OXIDATION" Oi ARSENIC IN" DIPPING BATHS. 3 



intervals between dipping is so different from ours as to be scarcely 

 at all comparable. 



FIELD EXPERIMENTS OF 1913. 



The experiments of 1913 involved the taking at fortnightly inter- 

 vals of samples from a number of vats, under as varied conditions 

 of use as possible. That is, the vats were in different sections of 

 the country; some were large vats at stock-yards centers, through 

 which hundreds of cattle were passed daily; others were small vats 

 in thinly settled localities, where only a few cattle were dipped at in- 

 frequent intervals. The samples were tested at the vat by the 

 bureau field method, 1 were tightly sealed with wax or paraffin to 

 prevent, by exclusion of air, oxidation en route, and were analyzed 

 at the laboratory. Unfortunately the methods of analysis since 

 published 1 had not then been completely worked out, for kaolin 

 was used as a clarifying agent instead of blood-charcoal. The 

 results, therefore, are not of the highest accuracy, but are sufficiently 

 correct for the purpose of making the comparative studies desired. 

 Also, the possibility of reduction by bacteria en route was not then 

 suspected and hence no provision was made for its prevention. For 

 the figure for actual arsenious oxid it was therefore necessary to rely 

 in the majority of cases upon the reported result of the field test, 

 which again is not of high accuracy. 



For the purpose of making comparisons between different vats it 

 is necessary to compare the extent to which they were used, and 

 since vats are of very different sizes and cattle are dipped at varying 

 intervals, it is necessary to reduce the corresponding figures to a 

 common denominator. The "figure of use" (abbreviated "F. U. "). 

 therefore, is a figure which stands for the number of cattle dipped per 

 100 gallons of bath (capacity of vat) per fortnight. 



The results afford the desired information most clearly and with 

 sufficient accuracy when plotted. In the diagrams (figs. 1 and 2) 

 the weeks during which each vat was in use are laid off horizontally, 

 and the percentages of arsenious oxid, found by analysis, are laid off 

 vertically. The large shaded circles where the lines begin to diverge 

 indicate the points at which the vats were filled with entirely fresh 

 bath; the small circles on the lines i i id icatc the results actually obtained 

 by analysis. The circles lying on the full lines indicate percentages 

 of actual arsenious oxid; that is, arsenic in the form in which it was 

 originally introduced. The ciroles lying on the broken lines indicate 

 percentages of "total arsenious oxid," which includes all the arse- 

 nious oxid present, whether in its original condition or after under- 

 going oxidation to arsenic oxid. 



i Hiit n<|, irtni.ni of \criotiltuw Bulletin 76. 



