RICHARDS. — ATOMIC WEIGHT OF BARIUM. 73 



initiation, which depends chiefly upon the relative amounts of argentic 

 nitrate and nitric acid present in each case. They moreover furnish 

 a means of correcting results obtained by the method in hand. A 

 solution containing two tenths of a gram of argentic nitrate, three- 

 grams of nitric acid, and a very small known amount of argentic chlo- 

 ride, evaporated for four or five hours, yields about 0.00006 gram too 

 much silver, and a similar solution containing only a few milligrams 

 of argentic nitrate yields about 0.0001 gram too little. The bearing 

 of these facts upon the subject will presently be made more evident. 



It was now possible to determine the solubility of argentic chloride 

 less crudely. Half a litre of the purest water, after being shaken 

 occasionally with the purest argentic chloride for two hours, yielded 

 0.50 milligram of silver, and a similar preparation, which had been 

 allowed to stand for twenty-four hours with more frequent shaking, 

 yielded 0.G0 milligram. The solubility of this argentic chloride is 

 thus found to be about 1.5 milligrams per litre. The result is not far 

 from the mean of the colorimetric tests.* 



To determine the influence of nitric acid upon the solubility, four 

 grams of this substance were added to over a litre of pure water, 

 and the mixture was shaken with the same argentic chloride. 300 

 cubic centimeters of the solution yielded 0.47 milligram of silver, and 

 two portions of 400 cubic centimeters each yield 0.56 and 0.57 milli- 

 gram of silver respectively. After adding the appropriate correction, 

 and taking the mean of these determinations, the solubility is found 

 to be about 2.3 milligrams per litre. 



In a number of analyses exactly equivalent amounts of baric chlo- 

 ride and argentic nitrate in dilute solution were shaken together, and 

 both chlorine and silver were determined in the filtrate. These analy- 

 ses were primarily to determine the atomic weight of barium, and will 

 be described later; but since the chlorine was found to be present in 

 the filtrate in amounts almost exactly equivalent to the silver, they may 

 be used also to measure the solubility of argentic chloride in solutions 

 containing about 2.5 cubic centimeters of nitric acid, and 3 to 8 grams 

 of baric nitrate. In one case, where the solution had been shaken 

 with the argentic chloride for ten days, the solubility was found 

 to be about 1.6 milligrams per litre ; in another, violently shaken, 

 but allowed to stand for a shorter time, it was found to be about 1.7 



* It is noteworthy that Kohlrausch and Rose have found the solubility of 

 argentic chloride to be 1.52 milligrams per litre at 18°. This determination 

 was based upon the electrical conductivity of the solution. (Zeit. Physikal. 

 Chem.,XII. 234.) 



