66 HOW CROPS GROW. 



acids, 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 asoap, 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 36 2 ; palmitin yields palmitic acid, 

 Ci 6 H 32 2 ; and olein gives oleic acid, C 18 H 34 2 .* The 

 so-called stearin candles are a mixture of stearic and 

 palmitic acids. The glycerin, C 3 H 8 S , 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 saponification 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 add. Glycerin. 



C 51 H*,0 6 + 3(H 2 0) = 3(C 16 H 32 4 ) + C 3 H 8 O 3 



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 CarWiydrates. 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- 



* Oleio acid differs from steario aoid in containing two atoms less of 

 hvdrojren. and is one of a serifs that bear this relation to the fatty acids 

 of corresponding content of carbon. 



