198 PROCEEDINGS OF THE AMERICAN ACADEMY 



carbon dish similar to that described by Professor Cooke,* and, after 

 being fused by means of a blowpipe directed downwards, the silver 

 was allowed to cool in a reducing flame. The buttons were hammered 

 upon a clean anvil, scrubbed with sand, rolled out between two plates 

 of pure silver, cut with a hard steel chisel, boiled successively with 

 hydrochloric acid and ammonia, scrubbed once more with sand, and, 

 after heating with melted potassic hydrate in a silver crucible, finally 

 scrubbed, washed, and dried. 



In order to prove the absence of any absorbed gases in the resulting 

 metal the following experiments were made. 



I. 1.3412 grams of silver heated in vacuo to a low red heat weighed 



after cooling 1.3412 grams. 

 II. 1.5763 grams after being subjected to the same treatment weighed 

 1.5763 grams. 

 The absolute constancy of these weights is sufficient proof of the 

 point in question. The silver yielded a perfectly clear solution upon 

 treatment with nitric acid and subsequent addition of water, and gave 

 every evidence of being chemically pure. 



In order to determine the purity of the hydrobromic acid previously 

 made, the solution of a known weight of the pure silver described 

 above was decomposed by a slight excess of this liquid, and the result- 

 ing precipitate was weighed. The metal was dissolved in a very slight 

 excess of warm pure nitric acid diluted with two volumes of water, 

 the whole being contained in the half-litre Erlenmeyer flask which 

 was afterward to serve for the precipitation. The very small amount 

 of gas formed by the decomposition of the nitric acid was forced to 

 pass through a zigzag tube provided with bulbs, in order that the 

 infinitesimal amount of spray might be retained. The tube apparatus 

 was not ground into the flask, but fitted only with moderate tightness, 

 the joint being sealed by water held in place by capillary attraction. 

 After the complete solution of the silver, the contents of the flask were 

 gently boiled to drive off the lower oxides of nitrogen, and the whole 

 was diluted to about two hundred cubic centimeters. To this hot 

 liquid was added very gradually the least possible excess of a dilute 

 solution of known strength made from the hydrobromic acid above 

 described, and the mixture was constantly and violently shaken, the 

 flask being closed with a smooth rubber stopper. After settling, the 

 precipitate was thoroughly washed with hot water, and collected in a 



* These Proceedings, xvii. 17. 



