CHAPTER II 



QUALITATIVE PROOF OF THE CORRECTNESS OF 

 THE CHEMICAL VIEWPOINT 



PREPARATION OF PROTEINS FREE FROM IONOGENIC IMPURITIES 



The first problem confronting the chemist is to find a method 

 which permits him to settle definitely the problem whether only 

 one or both ions of a salt combine with a protein. This decision 

 was not possible with the old methods. Those who believe in 

 the adsorption theory assume that both ions of a salt are adsorbed 

 by colloids and Pauli holds that both ions of a salt are adsorbed by 

 the non-ionized molecules of protein. 1 



When a block of gelatin is put into a salt solution, the solution 

 enters into the interstices between the gelatin molecules constitut- 

 ing the block. When such a block of gelatin is melted, of course, 

 both ions of the salt are found, but nobody can tell whether the salt 

 found was only the salt contained in the interstices of the original 

 gel or whether it was in combination with the gelatin. This diffi- 

 culty can be circumvented by using solid gelatin in the form of a 

 very fine powder of grains approximately equal in size. When 

 such powdered gelatin is exposed to a salt solution for some time, 

 we can ascertain with certainty by a process of washing whether 

 one or both ions are in combination with the gelatin. After 

 a small mass of the powdered gelatin has been exposed to a 

 salt solution for about 1 hour, it is put on a filter and perfused, 

 with stirring, about six times or more with 25 c.c. of ice-cold 

 distilled water. The water must be cold since otherwise the 

 granules will coalesce, rendering the process of washing futile. 

 By this procedure it is possible to remove the salt solution 

 between the granules of gelatin, without removing the ions in 

 chemical combination with the gelatin at least not by the six 

 washings. By using this method of washing we can ascertain 



1 PAULI, W., Fortschr. naturwiss. Forschung, vol. 4, p. 223, 1912. 



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