ALBUMEN. 17 



of a few drops of acetic acid is therefore always advisable in 

 this case. Bichloride of mercurv, and nitrate of the black 

 oxide of mercmy throw down whitish precipitates. Either of 

 these tests will detect the presence of ^ part of dry albumen. 

 Precipitates of various colours and appearances are thrown do^^'n 

 by sulphate of copper, nitrate of silver, the acetates of lead, 

 protochloride of iron, alum, tannin, creosote, alcohol, &c. 



The precipitates which the metallic salts throw down with 

 albumen are usually mixtures of two distinct substances, one a 

 compound of albumen with the acid, the other a compound of 

 albumen with the metallic oxide ; the former is usually some- 

 what soluble, the latter insoluble. 



The alkalies and their carbonates form soluble compounds 

 with albumen, and frequently require to be neutralized before 

 the ordinaiy tests can be efficiently used. 



The tests in most general use are heat, and nitric acid. 

 When they both produce turbidity or a precipitate, the existence 

 of albumen may be considered as proved.' 



Coagulated albumen. Coagulated albumen may be obtained 

 by submitting the white of egg or the serum of the blood to a 

 temperature of from 160'' to 180^ ; 167° according to Simon. 



The coagulated mass must be then rubbed in a mortar, and 

 successively digested in water, alcohol, and ether, until all 

 substances soluble in those fluids are removed : it must then be 

 carefully dried. 



"When obtained in this manner, it usually contains from 

 1 to 2% of phosphate of lime, an earth which solulile albumen 

 seems to have the power of dissolving. 



In order to obtain it free from this impurity, the follomng 

 process may be employed. Coagulate albiunen ^-ith dilute 

 hydrochloric acid, wash the precipitate with water acidulated with 

 the same acid, and then add so much cold water as may suffice 

 to dissolve it. On the addition of carbonate of ammonia, co- 

 agulated albumen is separated as a flocculent, white precipitate. 

 To remove any fat that may be present, it should be digested 

 in hot alcohol or ether. 



When dry, it is yellow and transparent ; it swells upon being 

 placed in water, but is only very slightly soluble in it. In its 

 ordinary chemical relations it resembles protein. 



' An apparent exception in the case of the urine will be suhseqnentlv noticed. 



2 " 



