ULLETIN OF THE 



No. 259 



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

 July 13, 1915. 

 (PROFESSIONAL PAPER.) 



STUDIES ON CHANGES IN THE DEGREE OF 

 OXIDATION OF ARSENIC IN ARSENICAL DIPPING 

 BATHS. 



By Robert M. Chapin, Senior Biochemist, Biochemic Division. 

 INTRODUCTORY. 



In the approximately four years during which arsenical dipping 

 baths have been extensively employed for eradicating the Texas- 

 fever tick in this country, and in the even longer period during which 

 they have been put to similar use abroad, it has been discovered, along 

 with other interesting and important facts, that the arsenic in such 

 baths is prone to change its degree of oxidation. Arsenic is one of 

 the considerable number of chemical elements which may be said to 

 lead double lives; that is, they form two distinctly different series of 

 compounds in which the element acts in many respects as if it were 

 indeed two wholly different elements. Thus the element arsenic 

 forms two oxids, first, arsenious oxid, in which two atoms of arsenic 

 are combined with three atoms of oxygen, and, second, arsenic oxid, 

 in which two atoms of arsenic are combined with five atoms of 

 oxygen. Both these oxids are essentially acid in nature; that is, 

 they readily combine with alkaline substances (bases) to form salts. 

 For example, when arsenious oxid is treated with sodium carbonate 

 or sodium hydroxid there is produced sodium arsenite, while arsenic 

 oxid, similarly treated, yields sodium arsenate. The common white 

 arsenic of commerce is merely arsenious oxid. So when in the 

 ordinary preparation of dipping baths, white arsenic is heated with a 

 solution of caustic soda or of carbonate of soda, the resulting liquid 

 entially simply a solution of sodium arsenite. 



Soon after arsenical dipping baths had conic, into extensive prac- 

 tical use I' was discovered that the sodium arsenite frequently 

 eemed to disappear slowly with continued use of the bath. Thence 

 it was only one step to discover thai the element arsenic was in fact 



Note. ThJ bulletin will be of Inl i who employ arsenical dipping ImUis in eradi- 



cating the 1 e a fevw tick, 

 94290*— BalL 269— U 



