PROTEIN. 169 



tion by acetic acid, added only to a very small excess, because 

 too much would again dissolve the protein. The gelatinous pre- 

 cipitate is collected on a filter, and washed till every trace of 

 acetate of potash is removed. 



Protein thus purified constitutes gelatinous, translucent, grey- 

 ish flocks which, when dried, assume a yellowish colour, and be- 

 come hard and brittle, and easily pulverized. The powder is 

 amber yellow, destitute of smell and taste, absorbs moisture from 

 the atmosphere ; which it again loses when heated to 212. 

 When heated, it undergoes decomposition before it melts. It 

 swells up, gives out empyreumatic oil, ammoniacal water, and 

 inflammable gas, and leaves a porous charcoal, which burns rea- 

 dily in the air without leaving any residue. 



Protein sinks in water, and when left in that liquid, softens 

 and swells* and assumes the original appearance which it had be- 

 fore it was dried. It is insoluble in water, alcohol, ether, and 

 volatile oils. When boiled in water, it is partly dissolved, but 

 the process is so slow, that after sixty hours boiling, most of the 

 protein still remains unacted on. When the dissolved portion 

 is evaporated, the matter remaining is translucent and yellow, 

 and consists of two substances, one of which dissolves in alcohol^ 

 and the other not. 



Protein combines both with acids and bases. It dissolves in 

 all very dilute acids, and forms with them a kind of neutral com- 

 pound, which is insoluble or difficultly soluble when there is an 

 excess of acid present. Hence, if to a solution of protein sulphu- 

 ric, nitric, phosphoric, or muriatic acid be added, the protein pre- 

 cipitates in combination with the acid added. And when the ex- 

 cess of acid is washed away, the precipitate again dissolves. 

 Acetic acid and phosphoric acid constitute an exception, as they 

 dissolve protein even when added in excess. When treated with 

 them in a concentrated state, the protein first gelatinizes, and 

 then dissolves. From the solution in acetic acid protein is pre- 

 cipitated by prussiate of potash, by tannin, and by an alkali. 



The action of the strong acids produces alterations on pro- 

 tein. Concentrated muriatic acid, when air is excluded, gives a 

 yellow solution, which becomes brown when oxygen gas is ad- 

 mitted. When the muriatic acid is allowed to act upon protein 

 in an open vessel, the colour of the solution gradually deepens 

 ligo blue. When heat is applied, the liquid becomes black, 



