176 PROCEEDINGS OF THE AMERICAN ACADEMY. 



that time they gained only two tenths of a milligram, showing that 

 the diffusion of moisture through the stopper was very slow. In order 

 to prove the efficiency of the drying and fusing apparatus, the bottle 

 with its contents were returned to it, and the stopper was removed by 

 means of a wire while a current of dry air was allowed to pass through 

 the whole apparatus. This current was continued for half an hour, 

 the boat and bottle being warmed to about 120°. After suitable cool- 

 ing the substance was found to have lost one tenth of a milligram, 

 being one tenth heavier than it was in the first place. These weights 

 were not included above in order to avoid complications ; they do not 

 belong necessarily to the analysis, but merely serve to show that the 

 apparatus was wholly sufficient for its purpose. 



The boat and its contents were conveyed with great care to a large 

 Bohemian beaker, and the weighing bottle was rinsed out many times 

 with the purest water. When the zincic bromide had wholly dis- 

 solved, the perfectly clear solution was transferred through a large 

 funnel to the glass stoppered Erlenmeyer flask intended to serve for 

 the precipitation. The boat was easily washed by allowing it to rest 

 in the funnel, and of course beaker and all were rinsed with the most 

 scrupulous care. The total volume of the thus diluted zincic bromide 

 amounted to about two hundred and fifty cubic centimeters. 



The silver to be used for the precipitation weighed 5.04328 grams 

 in the air, or 5.04313 grams in vacuum. It was dissolved in ten cubic 

 centimeters of nitric acid diluted with water in a large flask provided 

 with a bulb tube, and the absolutely clear solution was freed from 

 lower oxides of nitrogen by standing upon the steam bath. The con- 

 tents of the bulbs, usually containing only a few hundredths of a milli- 

 gram of silver, were washed back into the flask, and the whole was 

 diluted to about half a litre. 



The addition of the argentic nitrate to the zincic bromide took place 

 in the dark-room,* and great pains were taken to prevent exposure of 

 the materials to anything but non-actinic light from this time until the 

 final weighing of the argentic bromide. Of course every trace of sil- 

 ver was washed into the flask containing the zincic bromide. After 

 the whole had been very thoroughly shaken and allowed to stand for 

 several days, 0.21 cubic centimeter of hydrobromic acid (one cubic 

 centimeter was equivalent to a milligram of silver) failed to produce 

 an evident precipitate, even when the solution was lighted by a bril- 

 liant condensed beam of yellow light. On the other hand, 0.60 cubic 



* See previous papers upon barium and strontium. 



