137 



NOTES ON THE CHEMICAL CONTROL OF 

 CATTLE-DIPPING TANKS. 



BY 



C. O. Williams, B.Sc, A.E.C.S., 

 Chemist, School of Agriculture, Cedara. 



Read July 10, 1922. 



In these notes an attempt is made to place on record the 

 main results of certain investigations carried out at Cedara during 

 the past year on the chemical behaviour of arsenical dip fluids 

 in cattle tanks, and are really a continuation of the notes recorded 

 in a paper read before this Association in July, 1921, and 

 published in this Jouuxal, vol. xviii, pp. 147-153, December, 

 1921. 



Effect of Coal Tar Disinfectants in Arsenical Dip Fluids. 



In the above-mentioned paper it was stated by the vi'riter 

 (see page 150 of the above Journal) that the presence of coal tar 

 disinfectants in the two Cedara tanks might be the cause of the 

 abnormal amount of oxidation taking place in them. This state- 

 ment was based on the conclusions of American investigators, 

 who found that the reducing organisms are more sensitive to such 

 substances than the oxidising organisms. In order to test this 

 statement under ordinary practical conditions, both of the Cedara 

 tanks were cleaned out, and in the new tank a certain proprietary 

 dip which contains a fair proportion of these coal tar derivatives 

 was used, while in the old tank only plain arsenite of soda, was 

 used. Furthermore, in order to ensure that there would be a 

 fairly large amount of disinfectant in the new tank, there was 

 added also at the commencement of the investigation some Hycol 

 at the rate of one gallon to every thousand gallons in the tank. 



From the commencement of this investigation (May, 1921) 

 up to the end of August, between 100 and 125 head of cattle were 

 dipped at approximately fortnightly intervals in each tank; after 

 that the dipping took place at weekly intervals. The sa.mples 

 from each tank were taken about once a fortnight, immediately 

 after dipping had taken place, to ensure that the contents of the 

 tanks were well stirred. Unfortunately, towards the end of Sep- 

 tember the old tank developed a bad leak and it had to be 

 abandoned about three months after it had been refilled for the 

 purpose of this investigation. 



In addition to the above series of tests, periodical tests were 

 also made of the fluids from several private tanks in this neigh- 

 bourhood, and a few samples from tanks in other districts in 

 Natal. These private tanks are divided into two groups, the first 

 including those filled with the same proprietary dip as used in 



