, MIXING THE CHEMICALS, 39 



able gas. It is impracticable, however, to use two parts of water in 

 field work, for with this proportion ot water the residue, especially 

 where small dosages of powdered cyanid are used, will frequently con- 

 geal within an hour's time — the usual period for leaving the tents on 

 the trees. Although this proportion of water is apparently sufficient 

 to dissolve the sulphate at first so that a complete reaction takes 

 place, it appears unable to hold the sulphate in solution long enough 

 afterwards to prevent inconvenience in field work. It is of course evi- 

 dent that a "frozen" generator does not always signify an unsatis- 

 factory generation. With three parts of water, however, the residue 

 seldom congeals, and this is the proportion we have used in all of our 

 field work and which we recommend. The water should be meas- 

 ured carefully with a glass or dipper graduated to ounces. 



THE MOST ECONOMICAL PROPORTION OF CHEMICALS TO USE IN GENERATING 

 HYDROCYANIC-ACID GAS. 



In the preceding discussion it has been shown that for various 

 reasons 1 fluid ounce of commercial sulphuric acid and 1 ounce (avoir- 

 dupois) 96 to 100 per cent potassium cyanid in combination with 3 

 fluid ounces of water give a complete reaction. Thus the 1-1-3 for- 

 mula, hitherto recommended by the Bureau of Entomology, is fully 

 indorsed. 



A review of the use of hydrocyanic-acid gas for fumigation, both in 

 California and elsewhere, shows frequent divergence from the more 

 economical and satisfactory proportion of chemicals indicated above. 

 One book recognized as an authority on fumigation methods recom- 

 mends the use of ' ' one-half more acid than cyanid and one-half more 

 water than acid." Many of the entomologists and horticulturists in 

 the eastern United States advise in their recommendations for nur- 

 sery fumigation two parts of acid and four parts of water to each 

 part of cyanid. 



MIXING THE CHEMICALS. 



It is preferable to pour the water into the generator first and then 

 add the acid. The pouring of the water onto the acid is more likely 

 to cause splashing of the acid from the jar onto the fumigator. When 

 the acid and water are in readiness for generatmg the gas the fumi- 

 gator adds the pieces of cyanid to the mixture and hastily retreats. 

 As already stated, the cyanid should be added while the mixture of 

 water and acid is hot. The advantage of this is shown in the fol- 

 lowing experiments performed by the Bureau of Chemistr}' of this 

 Department. One ounce of potassium cyanid, 1 fluid ounce of com- 

 mercial sulphuric acid, and 3 fluid ounces of water were used in each 

 case. 



Experiment No. 1. — The potassium cyanid was atlded to a nnxture 

 of acid and water in which the heat was exhausted, and it was found 



