Section go. Preparation of Solutions. 243 



fumes of metaphosphoric acid appeared. The cooled residue was taken 

 up in conductivity water and saturated with hydrogen sulphide, in order 

 to precipitate possible traces of arsenic or platinum. The metaphosphoric 

 acid solution thus obtained was converted to the ortho acid by boiling in a 

 platinum dish for three hours. That the conversion in this solution Avas 

 complete was shown by the fact that the conductance of the diluter solu- 

 tions prepared from it was not changed by heating to 156. 



The solution received January 17, 1906, from Mr. Abbott was part 

 of a stock solution which he had analyzed gravimetrically by precipita- 

 ting the phosphoric acid with magnesium ammonium chloride and weigh- 

 ing as magnesium pyrophosphate. The five analyses made by him gave 

 as a mean value 20.0866 grams of H 3 P0 4 per kilogram of solution. 

 Assuming 1 mol H 3 P0 4 = 98.02 grams, the concentration of this solu- 

 tion becomes 0.2049 mols per kilogram of solution. 



The nitric acid solution was made by diluting a portion of "C. P. 

 nitric acid," of specific gravity 1.42, taken from a newly opened carboy, 

 with half as much water, bubbling through it for one day a current of 

 carefully purified air, so as to remove nitrous acid, and finally diluting 

 with enough conductivity water to give a very nearly 0.1 normal solution. 

 The stronger solution was tested for nitrous,* sulphuric and hydrochloric 

 acids, for ammonium salts (with Nessler reagent), and for non-volatile 

 residue. None of these impurities were present in quantity as large as 0.01 

 per cent of the nitric acid present. The acid was standardized by compari- 

 son with the sulphuric acid solution just described through a 0.1 normal 

 sodium hydroxide solution, and also directly against sodium carbonate. 

 Its concentration was thus found to be 99.70 and 99.87 (mean 99.78) 

 milli-equivalents per kilogram of solution. 



The barium hydroxide used for preparing the stock solution of this 

 substance was purified by twice crystallizing from hot water in procelain 

 vessels a "chemically pure" preparation of Merck's. The crystals so 

 obtained were dissolved in hot conductivity water, the solution filtered 

 immediately out of contact with ordinary air, the filtrate allowed to run 

 into about three liters of water of specific conductance 0.6 X 10" 6 con- 

 tained in a " Non-Sol" bottle (furnished by Whitall, Tatum & Co.). 

 After standing for 24 hours, this solution, from which crystals separated 

 on cooling, was forced over into a second "Non-Sol" bottle containing 

 enough more conductivity water to dilute it to about 0.2 normal. The 

 final solution was perfectly clear and remained so. 



*The test for nitrous acid was made by adding to 1 c.cm. of the stronger solution 

 100 c.cm. water, 10 c.cm. of an acetic acid solution of sulphanilic acid, and 10 c.cm. 

 of a solution of naphthylamine acetate, and allowing the mixture to stand. For com- 

 parison a minute quantity of nitrite was added in a duplicate test. The result 

 showed that, while one part of nitrous acid in a million could be detected, less than 

 this was present in the strong nitric acid. 



