164 SOAPS AND PROTEINS 



position of even the commoner fats and oils. Or, where such 

 complete analyses have been made or are available, they refer, 

 of course, only to a specific sample and, as every oil and fat 

 chemist knows, another sample obtained presumably from the 

 same sources and under the same conditions may still show wide 

 variations in composition. A single fat or oil varies for example 

 with the seasons. 



It lies without the limits of this volume to list more than a 

 few of the fats and oils which have been or may be used in the 

 manufacture of soaps and to indicate their approximate compo- 

 sition. The examples which follow are of interest either because 

 they furnish much of the material which is used in soap manu- 

 facture or because their qualitative composition is such that 

 they yield soaps with qualifications of interest to our discussion. 



2. The Oils, Fats and Waxes Entering the Soap Kettle 



From a purely chemical point of view there is little reason to 

 distinguish between the " oils " and the " fats " of the technical 

 chemists; and the same is true of the " waxes." All three sub- 

 stances are essentially nothing but mixtures of different esters. 

 In the case of the oils and fats these are almost exclusively glycer- 

 ids, and this still holds true for many of the waxes (as " Japan 

 wax "). At other times the waxes are still esters, but some other 

 alcohol may have taken the place of the glycerin. Nevertheless, 

 this practical distinction between the three groups of substances 

 the first being liquid at ordinary temperatures, the second semi- 

 solid or solid, the third definitely solid has some value. The 

 physical state parallels roughly the kinds and proportions of different 

 fatty acids appearing in the various esters, the fatty adds with the 

 lower melting points being those most common in the oils while those 

 with the higher melting points predominate in the fats and waxes. 

 This matter is of much importance, as will appear later, because 

 of the physico-chemical differences in the soaps which are formed 

 from these different stocks. 



A distinction in soap manufacture between the fats of vege- 

 table and those of animal origin has little purpose, for both con- 

 tain qualitatively the same list of glycerids. Nevertheless it is 

 well to remember that the two different origins may at times be 

 of importance because of differences in the types of impurities 

 which they bring along. 



