TOXICITY OF HYDROCYANIC ACID. 2O3 



By the second method the HCN is passed into an alkaline, 

 colloidal solution of silver iodide, which is made by adding 

 potassium iodide to a known normality of silver nitrate. The 

 time which is required to decolorize the solution is taken by 

 means of a stopwatch. The first method of analysis, is perhaps, 

 more accurate, but as it requires more time than the second, it 

 was used only as a check on the Agl method. By the use of 

 the second method, several samples could be tested during one 

 exposure, so that accurate record could be kept of the con- 

 centration of HCN. 



The insects used in the tests were kept in a container in a 

 water bath maintained at a desired temperature for i hour 

 before fumigating and the fumigation chamber was kept at the 

 same temperature. After fumigating the insects, they were 

 replaced in the water bath until the following morning, when 

 they were removed and the mortality was determined. Through- 

 out this work, unless otherwise stated, granular calcium cyanide 

 was used as a source of HCN. 



10 20 30 4-0 vSO 60 



E XPOSURE IN niNUTES 



FIG. 2. Curve showing the relation of concentration of HCX to length of 

 exposure and the effect of temperature upon the toxicity of HCX to Mucrosipaniella 

 sanborni. Solid line, 25 C.; dotted line, 20 C.; broken line, 30 C. 



