BY JAMES M. PETKIE. 



105 



The following table gives an approximate view of the 

 precipitation-limits with ammonium sulphate, of the proteins 

 present in a 10% salt-extract. 



Table v. — Fractional Satdration with Ammonium Solphate. 



Each of the nine tubes contained 10 cc. of fluid. Succes- 

 sively increasing amounts of ammonium sulphate were used, 

 and the point observed at which incipient precipitation took 

 place. This occurred in No. 7, with six-tenths saturation. 

 With a lower concentration, no salting out occurred, and 

 above this point the precipitation rapidly increased. 



Quantitative Precijntation by Alcohol. — Alcohol precipi- 

 tates globulins, albumins, proteoses, and peptones, in the 

 order named. Animal-peptones are stated by Mann to be 

 partly soluble, even in 96% alcohol, thovigh Kiihne and 

 Chittenden observe that the precipitation is much more com- 

 plete in the presence of salts. As plant-proteins vary con- 

 siderably in the strength of alcohol required for their pre- 

 cipitation, the following series of experiments was designed 

 to ascertain if any difference could be detected in the various 

 fractions obtained by gradually increasing strengths .'f 

 alcohol. For this purpose, a protein-extract was prepared 

 with 5% sodium chloride, and filtered clear. 



(o) Of this solution, 20 cc. were placed in each of eight 

 centrifuge-tubes, and the calculated proportions of alcohol 



