10 BULLETIN 1160, U. S. DEPARTMENT OF AGRICULTURE. 
TOXICITY OF CERTAIN BASES COMPARED WITH THEIR SALTS. 
Results are given in the preceding tables which show differences 
in toxicity between certain bases and their salts. The toxic con- 
centration for piperidine sulphate was found to be 0.035 moles, 
(ec-ual to 0.070 moles of the free base per liter) while that for piper- 
idine base was 0.59 moles, or an amount about eight times greater. 
Triethylamine base requires more than 1.5 moles, while its hydro- 
chloride requires only 0.22, a ratio of at least 7 to 1. A comparison 
of nicotine and nicotine sulphate was also made. A definite quantity 
of nicotine sulphate was prepared by titrating the free base with 
normal sulphuric acid, using methyl red as indicator and diluting to 
the desired strength. In this instance no difference in toxicity was 
observed, but exception can rightly be taken to a comparison of 
nicotine with nicotine sulphate in such small concentrations when 
0.3 per cent fish-oil soap is used in the solution. Nicotine is a weak 
base whose salts hydrolyze slightly in dilute solution and furthermore 
are decomposed by the free alkali of the hydrolyzed soap. These con- 
siderations do not apply to the conclusions reached with the salts of 
piperidine and triethylamine, for the latter compounds are salts of 
strong bases and much larger concentrations of them were used in 
relation to the soap present. Further study is being given to this 
subject and it will not be discussed at greater length here. 
TOXICITY AND VOLATILITY. 
The data obtained from these toxicity studies are of interest in 
another connection. The work of Moore and coworkers (5, 6, 7, 10, 12) 
indicates that the toxicity of volatile organic compounds when em- 
ployed in the vapor state against insects or applied directly to the 
surface of insects' eggs varies with the volatility. Up to a boiling 
point of 225-250° C, toxicity, it is asserted, increases as the boiling 
point rises and the volatility decreases. Compounds with higher 
boiling points generally have such low volatility that their vapor 
concentrations are not great enough to kill within a reasonable time. 
Other studies by Moore, and Moore and Graham (8, 9, 11) with 
contact insecticides led to the conclusion that " volatility is an index 
of the ability of the compound to gain entrance into the insect and is 
therefore closely correlated with toxicity." It was further stated 
that compounds more volatile than xylene evaporate too quickly to 
be effective. 
While the results of the present study show that, in general, the 
most toxic compounds employed were among the least volatile and 
the least toxic compounds were the more volatile ones, there are so 
many exceptions that the writers believe neither volatility nor the 
boiling point can be used as a safe index of toxicity when the compound 
is employed as a contact insecticide. For example', quinoline with a 
boiling point close to that of nicotine has, in these experiments, only 
about one-three hundred seventy-fifth the toxicity of the latter. On 
the other hand, tetramethylammonium chloride, a nonvolatile salt 
at ordinary temperatures, is one of the most toxic substances tested. 
The tetraethyl- and tetrapropylammonium compounds are also 
nonvolatile, yet they show considerable toxicity. Benzylamine and 
aniline have closely similar boiling points but differ widely in toxicity; 
and this is also true of cyclohexane and benzene. Piperidine with a 
