184 CHEMISTRY OF THE PROTEIDS CHAP. 



of hetero-albumose. The maximal capacity for binding hydrochloric 

 acid, which was observed, amounted to 314 mgrms. for 1 grm., therefore 

 its equivalent value is only 116. Looked upon as a base, it is at least 

 23 -acid, but probably much more so. Its hydrolytic dissociation 

 is great. 



How very real the difficulty of preparing individual albumoses is, 

 becomes evident on reading the recent paper of Haslam. 1 He points 

 out the absolute necessity of ascertaining that each fraction is not only 

 free from the succeeding, but also from the preceding fractions. 



To show that a proteid-precipitate is freed from the substances of 

 the nitrate, Haslam proceeds as follows : The precipitate is dissolved 

 in water, and the whole made to a given volume ; the requisite 

 amount of salt or of alcohol to produce precipitation is added ; the 

 mixture is allowed to stand for twenty-four hours, and is then filtered. 

 If no proteid, or other substance which is being got rid of, is found in 

 the filtrate, then the precipitate is pure. If not, the amount of 

 organic nitrogen in the filtrate is estimated by Kjeldahl's method. 

 The precipitate is then redissolved, again made to the same volume, 

 and treated in exactly the same way as at first. The second filtrate 

 is now again examined for organic nitrogen. If the amount of 

 nitrogen in the second filtrate is the same as that in the first, it is 

 due to small amounts of the precipitate being soluble in that particular 

 medium, and the precipitate is therefore free from all extraneous 

 nitrogenous matter. If, however, the amount of nitrogen in the first 

 filtrate is greater than that in the second, there is still nitrogenous 

 impurity to be got rid of, and further precipitations are needed. 



If, however, the substance to be purified is in the filtrate, and the 

 proteids that are being got rid of are in the precipitate if, for example, 

 serum albumin is to be freed from globulin the following procedure 

 is necessary. As it is impossible to completely remove all the globulin 

 from a solution containing also albumins and peptones by half satur- 

 ating the solution with ammonium sulphate, as some of the globulin is 

 kept in solution by the albumin, recourse must be had to ' fractional 

 precipitation.' If to serum an equal volume of saturated ammonium 

 sulphate is added, most of the globulin is precipitated, but some 

 accompanies the albumin and is present in the clear filtrate ; for if to 

 the latter some saturated ammonium sulphate be added until a small 

 precipitate appears, if this precipitate be filtered off and be re-dissolved 

 in water, it is possible by the addition of an equal volume of saturated 

 salt-solution to obtain a precipitate of globulin, demonstrating the 

 presence of globulin in the original filtrate. But even if no second 

 1 H. C. Haslam, Journ. of Physiol. 32. 267 (1905). 



