<->,^ 



CG Report of the Department of Entomology of thd 



same time uniform chemical action is obtained and sj)attering 

 avoided. 



xA.lthough the tests indicate that a formula of 1-1^-3, that is 

 1 part by weight of KCN, 1^ times as much acid and 3 times as 

 much water by volume as of KCN, gave best reactions, the 

 formula generally recommended for orchard and nursery work, 

 viz.: 1-1^-2^, that is 1 part by weight of KCN, 1^ times as much 

 acid by volume and 1^ times as much water as acid gave as 

 good results under most conditions, hence if preferred can be 

 followed. If too violent action results more water can be added. 



ABSORPTION OF TiHE GAS. 



From results obtained in fumigation of forcing houses, we 

 were led to assume that the hydrocyanic acid gas either had a 

 tendency to bank or was rapidly absorbed as it came in contact 

 with moist soil. 



Some tests made during winter of 1899 and the following 

 winter on diffusion of gas showed that about 50 per ct. of the 

 gas was absorbed by the moist earth. These tests also showed 

 that under cloth-covered fumigators the diffusion was quite 

 uniform. 



Pennyi has shown that in the presence of moist soil over 50 

 per ct. of the available gas present in a cubic foot of space is 

 absorbed. For example, if .15 grm., an amount recommended 

 for fumigation of nursery stock in closed boxes, is used in 

 orchard work where it comes in contact with moist earth, only 

 .075 grm. of this amount becomes available for killing the scale- 

 insects. 



These conditions, together with failure, in some cases, to kill 

 all the scale-insects on low branches and at base of trees, indi- 

 cate that double the amounts of KCN generally recommended 

 for fumigation of nursery stock should be used in orchard work, 

 at least Tf complete extermination is the object sought. The 

 foregoing tests show that on fairly vigorous orchard trees no 

 injury to tree will result from use of this increased amount of 



^Dfl. Coll. Agr. Exp. Sta. 12th Ann. Rept. p. 220. 



