22 CIRCULAR 3' 



apartment buildings, etc., the use of some form of solid from which 

 hydrocyanic acid gas . can be produced is often desirable, since it 

 does away with the necessity for an elaborate piping system or for 

 crock or barrel generators. 



There are two types of such solids now on the market. One of 

 these consists of liquid hydrocyanic acid absorbed in some inert 

 material from which it evaporates on exposure to air. This inert 

 material is pressed into waferlike discoids each containing approxi- 

 mately one-half ounce of liquid hydrocyanic acid (fig. 19). These 

 discoids are marketed in tightly sealed cans of various sizes and sold 

 on the basis of the net content of hydrocyanic acid. The other type 

 of solid is calcium cyanide, and the hydrocyanic acid is produced by 

 chemical reaction with the moisture in the air. Its use will be dis- 

 cussed under the powder method. 



APPLYING THE DISCOIDS 



When large quantities of discoids are used, especially in hot 

 weather, it is advisable to chill the cans before fumigating. This 

 will greatly retard the generation of the gas and thus increase the 

 safety of operation. If solid carbon dioxide is available, a liberal 

 quantity thrown over the tops of the cans in each opened case a few 

 hours before fumigating will chill the discoids. Placing cans of 

 discoids in cold storage will have the same effect. 



The proper number of cans of discoids should be placed on each 

 floor to be fumigated, and the distribution of the fumigant should be 

 started on the top floor, always from a predetermined point and 

 approaching the exit. The cans are opened with a specially devised 

 can opener that makes a clean cut close to the rim (fig. 20). If 

 several operators are engaged in the work, one can open the cans 

 while the others scatter the discoids over the floor or among the 

 machinery. The men should take turns opening the cans, so that 

 one man will not be exposed too long to the heavy concentrations near 

 the newly opened cans. 



Discoids should not be placed directly on painted or varnished floors 

 or woodwork, for the liquid hydrocyanic acid is likely to injure the 

 finish. Two or three thicknesses of newspaper or wrapping paper 

 will provide adequate protection against any liquid that may ooze 

 from the discoids. 



When discoids are used, the fumigators are exposed to the gas 

 while they are opening the cans and distributing the contents. 

 Good gas masks are necessary and will prevent them from breath- 

 ing poisonous fumes, but there is also some danger from the direct 

 absorption of hydrocyanic acid gas through the skin and of en- 

 countering concentrations of the gas above the capacity of the 

 mask. Williams 4 has estimated that a man protected by a good gas 

 mask can remain in air containing 2 ounces of hydrocyanic acid gas 

 per 1,000 cubic feet for half an hour without being affected; in a 

 concentration of 4 ounces per 1,000 cubic feet this time should be 

 reduced to 15 minutes, and in one of 8 ounces to 5 minutes. The same 

 author calculates that, in distributing discoids at the rate of 8 ounces 

 of hydrocyanic acid per 1,000 cubic feet, a fumigator will be actually 

 exposed for the greater part of the time to from 1 to 2 ounces per 



* Williams, C. L. fumigants. Pub. Health Repts. [U. S.] 46 : 1018. 1931. 



