Section 100. Preparation of the Solutions. 28/ 



The solutions of the acid were always prepared just before the con- 

 ductance was measured by dissolving weighed portions of it in a known 

 weight of conductivity water in a Jena flask. The solutions were pre- 

 pared and transferred to the conductivity vessel in contact with only 

 purified air. The water used for dissolving the acid, and in general 

 throughout this investigation, had at 18 a specific conductance which 

 always lay between 0.15 and 0.60 X 10~ 8 reciprocal ohms. The solutions 

 of the acid even when kept for several hours in the conductivity-vessel 

 showed a change in conductance of not more than 0.1 per cent. 



The ammonium hydroxide solution used was an approximately 0.1 

 normal one made by diluting with conductivity water a special sample 

 of strong ammonia water (spec, grav., 0.90) furnished by the Baker & 

 Adamson Chemical Co. and certified to be free from amines, carbonates, 

 and silicates. The solution was titrated by running a slight excess of it 

 directly into a known weight of standard hydrochloric acid, and running 

 back to the end-point with hydrochloric acid with the help of methyl 

 orange. The solutions were all measured by weight, not by volume. 

 The hydrochloric acid was itself standardized by precipitating a known 

 weight of it with silver nitrate and weighing the silver chloride. The 

 solution was kept in a two-liter "non-sol" bottle (furnished by Whitall, 

 Tatum & Co.). To protect it from evaporation and contamination 

 it was connected through another bottle of ammonium hydroxide solu- 

 tion of the same strength with a long soda-lime tube through which 

 air was admitted when samples were withdrawn. The solution was trans- 

 ferred through delivery tubes into the conductivity vessel or into a Jena 

 flask in which it was diluted or mixed with the acid solution, in contact 

 with only purified air. In order to use comparatively fresh solutions for 

 the measurements, a new stock solution was prepared in the same way in 

 the course of the experiments, so that the solution employed was never 

 more than ten days old. Determinations of the alkaline strength showed 

 that during this period the change in it was less than 0.1 per cent. 

 The conductance of this solution was found to be substantially identical 

 with that of one prepared from liquid ammonia by Mr. R. B. Sosman. 



The solutions of the salt, both alone and with an excess af acid or base, 

 were prepared by introducing into a Jena flask provided with a perforated 

 ground-glass stopper and filled with purified air a weighed quantity of the 

 solid acid, and then introducing without opening the flask the proper 

 quantity of conductivity water and of the stock ammonium hydroxide 

 solution to produce as nearly as possible any desired round concentrations. 

 These were in general attained within 0.1 or 0.2 per cent, but the exact 

 concentration was always considered. 



The content by weight of the various solutions obtained as above 

 described was reduced to volume concentration by means of the density 

 of the solution, which in the case of the acid or salt solutions was calcu- 



