DETAILS OF TREATMENT. 



Generation of the Gas- Hydrocyanic acid gas is generated by 

 the action of sulphuric acid on potassium cyanide in the presence of 

 water. The required quantities of the cyanide and water are first 

 placed in the generating vessel, the cyanide being then covered with 

 the tent or sheet and the vessel slipped under almost to the base of 

 the tree ; reaching in, the operator then adds the acid, pouring it 

 slowly into the vessel so as to avoid its splashing and thus burning 

 his hand or the cloth. He immediately withdraws and the men 

 shovel a little soil on the edges of the cloth all around to more 

 thoroughly prevent the escape of the gas. 



The rapidity of the evolution of the gas depends largely upon the 

 size of the pieces of cyanide. If these are like powder, the reaction 

 is violent and immediate; but if in lumps, the reaction takes place 

 more slowly and continues for a minute or longer. The slow reaction 

 is desired, partly because less injury results to the foliage immediately 

 above the vessel. But the lumps must not be too large, for then the 

 reaction is liable to be imperfect owing to a black coating (carbon ?) 

 forming over the lumps and preventing further decomposition by the 

 acid. The water should not be added too soon or part of the cyanide 

 becomes dissolved and gives a violent reaction. The residue which 

 remains in the dishes is buried ; and the dishes are washed in clean 

 water before being again used. 



The weighing of a large number of doses at one time and keeping 

 them in envelopes or boxes until used was attempted but found to be 

 disadvantageous owing to the affinity of the cyanide for water. 



Time Necessary for Treatment, The cover is left over the tree 



for thirty minutes in the case of small trees and forty-five in the case 

 of those over twelve feet in height. At the expiration of this period 

 the generating vessel. is removed and the residue buried in the soil; 

 the dish is then washed out preparatory to treating another tree. 



A number of trees are fumigated together, the endeavour being to 

 treat as many at a time as can be covered and uncovered during the 

 period of exposure. In this way the men are kept continuously busy, 

 the time for the removal of the first tent arriving by the time that 

 the last tree is covered. The largest number of trees fumigated 

 during one night has been 190. The average number has been only 

 a small fraction of this number owing to the delays caused by high 

 winds and rains, and in the conveyance of the outfit from farm to 

 farm and town to town. On several occasions, inclement weather 

 prohibited the work four nights in the week, and at one time there 

 were but two really favourable nights for a period of three weeks. 



Absence of Sunlight Necessary. The originators of the 



fumigation process observed that the gas was most efficacious and that 



