147 



NOTES ON THE CHEMICAL CONTROL OF CATTLE 

 DIPPING TANKS. 



By C. Williams, B.Sc, A.K.C.S., 



School of Agriculture, Cedar a. 



Bead July 13. 1921. 



In a previous paper by the writer on this subject published 

 in the Journal of this Association for May, 1915, the need for a 

 periodical chemical analysis of arsenical dip fluids from cattle 

 dipping tanks was emphasised. Although such apparatus as the 

 "Isometer" and the "Champion Dip Testing Apparatus" are very 

 useful as affording a quick method of ascertaining, approximately, 

 the amount of sodium arsenite in a dip fluid, they are liable to 

 serious errors in careless hands, while no account is taken by these 

 methods of the arsenic that is present in the fluid in the oxidised 

 form as arsenate. Although it may be true that under practical 

 conditions the amount of oxidation in dipping tanks is not usually 

 serious, yet cases come under the writer's notice from time to time 

 in which the amount of oxidised arsenic in the tank is too serious 

 to be ignored. As an illustration there are appended the results 

 of the periodical analysis of the fluid taken from both tanks on 

 the Cedara Experiment Farm during the past two years. After 

 each analysis the fluid was made up approximately to standard 

 strength, assuming that the oxidised arsenic has half the insecti- 

 cidal strength of the unoxidised form : — 



NEW TANK. 



