TOXICITY OF HEAVY METALS 71 



of the diminution of its toxicity as here observed, is clearly shown by 

 simple calculation according to the isohydric principle. The percentage of 

 dissociation of Cu(NO 3 ) 2 in the mixtures here employed should be deter- 

 mined by the concentration of the NO 3 radical. Following this generaliza- 

 tion, the data given in table I (C, a) have been obtained. Seventy-six per 

 cent, of the copper salt of the first combination is seen to be dissociated. 



TABLE I 



Now, if only one per cent, of the copper here actually present in the 

 mixture were ionized, the concentration of the Cu ion would correspond 

 to that in an o.ooooSm solution of Cu(NO 3 ), alone, which, as has been 

 shown, is stronger than is necessary to inhibit spore germination. It is 

 therefore apparent that the decrease in the toxicity of the copper salt shown 

 in these combinations with Ca(NO 3 ) 2 is not to be related to decreased 

 ionization of Cu(NO 3 ) 2 . 



Another theory to account for a similarly decreased toxicity of HgCU 



