490 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 16 
Fumigation Experiments. The same solutions were used in this 
as in the spraying tests, the difference being alone in the method of 
application. Five cc. of each solution were placed at the bottom of a 
glass cylinder one and one-half inches in diameter and six inches high. 
Infested leaves were placed inside the upper end of the cylinder, about 
four inches from the solution. The upper end of the cylinder was then 
closed with a cork. Exposure was for the same length of time as in 
spraying. The data given in Table II show a close correlation between 
the effect of spraying and fumigating,—further proof of the relation be¬ 
tween volatility and toxicity, and also that nicotine is a tracheal rather 
than a true contact insecticide. 
Table II. Toxicity to Aphids 2 from Spraying and From Fumigating with 
Nicotine Sulfate in Solutions of Varying Alkalinity 
No. 
pH 
value 
Nature of Solution 
Ptrcent. of Aphids dead 
Spraying 
Fumigation 
1 
6.5 
Nicotine as sulfate, 1-1000, distilled water 
53.6 
48.1 
2 
6.7 
Nicotine as sulfate, 1-1000 plus 2.4 cc. n/1 
NaOH, in distilled water 
49.7 
55.5 
3 
7.2 
Nicotine as sulfate, 1-1000 plus 4.8 cc. n/1 
NaOH, in distilled water 
60.9 
58.9 
4 
7.4 
Nicotine as sulfate, 1-1000 in tap water 
51.0 
62.9 
5 
7.6 
Nicotine as sulfate, 1-1000 in tap water plus 
soap at the rate of 4 It s per 100 gals. 
65.3 
66.6 
6 
7.8 
Nicotine as sulfate, 1-1000 plus 7.2 cc. n/1 
NaOH, in distilled water 
65.4 
88.4 
7 
7.9 
Nicotine (free) 1-1000, plus an amount of 
sodium sulfate equivalent to that formed 
in No. 6, in distilled water 
74.6 
82.9 
8 
8.2 
Nicotine as sulfate, 1-1000 plus 9.6 cc. n/1 
NaOH, in distilled water 
76.5 
75.7 
Check 
Untreated aphids 
7.7 
22.3 
2 Ivy aphid (Aphis hederae Kalt.). Green peach aphid [Rhopalosiphum persicae 
Sulzer). 
Summary. The graph shows the similarity between the loss of 
nicotine as determined chemically in the volatilization tests and the 
bio-assays in fumigating and spraying experiments. These curves are 
averages of from two to four series, where the same type of solutions 
have been tested in slightly different ways or on different species of 
aphids. Larger series would show more regularity in the curves but 
sufficient work has been done to prove the correlation between volatility 
and toxicity. This also shows the value of a slight addition of alkali 
to solutions of nicotine salts to supplement the alkalinity of the tap 
water, which in most instances is insuffiicent for freeing the nicotine 
from combining acids. The use of free nicotine, of course, obviates the 
