LESSON XV 



CRYSTALLISATION OF EGG ALBUMIN 



Fresh egg-white is mixed with an equal bulk of fully saturated, filtered 

 neutral ammonium sulphate solution. 100 c.c. of the former are measured 

 into a porcelain basin or strong beaker, and 100 c.c. of ammonium sulphate 

 solution are added in successive quantities of 10 or 15 c.c., the mixture being 

 thoroughly churned with an egg whisk after each addition. The whole should 

 be finally so thoroughly beaten up as to form a large proportion of light froth. 

 After the greater part of the froth has broken down, the mixture is thrown on 

 a folded filter-paper, moderately rapid filtration being obtained without the 

 use of a filter-pump. The filtrate is strongly alkaline to litmus, and smells of 

 ammonia. To the filtrate in a flask, or to as much of it as can be obtained in 

 a convenient time of filtration, further ammonium sulphate solution is very 

 cautiously added (best, drop by drop from a burette) until a slight permanent 

 precipitate remains, and this precipitate is afterwards just redissolved by the 

 equally cautious addition of water. Dilute acetic acid (10 per cent.) from a 

 burette is now added drop by drop until such a stage of reaction is reached that 

 a precipitate forms and only just redissolves. Finally one or two drops (not 

 more) of acid are added in excess of this, whereupon a bulky white precipitate 

 falls. The flask is now corked and allowed to stand. In 24 hours or less the 

 precipitate, which will have increased in quantity, will be found to consist 

 entirely of acicular crystals. Small portions should be examined under a 

 th objective, avoiding pressure 011 the cover slip. (F. G. Hopkins.) 



