34 FUMIGATION INVESTIGATIONS IN CALIFOENIA. 



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 loo 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 OP 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 IJ 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 svifficient 

 water is present, the potassium sulphate dissolves and there is no solid 

 residue. This was the result when ecpial 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 IN 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 throwni 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 frbm the 

 reaction by which hydrocyanic-acid gas is produced. Water dis- 



