48 THE PROTEINS. 



which is moistened with lead acetate solution and held 

 over the mouth of the test-tube. Upon acidifying the hot 

 solution with hydrochloric acid the sulphur previously 

 liberated is given off as hydrogen sulphid gas, which im- 

 mediately turns the paper brown. 



113. In the same manner as in the previous experi- 

 ment test with lead paper, the gas from a solution of albu- 

 bin when boiled with hydrochloric acid, as in the formation 

 of acid albumin. No discoloration appears; that is, the 

 albumin has not been decomposed to such a degree as 

 in the last experiment. 



114. The thoroughly washed, solid alkali albumin when 

 pressed upon moist litmus-paper reddens it, and its solution in 

 calcium hydrate has an acid reaction, if no excess of the latter is 

 present. To obtain these results, however, great care is necessary 

 to free it from the alkali used in its preparation. 



PROTEOSES AND PEPTONES. 



The peptones are the final products of the digestive 

 action of pepsin upon the albuminous compounds. The 

 albumoses are intermediate products between the albumi- 

 nous compounds and the peptones. They may both be 

 formed by the putrefaction of albuminous substances. 



The proteoses give the general reactions of the al- 

 buminous substances, but they do not, like the former, 

 coagulate on boiling. They are distinguished from the 

 peptones by giving a precipitate with nitric acid or potas- 

 sium ferrocyanid acidified with acetic acid. They are also 

 precipitated by saturating their solution with ammonium 

 sulphate or sodium chlorid, then acidifying. They diffuse 

 with difficulty through an animal membrane. 



The peptones do not give any of these reactions, but 

 respond to the general ones of albuminous compounds, espe- 



