ETHERS. 345 



suffer decomposition (a kind of fermentation aided by oxidation), 

 which results 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, 

 whilst 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, 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, whilst glycerin is set free. Some 

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

 the various kinds of soap. 



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 : 



18 H 3 30 2 )3 + 3NaOH = 3NaC 18 H 33 O, + C 3 H 5 (OH) 3 . 

 Oleateof glyceryl Sodium Sodium oleate Glycerin. 



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



Experiment 51. Boil 50 grammes of olive oil with 60 c.c. of a 15 per cent. 

 sodium hydroxide solution for about one hour. The soap which is thereby 

 formed remains dissolved in or mixed with water and glycerin. Cause sepa- 

 ration by adding a solution of 15 grammes of sodium chloride in 40 c.c. of 



