130 PROCEEDINGS OP SECTION B. 



and as the result of all the experiences gained, I must emphasise the 

 fact, that our Government standard formula, consisting of 8 lb. 

 arsenic, 4 lb. caustic soda, 1 gallon Stockholm tar, and 8 lb. tallow 

 dissolved in 400 gallons of water, is in eveiy respect absolutely satis- 

 factory. The only drawback of the formula is the care required in 

 the preparation of the fluid, and for this reason many concentrates 

 have been put on to the market, which require simple dilution with 

 water. According to the reports of our inspectors not one of the pro- 

 prietary mixtures satisfies the conditions of a perfect dip as completely 

 as our own formida. 



The active ingredient in ail dipping fluids, used for the destruc- 

 tion of our Queensland cattle tick ( Bhipicephalus annulatus, var. 

 Australis), is arsenious acid, made soluble in the form of arsenite of 

 soda. Experiences extending over many years taught us that only a 

 solution containing '2 per cent, or 8 lb. per 400 gallons can be relied 

 on to kill all ticks within five days, without causing any ill-effect to 

 the cattle dipped. 



A few months back a dipping fluid was tested and was found to 

 have hardly any effect on the ticks, although it contained nearly 

 10 lb. of ai*senic. A more exhaustive analysis revealed the fact that 

 nearly all the arsenic was in the form of arsbniate. Since that time 

 all fluids are tested qualitatively for the presence of arseniate, and if 

 any arseniate is found, the amount is determined gravimetrically. 



During the last three months sixty-eight dipping fluids from all 

 parts of the State have been tested, of which eleven contained high 

 amounts of arseniate, whereas the others were absolutely free from 

 arseniate and contained all the arsenic in form of arsenite. It is 

 well known that the oxidation of arsenious acid into arsenic acid is 

 accomplished by many oxidising agents, but it was not suspected that 

 by blowing air through the solution of arsenites a change into 

 arseniate would take place. Experiments undertaken with a view of 

 ascertaining the effect of a current of air on dipping fluids, coiTespond- 

 ing to the air which is continually churned into the liquid during the 

 operation of dipping, showed that such oxidation will take place (see 

 table I.), and that the presence of Stockholm tar and of carbolic acid 

 accelerates such oxidation. Of the dipping solutions tried, only the 

 Royal Dip, practically a pure solution of arsenite of soda, showed no 

 change during the experiments, but still several of the fluids which 

 containeil high amounts of arseniate were prepared from royal dip. 



Whether the quality of water, used in the preparation of the 

 solution, and soil and dirt have any influence on the oxidation, will 

 have to be found out by further experiments. 



For the determination of the arsenic in the dipping fluids a 

 simple and quick method was very desirable, as the gravimetric 

 methods are too slow, and the preparation of a clear filtrate free 

 from organic matters is veiy difficult. The fluids contain besides the 

 arsenite various substances as fatty acids, glycerine, resins, phenols, 

 hydrocarbon oils, sulphur compounds, kc, besides large amounts of 

 soil and dirt brought into the dip during the dipping operation. 



The method used in the New South Wales Agricultural Depart- 

 ment's Laboratory (provisionally adopted by the Association of 

 Oflficial Agricultural Chemists of Australasia, August, 1906), based on 



