EFFECT OF HC\ GAS AFTER COPPER FUNGICIDES 7 



exposure to HCN. When the order of mixing was reversed and a milk of lime sus- 

 pension was employed, the effect after HCN was the same. A 0.5 per cent solution 

 of copper sulfate neutralized with filtered lime water caused slight injury with 

 HCN. A 1 per cent solution of copper sulfate was neutralized with filtered lime 

 water and allowed to settle. The top, clear liquor was decanted and to the sedi- 

 ment was added fresh water to make 500 cc. When cucumber plants were sprayed 

 with this mixture and then gassed, the injury was moderate to severe. Plants 

 were killed when gas followed the use of a 4-50 solution of copper sulfate neutral- 

 ized with milk of lime, and were severely injured when gas followed Bordeaux 

 4-X-50 neutralized with filtered lime water prepared from fresh stone lime. 



Acid, neutral, and alkaline 4-X-50 mixtures prepared with milk of lime and 

 filtered lime water, and either used as such or first washed and dehydrated, 

 were compared to determine the influence of the form of lime and the reaction 

 of the spray on the compatibility of the residue with the gas (Tables 1, 5). When 

 acid Bordeaux 4-X-50 prepared with milk of lime was employed, slight injury 

 resulted in two instances and none in two; but on exposure of the sprayed plants 

 to gas, injury resulted in every instance, and it was intensified in the two cases 

 in which the spray itself was injurious. Neutral mixtures of 4-X-50 prepared with 

 milk of lime were safe of themselves, but in every instance they were injurious 

 with gas. Similar mixtures containing sufficient excess lime to give an alkaline 

 test to- litmus gave like results. When these mixtures were washed, none caused 

 injury of themselves, even the acid mixtures, yet all of them were injurious 

 when the sprayed plants were exposed to gas. When Bordeaux 4-X-50 was pre- 

 pared with filtered lime water, only the acid mixtures caused injury of them- 

 selves. Injury resulted in ever}- instance where gas acted on neutral or alkaline 

 mixtures, and it was intensified by the action of gas on acid mixtures. Washing 

 the mixtures did not effect any change in these results. Washing and dehydrating 

 a neutral 4-X-50 mixture prepared with milk of lime or filtered lime water (Table 5) 

 then bringing again to volume with water did not make it safe to use, but pro- 

 longing the interval between spraying and gassing appeared to remov'e or lessen 

 the danger of injury. The filtrates of neutral or alkaline Bordeaux 4-X-50 mix- 

 tures were compatible with gas, indicating that the incompatible principle is not 

 present in the filtrate and that it is neither calcium hydroxide nor calcium sul- 

 fate. (Fig. 3.) 



On the basis of this experimentation, it may be concluded that slightly acid 

 or neutral Bordeaux mixtures of lime and copper sulfate which are safe of them- 

 selves are positively incompatible with hydrocyanic acid gas; that mixtures 

 with increasing amounts of lime are extremely fatal to cucumbers under com- 

 mercial conditions of culture; that Bordeaux made with milk of lime or chemical 

 hydrated lime results in more injury when followed by gas than Bordeaux made 

 with lime water, although none are safe. The presence of moisture on the foliage 

 such as would occur from watering is not a necessary factor. Irrespective of the 

 ratio of lime to copper sulfate, injury will occur and the most severe damage may 

 be expected with mixtures containing an excess of lime. 



Sodium Carbonate with Copper Sulfate 



Burgundy precipitates of different ratios of sodium carbonate to copper sulfate 

 were prepared by adding a cool, dilute solution of copper sulfate to a similar solu- 

 tion of sodium carbonate, then bringing up to volume (Table 2). Burgundy 4-4-50, 

 a strongly alkaline precipitate, was employed three times, causing some injury 

 of itself in two experiments but none in the third. In all three experiments ex- 

 posure of the sprayed plants to hydrocyanic acid gas was fatal to the plants. 

 Precipitates of 4-2-50 and 4-3-50 ratios, also alkaline to litmus, caused no injury 



