RICHARDS. — ATOMIC WEIGHT OF BARIUM. 69 



Owing to the chemical errors which have just been pointed out, the 

 results given above are of no real value. For this reason the indi- 

 vidual data are omitted. The uncertainty of the result 112.073 is 

 probably as much as a unit in the second decimal place ; therefore 

 the atomic weight of barium computed from it, 137.43, cannot be re- 

 lied upon to within 0.2. The different errors tend to eliminate one 

 another, so that the result is by chance near the true one. 



Solubility of Argentic Chloride. 



Since it is evident that no satisfactory results are to be obtained 

 from the ratio just discussed, the careful investigation of the ratios of 

 silver and argentic chloride to baric chloride assumes even greater 

 importance than before. 



The solubility of argentic chloride is the most serious difficulty 

 which is to be overcome in this investigation. Gay Lussac knew that 

 the filtered liquid which remains after mixing equivalent amounts of 

 solutions of argentic nitrate and a chloride invariably gives a precipi- 

 tate with an excess of either reagent, showing that some argentic 

 chloride must remain in solution. Mulder, in 1857,* recognized very 

 clearly the same fact, and pointed out, with the help of a great num- 

 ber of detailed experiments, just what influence this fact has upon the 

 titration of silver by Gay Lussac's method. 



Mulder wrongly ascribed the solubility of argentic chloride to the 

 presence of the alkaline nitrate resulting from the decomposition, for 

 he believed that the curdy precipitate was wholly insoluble in pure 

 water, or in water acidified with a reasonable amount of nitric acid. 

 Six or eight years later Stas,f without knowing of Mulder's work, 

 clearly recognized the difficulty, but fell into serious blunders in in- 

 terpreting it. Before 1872, however, when his noted researches on the 

 " chemical statics " of argentic chloride and bromide began to appear,J 

 he had become familiar with Mulder's work, and had adopted many of 

 his points of view. 



In these last reseaches Stas found that freshly precipitated volumi- 



* Mulder, " Essayeer-Methode van bet Zilver," Scheikundige Verhande- 

 lingen en Onderzoekingen, 1 Deel, 1 Stuk, 1857. Translated by Grimm, " Die 

 Silberprobirmethode," Leipzig, 1859. 



t " Untersuchungen," etc., translated by Aronstein (Leipzig, 1867), pp. 46, 

 56, 59, and 295 



| Annates de Cliim. et de Pliys., 4th series, XXV. 22 ; and 5th series, III. 

 145 and 289. 



