212 



REJPORTS ON INVE;STIGATI0NS AND PROJECTS. 



by the determination of the specific gravity of neodymium chloride, and by 

 the examination of the absorption spectrum of aqueous solutions of neo- 

 dymium salts both in the visible and in the ultra-violet regions. The per- 

 centage of moisture in the dried salt was found to be very small, 0.003 P^^ 

 cent, and lowers the values for the atomic weight of neodymium given in the 

 previous Year Book by only eight one-thousandths of a unit. The specific 

 gravity of the fused salt at 25° referred to water at 4° was found to be 

 4.134, while Matignon's value, which was used in the previous calculations, 

 is 4.18. In the following table are given the final corrected values for the 

 different samples of neodymium chloride, based upon the atomic weight of 

 silver 107.870. This investigation has been published in the Proceedings of 

 the American Academy of Arts and Sciences, vol. 46, 215-244, 1910. 



Mr. T. Thorvaldson continued the investigation upon the atomic weight 

 of iron begun in the previous year by Mr. Cobb. In this investigation fer- 

 rous bromide was analyzed in the way commonly employed in this laboratory 

 by titration against an equivalent amount of silver and gravimetrically by 

 collecting the silver bromide produced. 



The ferrous bromide was formed by the solution of very pure metallic 

 iron in aqueous hydrobromic acid and crystallization of the salt from hydro- 

 bromic-acid solution. The metallic iron was a specimen of material obtained 

 from the American Rolling Mills Company. It contained the following im- 

 purities : sulphur 0.19 per cent, phosphorus 0.003 P^^ cent, carbon 0.018 per 

 cent, copper 0.05 per cent, manganese trace, and silicon trace. It was puri- 

 fied by solution in nitric acid, and double precipitation as hydroxide with pure 

 ammonia, with solution in nitric acid in the first case, but in sulphuric acid 

 in the second ; electrolytic reduction to ferrous sulphate ; electrolytic deposi- 

 tion from oxalate solution on a platinum dish ; solution in nitric acid and 

 crystallization of the nitrate; ignition of the nitrate to oxide, and reduction 

 to metal in a stream of pure hydrogen. 



The ferrous bromide was first dehydrated and then fused in a weighed 

 quartz boat in a current of nitrogen which had been saturated with hydro- 

 bromic-acid gas by passing through fuming hydrobromic-acid solution. The 

 salt was dissolved in slightly acidulated water, and before precipitation with 

 the silver-nitrate solution it was oxidized with a slight deficiency of potas- 

 sium dichromate. 



