63 



gauge and whose content of gas was subsequently determined by 

 titration. The gas was generated at the middle and either ends of the 

 frame and samples taken from all of these and opposite points after 

 different lengths of time. A solution of cyanide and sulphuric acid in 

 proportion of 1 part cyanide to 1^ parts acid to 2i parts water and an 

 amount equal to two-tenths gram potassium cyanide per cubic foot 

 air space was used in all of these tests. The amount of C3'anide remain- 

 ing in the residual solution was determined in each instance and 

 deducted from the amount calculated to be present if the gas were 

 completely generated and diffused. With this frame the residuum 

 averaged about 5 per cent; with a large box, mentioned below, about 

 3 per cent, and the percentage was found to decrease the more time 

 elapsed after generation. With the generator and intake at the same 

 end after three minutes it was found the amount varied from 70 to 197 

 per cent of the calculated amount with an average of 13 per cent. In 

 other words, the gas diffused irregularly, but remained largely in the 

 end where generated. The generator was then placed at the middle 

 and the intake at the end. Samples were taken after ten minutes, 

 thirty minutes, one, four, and twelve hours. In all of these the gas 

 was found to diffuse irregularly and in no instance was the diffusion 

 nearly complete. As far as could be detected the frame was tight, 

 but a loss of gas seemed to occur in some wa}', whether by leakage or 

 transfusion is a question. At any rate, after twelve hours not a trace 

 of gas was found. The average percentages of the calculated amount 

 for the four other periods were 46, 41, 27, and 13 per cent, respectively, 

 showing a regular decrease the longer the time, but never a complete 

 diffusion, the highest amount after ten minutes' time being 70 per cent. 



From these tests it seemed evident that by itself the gas would not 

 diffuse evenly in such a frame. A rough fan was therefore put in the 

 center, and a diaphragm placed horizontally through the center to 

 within a foot of each end, so that a thorough circulation might thus 

 be secured mechanically. 



By use of this mixer with the generator and intake at opposite ends 

 after live minutes 72.4 per cent of the calculated amount was secured, 

 and this with fairly constant results, only varying from 68.5 to 75 per 

 cent in four trials. As this fan was far from a perfect device, and 

 also promoted leakage, we concluded that these tests showed fairl}" 

 that in such a shaped frame the gas diffuses entirely irregularly and 

 never completely. In other words, it would be necessary in actual 

 usage to generate a very much larger amount of gas than necessary 

 were it diffused, in order to secure a sufficient amount in all parts to 

 be effective, with the danger of burning the plants at the point of gen- 

 eration if used too strong. Evidently the only way to determine this 

 was by tests in the field upon insects, as such a fan arrangement was 

 clearly impracticable. 



