890 APPENDIX. 



fats. It crystallizes usually in square tables. It presents peculiarities in its fusing- 

 points similar to those of palmitin. 



Preparation. From mutton suet, its separation from palmitin and olein being 

 effected by repeated crystallization from ether, stearin being the least soluble. 



Olein (Tri-olein). ^ffj}^ 1 J 3 . 



It is obtained with difficulty in the pure state, and is then fluid at ordinary 

 temperatures. It is more soluble than the two preceding ones. It readily under- 

 goes oxidation when exposed to the air, and is converted by mere traces of N0 2 

 into a solid isomeric fat. Olein yields, on dry distillation, a characteristic acid, 

 the sebacic, and is saponified with much greater difficulty than are palmitin and 

 stearin. 



Preparation. From olive oil, either by cooling to C. and pressing out the 

 olein that remains fluid, or by dissolving in alcohol and cooling, when the olein 

 remains in solution while the other fats crystallize out. 



Glycerin. C |j* 5 1 3 . 



This principal constituent of the neutral fats may, as above stated, be looked 

 upon as a triatomic alcohol. 



When pure, glycerin is a viscid, colorless liquid, of a well-known sweet taste. It 

 is soluble in water and alcohol in all proportions, insoluble in ether. Exposed to 

 very low temperature it becomes almost solid ; it may be distilled in close vessels 

 without decomposition, between 275-280 C. 



It dissolves the alkalies and alkaline earths, also many oxides, such as those of 

 lead and copper ; many of the fatty acids are also soluble in glycerin. 



It possesses no rotatory power on polarized light. 



It is easily recognized by its ready solubility in water and alcohol, its insolubility 

 in ether, its sweet taste, and its reaction with bases. The production of acrolein is 

 also characteristic of glycerin. 



C 3 H 8 O 3 2H 2 --= C 3 H 4 O (Acrolein). 



Preparation. By saponification of the various oils and fats. It is also formed 

 in small quantities during the alcoholic fermentation of sugar. 1 



Soaps. These may be formed by the action of caustic alkalies on fats. The 

 process consists in a substitution of the alkali for the radicle of glycerin, the latter 

 combining with the elements of water to form glycerin. Thus : 



Tristearin. Potassic stearate. Glycerin. 



/r\ TT r\\ T7" ) r\ TT f\ ) f^ TT i 



\v-'18 ll 35^-' /3 [ i~\ | o- 1 -*- [ f\ Q^18 n 35'~' I C\ _L ^3 AA 5 ( f\ 



C H I 3 H I K " H 3< 



Pancreatic juice can split up fats into glycerin and free fatty acids, and the bile is known to 

 be capable of saponifying these fatty acids/ The amount of soaps formed in the alimentary 

 canal is, however, small and unimportant. 



ACIDS OF THE GLYCOLIC SERIES. 



Running parallel to the monatomic alcohols (GJBL+*0) is the series of diatomic 

 alcohols or glycols (C n H w + 2 2 ). Thus corresponding to ethyl alcohol is the dia- 

 tomic alcohol, ethyl-glycol. As from the monatomic alcohols, so from the glycols, 

 acids may be derived by oxidation ; from the latter (glycols), however, two series 

 of acids can be obtained, known respectively as the glycolic and oxalic series. 

 The first stage of oxidation of the glycol gives a member of the glycolic series. 

 Thus: 



Ethyl-glycol. Glycolic acid. 



C 2 H 6 2 + 2 = C 2 H 4 O 3 + H.,0, or more generally 

 C n H 2M + ,0, + O. 2 - C n H 2n 8 + H 2 0. 



1 Pasteur, Ann. d. Chem. u. Pharm., Bd. cvi., S. 338. 



