4 MASS. KXPKRIMKXT STATION BULLETIN 303 



ing to Butler^, adding milk, of lime to a 4-50 solution of copper sulfate until 

 phenolphthalein paper turns red is more simple, and the mixture is as harmless 

 as a strictly neutral wash. Both methods, however, have practical limitations. 



In the experiments reported in this bulletin, different forms of lime and different 

 kinds of base in different ratios with copper sulfate were used. Acid, neutral, 

 and alkaline mixtures of Bordeaux 4-X-50 were prepared with filtered lime water 

 and milk of lime. In many experiments the precipitates were washed on filter 

 paper or by decantation and then brought to volume. Washing was intended 

 to remove the excess of calcium hydroxide and some of the calcium sulfate, on 

 the assumption that these materials might possibly be factors in the incom- 

 patibility of the spray with HCN gas. 



Calcium cyanide, as Cyanogas, was used as the source of hydrocyanic acid gas 

 in many of the experiments. The following tabulation shows the various ways 

 in which it was used. The size of the famigating chamber was 1500 cubic feet 

 with a few exceptions which are noted. 



In other experiments, sodium cyanide was used at the rate of ]/l ounce to 

 1,000 cubic feet and in the generally accepted ratio of 1 ounce of sodium cyanide, 

 \}/2 ounces of concentrated sulfuric acid and 2 ounces of water by liquid measure. 

 It is claimed that these proportions produce the maximum volume of gas and 

 carry the reaction to completion. The plants were exposed to the gas as follows, 

 beginning 1 to 2 hours after sundown. 



Period of Interval Between 



Exposure Copper Treatment 



Hours and Fumigation 



Hours 



1 8 



2M 8 



3 6 



The greenhouse conditions to which the plants were exposed after gassing 

 varied with the weather, but these were the usual commercial growing conditions 

 prevailing under glass. The foliage of the treated plants was not at any time 

 wetted with water. The results were recorded usually 3 to (> days after exposure 

 to gas. 



Fungicides Employed 



In the study of the effect of hydrocyanic acid gas on cucumber plants sprayed 

 iLetter from Dr O. Butler, dated April 22, 1932. 



