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REPORT OF THE ENTOMOLOGIST, 131 
This table is based upon the cubical contents of the space inclosed by the tent 
vege that the lower part of the tent rests upon the ground, No harm will result 
to the tree if twice the quantity that i have recommended be used, but of course 
for the sake of economy, it will be desirable to use only such quantity of each in- 
gredient as will be necessary for destroying the scale-insects infesting the tree to be 
treated with this gas. The sulphuric acid should havea density of 65° when tested 
with an acid hydrometer; should its density be lower than this, use an extra ounce 
of the acid for every five degrees of density below 65°. 
The Cyanide and Soda Process.—The third method of rendering the hydrocyanic 
acid gas harmless to the foliage of the trees confined in it consists o mixing this 
gas with carbonic acid gas, the latter having the property of extracting the moisture 
from the former, forming gaseous carbonic acid. This appears to occur only under 
a certain degree of pressure: thus, if the two gases are generated in the same open 
generator within the tent and allowed to rise and fill the tent, the hydrocyanic acid 
gas will prove nearly as injurious to the foliage of the tree confined in it as it would 
if no carbonic acid gas had been present. 
The carbonic acid gas is produced by acting with sulphuric acid upon bicarbonate 
of soda or saleratus. The latter is first made into a thin paste with water, using 
about 1 fluid ounce of water to each 2 ounces by weight of the bicarbonate. Several 
seconds elapse after the sulphuric acid comes in contact with the soda paste before 
the evolution of the gas begins; a foamy mass soon appears, consisting of variously 
sized bubbles which rise up in the generator and finally burst, giving forth the 
colorless and odorless gas. A fiuid ounce of the acid will evolve all of the gas from 
about 3 ounces of the bicarbonate, weighed before it is mixed with the water. 
The bicarbonate has a tendency to settle to the bottom of the solution, forming a 
compact mass upon which the acid acts very slowly. On this account it is desirable 
to add the soda paste to the acid instead of following the usual method of adding 
the acid to the soda. I have used marble dust in place of the bicarbonate of soda, 
and the result obtained by its use was as satisfactory as when the bicarbonate had 
been used; it possesses none of the adhesiveness of the bicarbonate and consequently 
does not form a compact mass in the bottom of the solution. 
The best results have been obtained when both the hydrocyanic acid gas and the 
carbonic acid gas were produced in the same apartment of the generator. 
The cyanide is first dissolved in water, as described above, using 5 pounds of the 
cyaniole to each gallon of water, and for every 10 fluid ounces of this solution use 
9 ounces, by weight, of the bicarbonate. The bicarbonate is first made into a thin 
paste with water, as above described, after which it is added to the proper quantity 
of the cyanide solution and thoroughly stirred; the whole is then added very slowly 
to the proper quantity of sulphuric acid, previously poured into the lower apartments 
of the generator. : 
The following table will give a good idea of the proper quantity of each ingre- 
dient to be used for the differently sized trees: 
H Cyanide | Bicarbon- ‘Sulphuric 
Height Diameter solution jate of soda} acid 
| (in feet). | (in feet).; (fluid |(ouncesby} (fluid 
/ ounces).| weight). | ounces). 
| 
| 
6 | 5 | a 13 13 
10 | 10 12 | 11 11 
12 8 | 9 | 8 8 
16 12 | 28 27 25 
20 14 | 7 43 40 
The hydrocyanic acid gas will be just as effective if twice the amount of the 
bicarbonate of soda that I have recommended be used, together with a sufficient 
quantity of sulphuric acid to evolve all of the carbonic acid gas from it. This 
latter gas does not act as a diluent, as some persons have supposed, but simply as a 
drier, its sole office being to extract the moisture from the hydrocyanic acid gas, 
thus rendering the latter gas harmless to the foliage of the trees confined in it. 
The carbonic acid gas does not injure the foliage of orange trees confined in it; 
when sufficiently pure, it stupefies the scale-insects confined in it for half an hour, 
but they wholly recover from the effects of the gas after the lapse of a few hours. 
I noticed that when the trees were treated with the cyanide and soda process in 
the hottest part of a very hot day the foliage was almost as severely injured as 
when the hydrocyanic acid gas had been used alone. “We may conjecture that this 
results from the fact that at a high temperature the carbonic acid gas is freed from 
the aqueous vapor, leaving the latter in a proper condition for again uniting with 
