528 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



METHODS OF DETERMINING THE TOXICITY OF HYDRO- 

 CYANIC ACID GAS 



By George A. Coleman 



Recent investigations point to the conclusion that a large percentage 

 of the killing value of the hydrocyanic acid gas generated in practical 

 fumigation work is lost through leakage of tents. 



In order to determine the toxic value of the different percentages 

 of hydrocyanic acid gas an extensive series of experiments with known 

 percentages of the gas was planned, including the study of large num- 

 bers of various species of scale insects in various stages of development 

 from the egg to the adult, as well as other insects. This is now being 

 carried on in the insecticide laboratory of the University of California 

 by the author and a number of assistants under the direction of 

 Professor Wood worth. 



Since no such extensive work has been previously done along this 

 line, it has been necessary to develop new methods of experimentation 

 and apparatus. These have proven so satisfactory for the purpose 

 that a description of the apparatus and methods of handling the 

 scale insects may be of interest to other workers in this field of inves- 

 tigation. 



The average dosage used in practical fumigation work rarely pro- 

 duces above 0.36 per cent HCN which Professor Woodworth esti- 

 mates has an average efficiency of not to exceed 0.09 per cent HCN. 

 Our work, therefore, is with percentages of gas from per cent to 0.36 

 per cent. 



In our experiments we begin with a very low percentage and increase 

 it at will to any strength desired. The method used enables us to 

 begin with a production of 0.005 per cent HCN or less and increase 

 the production each time by this amount. 



After considerable experimenting with the different cyanides and 

 acids, we find the use of purified potassium cyanide (98-99 per cent 

 or c. p.) and c. p. sulphuric acid (sp. gr. 1.84) gives the best results. 

 For the gas generating vessel we use an ordinary Woulff bottle with 

 three necks, of about 1000 cc, capacity. In this bottle is first placed 

 500 cc. of distilled water to which is added 5 grams of cyanide, and 

 thie acid is added as the gas is required. Beginning with sufficient 

 cyanide to produce 0.005 per cent HCN in the air as it passes through 

 the liquid solution, it is only necessary to add 0.1 cc. of concentrated 

 H2SO4 in order to produce this percentage. As it is rather difficult 

 to measure out so small a quantity of acid we use a 10 per cent solution 

 and add 1 cc. instead of 0.1 cc. 



