268 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



the temperature at which the material is stored and the type of con- 

 tainer. Before publishing any of the results it is intended to repeat 

 the Avork on samples packed under Government supervision. 



Work on the rate of deterioration of nicotine solutions and nico- 

 tine dusts of various strengths, packed and stored under different 

 conditions, shows that nicotine solutions and certain types of nicotine 

 dusts deteriorate very slowly when packed in tight containers. Nico- 

 tine dusts containing calcium hydrate or carbonate lose strength more 

 rapidly than dusts made up with clay, Kieselguhr, and sulphur. 



An investigation has recently been begun to develop an insecti- 

 cide for use in the control of insects infesting grains in storage 

 and in transit, to take the place of carbon disulphide, the use of which 

 has been prohibited by the railroads. This work is being carried on 

 in cooperation with the Bureau of Entomology. The investigation 

 has not j^rogressed far enough to reach definite conclusions, but 

 some very promising results are being obtained. 



The investigation begun two years ago to determine what, chemi- 

 cal changes calcium arsenate undergoes during storage has been com- 

 pleted and tlie results are in process of publication as a department 

 bulletin under the title " Chemical changes in calcium arsenate 

 during storage." This work was taken up as a result of the belief 

 by certain manufacturers and users of this product that it deterior- 

 ated rapidly and was unfit for use after standing for a few months. 

 Results of much interest and value have been obtained. They show 

 that carbon dioxide is very slowly absorbed by the calcium arsenate 

 (or by the calcium hydrate which is present in commercial calcium 

 irsenates) when kept in certain types of coimnercial containers, 

 resulting in a slow gradual increase in water soluble arsenic, which 

 reaches a maximum after about 8 months in the case of the most 

 open containers, such as sugar barrels. Material packed in tight 

 containers, such as metal drums or heavy hardwood barrels, showed 

 practically no change after 20 months' storage. In a few cases where 

 calcium arsenate was stored in veneer drums and sugar barrels, the 

 deterioration at the end of 20 months was such as to render the 

 material of doubtful safety for application on certain plants having 

 tender foliage. 



An investigation is being made of the properties of oil emulsions 

 with the object of assisting the manufacturer or grower to make 

 cheaper and more satisfactory emulsions. The value of this work 

 is self-evident when it is considered that large amounts of oil sprays 

 are used each year, particularly on citrus fruits, and that at present 

 these are often unstable and cause damage to the trees. 



A paper, " Errors caused by nitrates and nitrites in the determina- 

 tion of arsenic by the distillation method and a means for their 

 prevention," was also published, 



PREVENTION OF PLANT DUST EXPLOSIONS AND COTTON GIN FIRES. 



Investigations by the Bureau of Chemistry have shown that the 

 dust that is produced in the handling and milling of grain of all 

 kinds, when mixed with air in proper proportions, is highly explo- 

 sive. It forms a mixture similar to the explosive mixtures of gas 

 and gasoline. A large number of disastrous explosions have occurred 

 in the thrashing and milling of grain, resulting in extensive losses 



