EDWIN JOSEPH COHN 713 



(Baker and Adamson: c. p.), 5 gm. of potassium sulfate and 0.7 

 gm. of mercuric oxide were added, and the protein was digested. 

 When digestion was complete, the colorless solution was cooled and 

 diluted to about 250 cc. with distilled water. 1 gm. of sodium hy- 

 pophosphite was then added to reduce the mercuric oxide, and 

 75 cc. of saturated sodium hydroxide were added ^o neutralize the 

 sulfuric acid and liberate the ammonia. The ammonia was then 

 distilled into a measured amount of n/7 hydrochloric acid. The excess 

 of acid together with a blank containing the same amount of acid were 

 then titrated with n/14 sodium hydroxide, a combination of meth- 

 ylene blue and methyl red being used as indicator (39). Sodium 

 hydroxide of this strength was used, since each cc. required to neu- 

 tralize the blank in excess of that required to neutralize the unknown 

 then corresponds to 1 mg. of nitrogen, (atomic weight of N = 14.01). 



The Solubility of Serum Globulin. 



Serum globulin was the first protein that we purified from other 

 proteins, from acids, bases, and salts, and from its own soluble com- 

 pounds to a sufficient extent to obtain a product of constant 

 solubility, — a product that would dissolve in water to a constant ex- 

 tent. The results of five experiments are recorded in Table III. 

 They are in striking contrast to what they would have been had a 

 second protein, or a soluble form of the same protein, been present. 

 A twentyfold variation in the amount of suspended protein produced 

 no commensurate change in solubility, though there was a very slight 

 increase in solubility with an increase in the amount of the preparation. 

 The solubilities recorded are the average of three analyses. They 

 indicate that serum globulin prepared in this way only dissolves in 1 

 liter of water at 25°C. to the extent of approximately 0.1 gm. 



Serum globulin has now been prepared in this manner a second 

 time, and several further precautions taken both in its purification, 

 and in the determination of its solubility. The globulin in the first 

 preparation (IV) was derived from citrated plasma of the cow, in the 

 second from cow serum. In both preparations the so called pseudo- 

 globulin fraction was used. This fraction is supposedly freer from 

 lipoid (40) and from phosphorus (40, 41) than is euglobulin. Whether 



