CYANIDE FUMIGATION OF MUSHROOM HOUSES 5 



The concentration curves shown in figure 2 represent the averages 

 of all those secured in fumigating commercial mushroom houses in 

 the mushroom-growing district of Pennsylvania with approximately 

 equivalent dosages of the three materials. Mean concentrations were 

 calculated only to the point where the concentration of gas dropped 

 to 0.4 mg per liter, because beyond that point there is little fumigating 

 effect in a mushroom house. 



By taking from the curves of figure 2 the concentrations indicated 

 at the peak and obtaining the mean from the area below the curve 

 as found by a planimeter, the figures given in table 1 are obtained. 



Table 1. — Maximum and mean concentrations of hydrocyanic acid gas at 

 5-minute intervals during fumigation of mushroom houses by different methods 

 of gas generation 



[Averages from a number of commercial houses in eastern Pennsylvania] 





Method of generation of gas 



Maximum 

 concentration 



Mean con- 

 centration 



Pot method 



Mg per liter 



2.81 



2.93 



1.15 



.89 



Mg per liter 

 1.20 



Liquid from tank 



1.23 



Calcium cvanide (powder) 



.80 



Calcium cyanide (granular). 



.65 







Granular calcium cyanide has been by far the most popular fumi- 

 gant for mushroom houses at peak heat for the last few years. It is 

 easily handled and not excessively dangerous. The highest peak con- 

 centration secured in any house was 1.88 mg per liter, while in several 

 fumigations the peaks were below 0.5 mg per liter. Of those reaching 

 a peak concentration above 0.8 mg per liter, most dropped below 0.4 

 mg per liter within 60 minutes. In most cases the peak concentration 

 is reached within 15 minutes. The fact that leakage is almost as im- 

 portant a factor as absorption in lowering the concentration is shown 

 by one fumigation with this material in an exceptionally tight house, 

 in which the concentration reached 1.62 mg per liter and required 

 over 100 minutes to drop to 0.4 mg per liter. Figure 2, cl shows the 

 average curve secured with this material. The concentration dropped 

 to 0.4 mg per liter in 56 minutes. 



Calcium cyanide in powdered form is more bulky than the granular 

 form and is somewhat more difficult to handle. As a rule, the peak 

 concentration is somewhat higher than that obtained with the granu- 

 lar form, and is usually reached in a shorter time. The average curve 

 obtained with it is shown in figure 2, c. Seventy-five minutes was 

 required for the concentration to drop to 0.4 mg per liter. 



The average curve with sodium cyanide and acid is shown in figure 

 2, a. In these cases 63 minutes was the average time required for the 

 concentration to drop to 0.4 mg per liter. As a rule, the peak con- 

 centration is reached within 3 minutes, the generation of gas being 

 very rapid. 



Liquid hydrocyanic acid gave a high peak in about the same time 

 as sodium cyanide. The slight delay in the rise to peak concentration 

 shown in figure 2, b, is caused by the difficulty of measuring small 

 quantities by weighing. It is necessary to run the liquid into the 

 house rather slowly in order to weigh it accurately. Otherwise as 



