86 HOW OEOPS GROW. 



acids, which remain combined with the alkali-metal, 

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

 fats are therefore termed glycerides. 



Exp. 41.— Heat a Wt of tallow with strong solution of caustic potash 

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

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

 ter predomiDates. An oil will separate wliich gathers at the top of the 

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

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

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

 ponding to the elementary fats from which it was produced. 



When saponified by the action of potash, stearin yields 

 stearic acid, CisHsgOa ; palmitin yields palmitic acid, 

 CisHsaOa ; and olein gives oleic acid, CisHg^Oa.* The 

 so-called stearin candles are a mixture of stearic and 

 palmitic acids. The glycerin, CsHjOs, 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 niolecule of fat and three molecules of water into 

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



PalTnitin. Water. PaZmitic acid. Glycerin. 



CjiHjsOe -I- SOlfi) = 3(C„HsA) + CsHgOj 



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 Carlliydrates. — 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 of 

 irogen, and Is one of a series that I 

 corresponding content of carbon. 



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

 of corresp 



