rj6 Conductivity of Aqueous Solutions. Part VI. 



62. PREPARATION OF THE SUBSTANCES AND SOLUTIONS. 



Two separate solutions of sodium hydroxide were used in this work. 

 Each was prepared by mixing a solution of sodium sulphate with one 

 of barium hydroxide. These two substances were first purified by crystal- 

 lizing commercial "chemically pure" samples four times from water. The 

 sodium sulphate was then tested for impurities with negative results by 

 adding ammonia, ammonium carbonate, and sodium phosphate. The 

 barium hydroxide was first tested for silica or other insoluble matter and 

 for other metals than barium, but these were not present in appreciable 

 quantity.*- In preparing the sodium hydroxide solutions, a nearly satu- 

 rated barium hydroxide solution was first made up with conductivity water 

 and filtered into a tared 7-liter bottle filled with carbon-dioxide-free air; 

 the exact strength of this solution was next determined by titrating a 

 portion with standard hydrochloric acid, and the quantity of it was ascer- 

 tained by weighing the bottle ; a quantity of sodium sulphate equivalent to 

 the barium hydroxide was then weighed out, dissolved in water, and run 

 into the bottle. After the precipitate had settled, two portions of the clear 

 solution were drawn out, and one was analyzed for barium by neutralizing 

 with sulphuric acid and adding considerable sodium sulphate, the other for 

 sulphate by neutralizing with hydrochloric acid and adding considerable 

 barium chloride.f Then a quantity of sodium sulphate or of barium hy- 

 droxide solution corresponding to the excess of barium or sulphate thus 

 found to be present was added to the main solution ; and this solution, 

 after the precipitate had completely settled, was forced over into a clean 

 dry bottle. Throughout these operations and in the subsequent use of the 

 solution any air that was admitted to the bottle had to bubble through 

 potash solution and soda-lime tubes. The final solution contained less 

 than 0.1 per cent of barium sulphate (expressed in equivalents and referred 

 to the sodium hydroxide present) 4 It was standardized by weight 

 using phenolphthalein as an indicator against a pure hydrochloric acid 



*This was done by evaporating 5 grams of the solution with hydrochloric acid, 

 dissolving the salt in water, and collecting the residue, which was found to weigh 

 2.5 mg. or 0.05 per cent of the original weight, but of this only 0.5 mg. or 0.01 per 

 cent volatilized with hydrofluoric acid. To the filtrate from the residue a slight excess 

 of sulphuric acid was added, the precipitate filtered out, the filtrate evaporated, and 

 the residue ignited and weighed; it was found to weigh only 1 mg. or 0.02 per cent. 



fThus in the case of the second solution so prepared, there was found to be an 

 excess of barium of 0.13 and of sulphate of 0.08 milli-equivalents per kilogram; and 

 therefore 0.05 milli-equivalents of sodium sulphate were added for each kilogram of 

 solution. 



JThus it follows from the data of the preceding note that the second solution con- 

 tained 0.08 milli-equivalents BaSOi per kilogram, which is 0.08 per cent of the NaOH 

 present (105.3 milli-equivalents). 



