THE PHYSICAL PROPERTIES OF THE PROTEINS 11 



in 100 c.c. of solution when precipitation of globulin commences in 

 a solution of egg-albumin, where the protein is present to the extent 

 of 2 grams in 100 c.c. after admixture with the salt solution. 



It will be noticed from the above table that the capacity for pre- 

 cipitation depends on both the acid and the metal of a salt. The 

 metals show a decreasing power of precipitation, passing from left to 

 right of the table, whereas the acids show a decreasing power, passing 

 from the top to the bottom. The same result is obvious when the 

 numbers are expressed in terms of factors of normal solutions. 



FACTORS OF NORMAL SOLUTIONS NECESSARY TO START PRECIPITATION OF 



GLOBULINS. 



1-5-1-69 N. 



Li 2 S0 4 



Na 9 SO 4 



Na 2 HPO 4 



K 2 HPO 4 

 CH,CO 2 Ka 



CH 3 CO 2 N 



K citrate 



Na citrate 



K tartrate 

 Na tartrate 



Some salts fail entirely to precipitate proteins owing to their small 

 solubility in water. Thus, according to the above tables, on the as- 

 sumption that the capacity for precipitation depends both on the 

 acid and the metal, some concentration between 11*39 anc ^ X 3'39 P 61 " 

 cent, of complete saturation by potassium sulphate should precipitate 

 globulin. Potassium sulphate dissolves, however, only to the extent 

 of 1074 parts in 100 parts of water at 15. Similar remarks apply 

 to potassium nitrate, potassium bicarbonate and potassium chlorate. 



The application of the salt precipitation method to the separation 

 of the products obtained by the digestion of proteins by proteoclastic 

 ferments by Kiihne and his pupils, Chittenden and Neumeister, has 

 been mentioned already. They distinguished between "primary" 

 proteoses, which are precipitable by sodium chloride or magnesium 

 sulphate, " secondary " proteoses, which are precipitable in the filtrate 

 from the primary proteoses by ammonium sulphate, and " peptones," 

 which cannot be precipitated by salts. A revision- of this work was 

 undertaken in Hofmeister's laboratory by his pupils, Pick and Zunz, 

 who used for the purpose of separation of fractions varying concen- 

 trations of one salt (cf. Kauder's researches, p. 10). The former used 

 ammonium sulphate, and the latter zinc sulphate, a salt which had 

 been previously employed for protein precipitation by Bomer. 



Pick, by half-saturation of Witte's peptone solution with am- 

 monium sulphate, separated a so-called hetero- and proto-proteose 

 fraction. From the filtrate containing the \ " secondary " proteose 



