176 
Mr. Riley said it was true, that this was not only an English but a 
European practice. 
Mr. Coquillett's paper on the use of hydrocyanic acid gas was read 
by Mr. Garnian. 
HYDROCYANIC ACID GAS AS AN INSECTICIDE. 
By D. W. CoQriLLETT. Log Angeles, Cal. 
. ad by the secretary in the authors absence/ 
One of the most important properties to be desired in any given in- 
secticide is that it possess the ability to completely exterminate the 
insects against which it is directed. As a rule which has but few 
exceptions, the more prominently injurious insects are very prolific, and 
even if only a few individuals remain upon the plant, these in a com- 
paratively short time will multiply to such, an extent as to render it 
necessary to again employ artificial means for their destruction. For 
this and other reasons that might be mentioned, it is of the utmost im- 
portance that the insecticide employed will result in the almost or com- 
plete eradication of the insects against which it is directed. 
Those who have had any experience with the destruction of scale 
insects on citrus trees by the use of liquid sprays of various kinds, soon 
become aware of the fact that even by the use of the best mechanical 
devices and the exercise of the greatest care in applying the spray, 
quite a large percentage of the insects will escape destruction. This 
fact wa> abundantly demonstrated a few years ago. during the preva- 
lence of the Fluted Scale (Icerya purehasi) in some of the orange 
groves of Southern California prior to the advent of the Vedalia card!. 
\ialis. At that time the Supervisors of Los Angeles County offered a 
reward of $1,000 for an effectual remedy for destroying this pest, and 
appointed a committee of three, of which the winter was a member, be- 
fore whom the various remedies were to be tested. One of the rules 
formulated by this committee was that the successful remedy must be 
able to entirely eradicate the Fluted Scales upon any given tree. Up- 
wards of three dozen different tests were made, many of them by men 
who from long experience had become very expert in the matter of 
applying sprays to the trees, and yet in not a single instance were all 
of the scales exterminated upon one of the trees. In some instances, a 
curled leaf or a piece of loose bark would be the means of protecting 
the insects from the spray: and no matter how thoroughly the spray- 
ing was done, or how long-continued was the operation, a few of the 
insects were certain to escape the effects of the spray. 
It was with a view to remedy this important defect that in the au- 
tumn of 1886 the writer began a series of experiments with various 
kinds of gases by inclosing the infested tree in a gas-tight envelope or 
