62 



were covered with water after a slight shower we found that they were 

 badly injured by this strength, though we doubt they would have been 

 hurt had they been dry. Possibly a less time may be sufficient, but 

 we doubt that in handling fifty or one hundred covers it would be of 

 much advantage, as they could hardly be changed and the gas gen 

 erated in less time. The very much larger amount of gas than h 

 necessary in a larger box or frame is due to the relatively large soil 

 surface, and the fact that more or less necessarily leaks out around the 

 edges at the bottom. In using these covers for such insects as melon 

 lice it would rarely be necessary to fumigate every hill. But were 

 every hill fumigated, with hills 5 by 5 feet, the chemicals for the 

 treatment would cost not over 75 cents per acre, and with one hun- 

 dred covers two men should be able to fumigate 3 to 5 acres a day. 

 Upon the first opportunit}^ we shall try this treatment with fifty or one 

 hundred covers over an acre or two during the present season. 



The fumigation of plants grown in rows is, however, more difficult, 

 and presents some obstacles. A frame 15 feet long, with two sides 

 slanting so that in cross-section the frame was triangular, 20 inches 

 wide at the open bottom and 8 inches high, was first used, but it was 

 soon found, as had been expected, that the gas would not diffuse 

 readily in such a shaped covering. 



It seemed desirable, therefore, to determine the exact manner of 

 diffusion of the gas in such an elongated frame, and also points as 

 regards (1) the amount of gas produced by a given amount of KCn, 

 sulphuric acid, and water, (2) the influence of the soil and wet plants 

 upon the strength of the gas, and (3) whether the strength of the gas 

 deteriorates after a given time. This work was taken up by the station 

 chemist, Mr. C. L. Penny, who has very carefully secured and ana- 

 lyzed samples of the gas under various conditions to determine these 

 points. Only a mere summary of the results can now be given. Dur- 

 ing the present summer we purpose studying the manner of diffusion 

 of the gas in a room such as nurserymen use as a fumigatorium, and 

 later will publish a detailed account of all the experiments. 



A frame covered with rawhide paper, 13^ feet long and 18 inches 

 square at the ends, was constructed for this work. The bottom was 

 taken off and the frame aired after each test, and sealed with putty when 

 replaced. The gas was generated by running the acid into the cyanide 

 solution by means of a stopcock so that there was no possibility of loss 

 or leakage. A known amount of gas was drawn off — after passing 

 through a drying tube — into several large bottles, by first exhausting 

 these with an air pump. A 36-gallon kitchen hot-water boiler was 

 nearly exhausted of air, and a mercury gauge attached. Between this 

 and the reservoir of bottles was placed a train of wash bottles contain- 

 ing nitrate of silver solution, and all were then connected. Upon 

 opening a valve the larger tank thus drew a quantity of the gas through 

 the wash bottles whose volume was easilv determined by the mercury 



