EFFFXT OF HCN GAS AFTER COPPER FUNGICIDES 11 



Table 5. The Effect on Cucumber Plants of HCN Gas Following 

 Treatments with Copper Fungicides 



Fumigation Trcatmenl 



I II III IV 



Cyanogas Used grams -lyi 4}'2 4H 5 



Period of Exposure hours 10 12 10 10 



Interval Between Copper Treatment and 



Fumigation hours 9 32 57 105 



per cent with no well-defined practice. Basic copper acetate was injurious in two 

 out of six experiments, and norma! copper acetate in two out of five (Fig. 4). 

 This may ha\'e been due to some difference in the amount of spray applied or 

 to variations in atmospheric conditions in the greenhouse. Injury followed the 

 exposure of the sprayed uninjured plants to gas; and in those instances where 

 injury resulted from spraying, it was intensified by the action of gas. The soluble 

 copper salt formed by the action of gas was much more toxic than copper acetate 

 itself. A 0.25 per cent dilution was less injurious than higher concentrations, this 

 also holding true with gas (Pig. 5). 



Copper sulfate in 0.01, 0.02, 0.03, and 0.05 per cent solutions -was neutral to 

 litmus but gave faint positive chemical tests for soluble copper. A 0.07 per cent 

 solution was acid to litmus. In none of the experiments were cucumber plants 

 injured by copper sulfate sprays used alone in these concentrations or by the 

 exposure of the sprayed plants to gas. It is evident, therefore, that cucumber 

 plants will tolerate a small amount of water soluble copper without manifesting 

 injury. 



Hammond's Copper Solution, an ammoniacal copper' concentrate guaranteed 

 to contain .\05 per cent active copper, was not injurious to cucumbers of itself 



