24 
attached to a framework on a wagon or sled, while to its upper end is 
attached a long stick of timber, the latter being attached near its middle 
to the top of the post, like the sweep of an old-fashioned well. The 
tent is then attached to one end of the sweep, and by pulling downward 
on the opposite end the tent is raised up, and may then be swung 
around and let down over a tree. 
After the tent is placed over the tree the next step is to charge it 
with the gas. The materials used for the production of the gas consist 
of commercial sulphuric acid (Ky SO,), fused potassium cyanide (KON), 
and water, the proportions being 1 fluid ounce of the acid, 1 ounce by 
weight of the dry cyanide, and 2 fluid ounces of water. The generator 
is placed under the tent at the base of the tree; it consists of a common 
open earthenware vessel. The water is first placed in the generator, 
then the acid, and last the cyanide, after which the operator withdraws 
to the outside of the tent and the bottom of the latter is fastened down 
by having a few shovelfuls of earth thrown uponit. The tent is allowed 
to remain over the tree for a period of from 15 to 30 minutes, according 
to the size of the tree. 
It was found by experimenting that the trees were less liable to be 
injured by the gas when treated at night than they were when operated 
upon in day time, and at the same time the gas is just as fatal to the 
scale insects when applied at night as it would be if applied in the day 
time; and indeed it appears to be even more fatal when applied at night. 
This is accounted for by reason of the fact that in the day time the light 
and heat decompose the gas into other gases which, while being more 
hurtful to the trees, are not so fatal to insects. At night the trees are 
also more or less in a State of rest, and therefore are not so liable to be 
injured by the gas as they would be in the day time, when they are 
actively engaged in absorbing nourishment and replacing wasted tissue 
with new materials. 
Of the different materials used in generating the gas, the most 
important is the potassium cyanide; of this there are three grades: 
The mining cyanide, commercial cyanide, and the C. P. (chemically 
pure). Of these three brands, the mining cyanide is wholly unsuitable 
for the production of the gas, and the ©. P. is too expensive; the com- 
mercial brand (fused) is the only one that is used for producing the 
gas, but even this varies greatly in strength, containing all the way 
from 33 to 58 per cent. of pure potassium cyanide. It is, therefore, of 
the utmost importance that the operator should know the exact per- 
centage of pure potassium cyanide that his cyanide contains, and when 
large quantities of it are purchased at one time it would be advisable 
to obtain one or more analyses of it by a reliable analytical chemist ; 
or if it is not possible to submit the cyanide to such person, an analysis 
of it could be made by almost any person accustomed to the use of 
chemicals or drugs. 
The only substance required for this purpose is the crystals of nitrate 
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