9 
soap solution such a treatment may sometimes be of value, although 
only when the use of hydrocyanic-acid gas is impossible or for some 
reason undesirable. 
Among the sprays, the best brands of whale-oil soap, used in the 
proportion of 1 to 14 ounces per gallon of water, have been found to 
destroy all of the white flies except the eggs, a small percentage of 
the nearly mature pup, and from 25 to 50 per cent of the adults 
which escape the spray by flying from the plants. It is not advisable 
to syringe tomato plants in greenhouses at any time, when avoidable, as 
syringing interferes with pollination and produces a damp atmosphere 
which promotes rot, but the injury by syringing may be as nothing 
compared with that which is caused daily by the insects. When the 
use of hydrocyanic-acid gas is impractical, an all-night fumigation with 
a tobacco extract is recommended, followed during the next day by 
a syringing with a solution of whale-oil soap or its equivalent. 
Comparative cost of the treatment.—Potassium cyanide costs from 
about 30 to 50 cents per pound, according to the amount purchased. 
Commercial sulphuric acid costs from about 23 to 10 cents per pound. 
The entire cost for a single fumigation of a greenhouse containing 
20,000 cubic feet is between 20 and 30 cents. The labor required is 
scarcely, if any, greater than for fumigation with other materials. 
A single fumigation with a suitable tobacco extract would cost, in a 
house of the same size, at least $1.50, and the cost of labor for the 
syringing which is recommended to follow such fumigation would prob- 
ably not be less than $1. The soap required would cost only a few 
cents, though possibly as much as the materials used in a fumigation 
with hydroeyanic-acid gas. 
CAUTIONS. 
Hydrocyanic-acid gas is one of the deadliest poisons known, and 
should always be handled with the greatest care. Never hold the 
potassium cyanide in the bare hand when pulverizing, but wrap up 
the lumps in two or more thicknesses of cloth before breaking with a 
hammer. Dust or small pieces of potassium cyanide should not be 
thrown away in exposed places, but always buried, as should the con- 
tents of the receptacles of the chemicals after the fumigation. Never 
inhale air in a greenhouse after the generation of gas has begun, 
and provide against anyone entering the house before it is properly 
ventilated. 
Approved: 
JAMES WILSON, 
Secretary of Agriculture. 
Wasuineton, D. C., February 15, 1905. 
O 
