INDUSTRIAL FUMIGATION AGAINST INSECTS 51 



this gas may be used with good results. With the miller who does his 

 own fumigating the pot or barrel method is popular, but professional 

 fumigators prefer to use liquid hydrocyanic acid and avoid the labor 

 of handling barrels, water, and acid. Regardless of the method of 

 generation, the gas is the same, and if the mill has been properly 

 prepared excellent results can be expected. 



Distribution of the fumigant. — To obtain quick equalizing of the 

 fumigant, it should be evenly distributed throughout the mill, except 

 that floors containing more machinery than others should receive 

 a heavier dosage. With all methods of application gas concentra- 

 tions soon become uniform throughout the mill. 



Length of exposure. — In the average mill heavy concentrations 

 of the gas can be maintained only for a very short period; hence 

 an exposure of from 10 to 24 hours is usually all that is practical. 



MACHINERY PIPING METHOD 



Recently a method has been developed by which hydrocyanic acid 

 is applied directly into the milling machinery instead of into the 

 open mill space. A series of pipe lines connects each piece of ma- 

 chinery with a manifold outside the mill. Spray nozzles that open at 

 a set pressure deliver uniform quantities of fumigant to each piece 

 of equipment, and when the pressure is removed they close auto- 

 matically so that they cannot be clogged with milling stock between 

 fumigations. 



By applying the fumigant directly into the machinery, concentra- 

 tions high enough to penetrate the stock left in the milling equip- 

 ment are obtained with a smaller quantity of gas ; hence it is unneces- 

 sary to dismantle and clean out the machinery. The saving in time, 

 labor, and fumigant makes it possible to fumigate twice as often as 

 by the open-space method at no greater cost. The cost of installing 

 the system of piping amounts to about 50 cents per barrel capacity 

 of the mill. 



Although it is unnecessary to follow the procedure recommended 

 for open-space fumigation, there are a few rules that should be 

 followed in preparing the mill for fumigation. 



Preparation of the mill. — The grain feeder or regulator above the 

 first break should be closed and the mill allowed to run. The entire 

 mill crew should be given rubber mallets and assigned the task of 

 hammering slide spouts, cleaning feed gates and suction lines, and 

 moving as much accumulated stock into the mill stream as possible. 



As soon as the rolls are opened after the feed has been shut off, 

 the elevator-boot slides should be pulled up and the accumulations of 

 milling stock pulled out of reach of the belt cups. 



The mill should be run for an additional 15 minutes to remove 

 as much milling stock as possible. 



After the mill has been shut down, the roof vents from the cyclone 

 dust collectors should be tightly sealed. This is extremely important, 

 since the cyclone dust collectors are directly connected with almost all 

 machines. The best method is to remove the mushroom-shaped caps 

 and replace them with tightly fitting metal caps. Covering the 

 vents with paper or combinations of paper and burlap or tarpaulin 

 is not entirely satisfactory and is not recommended. 



