Containing traces of copper, .0025%. 



The cultures described in the foregoing tables indicate sev- 

 eral interesting facts more or less applicable to field conditions. 



(1) Precipitated carbonate of copper is shown to have a 

 much more toxic effect upon corn than the finely pulverized 

 ores of chalcocite or chrysocolla. With the precipitated car- 

 bonate 0.025 per cent in the soil was distinctly toxic, while with 

 chalcocite and chrysocolla about 0.08 per cent was required to 

 produce an equal effect. Inasmuch as all of these combinations 

 of copper may occur in a soil subject to mining detritus, a mere 

 determination of total copper in soils containing doubtfully toxic 

 quantities cannot convey trustworthy information as to the in- 

 juriousness of the amounts present. 



Moreover, since it has been shown that in the case of pre- 

 cipitated carbonate, and sulphate of copper, equivalent quantities 

 of these salts in solution are equally toxic, it is probable that the 

 greater toxicity of the carbonate is due to its greater solubility 

 under soil conditions. It is, in fact, shov/n in table I, ' ' Solubili- 



