502 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



SPECIAL INVESTIGATIONS. 



The investigations begun some time ago to discover a chemical 

 method to determine stems in insect powder, determine reasonable 

 standards for insect i^owder, and study the process of manufacture 

 of insect powder and composition of raw materials, as well as the 

 finished product, have been completed and a bulletin giving the re- 

 sults has been prepared for publication. 



Results of the chemical analyses of several hundred authentic 

 samples of insect flowers, stems, and powders are given in the bul- 

 letin, on the basis of which permissible amounts of sand and stems 

 in insect powder have been determined and issued in Service and 

 Eegulatory Announcements No. 22. 



Service and Regulator}- Announcements No. 21, giving informa- 

 tion relative to the various new State insectcide and fungicide laws, 

 was issued during the year. This publication supplements Service 

 and Regulatory Announcements No. 13, issued September 13, 1916. 



A bulletin (U. S. Department of Agriculture Bulletin 795) entitled 

 " The Adulteration of Insect Powder with Powdered Daisy Flowers,'^ 

 Avas prepared by scientists of the Board in collaboration with the 

 Bureau of Chemistry and published by that Bureau. In this bulletin 

 it is shown that a chemical analj^sis is insufficient to show adultera- 

 tion of insect powder Avith daisy flowers. It is further shown that 

 the adulteration of insect powder with daisy flowers can be definitely 

 determined by microscopic examination, and the distinguishing char- 

 acteristics of powdered daisy flowers are outlined. 



During the year a bulletin (U. S. Department of Agriculture 

 Bulletin 750) was issued in collaboration with the Bureau of 

 Chemistry, entitled " A Method of Preparing a Commercial Grade of 

 Calcium Arsenate." This bulletin embodies the results of experi- 

 ments made to determine the best method for preparing a grade of 

 calcium arsenate on a commercial scale. 



Chemists of the board have made various basic investigations rel- 

 ative to tlie composition and properties of various calcium arsenates. 

 The results of these investigations are being collated with the idea of 

 publication for the benefit of the public. 



Aside from the routine work of testing the efficacy of proprietary 

 fungicides, the plant pathologists of the board working in coopera- 

 tion with the Bureau of Plant Industry have continued and enlarged 

 the investigations relative to the practical value of several types of 

 fungicides, and considerable information and more conclusive data 

 have been obtained. These investigations involve studies in respect 

 to the efficacy of dusting mixtures for use in controlling various 

 plant diseases ; a study of the relative values of the various types of 

 sulphur compounds, such as the sodium polysulphids and calcium 

 polysulphids ; studies of the effect of combining different types of 

 arsenicals, such as lead arsenate and calcium arsenate, on the fungi- 

 cidal value and injurious properties of these sulphur compounds; 

 and a comparative study of the results of tests with Bordeaux mix- 

 ture containing various amounts of copper to obtain data concerning 

 the amount of copper necessary in commercial Bordeaux mixture to 

 insure satisfactory control of certain plant diseases. Laboratory 

 methods for the study of fungicides relative to their action against 



