemistry for a

description of other substances known as by-products.
5. An ordinary gas tip burning five cubic feet
of gas per hour will vitiate with .2 per cent, of
OO2 5,000 cubic feet of air in one hour; count
your gas burners at home and by calculation
find out to how many people they are the
equivalent in this respect.
