THE CHEMISTRY OP ALBUMINS 183 



into 50 c.c. of water, stirring meanwhile ; a white precipitate 

 is formed. This can be filtered off and a portion of the fUtrate 

 boiled, when a further precipitate is obtained. 



It wiU thus be seen that the egg-white can be separated 

 readily into two substances, one soluble, the other insoluble, 

 in cold water. The insoluble portion is known as globulin, the 

 soluble substance is albumin. 



As the word albumin is also used in a more or less generic 

 sense, it is better perhaps to refer to this body as egg-albumin. 

 A related substance can be obtained from blood serum and 

 is known as serum albumin, and also from milk, when it is 

 known as lact-albumin. 



A larger quantity of egg-albumin solution may now be 

 prepared by adding further quantities of egg-white to water, 

 stirring, and filtering off the globulin ; the solution of egg- 

 albumin can then be used for investigating certain typical 

 properties of this class of substance. In the first place 

 a number of simple qualitative tests may be carried out, 

 which will indicate the presence of certain elements in 

 albumin, and the class of chemical substances to which it 

 may be referred. 



Experiment. — 5 c.c. of the solution may be warmed with a 

 Uttle strong caustic soda ; an evolution of ammonia can 

 readily be detected which indicates the presence of nitrogen, 

 and further that it is most probably present, in part at least, 

 in combination as a so-called amino group or NHg. 



Experiment. — A few drops of lead acetate are added to a 

 20 per cent, solution of caustic soda ; a precipitate is formed 

 which readily redissolves. If a little of this solution is boiled 

 with a solution of egg-albumin, it rapidly darkens owing to 

 the formation of sulphide of lead ; this indicates the presence 

 of sulphur in the egg-albumin. 



Experiment. — On warming with strong caustic soda and 

 adding a few drops of dilute copper sulphate solution a violet 

 colour is obtained. This is known as Piotrowski's reaction. If 



