308 CONSIDERATION OF CARBON COMPOUNDS. 



decomposed at a higher temperature with the formation of 

 numerous products, some of which have an extremely disagree- 

 able odor, as, for instance, acroleine, C 3 H 4 O, an aldehyde which 

 in composition is equal to glycerine minus two molecules of 

 water: 



C 3 H 5 3HO 2H 2 O = C 3 H 4 O. 



Some fats keep without change when pure; as they, however, 

 generally contain impurities, such as albuminous matter, etc., 

 they 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 oleine 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 oils with 4 per cent, of concentrated sulphuric acid; the acid 

 does not act on the fat, but quickly destroys the albuminous 

 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 generally found under the skin, around the in- 

 testines, and on the muscles, 



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

 palmitine and stearine with some oleine. Butter consists of the 

 glycerides of butyric acid, caproic acid, caprylic acid, and capric 

 acid. 



The principal non-drying vegetable oils (consisting chiefly of 

 oleine) 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 hydrates, or with a 

 number of other metallic oxides, decomposition takes place, the 

 fatty acids combining with the metals, whilst glycerine is set 

 free. Some of the substances thus formed are of great impor- 

 tance, as, for instance, the various kinds of soap. 



