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° 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° C. The specific gravity of solid fats may be taken at an elevated temperature, preferably that of a boiling water bath.
Free acidity is estimated by weighing out from 2 to 5 grammes of the fat or oil, dissolving in neutral alcohol (purified methylated spirit) with gentle heat, and titrating with a standard aqueous or alcoholic solution of caustic soda or potash, using phenol-phthalein as indicator.
The contents of the flask are well shaken after each addition of alkali, and the reaction is complete when the slight excess of alkali causes a permanent pink coloration with the indicator. The standard alkali may be N/2, N/5, or N/10.
It is usual to calculate the result in terms of oleic acid (1 c.c. N/10 alkali = 0.0282 gramme oleic acid), and express in percentage on the fat or oil.