USE OF GASES AGAINST HOUSEHOLD INSECTS 447 



and put in a paper bag beside the jar. All hats, coats, or 

 other articles that will be needed before the work is over, 

 should be removed from the room. When everything is 

 ready, the operator should drop the bag of cyanide gently 

 into the jar, holding his breath, and should walk quickly 

 out of the room. The steam-like gas does not arise 

 immediately under these conditions, and ample time is 

 given for the operator to walk out and shut the door. If 

 preferred, however, the paper bag may be suspended by a 

 string passing through a screw eye in the ceiling and then 

 through the keyhole of the door. This is called stringing 

 a room (Fig. 152). In this case the bag may be lowered 

 from the outside after the operator has left the room and 

 closed the door. 



The writer has most often started the fumigation toward 

 evening and left it going all night, opening up the rooms 

 in the morning. The work can be done, however, at any 

 time during the day and should extend over a period of 

 five or six hours, at least. Experiments show that better 

 results will be obtained in a temperature of 70 degrees F. or 

 above, than at a lower temperature. 



At the close of the operation, the windows and doors 

 may be opened from the outside. In the course of two or 

 three hours the gas should be dissipated enough to allow 

 any one to enter the room without danger. The odor of 

 the gas is like that of peach kernels and is easily recognized. 

 The rooms should not be occupied until the odor has gone. 



Fumigating a large house. — The fumigation of a large 

 house is simply a repetition in each room and hall of the 

 operations already described for a single room. All of the 

 rooms should be made tight and the proper amounts of 

 water and sulphuric acid should be measured and poured 



