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The employment of this gas for disinfecting houses of insect pests 
and vermin has also suggested itself and has been a matter of some 
experimentation, and the feasibility of using the gas for such purposes 
is not to be questioned. Nevertheless, this gas is so extremely poison- 
ous and deadly that its employment in dwelling-houses can under no 
circumstances be recommended to anyone who has not had previous 
experience with it, as the least carelessness would probably mean the 
loss of human life. For house disinfection the use of the gas is sub- 
stantially as in fumigation of nursery stock. 
In all work with hydrocyanic-acid gas, its extremely poisonous nature 
must be constantly kept in mind and the greatest precautions taken to 
avoid inhaling tt. 
Fumigation of nursery stock.—For the fumigation of nursery stock 
or imported plant material in a dormant or semi-dormant condition, a 
building or room should be provided, made so that it can be closed prac- 
tically air-tight and fitted with means of ventilation above and at the 
side, operated from without, so that the poisonous gas can be allowed 
to escape without 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 cyanide (98 per cent), 1 ounce; commercial sulphuric acid, 
1 ounce; water, 3 fluid ounces to every hundred 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.—In the fumigation of growing stock, citrus or 
other, the treatment consists in inclosing the tree with a tent and filling 
the latter with poisonous fumes generated in the same way as described 
for nursery stock except that less of the chemicals is used. The treat- 
ment is made at night for trees in foliage, which includes all work in 
citrus orchards, to avoid the much greater likelihood of injury to tender 
foliage in the sunlight. 
The proportions of the chemicals vary with the size of the tree and, 
as now employed in California, are considerably in excess of the 
amounts recommended a few years ago, or as recently as 1898. The 
gas treatment was first chiefly used against the black scale and at a sea- 
son 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 scale, and to do more effective work even than formerly 
with both of these scale insects. The proportion of chemicals ordi- 
