33 
the necessity of anyone entering the chamber. The gas is generated 
by combining potassium cyanide, sulphuric acid, and water. The 
proportions of the chemicals are as follows: Refined potassium cyan- 
ide (98 per cent), 1 ounce; commercial sulphuric acid, 1 ounce; water, 
3 fluid ounces to every hundred cubic feet of space in the fumigating 
room. For comparatively green or tender material the same amounts 
may be used to 150 cubic feet of space. 
The generator of the gas may be any glazed earthenware vessel of 
1 or 2 gallons capacity and should be placed on the floor of the fumi- 
gating room, and the water and acid necessary to generate the gas 
added to it in the order named. The cyanide should be added last, 
preferably in lumps the size of a walnut, and the premises promptly 
vacated and the door made fast. -Treatment should continue forty 
minutes. 
ORCHARD FUMIGATION. 
The methods of fumigating citrus stock in California are now 
(1908) being given a thorough investigation by this Bureau. As 
already noted, the gas process has been a leading method in Cali- 
fornia for more than twenty years, but the results, while normally 
good, have not always been satisfactory. The object of the investiga- 
tion now under way is to thoroughly standardize the process; in other 
words, (1) to determine the proper strength to be used for the differ- 
ent scale pests under different climatic conditions, and also under the 
different seasonal conditions of the tree; (2) to determine the physi- 
ological effect, if any, on the tree and fruit; and (3) to perfect the 
mechanical means of handling tents and generating the gas, and de- 
termine the proper quantity and quality of chemicals to use. The 
results of this investigation will be the basis of a special report on gas 
fumigation, and will probably modify somewhat the directions given 
below, which are reproduced from the previous edition of this bulletin. 
The fumigation for the white fly in Florida is a special problem 
and has been under investigation by this Bureau for two years. The 
results of this investigation, including general directions for fumiga- 
tion, will be given in Bulletin No. 76. 
Amounts of chemicals to use—The amounts of chemicals used vary 
with the size of the tree and, as now employed in California, are con- 
siderably in excess of the amounts recommended as recently as 1898. 
The gas treatment was first chiefly used against the black scale and at 
a season of the year when these scales were all in a young stage and 
easily killed. The effort is now made not only to kill the black 
scale, but also the red and purple scales, and to do more effective 
work than formerly against the black scale. The amounts of chem- 
icals ordinarily advised and commonly employed in Los Angeles, 
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