EFFECT OF HCN GAS AFTER COPPER FUNGICIDES 5 



with copper fungicides, consideration was given to most of the diverse forms of 

 copper sprays recommended by investigators or introduced by manufacturers, 

 as classified by Holland and Gilligan (11). The effect of gas on plants sprayed 

 with Bordeaux containing different ratios of lime to copper sulfate was especially 

 investigated. Attention was also given to mixtures prepared with sodium carbon- 

 ate and sodium hydroxide. Alany proprietary Bordeaux substitutes were con- 

 sidered; namely, such brands as Corona, Bowker, Dow, Grasselli, Rex and Riches 

 Piver. Such stainless copper sprays as ammoniacal copper carbonate, Fung- 

 trogen and Hammond's Copper Solution were also tested. Other copper fungicides 

 used were basic and normal copper acetates from the General Chemical Company, 

 copper carbonates from the Corona Chemical Company, basic copper sulfate 

 from Marsh Brothers, and factory-prepared basic copper sulfates of variable 

 copper content prepared with calcium, magnesium, and sodium carbonates, and 

 described by Holland et al. (6, 9). 



Since it has been alleged that the reaction of the spray has a great bearing upon 

 its compatibility with gas, the filtrates of the diluted sprays were carefully tested 

 with litmus paper and a freshly prepared 10 per cent solution of potassium ferro- 

 cyanide. The chemical test is preferable to litmus for determining the presence 

 of soluble copper and the reaction of the spray, but within narrow limits neither 

 method, of course, indicates the amount of excess base. 



RESULTS WITH CUCUMBER PLANTS 

 Lime with Copper Sulfate 



In Table I are presented summarized data showing the effect on cucumber 

 plants of a Bordeaux-hydrocyanic acid gas regime in which ratios of lime to 

 copper sulfate were used ranging from 4-0.6-50 to 4-24-50. 



When a 4-1-5Q mixture was used, injury occurred after gas in each of the thirteen 

 experiments, being severe or very se\ere in nine, moderate in one, and slight in 

 three of the experiments (Figs. 1, 2). A litmus test of the filtrate applied in live 

 experiments was neutral, and the copper test negative. When mixtures of 4-4-50, 

 4-8-50, 4-12-50, 4-16-50, and 4-24-50 preceded gas, severe injury occurred in each 

 case (Fig. 1). In some instances injury increased as the ratio of lime to copper 

 sulfate increased from neutral to 4-2-50 mixtures, while higher ratios showed a 

 severe injurious effect which sometimes resulted in the death of the treated plants. 

 The results of other experiments showed that the degree of injury with ratios of 

 4-1-50 to 4-8-50 was quite similar, or they showed only narrow distinctions 

 (Fig. 1). Mixtures represented by the ratios 4-0.6-50 and 4-0.8-50, which yielded 

 positive tests for copper, were of themselves injurious and the injury was greatly 

 intensified by the action of gas. A 4-0.9-50 mixture prepared with milk of lime, 

 giving a positive test for soluble copper, caused no injury of itself, but very 

 severe injury when followed by gas. A similar mixture prepared with chemical 

 hydrated lime and yielding no soluble copper caused injury with gas but no 

 injury of itself. Thus, in six instances where soluble copper was detected in the 

 diluted spray, the gas either caused or greatly intensified injury. When gas 

 followed such weak Bordeaux mixtures as 1-3^-50 (Fig. 2) and 1-1-50, injury 

 resulted and this held as well when the sprayed plants were gassed 130 hours 

 after the copper treatments as after 34 hours. No significant or consistent con- 

 trast in injury resulted from substituting milk of lime for chemical hydrated lime 

 in the preparation of Bordeaux. A slight difference, however, in the purity of the 

 lime products employed would be sufficient in the narrow ratios used to account 

 for any slight difference in injury. 



Plants sprayed with a 1-50 mixture of slaked pulveri?.ed "fat" lime treated 

 with a 1 per cent solution of copper sulfate until neutral to litmus were killed by 



