34 FUMIGATION INVESTIGATIONS IN CALIFORNIA. 
Summing up, it may be said that 1 fluid ounce of commercial sul- 
phuric acid (93 per cent) to 1 ounce (avoirdupois) of 98 per cent 
potassium cyanid is certainly enough to carry the reaction to com- 
pletion in the liberation of hydrocyanic-acid gas and is perhaps an 
unnecessarily large amount. In practical field work where dosages 
of varying sizes are constantly being used, it is very convenient to 
reckon the acid in the same number of parts as the cyanid. The 
use of 1 part (fluid measure) of acid to each part of cyanid is there- 
fore recommended. 
The commercial potassium cyanid sold on the market is usually 96 
to 100 per cent pure. The commercial sulphuric acid on the market 
is sold as 66° Baume and should contain 93.5 per cent sulphuric acid. 
In California fumigation work, these grades are used and are to be 
understood wherever cyanid or acid is mentioned in this bulletin. 
In the dosage allotments cyanid is always measured in ounces or 
parts dry weight, while the acid is measured in fluid ounces or parts. 
THE EFFECT OF TOO GREAT AN EXCESS OF ACID. 
In the experiment mentioned, in which two series of hydrocyanic- 
acid gas generations were completed, the question immediately arose, 
why the residue in some generators, in which 1^ parts of acid were 
used, congealed, while in the case of those in which equal parts of acid 
and cyanid were used no such result was noted. The explanation is 
simple: When sulphuric acid acts on potassium cyanid, hydrocyanic 
acid, a gas, and potassium sulphate, a solid, are formed. If sufficient 
water is present, the potassium sulphate dissolves and there is no solid 
residue. This was the result when equal parts of acid and cyanid 
were used. When one-fourth more acid than cyanid is employed, 
there is a large excess of acid. The potassium sulphate is not as 
soluble in water containing excess acid as it is in water alone ; hence 
it undergoes partial crystallization, resulting in a mushlike residue or 
congealing into a solid mass. 
WATER AS A FACTOR IX FUMIGATION. 
There are several reasons why water should always be employed 
in fumigation: It is very useful in dissolving the potassium cyanid 
and hastening and completing the chemical reaction with the acid. 
A piece of cyanid thrown into a mixture of acid and water imme- 
diately gives up a portion of its mass in solution. Scarcely has the 
cyanid dissolved when it is partially converted into gas. The heat 
liberated during this process assists in forcing the solution of more 
cyanid, which is also partially converted into gas. This continues 
until the chemicals are exhausted and the reaction stops. 
Potassium sulphate, a solid, is the by-product resulting from the 
reaction by which hydrocyanic-acid gas is produced. Water dis- 
