THE SOLUBILITY OF ARGENTIC CHLORIDE. 20, 



been any " crystal germs " existing in the more dilute solution, hence 

 one must assume that the undissociated part of the argentic chloride 

 is really in a different state, when it is dissolved out of salt long formed 

 from that in which it is when in the act of precipitation. The 

 observation at least adds one more anomalous fact, perhaps giving a 

 clue to some of the other anomalous facts, concerning the solubility of 

 argentic chloride. 



The application of these observations to the nephelometric analysis 

 of a very dilute silver chloride solution is obvious. It is a difficult 

 matter to prepare a standard which will behave in exactly the same 

 way as the solution to be estimated. By adding appreciable quantities 

 of nitric acid to each, it is nevertheless possible to hasten the precipita- 

 tion of each so greatly as to cause them to proceed at a speed almost 

 equal ; and the maximum cloudiness thus quickly attained persists 

 unchanged in relative intensity for hours. It seems highly probable 

 that the result thus reached really represents the amount of dissolved 

 argentic chloride ; especially because the same result is attained after 

 a much longer time even when no electrolyte is present. 



The actual extent of the solubility of argentic chloride thus esti- 

 mated varied through wide limits, as has already been stated. For the 

 solution freshly filtered from the curdy precipitate in the usual condi- 

 tion at 20 the amount dissolved was ordinarily about 1.5 milligrams 

 per liter, a result about equal to that of Kohlrausch and Rose and others. 

 On long standing such a solution was found to decrease in concentra- 

 tion, on one occasion to as little as 1.1 milligrams per liter, although 

 no visible precipitate was seen on the glass. The trace of material 

 represented by this difference was probably adsorbed by the glass. 

 This observation points out the necessity of determining the strength 

 of an unknown solution immediately after its filtration, a precaution 

 which was carefully heeded in the quantitative part of the work. 



Although sodic nitrate and nitric acid hasten the precipitation 

 of the curdy opaque form of argentic chloride, they augment slightly 

 the amount which finally remains in solution. By means of the 

 nephelometer it was found that a saturated solution of curdy argentic 

 chloride in the presence of about tenth normal sodic nitrate and a 

 small amount of nitric acid usually contained as much as 3 milli- 

 grams of the slighly soluble halide per liter. A mixture of this type 

 was present at the conclusion of each nephelometric experiment 

 recorded in the experiment on the ratio between sodic chloride and 

 silver, and the bearing of the actual value on the investigation will 

 be there discussed. 



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