7 
will emerge from the pupa cases. The larvee, when destroyed, as they 
should be by the fumigation, change in two or three days from their 
normal glistening, greenish color to a yellowish or brownish color. 
When this result is not obtained by the first test, one or more further 
tests should be made, increasing the amount of potassium cyanide 
0.001 gram per cubic foot of space for each test, with three days inter- 
vening to note results, until an amount is reached which is sufficient to 
destroy the larvee, or until the tender leaves of the plant show injuries 
as a result of the fumigation. 
Tests, thus far, with other greenhouse plants likely to be attacked 
by the white fly, according to available records, have all been for a 
much shorter exposure than three hours and with a much larger 
amount of potassium cyanide, but it is probable that in case plants 
other than the cucumber and tomato require treatment for this insect, 
preliminary tests in a fumigating box or in a small greenhouse will 
show that the amount of chemicals and length of exposure recom- 
mended for these two can be used without the slightest danger to other 
plants. In most cases much larger rates of potassium cyanide per 
cubic foot can be used. 
Time to fumigate, preparation of greenhouse, and method of gener- 
atiny gas.—Fumigation of plants with hydrocyanic-acid gas should be 
at night and the foliage of the plants should be dry. The greenhouse 
to be treated should be made as tight as possible, all entrances but one 
closed and locked, and arrangements made to open a few ventilators 
from the outside at the expiration of the period of exposure. A house 
when fumigated should not be unnaturally tight as a result of rain 
or snow, otherwise the greater amount of gas confined in it under 
these conditions may injure the plants. The materials used for the 
generation of the gas are 98 per cent potassium cyanide, commercial 
sulphuric acid, and water, the proportions generally used being one- 
half more acid (liquid measure) than potassium cyanide, and one-half 
more water than acid. Having determined the cubic contents of the 
house and the total amount of potassium cyanide, sulphuric acid, and 
water to be used; these should be divided into parts representing each 
25 feet of length of the greenhouse. Owing to the small amounts of 
the acid and water, small receptacles must be used. Six or 8 inches 
is a desirable height for the receptacles, while the diameter should be 
as small as possible to use, preferably not more than 23 inches. They 
should be either of earthenware or glass. In many cases, ordinary 
glass tumblers will be suitable, though the diluted acid should never 
more than one-fourth fill the receptacle; otberwise the violent chem- 
ical action which follows the introduction of the potassium cyanide 
might result in the loss of considerable of the material. Each lot of 
the potassium cyanide should be pulverized or broken up into small 
pieces, wrapped in thin paper, and laid beside one of the receptacles, 
