OF ARTS AND SCIENCES. 



205 



It is certain that the hydrobromic acid used in making this prepa- 

 ration, notwithstanding the care taken in its manufacture, contained 

 a trace of alkali from the glass retort used in distilling; and the pres- 

 ence of this impurity would tend to lower the observed atomic weight 

 of copper. In order to correct this evil, and also in tlie hope that 

 free hydrobromic acid might prevent the very slight formation of basic 

 salt which invariably took place on the evaporation of water from the 

 neutral salt, tlie attem{)t was made to cry.stallize the cupric bromide 

 from acid solutions. The crystals were still basic, owing to the sur- 

 face decomposition of exposed scales, but nevertheless two small dis- 

 tinct preparations of such crystals were dissolved, allowed to deposit 

 their basic salt, and each analyzed for copper and bromine. Neither 

 of these analyses was wholly satisfactory, but for the sake of com- 

 pleteness their final results are given below. 



Pkehminart Results: Third Series. 

 Solution of Crystals. 



All the results thus far given were regarded merely as preliminary 

 ones ; and a complete series in which all possible care should be taken, 

 both in preparation and analysis, remained still to be made. But 

 before proceeding to the final determinations it was thought well to 

 make several experiments with the object of proving the exactness 

 of certain operations of the work. In the first place, two samples of 

 the asbestos used for filtering were tested several times for constancy 

 in weight, after heating to different temperatures ; and the greatest 

 loss of any one mat between 130° C. and 700° C. was found to be less 

 than one tenth of a milligram. 



In the next place the copper films of experiments 1 and 2 were 

 heated in their crucibles to 500° C. in a stream of pure hydrogen, which 

 was supplied through a curved tube and a perforated lid after the man- 

 ner of Rose. The platinum rim left unprotected by the copper film 

 was so small that absorption of hydrogen must have taken place only 

 in unweighable quantities. No change in the weight of the copper 

 was observed. 



