RICHARDS. ATOMIC WEIGHT OF BARTUM. 77 



at once with standard hydrochloric acid* was found to require 3.40 

 cubic centimeters of the solution in order to remove the color of the 

 trace of phenol phthalein added, and 0.64 cubic centimeter more to 

 reach the point at which methyl orange began to show an excess of 

 acid. An excess of yet 0.26 cubic centimeter was added in order to 

 be certain of the end-point. According to page 57, the correction to 

 be added to the weight of the baric chloride corresponding to the first 

 addition of acid was 0.71 milligram, while the correction correspond- 

 ing to the second addition was 0.03 milligram. Hence, the true 

 weight of the baric chloride in vacuum, if none had been decomposed 

 by heat, would have been 6.36974. 



The solution was transferred with the greatest care to a glass stop- 

 pered Erlenmeyer flask, and diluted to about one hundred and fifty 

 cubic centimeters with cold water. To it was then gradually added 

 in the dark room the cold solution of about 6.72 grams of silver 

 (about 3^ excess). The metal had been dissolved in thirteen cubic 

 centimeters of the purest nitric acid, the lower oxides of nitrogen had 

 been expelled, and the whole had been diluted to over six hundred 

 cubic centimeters. 



The precipitate was shaken occasionally with the liquid for several 

 days in perfect darkness ; and the filtrate, which could contain no 

 trace of chlorine, was separated by means of the indispensable Gooch 

 crucible. After having been parsed several times through the cruci- 

 ble, in order to avoid the loss of any shreds of asbestos, the filtrate 

 was set aside. The precipitate was violently agitated with renewed 

 portions of cold water until the wash water was absolutely neutral, 

 and was then transferred to the crucible by means of a jet of water. 

 The last particles of argentic chloride were removed by shaking the 

 stoppered flask violently with a little water. Subsequent testing with 

 ammonia and nitric acid showed that no argentic chloride remained in 

 the flask. The thirteen hundred cubic centimeters of wash water were 

 evaporated, and the small amount of resulting argentic chloride was 

 collected upon a small washed filter of the best quality. After the 

 rapid ignition of the filter paper in a porcelain dish, the ash was found 

 to contain 0.70 milligram of silver, according to Volhard's method. 

 Hence, 0.93 milligram of argentic chloride had been dissolved. The 

 main mass of the precipitate was dried at 180° ; and after having been 

 carefully weighed it was transferred to a porcelain crucible, weighed 

 again, fused in an air bath, and weighed yet again. It is needless to 



* See page 66 of tins paper. 



