THE TOBACCO BEETLE. 19 



of destroying certain classes of insects and is a standard weapon 

 against insects infesting mills and warehouses. It may be used to 

 advantage in controlling the tobacco beetle, although this pest has 

 been found to be considerably more resistant to fumigants than most 

 insects. The insulation afforded by the pupal cells and by com- 

 pressed tobacco seems to protect the larva3 or pupse within from the 

 action of the fumigant. A few insects protected in this manner are 

 likely to survive, although all stages not specially protected are 

 killed. In most cases, however, only a small percentage of the in- 

 sects survive, and these, if an additional treatment is thought ad- 

 visable, may be destroyed by a second fumigation giv^n about two or 

 three weeks later. Adults and eggs are the only stages likely to be 

 present at this time, and these unprotected stages are easily destroyed 

 by the fumigant. In the treatment of infested tobacco it has been 

 determined by many experiments that stronger dosages of fumigants 

 must be used than are employed ordinarily against other insects. 



Expert tobacco men have examined and kept under observation 

 tobacco and cigars fumigated with carbon disulphid and hydrocyanic- 

 acid gas, and all were of the opinion that these fumigants had no 

 noticeable effect upon the tobacco. In order that it might be deter- 

 mined whether or not any deposition of cyanogen in cigars occurs as 

 a result of the hydrocyanic-acid gas treatment, different lots of 

 freshly made cigars were fumigated with heavy dosages and sent to 

 the Bureau of Chemistry, United States Department of Agriculture, 

 for examination. No trace of hydrocyanic-acid was found in any of 

 the samples. Duplicates from each lot were also submitted to expert 

 cigar men, and all reported no apparent difference between the fumi- 

 gated and unfumigated cigars. 



The properties and characteristics of the various chemicals used 

 in fumigation shoidd he understood thoroughly in every particular 

 hy the operator in order that necessary precautions may he taken and 

 the work done properly. The process of fumigation, however, is 

 simple and easily applied. 



HYDROCYANIC-ACID GAS. 



For the generation of hydrocyanic-acid gas in fumigation, sodium 

 cyanid (XaCN) or potassium cyanid (KCN), sulphuric acid 

 (H2SO4), and water are necessary. The hydrocyanic-acid gas, ^ 

 which is the killing agent, is produced by the action of the sulphuric 

 acid (diluted with water) on the sodium or potassium cyanid. A 

 high grade of the cyanid should be used, as the presence of adul- 

 terants reduces greatly the amount of hydrocyanic-acid gas given 



^ Hydrocyanic-acid gas is colorless and one of the most deadly poisonous gases known. 



