ALBUMOSES AND PEPTONES 



185 



precipitate of globulin had been obtained on adding an equal volume 

 of a saturated solution, this would not necessarily prove that no 

 globulin was present in the fraction ; for on adding a further quantity 

 of the saturated salt-solution beyond the half-saturation-point, a small 

 precipitate appears, which is a sub-fraction. This sub-fraction-precipi- 

 tate when dissolved in water may, on the addition of an equal bulk 

 of saturated salt-solution, again show a precipitate consisting of 

 globulin. This method of taking sub-fractions, if pushed far enough, 

 is an extremely delicate test, for the more easily precipitable bodies 

 must tend to come down before the more soluble ones. 



The following table shows how, after repeated precipitation, the 

 amount of nitrogen in the final filtrates becomes constant. For the 

 experiment Witte's peptone was used, from which the greater part of 

 the primary albumoses had been separated. The albumose-precipitate 

 was by repeated precipitation completely freed from peptones. 



The results obtained in this table were obtained by using 

 ammonium-sulphate as the precipitant, but sodium-sulphate at 37 

 has the same salting-out capacity as ammonium-sulphate, as shown by 

 Pinkus ; l and Haslam uses this salt in preference, as it renders 

 Kjeldahl's determinations easier. 2 



The next table shows the results obtained when separating the 

 mixed albumoses from a mixture obtained by the peptic digestion of 

 commercial casein. 



1 Pinkus, Journ. of Physiol. 27. 57 (1901). 



2 Haslam gives in his paper special directions for the estimation of organic nitrogen 

 in the presence of ammonium-sulphate. 



