150 



CHEMICAL CONTROL OF DIPPING TANKS. 



2. A solution was made up as in (1), but 2 grams of fresh 

 dung were added immediately after the first analysis, and the same 

 amount added to the bottle every week. 



First 

 Analysis 



After 

 2 weeks 



After 

 4 weeks 



After 

 6 weeks 



After 

 8 weeks 



After 

 10 weeks 



a. Arsenite (as As 2 3 ) 



b. Total Arsenic (as As 2 3 ) 



per cent. 

 0151 

 0-155 



per cent. 

 0-151 

 0154 



per cent i per cent. i per cent. 

 0-117 j 0-068 ! 0-039 

 0155 0154 0154 



per cent. 

 0-028 

 0-154 



3. The third solution was made up as in (1) with 10 grams of 

 fresh dung added immediately after the first analysis. After 

 oxidation had well set in (after a period of 4 weeks) weekly addi- 

 tions of fresh dung were made. 



First 

 Analysis 



After 

 2 weeks 



After 

 ■1 weeks 



After 

 6 weeks 



After 

 8 weeks 



After 

 10 weeks 



a. Arsenite (as As 2 3 ) 



b. Total Arsenic (as As 2 3 ) ... 



Iper cent. 

 0-151 

 0155 



per cent. 

 0139 

 0-152 



per cent.per cent, iper cent.per cent. 

 0103 I 0060 | 0030 | 0-021 

 0-154 I 0-154 0-154 ! 0-154 



The figures in these tables show that weekly additions of fresh 

 dung to stoppered bottles containing solutions of sodium arsenite 

 did not prevent the progressive oxidation that goes on in the 

 original inoculated fluid. 



Since the above experiments were carried out the writer has 

 had access to two papers by Green* in which he states that he has 

 succeeded in isolating a bacterium causing oxidation of arsenite 

 to arsenate in dipping tanks, and also an organism which brings 

 about the opposite change. He maintains that the latter organism 

 does not thrive in a dilute dung decoction and that there must 

 also be present small amounts of urine. It is therefore quite pos- 

 sible that in the experiments of which the results are given above 

 this was the missing factor, or rather, the one which was present 

 in an insufficient amount. 



This, however, would not explain the continuous oxidation 

 that has been going on in the two tanks at Cedara. In these tanks 

 a proprietary dip containing a certain proportion of a coal-tar dis- 

 infectant in its composition was used throughout the period in 

 question, while to the old tank, in addition, there has been added 

 a few gallons of a similar type of disinfectant occasionally. Chapinf 

 points out that too little disinfectant in the tank is worse 

 than none at all, because the reducing organisms are more sensi- 

 tive to it than those causing oxidation. It, therefore, seems 

 probable that this has been the fault in the control of the Cedara 

 dipping tanks. It is, therefore, proposed to clean out both of 

 these tanks, put fresh dip fluid in, but to avoid in the future the 



* H. H. Green : Fifth and Sixth Reports of the Director of 

 Veterinary Research", pp. 611 et seq. 



t R. M. Chapin : "Studies on Changes in the Degree of Oxidation 

 of Arsenic in Arsenical Dipping Baths," Bulletin No. 259 of U.S. Dept. 

 of Agriculture. 



