THE CHEMISTRY OP ALBUMINS 185 



paration of crystalline albumin is taken, with some modifica- 

 tion, from the monograph on ' The General Characters of the 

 Proteins ' by Dr. Schreyver, p. 20. 



Egg-white is beaten to a froth (to break up the membranes) 

 with exactly its own bulk of saturated ammonium sulphate 

 solution. The mixture, after standing overnight, or at least 

 for some hours, is filtered from the precipitated globulin. 

 The filtrate is now measured. Ten per cent, acetic acid 

 (glacial acetic acid diluted to ten times its bulk) is then 

 very gradually added from a burette, until a v;ell-marked 

 precipitate forms. The object of the addition of acid is 

 to neutralise the alkahnity which is developed in the 

 ammonium sulphate solution on standing. The formation 

 of a precipitate indicates the point of neutrahsation. A 

 further quantity of acid is now added, 1 c.c. for each 100 c.c. 

 of the filtered mixture as already measured. A bulky precipi- 

 tate is thus produced, which is at first amorphous, but which 

 becomes crystalline in the course of four or five hours, if shaken 

 from time to time. To obtain the full yield, the material 

 should stand for twenty-four hours. The precipitate can then 

 be filtered off, and allowed to drain on a plate of porous 

 porcelain. The precipitate will probably contain ammonium 

 sulphate, from which indeed it is not easy completely to free it ; 

 but it can be obtained in a purer state by redissolving in water, 

 adding haK-saturated ammonium sulphate, containing acetic 

 acid in the proportion of 1 per 1000, till a permanent pre- 

 cipitate forms, and finally a further 2 c.c. of ammonium 

 sulphate in excess of this. 



Albumin substances belong as a rule to the class of com- 

 pounds known as amphoteric, that is, they are capable of acting 

 both as weak acids and as weak bases. A solution of albumin 

 in dilute alkaU is sometimes known as alhaU-alhumin. If 

 acid is added very carefully to such a solution, the albumin 

 is first precipitated and then redissolved, forming so-called 



