146 PHYSICAL CHEMISTRY 



This seems to be the action of organic preparations of heavy 

 metals such as "argyrol." 



The toxicity of each cation may be decreased more or less by 

 certain other cations. For this reason, the toxicity of a salt 

 is reduced when it is added to solutions containing other salts 

 (as is always the case where it is desired to disinfect). Only 

 the most toxic salts, therefore, are reliable for disinfection. 

 Copper salts may ibe used in some cases but salts of mercury 

 are better. The salts of the precious metals are the most reliable. 



The salts of the lighter metals may be toxic, especially if their 

 solutions are pure and kept pure by replacing the contaminated 

 solution with fresh ones. Some discrepancies seem to exist be- 

 tween the solution-tension series and the toxicity series, but 

 these would probably be lessened if all of the salts were abso- 

 lutely pure and if some indifferent substance could be found 

 to equalize the osmotic pressure. Hober (1908 a) studied the 

 relative efficiency of slightly hypotonic solutions in causing 

 cytolysis of erythrocytes (hemolysis). The ionic series with 

 increasing hemolytic power is as follows: 



S0 4 <C1 <Br <NO s <CNS <I and 

 Li, Na <Cs <Rb <K 



Lillie (1909 a) observed the same anionic series for the 

 cytolysis of sea urchin eggs, but Na' was more toxic than K\ 

 The same anionic series was found to hold for the cytolysis 

 (dissolution) of cilia (Lillie, 1909 c; Hdber, 1909 b), but the 

 cationic series is different for different species of animals. In 

 general, it may be said that the iodides of the alkali metals, 

 when pure, exert a cytolytic action. 



It has been shown by Kahlenberg and True (1896) and others 

 that the toxicity of strong acids depends on the concentration 

 of the hydrogen ions. Mineral acids cause death of seedlings 

 and cytolysis of many plant cells when the concentration exceeds 

 1/6400 normal. For disinfection .in or stronger solutions may 

 be used. 



The toxicity of the weak acids depends on several factors, 

 so that no general rule may be made in regard to them. Their 

 power of reducing the surface tension of water is the index of 

 one factor. Acetic acid and sulphurous acid are used in dis- 

 infection. 



