334 PROTEIN-COMPOUNDS. 



state. The solution of this true alkaline albuminate is distinguished 

 by the circumstance that, on boiling, numerous vesicles are formed 

 at the bottom of the vessel, which adhere so tenaciously as to im- 

 part a brown colour to this organic substance in process of forma- 

 tion ; its surface also becomes covered on evaporation with a trans- 

 parent film of coagulated albumen (Scherer), which has frequently 

 caused this albuminate of soda in the animal fluids to be mistaken 

 for casein. This alkaline solution yields, however, on boiling, a 

 perfect coagulum in the form of flakes or masses, if any neutral 

 alkaline salt (such as sulphate of soda, chloride of sodium, or 

 hydrochlorate of ammonia) either in the form of a saturated solu- 

 tion, or in the dry state, has been added to it, previously to its 

 being boiled. 



Acids and metallic salts behave to these alkaline solutions of 

 albumen, nearly in the same way as to those of pure albumen ; but 

 the quantity of the metallic salt which is added, often induces modi- 

 fications, the newly formed albuminates being in some cases soluble 

 and in others insoluble in an excess of the metallic salt or of the 

 albuminate of soda. The greater number of these compounds 

 are however soluble in alkalies. 



Organic acids added in excess to albuminous solutions, behave 

 in the same manner as alkalies added in excess, causing the albu- 

 men to remain dissolved on boiling; if, however, neutral alkaline 

 salts, such as sulphate of soda, chloride of sodium, or hydrochlorate 

 of ammonia be added to these solutions, the albumen separates on 

 boiling into flakes or clots. Further, these acid solutions on being 

 evaporated are covered with a membrane similar to that which is 

 formed by casein in acid or alkaline milk. 



Coagulated or boiled albumen possesses all the properties which 

 we have already noticed as exhibited by the insoluble protein-com- 

 pounds in general. We will, therefore, simply observe that the 

 albumen in its transition from the soluble to the insoluble state, 

 losesa portion of its sulphur; for sulphuretted hydrogen is developed 

 in appreciable quantity: with acids it enters into combinations that 

 are insoluble in water containing acids, but swell and assume a gela- 

 tinous form in pure water, before undergoing solution in it. It may be 

 so perfectly combined with caustic alkalies, as to cause their alkaline 

 reaction entirely to disappear. When heated with concentrated 

 hydrochloric acid it dissolves and assumes a blue colour which in- 

 clines more to purple than is the case with any other of the protein- 

 compounds. If albumen be boiled for a long time in water, atmo- 



