SODIUM CYANID FOB FUMIGATION PURPOSES. 
85 
STRENGTH OF SODIUM CYANID EXPRESSED IN TERMS OF 
POTASSIUM CYANID. 
The strength of sodium cyanid is commonly reckoned in terms of 
potassium cyanid. Chemically pure potassium cyanid is 100 per cent 
pure, while chemically pure sodium cyanid is commonly spoken of as 
133 per cent pure. The explanation for this is that pure sodium cya- 
nid contains, for the same weight, practically one-third more cyanogen 
(available hydrocyanic-acid gas) than potassium cyanid and this 
greater strength is expressed in terms of the potassium salt for con- 
venience sake. Thus we have 133 per cent sodium cyanid, meaning 
that, when absolutely pure, it contains 33 per cent more cyanogen 
(available hydrocyanic-acid gas) than a pure potassium cyanid. It 
is evident, therefore, that if 1 pound of pure sodium cyanid can be 
purchased as cheaply as 1 pound of pure potassium cyanid, there will 
result a great economy by the use of the former provided the genera- 
tion of the gas be equally perfect for each. The price is, however, 
usually based on the percentage of cyanogen present and the saving 
in cost may be thus offset to a large extent. 
PROPORTION OF CHEMICALS. 
A large number of experiments was carried on with a high-grade 
sodium cyanid, with the idea of determining the best proportion of 
chemicals for use. As a result of these tests Mr. McDonnell recom- 
mended a 3-4-6 formula: 3 ounces (avoirdupois) of cyanid, 4 fluid 
ounces of sulphuric acid, and 6 ounces of water. Reduced to its lowest 
units for rapid work in the field, the writer has used 1J fluid ounces of 
acid and 2 ounces of water to each ounce (avoirdupois) of cyanid of 
sodium. This 1-1 ^-2 formula is recommended. 
The 1-1 ^-2 formula with a high-grade sodium cyanid produces 
exactly as satisfactory a generation in the laboratory as can be 
obtained from a high-grade potassium cyanid, using the proportion 
of chemicals adapted for the best generation of gas with the latter. 
This is exhibited by a comparison of the generation from two high- 
grade commercial products, as shown in the following table: 
Kind of cyanid. 
Proportion of — 
Purity of 
cyanid. 
Per cent 
of total 
Cyanid. 
Acid. 
Water. 
evolved. 
1 
1 
1 
2 
2 
Per cent. 
98 
124 
93. 8& 
94.32 
Although these laboratory determinations exhibited that the yield 
of gas, or reaction, with a high-grade sodium cyanid is as satisfactory 
as with a potassium cyanid, the writer did not feel justified in recom- 
mending its use until these results could be confirmed by actual field 
experience. 
