ETHERS AND ESTERS. 525 



decomposition (a kind of fermentation aided by oxidation), which re- 

 sults in a liberation of the fatty acids, which impart their odor and taste 

 to the fats, causing them to become what is generally termed rancid. 



Some fats, especially some oils, suffer oxidation, which renders 

 them hard. These drying oils differ from other oils in being mixtures 

 of olein with another class of glycerides, containing unsaturated acids 

 with less hydrogen in relation to carbon than oleic acid. Drying oils 

 are prevented from drying by albuminous impurities, which may be 

 removed by treating the oil with 4 per cent of concentrated sulphuric 

 acid ; the acid does not act on the fat, but quickly destroys the albu- 

 minous matters, which, with the sulphuric acid, sink to the bottom, 

 while the " refined " oil may be removed by decantation. 



Fats are largely distributed in the animal and vegetable kingdoms. 

 They exist in plants chiefly in the seeds, while in animals they are found 

 generally under the skin, around the intestines, and on the muscles. 



Human fat, beef tallow, mutton tallow, and lard are mixtures of 

 palmitin and stearin with some olein. Butter consists of the glycer- 

 ides of butyric acid, capro'ic acid, caprylic acid, and capric acid, 

 which are volatile with water vapors, and of myristic, palmitic, oleic, 

 and stearic acids, which are not volatile. 



The principal non-drying vegetable oils (consisting chiefly of olein) 

 are olive oil, cottonseed oil, cocoanut oil, palm oil, almond oil. 



Among the drying oils are of importance : linseed oil, castor oil, 

 croton oil, hemp oil, cod-liver oil. 



Whenever fats are treated with alkaline hydroxides, or with a 

 number of other metallic oxides, decomposition takes place, the fatty 

 acids combining with the metals, while glycerin is set free. Some 

 of the substances thus formed are of great importance, as, for instance, 

 the various kinds of soap. 



The term saponification, as used by physiologists, is applied to the 

 decomposition which occurs when neutral fat is split into its constitu- 

 ents, glycerin and fatty acid. This decomposition is a hydrolytic 

 cleavage, and can be produced by the action of boiling alkalies, super- 

 heated steam, various enzymes, etc. In other words, the formation 

 of a soap is not an essential part of the process. 



Soap. Any fat boiled with sodium or potassium hydroxide will 

 form soap. Soft soap is potassium soap, hard soap is sodium soap. 

 The better kinds of hard soap are made by boiling olive oil with 

 sodium hydroxide : 



C 3 H 5 (C ]8 H 33 2 ) 3 + SNaOH = SNaC^O, + C 3 H 5 (OH) 3 . 

 Oleateof erlvceryl Sodium Sodium oleate Glycerin, 



(olive oil). hydroxide. (hard soap). 



