The amounts of caustic alkali (if any), carbonated alkali, and salt present are determined in the manner already described under Alkali and Alkali Salts. The glycerol content is ascertained by taking 2.5 grammes, adding lead subacetate solution, and filtering without increasing the bulk more than is absolutely necessary; the solution is concentrated to about 25 c.c., and the oxidation with bichromate and sulphuric acid conducted as described in the examination of Crude Glycerine. The solution, after oxidation, is made up to 250 c.c., and titrated against standard ferrous ammonium sulphate solution, the formula for the calculation being:-- {0.25 - 2.5} Per cent. of glycerol = { ---} x 40 { n } where n equals the number of c.c. of oxidised lyes required to oxidise the ferrous ammonium sulphate solution. The estimation of actual glycerol in this is necessarily a matter of considerable importance, and a very large number of processes, which are constantly being added to, have been suggested for the purpose. Hitherto, however, only two methods have been generally adopted, _viz._ the acetin and the bichromate processes. Unfortunately the results obtained by these do not invariably agree, the latter, which includes all oxidisable matter as glycerol, giving sometimes considerably higher results, and it has been suggested that a determination should be made by both methods, and the average of the two results considered the true value. This involves a considerable amount of time and trouble, and it will generally be found sufficient in a works laboratory to determine the glycerol by one method only in the ordinary course, reserving the other process for use as a check in case of dispute or doubt. _Acetin Method._--This consists in converting the glycerol into its ester with acetic acid, the acetic triglyceride, or triacetin being formed. This is then saponified with a known volume of standard alkali, the excess of which is titrated with acid, and the percentage of glycerol calculated from the amount of alkali absorbed.