84 PROCEEDINGS OP THE AMERICAN ACADEMY. 



The objections to this method have been stated already ; accuracy 

 with it is a question of judgment and keenness of sight upon the part 

 of the observer, and absolutely constant conditions of temperature, 

 illumination, and agitation on the part of the substance in the flask. 

 Although great pains were taken to have these conditions as con- 

 stant as possible, it cannot be claimed that they were absolutely so. 

 Moreover, the method is so hopelessly tedious that it was finally 

 abandoned. 



In the search for a new method, the following scheme was devised. 

 A slight excess of one or two decigrams of silver over and above the 

 amount required to precipitate a weighed quantity of baric chloride 

 was weighed out with the greatest care. This was dissolved and 

 added to the baric chloride as before. The mother liquor, contain- 

 ing argentic nitrate, baric nitrate, and nitric acid, but no trace of chlo- 

 rine, was filtered off with the greatest care through asbestos, and the 

 precipitate was thoroughly shaken and washed with pure water. The 

 wash waters were collected separately and evaporated on the steam 

 bath in a suitably covered dish to small bulk. The trace of argentic 

 chloride thus precipitated from them was filtered off and washed upon 

 a very small filter, and the few milligrams of argentic nitrate in the 

 filtrate were added to the original mother liquor. From this mixture 

 of liquids all the silver was precipitated and weighed as argentic 

 bromide.* The excess of silver originally weighed out is thus very 

 simply calculated from the weight of the argentic bromide without 

 involving a personal equation of any sort. Three analyses were made 

 according to this method. f 



* For the preparation of the liydrobromic acid used, see these Proceedings, 

 XXVIII. 17. The precipitate was assumed to contain 57.445 per cent of 

 silver. 



t After the present paper had gone to press, notice was received from Pro- 

 fessor Mallet that Stas had suggested to him, in a letter dated January 27, 1887, 

 a method very similar to the one just described. J. W. Mallet, Stas Memorial 

 Lecture, p. 33. [November 12, 1893.] 



