208 PROCEEDINGS OF THE AMERICAN ACADEMY 



cooling with, ice, the resulting odorless, black supersaturated solution 

 at once crystallized into a mass of brownish green needles, which were 

 collected on a perforated crucible and washed three times with a very 

 little water. These needles were wholly different in form and appear- 

 ance from the black scales previously prepared : they were undoubt- 

 edly identical with those described by Berthemot and Lowig.* The 

 dilute solution of these crystals deposited only a wholly insignificant 

 amount of the basic bromide upon standing, and this small amount 

 was undoubtedly formed by the rapid current of air drawn through 

 the Gooch crucible. After remaining for more than a week longer 

 there was no sign of further deposition, and the pure liquid was sub- 

 jected to analysis, with the results given below. 



Method of Analysis. 



The copper was determined in the same manner as before, except 

 that in expei'iment 18 the crucible serving as the negative electrode 

 was previously coated inside with a thin film of copper, so that the 

 external conditions before and after the analysis might be the same. 

 The data of this exi^eriment may perhaps make the understanding of 

 the method more clear. 



Experiment 18. 



grams. 



Weight of glass-stoppered flask with CuBrg solution = 93.872 

 Weight of glass-stoppered flask alone = 32.289 



Weight of solution taken = 61.583 



Corrected Weights, 

 grams. 



Crucible with copper before analysis = 36.5516 



1st drying crucible with additional Cu after analysis = 37.2260 



2d drying crucible with additional Cu after analysis = 37.22605 



Gain of copper film = 0.6744 



Correction to vacuum = 0.0000 



Weight of copper found = 0.6744 



Result. 



50 X 6744 ^ , 



Weight of copper in 50 grams solution = — . ^o.> — = 0.54755 



In precipitating the bromine from new portions of the solution, not 

 only was the resulting silver bromide weighed, but also the silver 



* Berthemot and Lowig, he. at. 



