422 
Journal of Agricultural Research 
Vol. XI, No. 9 
It was found that the concentration of hydrocyanic-acid vapor in the 
air over a simple aqueous solution of the gas quickly becomes constant 
if a relatively large volume of the solution were held in a small closed 
container. Furthermore, if the temperature is constant, it was shown 
that the concentration of the hydrocyanic-acid vapor in air under the 
above conditions was dependent on the concentration of the solution. 
A solution of hydrocyanic-acid gas was made by dissolving i gm. of 
sodium cyanid in i liter of water and adding 15 c. c. of 10 per cent sulphu¬ 
ric acid. (This is actually an aqueous solution of hydrocyanic-acid gas in 
a sodium-sulphate solution, probably containing a slight excess of sul¬ 
phuric acid.) The air in a closed container above a relatively large volume 
of such a solution contained approximately 0.3 per cent of hydrocyanic- 
acid vapor, 1 which is within the range of strength used for fumigation work. 
If air were slowly aspirated through this solution, it also would contain 
approximately 0.3 per cent hydrocyanic-acid vapor. Other solutions 
were made up similar to the above, but of different concentrations, the 
amount of sodium cyanid being reduced one-half in each succeeding 
culture until the minimum point of toxicity was reached. 
Houseflies (Musca domestica) were exposed to the following range 
of dilutions in closed test tubes (Table I): 
Table; I. — Concentration of gas used on houseflies 
Sodium 
cyanid per 
liter. 
Approximate 
concentration 
of gas. 
Sodium 
cyanid per 
liter. 
Approximate 
concentration 
of gas. 
Gm. 
Percent. 
Gm. 
Per cent. 
I. 0 
O. 3000 
0. 0625 
0 .0187 
•5 
. 1500 
. 0312 
.0093 
•25 
.0750 
.0156 
. 0046 
■ 125 
•0375 
1 The method of calculating the amount of hydrocyanic-add gas in air: 
A standard sodium-cyanid solution is made up as above, containing i gm. of sodium cyanid per liter 
and is c. c. of io per cent sulphuric add. Air is aspirated first through this solution, then through Njioo 
iodin solution (containing a little sodium carbonate) until the latter is completdy decolorized, the ratio 
being 36,5 c. c. of air (the mean of a number of experiments) "ic.c. of Nhoo iodin. 
One equivalent of iodin is equal to two equivalents of HCN, according to the sense of the following equa¬ 
tion: 
HCN-§-I 2 =HI+ICN; therefore 
1 c. c. Nfioo 1=0.0001351 gm. HCN 
* 1 c. c. Nfioo 1 = 36.5 c. c. air 
36.5 c. c. air * *-0.0001351 gm. HCN 
. 0.0001351 
1 c. c. air — — , ■ ■ gm. HCN 
30.5 
1,000 c. c. air — ^ x |OOO=J 0 - gm, HCN in 1 liter of air 
30*5 30-5 
1 liter air —0.003 7 gm. HCN 
1 liter air — weighs 1.29 gm. at o° C. and 760 mm. 
Barometric pressure 755.6 
Thermometer 20® C. 
1,000 c. c.X“^X——937.2 c. c. air 
760 293 
937.2 c. c. wdghs 1.2099 gm. 
? :° ° 3 7 x 100—0.306 per cent HCN in air. 
1.2099 0 
