Mixix<; in i i 1 1 EM h \i.s. 39 
able gas. It is impracticable, however, to use t w < > parts <>l water in 
field work, for with this proportion <»f water the residue, especially 
where small dosages of powdered cyanid are used, w ill Frequently con- 
geal within an hour's time the usual period lor 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 held 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 he meas- 
ured carefully with a glass or dipper graduated to ounces 
THE Most ECONOMICAL PROPORTION <>i CHEMICALS 1*0 l-i I\ GENERATING 
BYDROCYAN 1< -ACID GAS 
In the preceding discussion it has been shown that for various 
reasons l fluid ounce of commercial sulphuric acid and l ounce (avoir- 
dupois) 96 to 100 per cent potassium cyanid in combination with '4 
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 himigator. When 
the acid and water are in readiness for generating the gas the i'umi- 
gator adds the pieces of cyanid to the mixture and hastily retreats. 
A- 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 oi Chemistry of this 
Department. One ounce of potassium cyanid, 1 fluid ounce of com- 
mercial sulphuric acid, and 3 fluid ounce- of water were used in each 
case. 
Experiment No. I. The potassium cyanid was added to a mixture 
ol acid and water in which the heal was exhausted, and it was found 
