254 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
may be used, but sulphuric acid and the bicarbouates are cheaper and 
better. The sulphuric acid retails at about 5 cents per pint; wholesale, 
cents. Marble dust, so extensively used in preparing soda water, 
is the cheapest carbonate, costing only 1 cent per pound, but is not 
economical in these small generators in view of its bulk and slowness 
of action. The bicarbonate of soda, which works best, sells in quanti- 
ties at 4 cents per pound. After decomposing it the residue is sodic sul- 
phate or Glauber's salts, which has a little value (about 1 cent per pound) 
and may be saved. jVIy experiments indicate that pounds sulphuric 
acid, $0.07, to 2 pounds bicarbonate of soda, $0.08, total, $0.15, mixed, 
will squirt 40 gallons 6 feet high over 1 acre at a cost of 15 cents. 
Forty gallons is the amount of water which has heretofore been applied, 
to the acre; but I have shown that an acre may be poisoned by one- 
third this quantity with my eddy jets, which reduces the above cost of 
chemicals and labor to about 5 cents per acre. This includes the labor 
since the driver can easily attend to the generator. Where the reser- 
voir is high, and when the cotton is of average height or lower, a part 
of this chemical force and expense will not be necessary. Also the acid 
will cost only one-half the above price if bought at wholesale rates, as 
it can be where several pounds are needed which, almost invariably is 
the case on ordinary plantations and large ones. Thus the gas-pres- 
sure process is made economic, and indeed very cheap. The ease of 
this method also strongly commends it. The management of the gen- 
erator involves almost no labor at all. It can be attended to by the 
driver without stopping and no assistance is needed. The appliances 
designated below settle the question of practicability. 
Since ordinary tight reservoirs with branching pipes and nozzles, as 
have been already described, can be used in this process for distributing 
the liquid it will be in order at once to give special attention to the ap- 
paratus and materials for generating the pressure. 
The generator need not be expensive, and for the slight pressure re- 
quired in sprinkling the under surfaces of plants great strength or 
weight is not necessary, while a large sheet metal can or stout barrel 
serves as a reservoir. Beer, wine, whisky, or kerosene barrels answer. 
The generator consists of two chambers, one for the acid, the other for 
the substance it is to act upon, and so arranged that by tipping one or 
both of the chambers, or by adjusting a shut-off between them, one of the 
materials can be fed into the other in any proportion or at any momen; 
desired, to control the pressure at will. These chambers may be con- 
nected end to end, side by side, or one partially or totally inside the 
other, or otherwise. In small generators they ought to carry at least 
enough chemicals to eject forty gallons; that for pure or diluted acid 
having a capacity for one quart or two pounds or more, and the other 
for the carbonate, or carbonate and water, to hold two or three quarts, 
since it is better to have the carbonate in excess and to add enough 
water to wet it thoroughly. A simple plan is to put the acid in an un- 
