96 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 
there sufficient water to readily dissolve the sodium sulphate formed, 
as a result of which the residue in the beaker became semisolid. 
With the proportions 3-4-4, 3-5-5, and 3-6-6, less than 2 per cent of 
the total amount of hydrocyanic acid yielded by the cyanid remained 
in the residue when operating on a pure salt. There is little difference 
in the results from the three proportions, and 4 fluid ounces of acid to 
3 ounces (avoirdupois) of cyanid appear to be sufficient. It is not 
necessary to have as much water present to keep the residue in the 
jar from ' 'freezing " as when potassium cyanid is used, because the 
sodium sulphate formed is more soluble than potassium sulphate. 
There was no trouble from this cause in the use of the 3-4-4 formula. 
These experiments were carried out on a warm day, and the vessels 
were placed on a tin roof. If they were placed on the ground under 
a tent, 'the tendency would be to cool more rapidly, and under such 
conditions it may be found necessary in order to prevent "freezing" 
to increase the proportion of water, though it is desirable to keep 
this as low as possible, as an excess of water lowers the temperature 
of the acid and also holds in solution more of the hydrocyanic-acid 
gas. ^ 
Using the 3-4-6 formula, which contains sufficient acid to decom- 
pose all of the cyanid and also enough water to readily dissolve all 
of the sodium sulphate formed and prevent "freezing," only about 
2\ per cent of the theoretical yield of the hydrocyanic acid remained 
in the residue. The following formula, therefore, is recommended as 
a good one for practical fumigation work in the field: 3 parts sodium 
cyanid, 4 parts acid, and 6 parts water — the sodium cyanid being 
expressed in ounces avoirdupois and the acid and water in fluid 
ounces. 
III. ACTION OF MINERAL ACIDS ON CYANID S AND HYDROCYANIC 
ACID. 
The reactions which take place when sulphuric acid acts on potas- 
sium and sodium cyanids have been given and the amounts of hydro- 
cyanic acid remaining in the residue after mixing these substances 
under certain conditions determined, it being assumed that the 
remainder was given off and available for fumigation purposes. 
This assumption, however, is not entirely correct, as all mineral 
acids cause more or less decomposition of hydrocyanic acid. With 
sulphuric acid this action, under the conditions in which fumigations 
are conducted, amounts to very little; in fact, it is scarcely worth 
considering, but in the case of an impure cyanid containing sodium 
chlorid (a frequent impurity), which on addition to sulphuric acid 
liberates hydrochloric acid, this decomposing action becomes a very 
important consideration and no doubt accounts for numerous reported 
instances of failure in fumigation work. It is possible to conceive of 
