40 FUMIGATION INVESTIGATIONS IN CALIFOENIA. 



that 23.25 per cent of hydrocyanic acid remained in sohition and was 

 not U berated. 



Experiment No. 2. — The potassium cyanid was added to a mixture 

 of acid and water when first combined, i. e., when the lieat was great, 

 and it was fovmd tliat only 10.68 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. 



A H-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 SCALE. 



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 {Leiyidosa/phes heckii Newm.) in all its 

 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 Ij ounces, and so on, increasing the dosage of 

 each succeeding series at th6 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 for 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 



