Distribution of HCN Gas in Greenhouse Fumigation 21 



Our experiments show that in greenhouses under fumigation 

 for rose-aphis, at a rate of 5/8-ounce to 1,000 cubic feet, a con- 

 centration of 0.000278 gm. HCN per liter is often reached and 

 frequently exceeded over the greenhouse benches. Contrasting 

 this with the amount of gas found necessary to kill in the con- 

 trolled minimum dosage experiments, it is found that at least 

 twice as much gas is present as should be necessary to effect a 

 kill. If the total amount of HCN gas were available from the 

 sodium cyanide at the rate of 5/8-ounce per 1,000 cubic feet, a 

 concentration of 0.000312 gm. per liter would be obtained. Such 

 complete evolution of gas is never obtained under ordinary con- 

 ditions, I or 2 per cent or more of gas being lost in the solution 

 or decomposed by the heat of the reaction. Nevertheless, a very 



'd ^£ f' 



i-r~ion 



H0U6£ 

 PLAN 



CAPACITY 

 4 666 cuJt. 



MINUTES 



Fig. 15. Graph of Fumigation No. 15 



A, left bench; B, middle bench; C, nght bench; D, left col- 

 lecting tube; E, middle collecting tube; F, right collecting tube; 

 G, comb collecting tube. 



large proportion, 90 per cent or over, is actually present and is 

 available for fumigation. The discrepancy between the amount 

 observed to be sufificient to kill in the minimum dosage experi- 

 ments and that necessary to kill in greenhouses seems to be due 

 to the manner of distribution of the gas, as well as the loss of 

 gas due to leakage. Thus almost the entire amount of gas gen- 

 erated is ineffective during the first few minutes of the fumiga- 

 tion, as the sharp uprush of gas carries most of it to the comb of 



