172 GLYCEEIN. 



(fatty oils), and a number of varieties occur at the same 

 time in plants and animals. In a pure condition they 

 are all colorless, inodorous, and tasteless, but, in conse- 

 quence of the presence of foreign substances, they are 

 generally more or less yellowish colored and have a 

 taste and smell. They float on water and are insoluble 

 in it. Only a few are soluble in alcohol. Several of 

 the liquid fats dry in the air, at the same time absorb- 

 ing oxygen ; others never become dry, but only more 

 consistent and rancid from the formation of an acid. 

 They are not volatile. Most fats are mixtures of vary- 

 ing proportions of neutral glycerin ethers of stearic 

 acid (stearin), palmitic acid (palmitin), and oleic acid 

 (olein, elain). Upon the relative quantity of these 

 constituents depends the consistence of the fats ; they 

 are the more liquid the more olein they contain. 

 Human fat, beef and mutton tallow, hog's lard, cocoa 

 butter, palm-oil, and tree-oil consist essentially of 

 these three compounds. In other fats, however, there 

 are generally contained, in addition to these, glycerides 

 of other acids ; in butter, for instance, those of butyric, 

 caproic, caprylic, and capric acids. Only a few of the 

 natural fats are ethers of other alcohols; the principal 

 ingredient of spermaceti, for instance, is cetyl palmi- 

 tate (p. 74), 



The simple fats can be prepared artificially by heat- 

 ing tke fatty acid contained in them for a long time 

 with glycerin in closed vessels to 200. In the same 

 way compounds analogous to fats can be prepared. As 

 glycerin contains 3HO, it is capable of forming three 

 series of ethers. Only a few of these compounds will 

 be described here. 



Monoformin, C 3 H 5 j ^ C ^Q Is formed by heat- 



ing glycerin with oxalic acid to 190, and can be ex- 

 tracted from the mass with ether. Colorless liquid. 

 Can only be distilled in a vacuum without decomposition. 

 At 200 it is resolved into carbonic acid and allyl 

 alcohol. (See Preparation of Allyl Alcohol, p. 119.) 



