 The difficulty is that the establishing of a titer for tannin is not always convenient since it is extremely difficult to obtain the pure tannin.Neubauer proposed to remove this difficulty by establishing the titer not with regard to the tannin but with regard to crystallised oxalic acid, whereby he found that 83 g oxalic acid correspond to 41.20 g tannin.Löwenthal's method has been criticized.