9 
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PROPORTION OF CHEMICALS. 
The hydrocyanic-acid gas is produced by a combination of cyanid 
of potash and sulphuric acid in water. The most economical and 
efficient production of the gas, as demonstrated by a recent thorough 
investigation of the subject by the Bureau of Entomology in coopera- 
tion with the Bureau of Chemistry of the Department of Agriculture, 
is obtained by the following proportions: @ 
Cyanid of potash (98 per cent pure), by weight... 1 ounce avoirdupois. 
Commercial sulphuric acid, by measure.......... 1 fluid cunce. 
Wei eb aye Cas Une ce Seis ae tos Seedy ee 3 fluid ounces. 
This formula differs somewhat from some other formulas in use 
in mill fumigation.» Any combination of the three ingredients will 
produce gas, and hence any one of several formulas which have been 
recommended and are in use will yield more or less satisfactory 
results, but the greatest economy in materials with a maximum gas 
production is secured by following the above proportions. In this 
formula the acid and water are slightly in excess of the exact chemical 
needs, but it is essential that all the cyanid shall be converted and 
that there be sufficient water present to maintain a completely 
liquid residue. The use of less water, e. g., two parts, May cause a 
solid residue, due to undissolved potassium sulphate, the by-product 
resulting from the reaction by which hydrocyanic-acid gas is produced, 
aSee R.S8. Woglum, Bul. No. 79, Bur. Ent., U. S. Dept. Agr., p. 33, June 11, 1909. 
+ The formula (1:1:3) above quoted may look quite distinct from older ones which 
have been in somewhat general use by millers, fumigators, and others, but the differ- 
ence is very slight and may be explained. The old formula, as originally advised 
by Johnson (Fumigation Methods, 1902, p. 163), reads substantially that to determine 
the amount of acid and water one-half more acid (liquid measure) than cyanid and 
one-half more water than acid are used. ‘‘Therefore a room 20 by 30 by 10 feet 
requires 53 ounces, by weight, of cyanid; 80 ounces, liquid measure, sulphuric acid, 
and 120 ounces, liquid measure, water.’’ As originally advised by Johnson, the 
sulphuric acid was liquid measure, but later a more effective formula for fumigating 
mills and similar inclosures came into use, giving the acid by weight. A formula 
substantially as follows was substituted with better results: 
Cyanid of potash (98 per cent pure), by weight.. 1 ounce avoirdupois. 
Commercial sulphuric acid (93 per cent pure), 
DyAWele itis sees Goee Bae noon Stel ne tee eee 14 ounces avoirdupois. 
WWicl terest py siras pa eea serene Sete Wyte ne Rs oh 21 fluid ounces’ or 
ounces avoirdupois. 
In point of fact, the formula last quoted substitutes the computation of the acid by 
weight for computation by measure as used in earlier formulas. Thus, while the 
avoirdupois formula remains nearly the same, owing to the greater atomic weight of 
the acid, the chemical reaction is almost identical with the formula 1:1:3, which we 
now advise. 
Theoretically the difference in acid between the two formulas is so slight that in 
fumigating mills the results are about equal. In some cases there might be a slight 
acid deficiency, resulting in a proportionate deficiency in the amount of gas evolved. 
25795—Cir. 112—10——2 
