The glycerine water resulting from acid saponification methods requires to be rendered alkaline by the addition of lime--the sludge is separated, and the liquor evaporated to crude. The concentration may be performed in two stages--first to a density of 32 deg. Tw. (20 deg. B.), when the calcium sulphate is allowed to deposit, and the separated liquor concentrated to 48 deg. Tw. (28 deg. B.) glycerine, testing 85 per cent. glycerol and upwards. _Yield of Glycerine from Fats and Oils._--The following represent practicable results which should be obtained from the various materials:-- Tallow 9 per cent. of 80 per cent. Glycerol. Cotton-seed oil 10 " Cocoa-nut oil 12 " Palm-kernel oil 18 " Olive oil 10 " Palm oil 6 " Greases (Bone fats) 6-8 " The materials vary in glycerol content with the methods of preparation; especially is this the case with tallows and greases. Every care should be taken that the raw materials are fresh and they should be carefully examined to ascertain if any decomposition has taken place in the glycerides--this would be denoted by the presence of an excess of free acidity, and the amount of glycerol obtainable from such a fat would be correspondingly reduced. CHAPTER X. ANALYSIS OF RAW MATERIALS, SOAP, AND GLYCERINE. _Fats and Oils--Alkalies and Alkali Salts--Essential Oils--Soap--Lyes--Crude Glycerine._ _Raw Materials._--Average figures have already been given in Chapters III. and VIII. for the more important physical and chemical characteristics of fats and oils, also of essential oils; the following is an outline of the processes usually adopted in their determination. For fuller details, text-books dealing exhaustively with the respective subjects should be consulted. FATS AND OILS. It is very undesirable that any of these materials should be allowed to enter the soap pan without an analysis having first been made, as the oil may not only have become partially hydrolysed, involving a loss of glycerine, or contain albuminous matter rendering the soap liable to develop rancidity, but actual sophistication may have taken place. Thus a sample of tallow recently examined by the authors contained as much as 40 per cent. of an unsaponifiable wax, which would have led to disaster in the soap pan, had the bulk been used without examination. After observing the appearance, colour, and odour of the sample, noting any characteristic feature, the following physical and chemical data should be determined. _Specific Gravity at 15 deg. C._ This may be taken by means of a Westphal balance, or by using a picnometer of either the ordinary gravity bottle shape, with perforated stopper, or the Sprengel U-tube. The picnometer should be calibrated with distilled water at 15 deg. C. The specific gravity of solid fats may be taken at an elevated temperature, preferably that of a boiling water bath.