INSECT CONTROL, IN FLOUR MTLLS. 23 



and poured into each container. The acid should always be added 

 to the water and never vice versa. The mixing of water and sul- 

 phuric acid generates heat; hence care should be taken to pour the 

 acid slowly into the water to prevent too rapid a rise in temperature, 

 which might cause a cracking of the crocks. As the gas is formed 

 best when the mixture of acid and water is warm, the acid should not 

 be added until just before the fumigation is started. As soon as the 

 acid is poured into the generators the cyanid, which has already been 

 weighed out into proper amounts and placed in sacks, should be dis- 

 tributed, one sack by each generator, as illustrated in figures 8 to 11. 



Dropping of the Cyanid. 



By this time everything should be in readiness for the generation 

 of the gas. The building has been tightly closed, except for the doors 

 or windows through which those who drop the cyanid will leave 

 the building. Provision has been made for ventilating after fumi- 

 gation (p. 20), the building has been cleaned (p. 13), made tight 

 (p. 13), and manholes, slide doors, etc., in spouts, elevator legs, 

 etc., have been opened, and all persons have been accounted for, 

 those not assigned to dropping cyanid having left the building. 

 Starting on the top floor, begin dropping the cyanid carefully, though 

 quickly, into the generators, starting at the jars most distant from the 

 exit and working rapidly toward the exit. This requires quick, cool- 

 headed action. If a charge of cyanid is overlooked never go back to 

 drop it ; let it go — your safety comes first. When the last charge has 

 been dropped leave the floor, closing the door behind, and repeat the 

 operation on each successive lower floor. 



When the person in charge feels that it is not wise to attempt to 

 drop all charges of cyanid by hand because of difficulties in the way 

 of retreat the stringing method should he employed. Novices often 

 resort to this method, though experienced f umigators do not, except 

 in difficult situations. Where floors are so crowded with machinery 

 that a hasty exit can not be made, or in dropping charges in the 

 basement where one must run upstairs to the first floor before reach- 

 ing the exterior the use of the stringing method will eliminate 

 danger. This method consists in passing strong cord through con- 

 veniently arranged screw-eyes, each string finally passing from a 

 central point at the exit to and through a screw-eye in the ceiling, 

 so that it will hang directly over the spot where the generator 

 is to be placed. (See figs. 12, 13, and 14, 4-) The strings should be 

 so arranged that they may all be lowered into the jars by releasing 

 one main string. This may be done by carrying the strings leading 

 to each jar through screw-eyes in the ceiling or wall to one stout 

 cord at the exit, as illustrated in figure 12. After the strings have 



