14 MASS. EXPERIMENT STATION BULLETIN 303 



while 1:1 and 1:2 ratios give oif the largest amounts and most rapidly. In the 

 present experiments, all of the gas-treated residues contained hydrocyanic acid 

 gas and this increased with the amount of lime in the Bordeaux. 



The results indicated that an increase in the ratio of lime from neutral to 

 4-S-50 and 4-12-50 resulted in a corresponding increase in the amount of soluble 

 copper and HCN. Further increase in the ratio of lime up to 4-24-50 resulted in a 

 gradual decrease in the amount of soluble copper, but did not render the spray 

 and gas regime safer to cucumber plants. Since qualitative analyses of the resi- 

 dues were based on an equal weight, namely l/IO gram, the copper content ob- 

 viously should vary with the concentration of lime. Assuming that 4 pounds of 

 crystalline copper sulfate (25.46 per cent Cu) are employed in preparing Bordeaux, 

 then the amount of copper in the residue would vary with the proportion of lime. 

 The applications, although approximately of the same value of Bordeaux in each 

 case, are therefore not directly comparable as regards the relative amounts of 

 soluble copper found. This fact accounts for an eventual decrease in the amounts 

 of soluble copper as the lime content is increased above ratios of 4-8-50 and 

 4-10-50, based on an equal weight of the dry samples analyzed. 



Dow Bordow, which is an alkaline proprietary copper powder, yielded con- 

 siderable soluble copper on exposure to gas, but none by itself in two parallel 

 tests (Table 3). Being alkaline, these powders behave like Bordeaux mixtures 

 containing an excess of lime. 



The residue of factory-made basic copper sulfate (26.31 per cent Cu) on glass 

 when exposed to HCN never yielded sufficient soluble copper to cause injury. 

 When residues were exposed to gas, a trace of soluble copper was found in five 

 instances and none in two. No soluble copper was found in any of the residues 

 not exposed to gas. The results with Corona copper carbonate (18 per cent Cu) 

 were similar. 



Three te^ts of the residues of neutral Bordeaux 4-X-50 prepared with milk 

 of lime showed no soluble copper; but after exposure to gas, soluble copper was 

 present in all three, although in one case there was only a trace (Table 1). In 

 another comparative test of this mixture, soluble copper was found in both 

 residues, but that acted upon by HCN contained the greater amount. When 

 residues of neutral 4-X-50 mixtures prepared with filtered lime water were com- 

 pared, a trace of copper was found only in residues exposed to gas, and in each in- 

 stance the Bordeaux and gas regime caused injury to cucumber foliage. 



The analysis of spray residues on glass offered more consistent results than on 

 leaves, indicating some influence of the respiratory or transpiratory products or 

 of exudation of tlie leaf itself. 



The action of HCN gas on factory-prepared neutral basic copper sulfates and 

 carbonates did not produce sufficient soluble copper to cause injury to cucumber 

 plants. Gas reacted with neutral laboratory-prepared Bordeaux, and the amount 

 of soluble copper formed appeared to be greater when dispersed lime was used 

 in preparation, e.g., milk of lime or chemical hydrated lime, than when a solution 

 of lime such as filtered lime water was used, but the nature of the base did not 

 remove the hazard of injury. Laboratory preparation in the cold produces less 

 stable copper sulfates than heating which is the practice in the manufacture of 

 commercial sulfates and carbonates; while washing, dehydration, and air separation 

 of the commercial sulfates and-carbonates are considered less important factors 

 contributing to their safety with HCN gas. The results show beyond doubt that 

 homemade neutral Bordeaux 4-X-50, even if its preparation were practical, is 

 not safe with gas. 



It is logical to assume that a soluble double salt is formed in all cases when 

 hydrocyanic acid gas acts on Bordeaux mixture and that the amount varies with 

 the amount of free base, the concentration of the gas, the period of exposure to 



