10 CIRCULAR 457, U. S. DEPT. OF AGRICULTURE 



gating mushroom houses at peak heat. As hydrocyanic acid gas is 

 readily absorbed by moisture, the house, although damp, should not 

 be wet, with puddles of water standing in the alleyways, or much of 

 the gas will be lost before it is fairly liberated. Experiments have 

 shown that the maximum concentration of gas is reached in from 10 

 to 20 minutes after the cyanide is scattered. In view of the deadly 

 nature and the rapid evolution of this gas, every precaution should 

 he taken against accidents. In the case of a single house, the chem- 

 ical should be scattered in the central alleyway as evenly and quickly 

 as possible, beginning at the back of the house and working toward 

 the door. Special care should be taken that the alleyway is clear of 

 obstructions before the fumigation is begun, as a stumble over some 

 obstacle while walking backward and scattering the cyanide might 

 easily result fatally. In the case of a double house the material is 

 scattered in the two main alleyways, the workers starting together 

 at the far end and working toward the doors, timing themselves so 

 as to reach the doors simultaneously. After the operators have left 

 the house the doors should be closed and tightly sealed and left so 

 for about 12 hours. 



Caution: When entering a house after fumigation, use a gas mash 

 until the house has oeen thoroughly aired out. 



The same precautions are necessary as with sulphur to prevent 

 fumes from reaching and damaging growing mushrooms, although 

 this gas is not so harmful to them as sulphur fumes. In the case of 

 a double house, the other half of which is in bearing, the doors be- 

 tween them should be made gastight, all cracks and openings in the 

 partition tightly sealed, and the doors and ventilators of the house 

 in bearing opened. As a further precaution, it is desirable to 

 fumigate when the wind is blowing away from the house in bearing. 



The so-called pot method of fumigation, in which sodium cya- 

 nide and sulphuric acid are used, is almost as easy and convenient 

 as that with calcium cyanide, and gives a more rapid liberation 

 of gas and a much higher concentration. The material should be 

 used at the rate of not less than 8 ounces of sodium cyanide to 12 

 fluid ounces of a good grade (66° B.) of commercial sulphuric 

 acid and 16 fluid ounces of water per 1,000 cubic feet of air space. 

 Three or four 3-gallon glazed crocks may be used for generators. 

 The necessary quantity of water is measured out and divided among 

 these. They are then set at equal intervals in the central alleyway 

 of the house. The acid is similarly measured out and the necessary 

 quantity placed in a glass jar beside each generator. The sodium 

 cyanide having been similarly weighed out (it can be obtained in 

 14-ounce or 1-ounce "eggs" to save this work), and the proper quan- 

 tity for each jar having been put into a heavy brown paper bag (the 

 thickness of paper may be doubled for additional safety by using 

 two bags, one inside the other, for each charge), the operator takes 

 the twisted necks of the bags in his left hand, enters the house, and 

 pours the acid into each generator as he reaches it. Having reached 

 the back of the house, he then walks rapidly toward the door, plac- 

 ing one of the bags of cyanide in each generator as he passes it. 

 The acid requires a short time to eat through the paper bags, and the 



