CHEMICAL CONTROL OF DIPPING TANKS. 



151 



addition of any disinfectant to one of them, while adding the usual 

 amounts to the other. In this way it is hoped to be able to settle 

 this point definitely, for the dip fluids will be analysed at regular 

 intervals and kept under chemical control. 



Keeping Powers of the Standard Solutions of Iodine used in 

 Testing Dip Fluids. 



From time to time complaints have been received from farmers 

 and Government officials who have to test the strength of the 

 arsenical fluids of dipping tanks, that the results of their tests are 

 anomalous. In order to ascertain whether that may not sometimes 

 be due to a deterioration in the strength of the iodine solution 

 used in their apparatus, a few bottles of these standard solutions 

 were bought from one of the dealers and tested periodically against 

 a standard solution of arsenite. Altogether nine bottles of stan- 

 dard solutions for various kinds of dip fluids were tested, and it 

 was found that all the solutions were reasonably near the standard- 

 strength that they were supposed to represent. They also kept 

 their strength fairly well for three or four months, the loss of 

 strength in that period being not more than about 5 per cent., but 

 the deterioration of strength after about a year was very marked 

 in most cases, although the bottles were kept in a cupboard with 

 their stoppers on. It is conceivable that great carelessness will 

 often be observed in the storage of the iodine solution on the part 

 of farmers, who may often use a solution that has been in the 

 house for a year or more. Under these conditions it is probable 

 that large errors in the test will arise, and will explain the peculiar 

 results that are often obtained by them. 



'The Effect of the Addition of Certain Salts to Solutions of 

 Arsenite and Arsenate of Soda. 



1. On Arsenite of Soda: — 



In order to test whether the presence of certain salts in the 

 water used for making up dip fluids has any appreciable effect or 

 not on the solubility of the arsenic some arsenite of soda was dis- 

 solved in distilled water and to this fluid certain solutions were 

 carefully added until no further precipitation of the arsenite took 

 place. The results are recorded in the following table: — 



Proportion of Arsenious Oxide in the solution originally 



