5 
finished the garret or top floor, the operators should pass rapidly to the 
next, and so on to the basement, making their exit through the lower 
door to the street. 
Hydrocyanic-acid gas is lighter than air, and consequently rises; 
therefore the operation must be begun at the top of the house. 
The house should be locked up from the outside and, if necessary, a 
warning sign put up to caution against entrance. 
The preparation of the different rooms, getting their cubic contents, 
fixing the vessels, and preparing the charges, in a house of the size indi- 
cated in the table given above, will take from two to three hours, and 
this much time must be allowed for. The house should remain closed 
for the gas to become fully generated and do its work for four to six 
hours—preferably, however, and to get the greatest efficiency, over- 
night. 
At the close of the operation, or the following morning, the doors 
may be opened and the windows lowered or opened from the outside, 
and after an hour’s airing the house may be entered if no strong odor 
of gas is detected, and opened up even more thoroughly, if possible, to 
allow a complete airing for several hours. The house should not be 
reinhabited until all traces of the odor of the gas has disappeared. This 
odor resembles that of peach kernels. 
The contents of the generating jars should be poured into the sewer 
trap or disposed of in some place where they will not be a source of 
danger, and the jars thoroughly cleaned. 
THE CYANIDE AND GAS A DEADLY POISON. 
In the use of this gas for household fumigation it must not be lost 
sight of for a single instant that one is dealing with one of the most 
poisonous substances known, and that the accidental eating of a small 
portion of cyanide will necessarily be fatal, and that the inhalation of a 
few breaths of the gas will asphyxiate, and, if rescue be not prompt, 
also have a fatal termination. It is much better, therefore, if fumiga- 
tion be contemplated, to put-the work in the hands of someone who has 
had experience, if such a person be available; if not, to carefully con- 
sider all the recommendations and precautions in this circular and 
become thoroughly familiarized with them before undertaking the 
experiment. 
While the writer thus strongly emphasizes the dangerous and even 
fatal qualities of this gas when breathed by human beings, it 1s worthy 
of remark that in the thousands of operations which have been carried 
on with this gas in specially constructed houses for fumigation of nur- 
sery stock in different parts of the world, no case of fatal accident to a 
human being has ever been recorded. Furthermore, the abundant 
experience which has been gained by the different members of the force 
of this office and many others in the fumigation of dwelling houses has 
