Distribution of HCN Gas in Greenhouse Fumigation 7 



air had been passed through each, and were replaced by tubes 

 containing fresh NaOH solution. The titrating solution was 

 o.ooiiV silver nitrate. 



Description of the Tests 



The general plan of all the tests was to take a cross-section 

 of the house under fumigation, so disposing the tubes from the 

 apparatus that air was drawn from a point just beneath the peak 

 of the roof, midway of the length of the house, from a point 

 about a foot above the middle bench of the house, and from two 

 points, one on each side above the side benches. In some cases 

 a cross-section of half the house was made, in which case the 

 points from which air was drawn were beneath the peak of the 

 roof, a point immediately over the middle bench of the house, 

 another over the next bench toward the outer wall, and the last 

 from a point over the outermost bench nearest the wall. 



Five greenhouses were used in the fumigation, situated at 

 the College Farm in New Brunswick. Of these, three were of 

 identical dimensions (No. i, 2 and 4) 25,368 cubic feet, while 

 one other was a small propagator house (1,371 cubic feet;, and 

 the other a medium-sized fern greenhouse (4,866 cubic feet). 

 The tests were run in conjunction with fumigations carried out 

 for the purpose of controlling aphis in the large greenhouses, 

 and in cooperation with another series of experiments conducted 

 under the direction of Prof. M. A. Blake on the burning effect 

 of HCN gas upon garden vegetable plants. All the tests were 

 made after dark. The charge was placed and set In tne usual 

 manner for greenhouse fumigation, tall earthenware jars being 

 used, which were placed along the middle line of the green- 

 house. The commercial cyanide of sodium made by the Roess- 

 ler-Hasslacher Chemical Company and known as "Cyanegg" 

 was used in all the fumigations. The formula used was 1-1-3.* 



Taking for purposes of comparison all the fumigations wTth 

 a 5/8-ounce charge. No. 1,2, 3, 4 and 8, it will be noted that the 

 disappearance of the gas is rapid after a certain maximum con- 

 ccntrnt'on has been reached. This concentration, which coin- 

 cides with the time of complete diffusion of the gas throughout 

 the house is reached at from 4 to 6 minutes after the charge is 

 set off, and suffers steady diminution from that time on until it 

 falls below the killing strength. Although the average concen- 

 tration, as obtained from the sum of the concentrations obtained 

 at the various points in the house from which air was drawn, 

 is high for the first few minutes, it will be seen that if the con- 

 centration at the comb is eliminated, the resulting average is 



* Formula 1-1-3 — 1 oz., by weight, of sodium cyanide; 1 oz., by 

 measure, of concentrated sulfuric acid, sp. gr. 1.84; 3 oz., by measure, 

 of water. 



