BULLETIN OF THE 



in 



No. 76 



Contribution from the Bureau of Animal Industry, A. D. Melvin, Chief 

 April 29, 1914. 



(PROFESSIONAL PAPER.) 



LABORATORY AND FIELD ASSAY OF ARSENICAL 

 DIPPING FLUIDS. 1 



By Robert M. Chapin, 

 Senior Biochemist, Biochemic Division. 



INTRODUCTION. 



The use of arsenical dipping fluids for the treatment of cattle 

 infested with Texas-fever ticks is increasing. A mixture termed by 

 the Bureau of Animal Industry "standard arsenical solution" is pre- 

 pared from white arsenic, sal soda, and pine tar, and is largely used 

 for both official and private dipping operations. Proprietary dipping- 

 fluids also have appeared on the market to some extent. Previous 

 publications 2 of the bureau contain directions for the preparation of 

 "standard arsenical solution," together with general information of 

 importance to users of arsenical dips. 



During the last few years wide practical experience of the bureau 

 with all kinds of arsenical dips in the field has shown with increasing 

 forcefulness that one of the greatest obstacles to the successful use of 

 these preparations, and consequently to the effective prosecution of 

 the tick-eradication work now progressing so well over considerable 

 areas, lies in the uncertainty attached in many cases to the composi- 

 tion of these dips. There is no doubt that arsenical baths, properly 

 prepared and used, are very effective tickicides and cause little 

 injury to cattle. But the Texas-fever tick is a resistant organism. 

 Destruction only follows its immersion in rather strong solutions of 

 arsenious oxid, so strong in fact that if made only a little stronger 

 the cattle themselves will begin to show effects. That is, the margin 

 of safety within which solutions of this violent poison may be satis- 

 factorily used is rather narrow. Too little fails to kill the ticks; too 

 much injures the cattle. In either case the cause of tick eradication 



1 A popular account of laboratory tests for actual arsenious oxid and for total arsenic, together with 

 methods of field assay for dips used in tick eradication. Of special application to officials and others con- 

 cerned with the analysis and control of these preparations. 



2 Farmers' Bulletin 498; Bureau Animal Industry Circular 207. 



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