9 FARMERS’ BULLETIN 699. 
been in use since 1898 and has proved so uniformly effective for this 
purpose when properly applied that in spite of its extremely poison- 
ous character it has almost entirely replaced other and less poisonous 
gases.1. Rats and mice are also killed by its use, and it fortunately 
has the effect of first causing these animals to rush out from their 
holes into the open, so that the subsequent annoyance of dead rats 
and mice in walls and under floorings is not experienced. The 
absence of any bleaching or tarnishing tendency when pure materials 
are used is also a strong point in its favor. 
MATERIALS USED IN THE FUMIGATION PROCESS AND THEIR 
PROPORTIONS. 
In the formation of hydrocyanic-acid gas for the purposes of 
fumigation sulphuric acid in a diluted form is permitted to act on 
either sodium cyanid or potassium cyanid. In the resulting reaction 
hydrocyanic-acid gas is liberated, while the remainder of the salt 
unites with the sulphuric acid to form sodium or potassium sulphate, 
nonpoisonous compounds. Up to the year 1909 cyanid of potassium 
was used almost entirely for this purpose, but since that time cyanid 
of sodium has taken the place of potassium cyanid and the latter is 
not now easily obtainable.? Sodium cyanid in its pure form liberates 
nearly a third more hydrocyanic-acid gas per pound than does cyanid 
of potassium and is a satisfactory substitute for potassium cyanid. 
Its slightly greater cost is balanced by the larger yield of gas. 
Cyanid of sodium is now being manufactured in special 1-ounce 
molds for fumigation purposes. 
1 Carbon bisulphid has sometimes been recommended as' a substitute for hydrocyanic-acid 
gas. The extreme inflammability of this substance, however, and the explosiveness of its 
vapor when confined render it perhaps less available, and the danger in its use more than 
counteracts the danger to human beings from hydrocyanic-acid gas. It has been found, 
moreover, that hydrocyanic-acid gas is much more effective for the control of all groups 
of household insects, with the exception of the beetles, than is the other fumigant. 
2 Should potassium cyanid be obtainable, and used in the fumigation, 1 fiuid ounce of 
commercial sulphuric acid (about 1.84 sp. gr., or 66° Baumé) diluted with 3 fluid ounces 
of water (to increase the bulk of the liquid and insure complete chemical action) and 1 
ounce of high-grade (98 per cent) cyanid of potassium must be used for every 100 cubic 
feet of space. The formula per hundred cubic feet, therefore, is as follows: 
Potassium cyanid (98 per cent)________________-avoirdupois ounce__ 1 
Commercial) sulphuric /acidi oo ee eee ee fluid ounce_- nf 
Water.o% —* 22) 2 Se a ee ee eee fluid ounces__ 3 
Potassium ecyanid was formerly obtainable in various technical grades, ranging be- 
tween 40 per cent and 98 to 100 per cent actual cyanid, the remainder being an inert 
salt, usually sodium carbonate or sodium chlorid, which is of no value in fumigation and 
in the case of sodium chlorid is a positive detriment, as this substance, acted upon by 
sulphurie acid, produces hydrochlorie acid, which decomposes the hydrocyanic-acid gas. 
In cases of extreme adulteration as much as 60 per cent of the fumigant may be decom- 
posed in this manner, resulting in inferior effectiveness and tending to tarnish polished 
metal surfaces exposed to the gas. If chemically pure cyanid is used little tarnishing 
results. 
