76 PROCEEDINGS OF THE AMERICAN ACADEMY. 



due to the concentration of the silver solution, an experiment was 

 made by pouring a solution of a definite amount of pure baric chloride 

 into a very strong solution of argentic nitrate. 2.6088 grams (cor- 

 rected) of baric chloride yielded 3.5929 grams (corrected) of carefully 

 washed argentic chloride. The ratio deduced from these figures is 

 2 AgCl : BaCl 2 = 100 : 72.009, a result almost 2^0 lower than tne 

 last; and the consequent value of the atomic weight of barium is only 

 137.31. The argentic chloride was of a very deep purple color. 



The outcome of these experiments showed the necessity of Stas's 

 usual practice of having the silver solution very dilute ; in the subse- 

 quent work the dilution was usually 1 : 100, and sometimes even 

 greater.* Moreover, the nitrate was always in future poured gradu- 

 ally into the baric chloride, so that until the very last an excess of 

 chlorine should be present in the solution. 



In the first series of the final group of experiments the baric chlo- 

 ride was ignited at a dull red heat in air or nitrogen ; in the second 

 series the salt was ignited and fused at a bright red heat in a stream 

 of pure hydrochloric acid ; and in the third it was not ignited at all. 

 The simplest manner of explaining the method of procedure adopted 

 in the three series of analyses which follow is to give the detail of one 

 of the experiments. 



Experiment 20. Very pure baric chloride, which had been pre- 

 pared by many successive precipitations from aqueous solution by 

 hydrochloric acid and alcohol (Sample I.c), was coarsely powdered 

 and gradually heated to bright redness by means of a Berzelius spirit 

 lamp in a double platinum crucible. In order to prevent as much as 

 possible the decomposition of the salt, the long continued ignition was 

 conducted in a stream of pure nitrogen. A large part of the salt was 

 fused during the process. After having been cooled for eight hours 

 over phosphoric oxide in a desiccator, the tightly covered inner cru- 

 cible was rapidly weighed, and the weight of baric chloride was found 

 to be 6.36793 grams in the air. Since the atmospheric pressure and 

 temperature at the time of weighing were respectively 76 cm. and 

 20°, the salt would have weighed 6.36900 grams in a vacuum. The 

 solution of the baric chloride in pure boiled water in a large platinum 

 dish was perfectly clear, and the crucible itself was found to have lost 

 only 0.02 milligram in weight. The clear liquid upon being titrated 



* In some cases Stas used only fifteen to thirty cubic centimeters of water for 

 every gram of silver, in spite of his good advice to the contrary. Mem. Belg., 

 etc., XLIII. Part II. p. 11. 



