38 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 
such good results that the value of this comparatively new method of 
combating out-of-door insects is now well established. It is not to be 
supposed that work of this kind can be carried on in the case of forest 
trees, except on a very limited scale, to protect cherished trees in lawns 
or parks. This treatment is also effective against Aphides and leaf- 
mites — and indeed is calculated to destroy any insects whatever. 
Hydrocyanic acid (las. — Of the several gases experimented with by 
Mr. Coquillett, of which full accounts are given in my annual reports as 
Entomologist for 1S87 and 1>S8, the one named has given much the 
best results. 
A number of methods of generating this gas have been devised, of 
which the most satisfactory is now known as the k - dry-gas process." 
The necessity of drying the gas was very evident from the first, for 
it was found that the injury to foliage was very serious when the gases 
were charged with any considerable amount of aqueous vapor. In the 
dry-gas process the cyanide is dissolved by boiling in water for a few 
minutes, using I gallon of water for each 5 pounds of cyanide. To 
generate the gas, sulphuric acid is caused to flow upon the cyanide 
solution in a tine stream, causing the gas to be rapidly given off in the 
form of a whitish fog. The moisture is taken up by passing the gas 
through sulphuric acid, which by reason of the water taken up becomes 
diluted, but may still be employed to generate fresh quantities of gas. 
The gas is confined to the trees under treatment by means of a suit- 
able canvas tent or fumigator, of which a number of styles have been 
patented. They are constructed so as to be lowered over the tree from 
above or to inclose it from the sides. Full details for the construction 
of these tents, together with figures, are given in the reports cited 
above, to which the reader is referred, also for a detailed account of 
the use of various gases. 
INSECTICIDE apparatus.— The application of insecticides to fruit 
or forest trees maybe successfully accomplished by the use of the same 
devices employed in the case of low-growing plants, except that more 
force will be required as a rule, and hence larger and stronger machinery. 
The treatment of young trees or application to the lower part of the 
trunk or to the base or roots of larger ones may easily be effected by 
hand, but in the case of the branches and foliage of large trees other 
means must be employed. 
As has been already indicated, the principal insecticides are now 
used in the liquid form, and particularly in the case of work against 
the insect enemies of forest trees will this method prove the only prac- 
ticable one. The use of insecticides in the form of powders will occasion- 
ally be desirable, however, and heuce the treatment of the second part 
of the subject may be discussed under (1) devices for applying pow- 
ders aud (2) devices for applying liquids. 
Devices for Applying Powders. — Powder Blowers. — The appli- 
cation of powders to trees may be successfully accomplished by the 
use of long-discharge-tube power-bellows. 
