356 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



for their economical production on a commercial scale is being- 

 studied. 



An extensive investigation is being made of f umigants for treating 

 insect-infested grain in storage and in transit, in order to find a sub- 

 stitute for carbon disulphide, the use of which has been prohibited 

 by the railroad officials of the United States on account of the fire- 

 hazard. About 250 fumigants have been tested. 



Fumigating food products with hydrocyanic acid gas for the de- 

 struction of insects is now very widely practiced. In order to de- 

 termine whether or not they may be rendered unfit for human con- 

 sumption, a great variety of such fumigated products have been 

 analyzed and the quantity of hydrocyanic acid remaining in them 

 under different conditions of treatment has been determined. This 

 work is reported in Department Bulletin 1149, Absorption and 

 Retention of Hydrocyanic Acid by Fumigated Food Products. The 

 work is being continued and extended to include domestic and 

 imported dried and preserved fruits, candy, nut meats, etc. 



A detailed chemical and microscopical study of oil emulsions, used 

 for insecticides, particularly emulsions of kerosene with sodium 

 oleate, potassium stearate, and palmitate, has been completed, and 

 the results are published in the Journal of the American Chemical 

 Society, for July, 1923, under the title "Emulsions of mineral oil 

 with soap and water : The interf acial film." 



In cooperation with the Bureau of Entomology, a project for the 

 control of flies infesting domestic animals was continued during the 

 year. A preliminary report, entitled " Progress report of investi- 

 gations relating to repellents, attractants, and larvicides for the 

 screw-worm and other flies," was published in the Journal of Eco- 

 nomic Entomology for April, 1923. 



PKEVENTION OF PLANT-DUST EXPLOSIONS AND COTTON-GIN FIRES. 



Investigations to determine the causes of dust explosions and the 

 circumstances favorable to their origin are being made. Although 

 the general scope of the investigations is confined to grain handling 

 or milling operations, in some instances it has been possible to study 

 dust explosions in other types of industries. As a result of the in- 

 vestigation of a large number of explosions, it may be definitely con- 

 cluded that under certain conditions dust explosions can occur in 

 any industrial plant or manufacturing establishment where com- 

 bustible dust is created during the operating processes. The im- 

 portance of this work is more fully realized when it is considered 

 that over 21,000 establishments in the United States, manufacturing 

 products with an annual value in excess of $6,000,000,000, are subject 

 to the dust-explosion hazard. 



Special studies are being made to determine the practical possi- 

 bility of installing an effective dust-collecting system for the con- 

 trol 'of the explosive dust created during the handling and storing 

 of grain in terminal grain elevators. 



The investigations have been planned not only to study installa- 

 tions of dust-collecting and ventilating systems, but to ascertain the 

 lower explosive limits of the industrial-plant dusts that have caused 

 these explosions, and then to determine whether or not the present 

 systems are adequate. This has necessitated the establishment of a 

 dust explosion laboratory in the bureau, the function of which may 



