December, ’23] 
deong: volatility and toxicity of nicotine 
489 
toxic, or rain may wash off an application or dilute it to a point of 
inefficiency. 
It should be noted that a reduction in the amount of nicotine in 
solutions recovered from sprayed leaves is not necessarily due alone to 
volatilization but probably includes oxidation into other compounds. 
Nicotine oxidizes readily, turning brown when exposed to air. Under 
the action of oxidizing agents it yields a different product. The oxi¬ 
dation of nicotine seems to occur only when exposed to large quantities 
of air or over a considerable period of time. For example, in aspirating 
two to four hundred liters of air through a nicotine solution, and where 
the volatile nicotine passed through two or three feet of rubber tubing, 
it was only in rare cases that even a trace of nicotine was recovered in 
the washing liquid, but a close correlation was found between the 
amount of volatile nicotine recovered with damp silicotungstic paper, 
at the top of the tube, and that remaining in solution at the bottom of a 
short, closed, glass tube. This shows that the nicotine from a dust or 
spray that is in close proximity to the body of an insect would enter the 
tracheae unchanged but as the nicotine dissipates in the air it is soon 
oxidized. 
Spraying Experiments. Nicotine solutions with varying alkalinity 
were used as in Table I., but at dilutions of one to one thousand. This 
concentration was chosen rather than a stronger one as complete mor¬ 
tality was not desired in any of the experiments. Concentration of one 
to eight hundred gave one hundred per cent efficiency on certain species 
of aphids with numbers 7 and 8. A neutral solution of nicotine sulfate 
was used which had been prepared in the laboratory as was also the free 
nicotine used in number 8. The latter contained an amount of sodium 
sulfate equivalent to that formed in number 7 by the addition of the 
neutralizing sodium hydroxide. Distilled water was used in all cases 
except as noted. The spray was applied by means of an atomizer. 
Two counts were found necessary as a twenty-four-hour exposure did 
not give the full effect of the nicotine. 
A close correlation is noted in the percentage of mortality between 
those containing free nicotine (numbers 7 and 8), the latter by reason 
of the neutralizing alkali added. The lowest efficiency was noted in 
the nicotine sulfate (dextrorotatory nicotine) solution, thus proving 
that volatility is a primary factor in the toxicity of nicotine. The 
results in numbers 4 and 5 show the danger of depending entirely on 
natural alkalinity or the variable amount found in soap, for releasing 
all the nicotine. 
