244. Conductivity of Aqueous Solutions. Part VIII. 



This solution was tested for chloride, and the original substance was 

 tested for nitrate,* with negative results. That it contained no import- 

 ant quantity of non-volatile impurities was shown by precipitating the 

 barium by running the solution into an excess of the stock sulphuric 

 solution, allowing it to stand, filtering, and evaporating the filtrate first 

 in a porcelain beaker and finally in a weighed platinum dish. The residue 

 so obtained from 100 c.cm. of the cold-saturated barium hydroxide solu- 

 tion weighed 5.6 milligrams, of which only one milligram was shown to 

 be silica by treatment with hydrofluoric acid. Some of the remainder 

 was doubtless unprecipitated barium sulphate; but even if the whole of 

 it had been an impurity in the barium hydroxide, it would not amount to 

 more than 0.1 per cent. 



A more conclusive test of purity of both the barium hydroxide and 

 sulphuric acid was obtained as follows: 118.77 grams of the stock barium 

 hydroxide solution were run into 113.38 grams of the stock sulphuric 

 acid solution, previously heated to boiling. This should have left, 

 according to computation, a slight excess of acid in the clear filtrate. 

 The specific conductance of this filtrate was measured, and it was com- 

 puted therefrom that assuming only sulphuric acid to be present an excess 

 of 0.39 grams of its solution must have been added. Titration with 

 0.01 normal sodium hydroxide showed almost exactly the same quantity 

 (0.42 grams), indicating that not enough impurity was present to affect 

 appreciably the measured conductance. 



This last experiment evidently gives also a means of comparing the 

 stock solution of barium hydroxide with that of sulphuric acid, and 

 thus tying together the whole series of values. The concentration of the 

 barium hydroxide, so computed, is 0.17 per cent less than the adopted 

 value, a difference not greater than the discrepancies in the analyses by 

 independent methods of the same solution. 



The concentration of the stock solution of barium hydroxide was found 

 on March 20, 1906, by means of three titrations against the stock nitric 

 acid, using phenolphthalein as indicator, to be 210.83 milli-equivalents per 

 kilogram of solution. 



The stock solution of hydrochloric acid was made by bubbling the 

 gas produced by the action of pure sulphuric acid on pure sodium chlo- 

 ride through a little water and then absorbing it in conductivity water. 

 It was standardized against the barium hydroxide solution and found to 

 contain 114.42 millimols HC1 per kilogram of solution. Its conductance 

 at 18 agreed closely with the values obtained by Goodwin and Haskell. f 



*In making this test, about 1 gram was dissolved in acetic acid, and a drop of indigo 

 solution and several cubic centimeters of sulphuric acid (1.84 sp. gr.) were added. 

 The blue color remained, whereas when one drop of a 0.1 normal nitric acid was 

 added, the solution was decolorized at once. 



fProc. Am. Acad., 40, 413 (1904). Phys. Rev., 19, 386 (1904). 



