314 CHEMISTRY OF THE PROTEIDS CHAP. 



be seen that sodium is a much stronger kat-ion than is mercury, and 

 hence sodium will displace the mercury in the albuminate, a sodium 

 instead of a mercury albuminate being formed ; the mercury ions, 

 turned out of their union with the albumin, link on to the chlorine 

 an-ions to form sublimate, and as the solution is already saturated 

 with an excess of chlorine-ions, the HgCl 2 cannot dissociate, and we 

 arrive at the same result as if we had added a solution of sublimate 

 in a strong salt solution to the proteid. The sodium albuminate does 

 not coagulate, because all neutral salts, such as sodium chloride, fail to 

 produce coagulation. 



These experiments make it clear that it is by no means immaterial 

 whether tissues are fixed in sublimate or in sublimate-sodium chloride 

 solutions. Some years ago M. Heidenhain was good enough to 

 inform me by letter that his object in using sublimate dissolved in 

 salt solution was to increase the solubility of the former. At that 

 time I had made these experiments, but refrained from arriving at 

 any rash conclusion because I did not know then, nor do I now, to 

 what extent the electrolytic dissociation of sublimate is prevented by 

 the addition of salt, particularly as the new factor of increased solu- 

 bility of the mercury salt, owing to the formation of double salts, 

 comes in. 1 



When staining sections the instability of the mercury albuminate 

 must also be borne in mind. 



EXPERIMENT 10 

 To determine the coagulating power of the double salt HgCl 2 + 



Double salt by weight . . . 0'5 0'4 0'3 0'2 O'l 0'05 



After twenty-four hours the amount of sediment diminished from 

 A to F, showing that to get a complete precipitation, as far as this 

 is possible in the presence of sodium chloride, the fixative must be 

 to the object to be fixed in the proportion of 10 to 1. That pre- 

 cipitation was not complete was determined by adding some of the 



1 Experiments have been going on for some time to settle experimentally the precise 

 effect produced on tissues by adding sodium chloride to sublimate solutions in different 

 proportions. 



