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se of Poisonous Gases 
Snakes appear to be immune from the effects of certain kinds of 
poisonous gases, as phosgene, cnlorine, and tear chemicalse Tests con- 
ducted in a cave near San Marcos, Hays County, Texas, aovroximately 50 miles 
north of San Antonio, failed to produce any results when phosgene and chilo— 
rine fumes were forced under vressure into the recesses of a rocky cave 
infested with rattlesnakes. On the other hand, in the State of Washington, 
wien mustard gas was oumped into the crevices of a ted of lava rock, rattle— 
snekcs were driven out in a dezed condition and were easily killec with clubse 
Field employees of the Biolowzical Survey have had considerable success 
in destroying rattlesnakes with cruce calcium cyanidee It nas been found that 
two ounces of calcium-cyanide dust (about two tablespoonfuls) are required 
to kill a rattlésnake thet has taken refuge in a ground—squirrel or prairie— 
Gog vurrowe ‘The cyanide is placed well down into the burrow by means of a 
ladle or long-handled spoon and in a mass rather than scattored. A stone 
Or) piece of sod should be used to cover the entrance in preference to ‘som, 
which might slide into the hole and interfere with the formation of the gas. 
Uneer ordinary conditions, a snake will be killed by about 30 minutes 
exposure of the cyanide gas. 
It must be remembered that calcium cyanide is a deadly poison. It 
shoulé be kept in the original air-tight container and out of reach of irre— 
sponsiole persons, chilcren, and livestock. Small Quantities of cyanide 
may be Carried to the area to be treated in a can fitted with a ti sat eo. 
Mii hencline of the material should pe cone in the open aims 
the effectiveness of calcium cyanide gassing depends upon relative 
humicity, for moisture in the air combining wita the cyanide liberates 
ayérocyanic-acid gas, which remains active in the burrow for several hours, 
Giffusing in all .directionse Unsatisfactory results can De expectcéc, howemens 
waen calcium cyanide is used in rainy weather. Temperature is not a limiting 
factor, provided the snakes are not hibernating. The gquartity of calcium 
cyanide necessary to kill snakes in a den or cave Gepends upon the number of 
eubie feet of air space to be saturated with the poisonous gas. In general, 
it appears that 2 oices of cyanide will liberate a deadly concentration of 
ges in a space not exceeding 5 cubic feet, provided there is no leakase. 
Celcium cyanide is offered for sale in 1 and 5 pound cans. A list om 
dealers will be furnished by the Biological Survey, on redueste 
If snakes prove trounlesonme by entering houses or buildings used for 
workshons and storage, and the buildings are so constructed that they can be 
tigntly closed or sealed up for a short period, fumigation by hycdrocvanic= 
acid gas. is recommended. Full instructions for using this gas are contain 
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4 
as 
ed in a mimeographed leaflet, which may be obtained on application to the 
Bureau of Entomology anc Plant Quarantine, United States Department of Agri- 
culture, Washington, D. ©». Buildings in which hydrocyenic-acid is used 
mst be vacated for a day or more, for this gas is extremely deadly and mill 
destroy every living thing within the building. 
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