488 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
exception of number 2, a nicotine sulfate solution made in the labora¬ 
tory from pure nicotine combined with standard sulfuric acid to 
neutrality with phenolred. One cc. of this solution equaled .166 gm. 
nicotine. Number 1 was a neutral solution of nicotine sulfate in distilled 
water. Numbers 2, 3, 6 and 8 were four graduations of the ncessary 
amount of alkali necessary to equalize the combining acid. Numbers 4 
and 5 are the same as number 1 except in the use of tap water and 
of soap. One and two-tenths cc. of each solution were made up to 5 
cc. and applied with an atomizer to a large leaf, and after definite periods 
of time the remaining nicotine was washed off and the amount deter¬ 
mined. The final test was made in an open laboratory, where the air 
had free circulation but where precipitation during the experiment could 
not wash off the nicotine. The leaves while fresh were suspended from 
a cord and the spray applied to the surface. Field tests on living plants 
gave similar results to these but attempts to get comparative data with 
low and high humidity were impractical on account of slight precipita¬ 
tion. 
The data 1 on volatilization are given in Table I, in which will be 
found a comparison of the loss of nicotine in clear weather with a low 
humidity and rainy weather with high relative humidity. From this 
data, it will be seen that there is a marked difference between the 
volatility rate in clear and rainy weather. This is due in part to the 
slower evaporation rate of water during high atmospheric humidity, 
thus holding the nicotine longer in solution and hindering its volatili¬ 
zation. It is also possible that nicotine volatilizes more rapidly from 
the dry film in low atmospheric humidity. The difference in volatility 
between free (levorotatory) nicotine and the salt form (dextrorotatory) 
is very marked. The former after 24 hours has volatilized to the extent 
that only traces are found even by very delicate chemical tests, the range 
of recovery for the latter being from 29.9 to 46.1 per cent. This proves 
that the full amount of nicotine from a properly made spray is released 
in 24 hours and that from 85 to 90 per cent is available in the first 
three hours during clear weather, while the alkaloid combined with an 
acid may lack from 13 to 19 per cent of being volatilized after 48 hours 
of cloudy weather. Such long periods required for activation necessarily 
reduce the efficiency of a spray in two ways: the concentration of 
nicotine released may not be high enough at any one time to become 
hALl nicotine determinations were made by the silicotungstic acid method as 
reported by Chapin, U. S. Department of Agriculture, Bureau of Animal Industry, 
Bui. 133. 
