262 PROPERTIES OF NEUTRAL FATS. [BOOK I. 



and chloroform. When fluid they render paper which is coated 

 with them transparent (grease spots). When mixed with colloid 

 substances and water, they admit of being broken up into fine drops, 

 so that the fluid becomes white and opaque (an emulsion). Under 

 the influence of certain ferments (e.g. one of the ferments contained 

 'in the pancreatic secretion) they combine with the elements of water, 

 splitting up into glycerin and a fatty acid; thus : 



C 3 H 5 (OC M H 3 ,0) S + 3H 2 = C 3 H 5 (OH), + 3 (C H 31 0, OH). 



Tripalrnitin. Water. Glycerin. Palmitic acid. 



The rancid smell of decomposing fats is due to volatile acids 

 which are set free. 



When the neutral fats are boiled with solutions of the alkaline 

 hydrates or carbonates they undergo the process of saponification, i.e. 

 they combine with the elements of water, and decompose into 

 glycerin and fatty acids, the latter constituents combining at once 

 with the alkaline metal to form a soluble salt, termed a soap. Thus 

 when stearin, palmitin or olein is boiled with potash hydrate or with 

 sodium hydrate, the results of the operation are, in the first case, 

 potassium stearate, palmitate, or oleate, respectively and glycerin ; in 

 the second case sodium stearate, palmitate, or oleate, and glycerin. 



When boiled with litharge the neutral fats yield an insoluble lead 

 soap and glycerin. 



The term soap is applied to the metallic salts of the fatty acids, 

 and hence the term saponification is employed to designate the 

 process which results in the formation of these compounds. 



Stearin or Tristearin. C^^O.C^H^O)^ 



Stearin is the chief constituent of the more solid fats. Its 

 melting-point is higher than that of any other neutral fat, but varies, 

 according to the treatment to which it has been subjected, between 

 53 and 66. It is nearly insoluble in cold alcohol and ether, though 

 soluble in both these fluids when these are boiled. The insolubility 

 in cold ether is taken advantage of in the preparation of pure stearin. 



Stearin may be obtained from the suet of the sheep by extracting 

 it repeatedly with cold ether, and dissolving the residue in boiling 

 ether, which, on cooling, deposits crystals of stearin, in the form of 

 little leaflets which shine like mother-of-pearl. From a boiling 

 alcoholic solution stearin is deposited in brilliant scales, which are 

 almost square rhombic crystals having angles of 90'5. 



Palmitin or Tripalmitin. C 3 H 6 (0 . C 16 H 31 0) 8 . 



Is the more abundant of the two solid neutral fats in the adipose 

 tissue of man. It is more soluble in cold and in hot alcohol and ether 

 than stearin ; it is deposited from saturated solutions in the form of 

 fine needles, which radiate from a centre and appear as delicate 

 filaments. 



