FUMIGATION OF CITRUS TREES. 



45 



the acid has been diluted with water. With very dilute sulphuric 

 acid and up to a strength of 1 part acid to 1 part of water, which is 

 as concentrated a mixture as is ever used in fumigation work, nearly 

 pure hydrocyanic-acid gas is given off. By decreasing the propor- 

 tion of water used below 1 part, the amount of hydrocyanic-acid 

 gas resulting is also decreased until, when concentrated sulphuric 

 acid acts on a cyanid, hydrocyanic-acid gas is not given off, but rather 

 an entirely different gas called carbon monoxid. 1 



THE EFFECT OF DIFFERENT PROPORTIONS OF WATER. 



On temperature of gas. — Anyone who has watched the escaping gas 

 and steam from the reaction of potassium cyanid and sulphuric acid 

 wherein different proportions of water were used could not fail to 

 notice that the violence with which the generation starts and the 

 gas is given off is apparently greatest with the smaller proportions of 

 water. Experiments - carried on by this investigation showed that 



PPOPORT/OMS OP 

 CYAN/€\ ACID WAT£R 



PEP C£A/rOF 6/1 S G/ISFA/ OFF 



10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 



Fig. 10. — Chart showing total amount of gas evolved when different proportions of water are used. 



(Author's illustration.) 



the temperature of the escaping gas was considerably higher with 

 smaller proportions of water than with the larger proportions. In one 

 experiment the highest temperature of the escaping gas was 124° F. 

 with 1 part of water, but only 90° F. with 8 parts. The temperature 

 was approximately uniform with from 1 to 4 parts of water. 



On amount of available gas. — The Bureau of Chemistry of this 

 department, at the request of the Bureau of Entomology, performed 

 an experiment to determine the amount of hydrocyanic-acid gas 

 available when generated with proportions of water varying from 1 

 to 8 parts. The results have been incorporated in the accompanying 

 chart (fig. 10). 



In these experiments commercial sulphuric acid 66° Baume, analyz- 

 ing 92.77 per cent pure, and potassium cyanid 97.12 per cent pure 

 were used. Three ounces (fluid) of sulphuric acid and 3 ounces 



i See Part III of this Bulletin. 



