16 THE FAT OF MILK. 



PRODUCTS OF HYDROLYSIS. 



Glycerol. This is the simplest tri-hydric alcohol and has 

 CH 2 OH 



the constitution CHOH. It was discovered by Scheele in 



CH 2 OH 

 1 779 in olive oil, and was first recognised in butter in 1784. 



The anhydrous product is a thick syrupy liquid, which can 

 be obtained in crystals by cooling to a low temperature ; the 

 melting point of the solid glycerol is given as 17 C. by Henniger 

 and 20 by Nitsche. It boils at 290 C. under the ordinary 

 pressure, but undergoes slight decomposition ; it can readily be 

 distilled without change under reduced pressure. It is not 

 volatile with steam. An aqueous solution containing less than 

 75 per cent. glyce*rol can be boiled without loss ; but from solu- 

 tions containing more than 75 per cent, glycerol it is somewhat 

 volatile (Hehner). Anhydrous glycerol volatilises slowly at 

 100 C. When heated above 150 (?. it is inflammable. 



15*5 



The density at is 1*2655 ; the refractive index at the 

 15'5 



same temperature is 14748. 



When heated to its boiling point, especially if not pure, various 

 products, of which acrolein (C 3 H 4 0) is the most important, are 

 given off. Di- and tri-glyceric alcohols are also formed. 



By the action of acid oxidising agents e.g., chromic acid and 

 potassium permanganate in acid solution it is wholly converted 

 into carbon dioxide and water. Alkaline permanganate converts 

 it quantitativ ly into oxalic acid. By the action of bromine in 

 the cold glycerose is formed, which is an aldehyde ; by further 

 oxidation with bromine at a high temperature, or by boiling with 



CH 2 OH 



dilute nitric acid, glyceric acid CHOH is produced. 



COOH 

 COOH 



Tartronic acid CHOH is, under certain conditions, also 



COOH 



produced together with glycolic, glyoxylic, oxalic, and formic 

 acids. 



Glyceric acid appears to have a constitution similar to lactic 

 acid (tj.v.), from which it differs only by containing the group 

 CH 2 (OH) in place of CH 3 . It forms a lactone and a dehydro- 

 derivative, and contains an asymmetric carbon atom. 



By the action of fuming nitric acid (mixed with sulphuric acid 



