CYANIDE FUMIGATION OF MUSHROOM HOUSES 7 



the same series or the next higher in concentration in which no in- 

 sects or mites survived. The insects were removed when the concen- 

 tration had dropped to 0.4 mg per liter, and the area of the curves 

 is measured to that point except in the case of figure 3, d, which is 

 measured only to 0.8 mg per liter. 



Sodium cyanide was used as the source of the fumigant because it 

 was quickly handled and easy to control. Samples were taken, and 

 the concentration of the gas was determined by the official modi- 

 fication of the Liebig method. 1 



RESULTS OBTAINED 



a: 3 



UJ 



I- 



s 2 



a. 



o 



2 



a 



-£— V 



fry \ 



Since the temperature at the floor of the average mushroom house 

 is in the neighborhood of 100° F. at the time of peak heat, this tem- 

 perature was used in the fumigation-chamber tests. For practical 

 purposes the higher temperatures farther from the floor in the houses 

 may be ignored as 

 the insects that sur- 

 vive the heat there are 

 killed by lower concen- 

 trations of gas than 

 those at the compara- 

 tively cooler floor 

 level. At 100° in the 

 fumigation chamber 

 the springtails and all 

 stages of Sciara were 

 killed by a mean con- 

 centration of cyanide 

 gas of 0.81 mg per liter 

 in an exposure of 40 

 minutes. 



little affected by these 

 conditions, some hav- 

 ing survived even an 

 exposure of 90 min- 

 utes to a multiple fumigation remaining above 1.3 mg per liter, 

 and with a mean of 1.73 mg per liter. An exposure of 35 minutes 

 to a single fumigation reaching a maximum of 3.5 mg per liter, having 

 a mean of 1.8 mg per liter and dropping to 0.4 mg per liter in 35 min- 

 utes, also gave survivals. Figure 3 shows composite curves for all 

 fumigations made in the chamber at 100°, a and b being single fumi- 

 gations and c and d representing double fumigations in which two- 

 thirds of the charge was set off in the beginning of the fumigation 

 and the other third 15 minutes after the first one. 



From these curves the figures in table 2 are obtained, using, as in the 

 case of table 1, the mean concentration found by the readings of a 

 planimeter. 



10 



20 



40 



50 



60 



30 

 MINUTES 



Mites Were figure 3. — Average concentrations obtained in the fumi- 

 gation chamber divided into four groups representing 

 (a) lethal concentrations obtained with single fumiga- 

 tions, (6) sublethal concentrations from single fumiga- 

 tions, (c) lethal concentrations from double fumigations, 

 and (d) sublethal concentrations from double fumigations. 



1 Association op Official Agricultural Chemists, official and tentative methods 

 of analysis. Ed. 3. 593 pp., illus. (p. 51.) 1930. The procedure is briefly described 

 as follows : Liter samples drawn from the fumigation chamber by means of a siphon were 

 bubbled through a solution of sodium carbonate containing potassium iodide, and this 

 titrated with a 0.01 normal silver nitrate solution. 



