260 Conductivity of Aqueous Solutions. Part VIII. 



In the experiments extended to 218, 260, and 306 the agreement was 

 not so good, owing to greater contamination. In the first experiments 

 with hydrochloric acid, made in July, 1906, the final values at 18 differed 

 from the initial values by one to three per cent (except in the most dilute 

 solution). This seems to have been due to the presence of gold and 

 platinum dissolved from the lining; for the strongest solution had a light 

 yellow color after the heating, and a small precipitate of gold and a brown 

 coloration was obtained on adding stannous chloride. To diminish this 

 solvent action, the solutions in the later experiments made in September 

 were boiled at about 60 under reduced pressure just after they were intro- 

 duced into the bomb ; and it was then found that the initial and final 

 values at 18 ? greed within 0.3 per cent. The fact that the two sets of 

 experiments gave concordant results at 306 shows that the presence of 

 the gold or platinum had no influence at that temperature, probably owing 

 to the hydrolysis of their salts. Differences of about one per cent were 

 observed in some of the experiments with nitric and sulphuric acid, but 

 these solutions did not contain gold or platinum in appreciable quantity. 



In the course of the experiments with the 2 milli-normal nitric acid, the 

 remarkable phenomenon was observed in four or five cases that the con- 

 ductance rapidly decreased during the heating above 200, owing evi- 

 dently to decomposition of the acid. Thus, in one case after heating to 

 306 it was found that the final conductance at 18 was only five per cent 

 of the initial value. This decomposition was apparently started by minute 

 quantities of impurities accidentally introduced into the bomb ; for it was 

 found possible to prevent it by making up the solution with exceptionally 

 pure water and taking special precautions against contamination.* This 

 behavior is entirely analogous to that of silver nitrate as observed by 

 Noyes and Melcher and described in section 39, Part IV. 



*The nitric acid seems to decompose into nitrogen (or nitrous oxide), oxygen, 

 and water; for tests for nitrite and for ammonia made by the processes used in 

 water analysis on a 2 milli-normal solution which had been heated to 218 and had 

 greatly decreased in conductance showed that the quantities of these substances 

 present were less than 0.1 per cent of the nitric acid originally in the solution. 



