179 
trees taller than this an apparatus of some kind, furnished with ropes 
and tackle, will be required. The simplest apparatus of this kind con- 
sists of two upright posts, one on either side of the tree, with a pulley 
at the top of each and a rope passing through it and attached to the 
sheet. This simple device, which can be constructed in a short time by 
almost any person, can easily be moved by hand from tree to tree as 
occasion requires. In throwing the sheet over the tree the uprights are 
allowed to fall to the ground; being very light affairs, they are easily 
raised again when it is desired to remove the sheet from the tree. 
After the sheet is on the tree the slack at the bottom is gathered in 
and pressed firmly against the ground by stepping upon it, this being 
sufficient to prevent the escape of the gas between the lower edge of 
the sheet and the surface of the ground. The gas, being lighter than 
the air, rises and diffuses itself throughout the inclosed space without 
the aid of any kind of artificial means, aud this is true even in the case 
of trees thirty feet in height. 
The length of time that the gas should be confined on each tree 
will depend on the size of the tree, varying from fifteen to thirty or 
even to forty minutes. By employing a sufficient number of sheets or 
tents, no time need be wasted by those operating them, since, by a 
proper adjustment, the tent first placed on the tree can be removed as 
soon as the last one has been adjusted and charged with the gas, and 
the removal of the other tents will follow in their natural order. 
The use of this gas is fast superseding all other methods for destroy- 
ing scale insects on citrus trees iu southern California, and it could 
also be employed for the destruction of several other classes of injuri- 
ous insects. The complete eradication of insects on imported nursery 
stock is of the utmost importance, and for this purpose the gas treat- 
ment is especially adapted. It must be borne in mind, however, that 
the effects of this gas are not the same upon the various different 
Kinds of insects, and even among the scale insects themselves this 
fact is very noticeable. As a rule, the Diaspiure are more easily affected 
than any other kinds; and, as might be expected, the insects them- 
selves are more susceptible to the effects of the gas than are their 
eggs. Mites are but little affected by the gas beyond a temporary in- 
sensibility, or, at least, what appears as such, since in most cases they 
recover from the effects of their forced sleep, and appear to suffer no 
inconvenience therefrom. On the other hand, the gas is very fatal to 
spiders. Among the higher insects, the Diptera and Hymenoptera are 
very susceptible to its iufluence; Hemiptera and Ooleoptera less so. 
When I first began to use this gas as an insecticide, a great cry was 
raised against it on account of its very poisonous nature, as well as 
that of the chemicals used in its production. So very pronounced was 
this feeling that even the analytical chemists of this city refused to 
make an analysis of the potassium cyanide on account of its highly 
poisonous nature. And yet, in the past seven years, during which 
