CHAPTER X 

 FATS AND OILS, WAXES, AND LIPOIDS 



INCLUDED in this group are several different kinds of compounds 

 which have similar physical properties, and which, in general, 

 belong to the type of organic compounds known as esters, i.e., 

 alcoholic salts of organic acids. The terms " oil," " fat," and 

 " wax," are generally applied more or less indiscriminately to any 

 substance which has a greasy feeling to the touch and which does 

 not mix with, but floats on, water. There are many oils which are 

 of mineral origin which are entirely different in composition from 

 natural fats. These have no relation to plant life and will not be 

 considered here. 



The natural fats, vegetable oils, and plant waxes are all esters. 

 There is no essential difference between a fat and an oil, the latter 

 term being usually applied to a fat which is liquid at ordinary 

 temperatures. The waxes, however, are different in chemical 

 composition from the fats and oils, being esters of monohydric 

 alcohols of high molecular weight, such as cetyl alcohol, CieHaaOH, 

 myristic alcohol, CaoHeiOH, and cholesterol, C2-H45OH; whereas 

 the fats and oils are all esters of the trihydric alcohol glycerol, 

 CsH5(OH)3. Lipoids are much more complex esters, having 

 some nitrogenous, or phosphorus-containing, group and some- 

 times a sugar in combination with the fatty acids and glycerol 

 which make up the characteristic part of their structure. 



In general, waxes and lipoids have a harder consistency than 

 fats: but this is not always the case, since " wool-fat " and sper- 

 maceti, both of which are true waxes in composition, are so nearly 

 liquid in form as to be commonly called fats; while certain true fats, 

 like " Japan wax," are so hard as to be commonly designated as 

 waxes. It is plain that physical properties alone cannot be relied 

 upon in the classification of these bodies. In fact, there is no 

 single definite property by which members of this group can be 

 accurately identified. There are many other types of substances 



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