June ii, 1917 
Toxicity of Benzene Derivatives to Insects 
373 
stopper inside of the flask, and the compound was allowed to evaporate. 
After several different insects were used in preliminary tests, the house 
fly (Musca domestica L.) was selected as being typical and easy to breed 
in large numbers. The flies were bred in the insectary and kept under 
natural conditions, thus avoiding irregular results due to the different 
ages and physical conditions of the wild flies. Five flies were put into 
each flask, the chemical introduced, and the flask tightly stoppered. 
When all the flies in the flask were apparently dead, they were removed 
to a vial and given 24 hours to revive. If none revived, the time during 
which the flies were exposed to the vapor was recorded. But, if the 
flies revived, the experiment was repeated. The average of 50 tests for 
a certain quantity of any chemical was found to be practically the same 
as the average of 5 tests; hence, in each case 5 tests were conducted. 
Controls showed that flies could live in a closed flask for 20 or more hours. 
Since similar weights of the different chemicals do not contain the 
same number of molecules, and their toxicity could not, therefore, be 
accurately compared, it was decided to determine the toxicity in minutes 
for similar fractions of a gram-molecule of each chemical. Different 
quantities of each chemical were tested and curves plotted. As the 
quantity increased, it was found that each chemical had a point beyond 
which an increase would not give a reduction in the time required to kill. 
This is the point at which the air is saturated with the vapor, and differs 
for each chemical. As the quantity is decreased, a point is reached 
where the vapor is not of sufficient strength to kill. The plotted curves 
lie between these two points. 
After the curves were plotted, it was found to be impossible to compare 
similar fractions of a gram-molecule; hence, the different fractions of a 
gram-molecule necessary to kill in a fixed time of 400 minutes were deter¬ 
mined. A long period of time was selected as a more nearly correct index 
of toxicity. The fraction of the gram-molecule was determined by dividing 
the amount of the chemical necessary to kill in 400 minutes by the molecular 
weight of the substance. The sums given in the charts are the millionths 
of a gram-molecule necessary to kill five house flies in a 1-liter flask at a 
temperature of 70° F. 
The liquid benzene compounds were measured by volume in blood¬ 
counting pipettes, and the weight of this volume was determined from 
the weight of 1 c. c. of the chemical. Weighed quantities of the solid 
benzene derivatives were dissolved in a known volume of benzene. A 
certain volume of this solution would contain a definite quantity of the 
benzene derivative. The measured volume was placed on the paper and 
blown for a moment to evaporate the solvent. The rapid evaporation 
of the solvent resulted in a lowering of the temperature, thus preventing 
appreciable evaporation of the compound to be tested. 
