96 PHYSIOLOGICAL CHEMISTRY. 



rendering the menstruum incapable of holding the protein in solu- 

 tion, thereby causing the protein to be precipitated or salted-out 

 to use the common term. Mineral acids and alcohol also precipitate 

 proteins unaltered. Proteins are precipitated as albuminates when 

 treated with certain metallic salts, and precipitated as insoluble 

 salts when weak organic acids such as certain of the alkaloidal 

 reagents are added to their solutions. 



It is generally stated that globulins are precipitated from their 

 solutions upon half saturation with ammonium sulphate and that al- 

 bumins are precipitated upon complete saturation by this salt. Com- 

 paratively few exceptions were found to this rule until proteins 

 of vegetable origin came to be more extensively studied. These 

 studies, furthered especially by Osborne, and associates, have dem- 

 onstrated very clearly that the characterization of a globulin as a 

 protein which is precipitated by half saturation with ammonium 

 sulphate, can no longer hold. Certain vegetable globulins have 

 been isolated which are not precipitated by this salt until a concen- 

 tration is reached greater than that secured by half-saturation. 

 As an example of an albumin which does not conform to the defini- 

 tion of an albumin as regards its precipitation by ammonium sul- 

 phate, may be mentioned the leueosin of the wheat germ which is 

 precipitated from its solution upon /uz//-saturation with ammonium 

 sulphate. The limits of precipitation by ammonium sulphate, 

 therefore, do not furnish a sufficiently accurate basis for the 

 differentiation of globulins from albumins. It has further been 

 determined that a given protein which is precipitable by ammonium 

 sulphate cannot be " salted-out " by the same concentration of the 

 salt under all conditions. 



EXPERIMENTS. 



i. Influence of Concentrated Mineral Acids, Alkalis and Or- 

 ganic Acids. Prepare five test-tubes each containing 5 c.c. of con- 

 centrated egg albumin solution. To the first add concentrated 

 H 2 SO 4 , drop by drop, until an excess of the acid has been added. 

 Note any changes which may occur in the solution. Allow the 

 tube to stand for 24 hours and at the end of that period observe 

 any alteration which may have taken place. Heat the tube and 

 note any further change which may occur. Repeat the experiment 

 in the four remaining tubes with concentrated hydrochloric 

 acid, concentrated nitric acid, concentrated potassium hydrox- 

 ide and acetic acid. How do strong mineral acids, strong alkalis and 



