A REVISION OF THE ATOMIC WEIGHT OF MANGANESE. 37 



' SILVER. 



Five different specimens of silver were employed, a portion of each one of 

 which had already been used in an atomic weight research, and had been shown 

 to be of the highest grade of purity. Two of these specimens, Samples H and J, 

 were used in an investigation upon the atomic weight of iodine by one of us.^ 

 Sample H was prepared from silver nitrate which had been seven times re- 

 crystallized from nitric acid, five times recrystallized from water, and finally 

 precipitated with ammonium formate. Sample J was precipitated once as silver 

 chloride, electrolyzed once, and finally precipitated with ammonium formate. 

 Sample K was used in our first investigation upon the atomic weight of cad- 

 mium. ^ This sample was thrice precipitated as silver chloride and once elec- 

 trolyzed. Sample L was precipitated once as chloride, once as metal by am- 

 monium formate and was once electrolyzed. This sample has been used in the 

 analysis of cadmium bromide.^ Sample M was prepared for an investigation 

 upon the atomic weight of bromine, and had been twice electrolyzed after a 

 preliminary purification.'' Samples H, J, and L also were used in the latter re- 

 search, and were found to give values identical with those obtained with Sample 

 M. All five samples were finally fused in a current of pure hydrogen in a lime 

 boat. The fused lumps were cleaned with dilute nitric acid, cut into fragments 

 either with a clean steel chisel and anvil, or with a jeweler's saw, treated with 

 dilute nitric acid until free from iron, washed, dried, and finally heated to about 

 300° in a vacuum. 



DRYING OF MANGANOUS BROMIDE. 



The method of analysis was essentially that usually employed in this 

 laboratory for the analysis of metallic haUdes, and has been described in 

 the preceding papers on the cadmium hahdes. Weighed portions of the 

 bromide, after fusion in hydrobromic acid, were first titrated against weighed 

 portions of pure silver. Then the precipitated silver salt was collected and 

 weighed. 



The apparatus used for the fusion of the manganous bromide in a current of 

 nitrogen and hydrobromic-acid gases has already been described in detail on 

 page 23. 



The manganous bromide, contained in a weighed platinum boat, was heated 

 gently in a current of nitrogen, until the greater part of the crystal water was 

 expelled, then strongly in a current of nitrogen and hydrobromic acid until 

 fused. After the salt had cooled, the hydrobromic acid was displaced by nitro- 

 gen and this in turn by pure dry air, the purifying apparatus being constructed 

 in such a way that by means of stop-cocks any one gas or mixture of gases could 

 be employed, to the exclusion of the others. The boat was then transferred to 



» See page 108. ^ See page 6. 



' See page 22. * See page 56. 



