CHEMISTRY OF FUMIGATION. 93 
siderable amounts of sodium chlorid. While the amount of cyanid 
present is equivalent to that found in a high-grade potassium cyanid, 
owing to the presence of this chlorid they will yield considerably less 
gas, as subsequently shown in this paper, and are therefore not as 
valuable for fumigating purposes. 
II. PROPORTION OF CYANID, SULPHURIC ACID, AND WATER FOR 
BEST YIELD OF GAS. 
POTASSIUM CYANID. 
When dilute sulphuric acid acts on potassium cyanid, resulting in 
complete decomposition, the theoretical reaction is as follows: 
2KCN + H 2 S0 4 = K 2 S0 4 + 2HCN. 
According to this reaction 1 ounce (avoirdupois) of potassium 
cyanid (KCN 100 per cent) would require 0.75 ounce (avoirdupois) 
of sulphuric acid, H 2 S0 4 , or 0.81 ounce (avoirdupois) of commercial 
sulphuric acid containing 93 per cent sulphuric acid, which would be 
equal to 0.42 fluid ounce. 
The above reaction can not be obtained under the conditions exist- 
ing in fumigation work, and to get the best yield of gas it is necessary 
to have a considerable excess of sulphuric acid. Under such condi- 
tions it would be the acid potassium sulphate that would be formed 
and the reaction would proceed thus: 
KCN + H 2 S0 4 = KHS0 4 + HCN, 
or for each ounce (avoirdupois) of potassium cyanid there would be 
required 0.84 fluid ounce of 93 per cent sulphuric acid. This amount 
has been found in practice to give the best results, or, in round numbers, 
for convenience in practical field work, 1 part cyanid to 1 part acid. 
According to laboratory work the proportion of water that should be 
used with these amounts of cyanid and acid in order to obtain the 
best yield of gas was 2 parts. 1 In field practice, however, Mr. Wog- 
lum has pointed out 2 that it is not always practicable to use this 
amount on account of the fact that the residue sometimes solidifies 
in the generating jar, and he has therefore adopted and recommends 
3 parts of water, or a 1—1-3 formula. 
SODIUM CYANID. 
The action of sulphuric acid on sodium cyanid is identical with its 
action on the potassium salt, and is as follows: 
2NaCN + H 2 S0 4 = Na 2 S0 4 + 2HCN. 
1 Bui. 79, Bur. Ent., U. S. Dept. Agr., pp. 37-38, 1909. 
2 Ibid., p. 39. 
