THE ELECTRIC CONDUCTIVITY OF NITRIC ACID. 371 



varies according as the chloride is in the pulverulent or caseous condition. More 

 recently the same subject has been investigated by J. P. COOKE,* who states the 

 solubility is not affected by nitric acid. The method of estimating the traces of 

 halogen acids in the samples was as follows : 



10 cub. centims. of the sample to be examined were placed in a miniature flask 

 and 1 cub. centim. of a silver nitrate solution containing '05 gram of the salt was 

 added ; the turbidity, if any, was compared with that produced by the same 

 quantities of purified water, the silver nitrate solution and a fractional part of 

 1 cub. centim. of a solution of hydrochloric acid of known strength. It was found 

 in the course of experiment that a sample of nitric acid of 20 per cent, concentration 

 gave no turbidity with the silver nitrate, but on addition of '5 per million of 

 hydrochloric acid a turbidity was produced which appeared to be equal in amount 

 to a blank experiment, made at the same time, with water only ; but after standing 

 for some hours the turbidity in the former case was less than that in the latter, and 

 remained nearly white, instead of changing to a violet tint on exposure to diffuse 

 daylight. It was probable, therefore, that the chloride was being slowly decomposed 

 by the nitric acid. As a result of this observation, acids of concentration greater 

 than 20 per cent, were diluted down to this strength, and the comparison made with 

 the blank water experiment after the interval of one hour. It is not presumed 

 that the estimations are of absolute accuracy, especially as the greatest quantity of 

 haloid acids found in any sample was 3'8 parts per million, the average being less 

 than 2'0 parts. The correction to be applied for these amounts of impurity is of 

 the second order, and may reasonably be neglected. 



(iii.) Sulphuric Acid. 



The observations upon the solubility of barium sulphate in water and in dilute 

 nitric acid appear to be very discordant. According to FEESENIUS and HiNTzt one 

 part of barium sulphate in 400,000 water can be detected provided that a slight 

 excess of barium chloride is added, but only 1 in 100,000 parts if no such excess is 

 present ; under the same conditions, in presence of nitric acid of 7'8 per cent, 

 concentration, only 1 part of barium sulphate in 33,000 can be detected. 



These estimations were made with a view of examining the accuracy of the 

 quantitative determination of sulphuric acid by barium chloride, as the precipitant, 

 in the presence of various salts and acids which might be present in the course of 

 analytical experience ; otherwise the use of barium chloride rather than the nitrate 

 in the presence of nitric acid might be open to objection. Furthermore, it is evident 

 that the delicacy of the reaction between a barium salt and sulphuric acid will 

 depend cceteris paribus on the relative masses of the reacting substances. The work 



* 'American Journal of Science,' vol. 21, p. 220. 

 t ' Zeits. Analyt. Chem.,' 1896, vol. 33, p. 170. 

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