22 THE GENERAL CHARACTERS OF THE PROTEINS 



and magnesium sulphate ; in addition to these an albumin coagulating 

 at 73 was obtained, which cannot be so precipitated. 



Other coagulation points were determined by Fredericq. 



It is not in the least probable that such a process as fractional 

 coagulation can lead to a complete separation of a mixture of pro- 

 teins ; it is, moreover, irreversible, and in this respect cannot have 

 such a general application as, e.g., the separation by means of salt 

 precipitation. 



It remains to be considered, however, how far the coagulation 

 temperature may be 'regarded as a constant characteristic of any 

 individual protein. (NOTE. All proteins do not form heat-coagulable 

 solutions.) It was long ago observed that the reaction of the liquid 

 and the presence of neutral salts exercised a marked influence on 

 the coagulation temperature. In the case of natural fluids, such as 

 muscle-plasma, serum, etc., which contain salts, it was noticed that 

 the coagulation took place more readily in a slightly acid solution ; 

 the presence of larger quantities of acids, however, inhibited the 

 coagulation, owing to the formation of acid albumin. In the experi- 

 ments of Halliburton, already referred to, the fractional coagulation 

 was carried out with solutions having a certain definite acidity. 



The influence of salts was recognised by Aronstein (1874), wno 

 showed that a solution of egg-white, from which inorganic matter 

 had been almost completely removed by dialysis, lost its coagula- 

 bility. Subsequent researches were undertaken by Alexander 

 Schmidt and Heynsius, and it was found that the protein solutions 

 of Aronstein still contained alkali, although the neutral salts had 

 dialysed away. Heynsius made the further observation that by 

 very long-continued dialysis, by means of which nearly all the alkali 

 is removed, a solution is obtained which recovers its coagulability ; 

 the coagulation in this solution is inhibited, however, by the pre- 

 sence of minute quantities of acids and alkalis. Similar results were 

 obtained by Winogradoff and Haas. 



The capacity for coagulation of a solution depends, therefore, 

 both on its reaction and the quantity of neutral salts present ; the 

 smaller the quantity of the latter, the smaller the amount of alkali 

 necessary to inhibit coagulation. 



Careful quantitative studies on the influence of salts on the tem- 

 perature of coagulation have been undertaken by Starke and by 

 Pauli, the latter of whom has endeavoured by his researches to throw 

 some light on the chemico-physical process involved in the coagulation 

 of colloids. 



Starke determined the amount of various neutral salts that were 

 necessary to restore the coagulability of a protein solution, which had 

 been deprived of this property by dialysis. He found that in the 

 case of the salts of alkaline earths and magnesium, a few milligrams 

 per 100 c.c. of solution sufficed, whereas with the alkaline salts I 

 gram per 100 c.c. was required. Starke also investigated the in- 

 fluence of varying quantities of different salts on the temperature of 

 coagulation. This question was the subject of a more exhaustive 

 investigation by Pauli. The following table, which is one out of a 

 large number to be found in Pauli's earlier paper, illustrates the in- 

 fluence of varying quantities of different salts on a certain solution 

 of egg-white. In all cases 2 c.c. of the egg-white solution were 



