BUREAU OF CHEMISTRY. 355 



transmitted or stimulated by insects. The control of insect pests 

 depends upon effective and cheap insecticides and fungicides. Re- 

 search work on the chemistry of insecticides and fungicides there- 

 fore has tremendous economic significance. This is recognized by 

 the bureau as one of its most important fields of activity, which is 

 being developed and expanded as rapidly as possible. 



A study is being made of foliage injury by arsenicals and other 

 insecticides and fungicides in order to develop spray materials which, 

 while acting in an efficient manner, may be applied to tender foliage 

 without injury. Owing to the importance which calcium arsenate has 

 assumed in the dusting of cotton for control of the cotton boll weevil, 

 an extensive investigation of the physical and chemical properties upon 

 which its effectiveness in a measure depends is being made. The 

 field work conducted at Tallulah, La., during the year has resulted 

 in two achievements of importance — ^the development of a quick test 

 ior detecting high water-soluble arsenic in commercial calcium arse- 

 nate, and the discovery that the dew on cotton plants contains rela- 

 tively large quantities of plant exudate, which compounds, in the 

 presence of moisture, decompose calcium, arsenate, thus affording a 

 possible explanation of many cases of unanticipated plant injury 

 which have been observed in the dusting of cotton. 



Tlie demand for calcium arsenate for boll-weevil control has had 

 the effect of greatly increasing the price of arsenic and arsenicals. 

 This is now a serious matter for fruit growers and others using 

 arsenic in some form for the control of insect pests, and it is likely 

 to develop into a more serious one. Work is being actively prose- 

 cuted in the chemical technology of arsenical production for the pur- 

 pose of discovering methods for lowering the cost of production. 

 Some very suggestive results have already been obtained. During 

 the year Department Bulletin 1115. Chemical Changes in Calcium 

 Arsenate During Storage, was published. 



An investigation to determine the effect of copper sprays in in- 

 creasing the yield of potatoes and the effect of such sprays on the 

 composition of potato tubers and to determine the absorption and 

 distribution of copper in sprayed plants has been completed. The 

 copper sprays were shown not only to increase the yield of potatoes 

 but also to produce potato tubers having a higher percentage of 

 solids ; that is, more starch and nitrogenous compounds. The results 

 of this study are given in Department Bulletin 1146, The Influence 

 of Copper Sprays on the Yield and Composition of Irish Potato 

 Tubers. 



The relative toxicity of a number of arsenicals to several species 

 of insects was determined, and the results were reported in Depart- 

 ment Bulletin 1147, Chemical, Physical, and Insecticidal Properties 

 of Arsenicals. 



An investigation, in cooperation with the Bureau of Entomology, 

 of the toxicity of a number of the active constituents of plants and 

 synthesized organic compounds as contact insecticides was conducted. 

 The results of this work are reported in Department Bulletin 1160, 

 Studies on Contact Insecticides. 



Research to develop a contact insecticide as a substitute for nicotine 

 has resulted in the synthesizing of two new compounds, derivatives 

 of pyridine, which are highly toxic to certain insects. Work with 

 these compounds is being continued and the development of methods 



