24 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



assumed to contain that percentage of impurity. A change of only 

 0.002 in the atomic weight of sodium was caused by this difference. 



All the silver used in the final series of syntheses of silver chloride 

 was free from dissolved oxygen, and three of the specimens must 

 have been free from hydrogen also. The method of treating each is 

 sufficiently specified in the table of results and need not be further 

 discussed here. The silver used in this part of the work was the 

 purest we were able to prepare, and we know of no impurities which 

 it could have contained, except in some cases the insignificant trace 

 of hydrogen already mentioned. 



The boat used for the fusion was made from a mixture of pure 

 lime and calcic nitrate, and was contained in a porcelain tube closed 

 with Hempel stoppers. The tube was heated to bright redness in a 

 Fletcher furnace.* The resulting bars of silver were freed from the 

 adhering lime by scrubbing with clean, hard sand and successive 

 treatments with dilute nitric acid. The argentic nitrate was dissolved 

 away by ammonia, and many washings with water were followed by 

 drying the bar in a hard glass tube at about 400 in a vacuum. f 

 Water might otherwise become sealed into the microscopic cavities, 

 often present in fused silver, during the next operation of cutting into 

 blocks. The cutting is best carried out upon a silver plaque by means 

 of a clean steel coldchisel. The blocks thus cut were superficially 

 etched once more with nitric acid, so dilute that a possible trace of 

 iron could not assume the passive state, and the cleaning and drying 

 operations were repeated. The pieces then preserved in a desiccator 

 over potash are ready for weighing and analysis. 



After the details of the analysis have been discussed, the relation 

 of the purity of this silver to that of Stas will be made clear. 



UME. 

 The preparation of pure lime upon which to fuse the silver was a 

 matter of great importance, because of the danger that any impurity 

 in it might contaminate the silver. Its preparation was begun by dis- 

 solving marble in nitric acid, boiling with an excess of calcic hydroxide, 

 filtering, neutralizing, and twice recrystallizing the calcic nitrate. % 

 Calcic carbonate was then precipitated with ammonic carbonate, 

 repeatedly washed, and finally dissolved in redistilled nitric acid. 



*Proc. Amer. Acad., 30, 379 (1895). 



tThe silver used in Experiments R 1, R 2, and R 3 (p. 65) was wrapped in 

 pure silver foil during this ignition to prevent contact with hot glass. 



$ Calcic nitrate should be recrystallized 'below its transition temperature, 44, 

 a proceeding much facilitated by inoculation with the respective hydrate. 



