SODIUM CYANID FOR 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 \\ 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. 



gas 

 evolved. 



Potassium 



1 

 1 



1 

 1J 



\ 



Per cent. 



98 



124 



93.88 



Sodium 



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. 



