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Chapin (R. M.). Laboratory and field assay of arsenical dipping 

 fluids.— C/.^. Dept. Agric, WasJdngton, B.C., Bull., no. 76, 29th 

 April 1914, 17 pp., 6 figs. 



The author says that the use of arsenical dipping fluids for the 

 treatment of cattle infested with the Texas fever tick is increasing, 

 and that it is becoming a matter of great consequence that farmers 

 and others should have some more or less simple and ready means at 

 hand for determining whether their dip is in good working order and 

 really effective or not. It has now been more or less conclusively 

 shown by Laws, that arsenate is somewhat less than half as effective 

 upon ticks as arsenite of soda in these baths. The Texas fever tick is 

 very resistant and can only be killed by the use of a somewhat strong 

 solution, so strong, in fact, that if made only a Httle stronger the 

 cattle themselves will begin to show effects ; that is to say, the margin 

 of safety within which solutions of this violent poison may be satis- 

 factorily used is rather narrow. Too little fails to kill the ticks and 

 too much injures the cattle, and this fact contributes very largely to 

 the hesitation of farmers to use the dip as it should be used, and it 

 has in many cases aroused distrust and even opposition in those very 

 persons whose cooperation in tick eradication work is most desired. 



There are various points which need careful consideration. The 

 bath may be made of the wrong strength, which is a very common 

 occurrence ; impure material may be used, and mistakes in measure- 

 ments and calculations may be made, even by careful persons ; but 

 the greatest difficulty is to maintain the bath at the right strength 

 once it has been prepared. It is obvious that a fresh bath cannot be 

 made every time a few cattle are to be dipped ; the bath must be 

 used over and over again, possibly for several months, sufficient fresh 

 fluid being added from time to time to replace that carried out by 

 the cattle. During hot seasons evaporation tends to concentrate it. 

 The author suggests that this may be compensated for by marking 

 the level of the dip on the side of the vat before a period of disuse, 

 and then filhng up to the mark with water when the dip is used again. 

 Again, it is difficult to construct a vat holding from one to three 

 thousand gallons entirely free from leaks, and therefore it is uncertain 

 how far the lowering of the level of the dip is due to evaporation and 

 how far to leakage. Rain water, surface water or even sub-soil water 

 may find its way into the tank and alter the strength of the liquid 

 in the other direction. 



Over and above this there is the chemical difficulty caused by the 

 oxidation process which goes on in the solution of arsenite of soda 

 exposed to the ordinary conditions of the dipping tank. Many 

 are of opinion that the change is fairly slow and not important. But 

 the author states that, bearing in mind the small margin between 

 the efficiency of the liquid as a dip and the possibihty of its doing 

 harm to the cattle, these changes due to oxidation are worth careful 

 attention, whether they be caused by simple exposure to the air or, 

 as is held by Fuller, by the growth of micro-organisms. These latter 

 occasionally produce the converse result of reduction ; that is to 

 say, there is a possibihty of the conversion of arsenate to arsenite, 

 thus strengthening instead of weakening the dip. The primary con- 

 ditions which determine the direction in which changes usually take 



