EFFECT OF HCN GAS AFTER COPPER FUNGICIDES 15 



gas, the conditions favoring absorption of the gas, and the greenhouse tempera- 

 tures after gas. Water soluble copper would seem to preclude cuprous and cupric 

 cyanides also, since both are insoluble in water, according to Williams (15, p. 

 48-49) and Hodgman and Lange (5, p. 102, 103). Cuprous cyanide readily dis- 

 solves in solutions of alkaline cyanides with which it forms a number of crystalline 

 double salts. The calcium salt CaCu2(CX)45H20, according to Williams (15) 

 is very soluble in water. The injurious compound formed when gas acts on 

 Bordeaux is presumably calcium cuprocyanide or some similar product. An 

 equation showing the procedure in the reaction, or a more definite opinion re- 

 garding the formula of the toxic substance would be dangerous without more 

 confirmatory laboratory work, and is not needed from a practical point of view. 



CONCLUSION 



The presence of free lime or soda in the copper spray increases the degree of 

 injury; but injury may occur without it as is demonstrated by the behavior of 

 acid Bordeaux mixtures prepared with lime or soda, the acid basic and normal 

 copper acetates, and neutral Bordeaux 4-X-50 mixtures prepared with milk of 

 lime or filtered lime water. The danger of injury from the use of insufficient lime 

 would be as great as the danger from a slight excess. Therefore, if fungous diseases 

 are of sufficient importance in the greenhouse to warrant the use of copper fungi- 

 cides, fumigation with hydrocyanic acid gas should precede the application of 

 copper; or only commercial basic copper carbonates, basic copper sulfates, or 

 non-staining ammoniacal copper sprays should be used. 



SUMMARY 



Cucumber plants were not injured when sprayed with Corona copper carbonate 

 (18 or 50 per cent Cu) or commercial basic copper sulfates (26.31, 52.95, or 53.31 

 per cent Cu) followed by hydrocyanic acid gas. These diluted sprays are neutral 

 to litmus. Laboratory-prepared neutral Bordeaux mixtures with gas were in- 

 jurious. 



When cucumber plants were sprayed with basic copper sulfate to which chemi- 

 cal hydrated lime had been added, injury followed the use of gas and increased 

 proportionately with the alkali present. 



When cucumber plants were sprayed with acid copper fungicides, i.e., normal 

 and basic copper acetates, acid Bordeaux prepared with calcium hydroxide, 

 sodium carbonate, or sodium hydroxide, injury resulted from or was intensified 

 by an application of gas. 



Copper sulfate solutions containing 0.01, 0.02, 0.03,0.05, or 0.07 per cent copper 

 sulfate were not injurious to cucumber plants when used alone or followed by gas. 



Cucumber plants were injured when gas followed spraying with copper fungi- 

 cides containing calcium hydroxide, sodium hydroxide, or sodium carbonate, 

 even when the alkali component was reduced to yield mixtures neutral to litmus. 



Injury occurred whether hydrocyanic acid gas was evolved from calcium 

 cyanide (Cyanogas) or from sodium cyanide, and whether chemical hydrated 

 lime, milk of lime, or filtered lime water was used in the preparation of Bordeaux. 



The spray residue from injured leaves yielded water soluble copper; and the 

 amount of soluble copper and the degree of injury in general tended to increase in 

 proportion to the amount of alkali present in the fungicide within the limits of 

 ordinary ratios of base to copper sulfate. 



Residues of Bordeaux on glass, acted upon by gas, yielded both soluble copper 

 and hydrocyanic acid gas. These occurred in a fairly constant ratio and increased 



