39 ° 
Journal of Agricultural Research 
Vol. VII, No. 9 
tions in the field it was noticed that certain sprays of high concentrations 
of soap apparently did not wet the insects as thoroughly or spread over 
the glaucous leaves of the pea vines as well as less concentrated soap 
and nicotine solutions. It was also noted that the solutions of high 
concentrations were not as effective insecticides as were some of the 
more dilute mixtures. 
methods of determining the efficiency and wetting powers 
OF THE SOLUTIONS 
The efficiency, or the killing power, of the solutions was determined 
from actual field-spraying experiments. Peas were sprayed five times, 
spinach once, and strawberries once. The experiments were performed 
on 27 one-twentieth-acre plots. A power sprayer which maintained a 
pressure of 75 to 125 pounds was used to apply the materials. Three 
nozzles per row were employed, two lateral and one vertical. Before the 
spray was applied, the number of live aphids on the vines were counted 
for a certain distance in the center of the plot. Two hours after spraying, 
another determination of the number of live insects was made on the 
same vines as before, and from these figures the percentage of the insects 
killed was computed. When spraying strawberries to control the red 
spider, the number of live and dead mites on several leaves from each 
plant were counted, and the efficiency determined in this way. De¬ 
tailed results of this work are shown in Table I. 
The comparative wetting powers of the spray solutions were deter¬ 
mined by the method recommended by Cooper and Nuttall. 1 In this 
method a standard paraffin oil having a density of 0.8690 is run from a 
pipette through the solution to be tested, and the number of drops 
formed from a definite volume of oil are counted. The wetting power 
is directly prop6rtional to the drop number. It is advisable to use 
distilled water as a standard liquid, as there is variation in different 
samples of oil; hence, the wetting power of the solutions is expressed 
as the ratio of the drop number of the solution to that of distilled water 
multiplied by 100. 
The determination of the percentage of nicotine in the solutions was 
made by a test which was approved and adopted by the Bureau of Animal 
Industry on March 1, 1915. The method is well known and needs no 
description here. 
1 Cooper, W. F., and Nuttall, W. H. The theory of wetting, and the determination of the wetting power 
of dipping and spraying fluids containing a soap basis. In Jour. Agr. Sci., v. 7, pt. 2, p. 235. 1915. 
