86 HOW CEOPS GROW. 



acidt, which remain combined with the alkali-metal, 

 and to glycerin, a substance which acts as a base. The 

 fats are therefore termed glycerides. 



EXP. 41. Heat a bit of tallow with strong solution of caustic potash 

 until it completely disappears, and a soap, soluble in water, is obtained. 

 To one-half the hot solution of soap, add hydrochloric acid until the lat- 

 ter predominates. An oil will separate which gathers at the top of the 

 liquid, and, on cooling, solidifies to a cake. This is not, however, the 

 original fat. It has a different melting point, and a different chem- 

 ical composition. It is composed of the three fatty acids, corres- 

 ponding to the elementary fats from which it was produced. 



When saponified by the action of potash, stearin yields 

 stearic acid, Ci 8 H 86 2 ; palmitin yields palmitic acid, 

 C 16 H 82 2 ; and olein gives oleic acid, C 18 H 34 02.* The 

 so-called stearin candles are a mixture of stearic and 

 palmitic acids. The glycerin, C 8 H 8 8 , that is simul- 

 taneously produced, remains dissolved in the liquid. 

 Glycerin is found in commerce in a nearly pure state, as 

 a colorless, syrupy liquid, having a pleasant, sweet taste. 



The chemical act of saponiflcation consists in the re-arrangement of 

 the elements of one molecule of fat and three molecules of water into 

 three molecules of fatty acid, and one molecule of glycerin. 



Palmitin. Water. Palmitic acid. Glycerin. 



CsiH^Oe + 3(H 2 0) = 3 (C 16 H 32 O 2 ) + C 3 H 8 O S 



Saponification is likewise effected by the influence of strong acids 

 and by heating with water alone to a temperature of near 400 F. 



Ordinary soap is nothing more than a mixture of stearate, palmitate, 

 and oleate of potasssium or of sodium, with or without glycerin. Com- 

 mon soft soap consists of the potassium compounds of the above- 

 named acids, mixed with glycerin and water. Hard soap is usually the 

 corresponding sodium-compound, free from glycerin. When soft soap 

 is boiled with common salt (chloride of sodium), hard soap and chlo- 

 ride of potassium are formed by transposition of the ingredients. On 

 cooling, hard-soap forms a solid cake upon the liquid, and the glycerin 

 remains dissolved in the latter. 



Relations of Fats to Carbhydrates. The oil or fat of 

 plants is in many cases a product of the transformation 

 of starch or other member of the cellulose group, for the 

 oily seeds, when immature, contain starch, which van- 



* Oleic acid differs from stearic acid in containing two atoms less ol 

 hydrogen, and is one of a series that bear this relation to the fatty acids 

 of corresponding content of carbon. 



