40 FUMIGATION INVESTIGATIONS IN CALIFORNIA. 
that 23.25 per cent of hydrocyanic acid remained in solution and was 
not liberated. 
Experiment X<>. ... — The potassium cyanid was added to a mixture 
of acid and water when first combined, i. e., when the heat was great. 
and it was found that only 10.08 per cent of hydrocyanic acid 
remained in solution. 
Caution. — The cyanid should never be placed in the water before 
the acid is added. If the acid is added to the cyanid in solution, a 
very violent reaction takes place, which will sometimes throw much 
of the liquid from the vessel. In one instance about 1 pound of 
cyanid was dissolved in water in a 2-gallon generator. Acid was then 
added, producing a disturbance so violent as to throw some of the 
liquid almost to the top of a two-story barn. 
V 1 l-gallon generator will serve for a dose of about 15 ounces of 
cyanid without boiling over, or a 2-gallon generator for approximately 
20 ounces. 
The residue from the reaction contains more or less sulphuric acid 
which has not been used. This residue should never be deposited 
against or at the base of a tree, as it may penetrate to the roots, 
especially in light sandy soils, destroying a part if not the entire tree. 
PURPLE SCALE FUMIGATION. 
PRELIMINARY EXPERIMENTS FOR THE CONTROL OF THE PURPLE SCAJ.h. 
During the month of November, 1907, experiments were under- 
taken at Orange, Cal., to determine the dosage required for the 
destruction of the purple scale (Lepidosa phes heckii Xewm.) in all it- 
stages, as well as to determine the effect of exposures of different 
durations. The orchard under treatment contained orange trees 
varying from 7 to 14 feet in height. The infestation with the purple 
scale was very severe on many of the trees. 
In the first experiment the duration of exposure was thirty minutes. 
In this experiment a series of tests was made to determine the effect 
of different dosages. These tests were as follows: One series of trees 
was dosed at the rate of three-fourths ounce of cyanid per 100 cubic 
feet of inclosed space; a second series at the rate of 1 ounce, a 
third at the rate of \\ ounces, and so on, increasing the dosage of 
each succeeding series at the rate of one-fourth ounce per 100 cubic 
feet. The largest dosage used was 2\ ounces per 100 cubic feet. 
The second and third experiments were the exact counterparts of 
the first in all respects except that the duration of the exposures was 
respectively one hour and one and one-half hours. 
From the data secured from these experiments it should be pos- 
sible to determine the killing dosage tor the purple scale for that 
particular length of time, provided a sufficient strength of gas was 
reached. To insure that the dosage sought would fall within the 
