254 PROCEEDINGS OF THE AMERICAN ACADEMY. 



questions as the possible presence of gases in the oxide, the possibility 

 of incomplete reduction, and the danger of contamination from the con- 

 taining vessels, should obvioush receive attention. 



a 



The balance and weights used in the present Btudy were the Bame as 

 those used in other recent determinations of atomic weights. 4 It is need- 

 less i" Btate that the weights were carefully justified, and that all the 

 usual precautions necessary to procure accuracy in such work were ob- 

 served. All the weighings were reduced to the vacuum standard, and the 

 values of the atomic weights refer to the universally accepted Btandard 

 = 16.1 



One of the most important steps in Buch an investigation is clearly the 

 choice of the substance to be analyzed, and the choice usually requires a 

 careful preliminary qualitative ami quantitative Btudy of many compounds 

 of the element under consideration. This work occupied a number of 

 weeks, and in the course of it we found that the preparation of either 

 ferrous or ferric balides in a pure anhydrous state offered so many diffi- 

 culties that a> yet no satisfactory method for the purpose has been de- 

 vised. Ferric oxide, on the other hand, can he obtained in a variety of 

 ways, hence the choice of the early experimenters seems to have been 

 a wise one. The first step in a systematic treatment of the suhjecl is 

 obviously a repetition of the discordant work of half acenturj ago, with 

 especial reference to the possible errors noted above. 



Owing to the fact that most oxides formed from nitrates are known to 

 include considerable quantities of 0x3 gen and nitrogen, t ignition of ferric 

 nitrate as a means of obtaining ferric oxide was at first rejected, and ferric 

 hydroxide was used instead. Very pure iron ribbon was dissolved! in 

 sulphuric acid, and the metal was then deposited electroly tically from an 

 amnionic oxalate solution. After the film had been dissolved in the pur- 

 est nitric acid, the carbon was removed by filtration, and the iron ivaa 

 precipitated as ferric hydrate hy the addition of an excess of ammonia 

 which had been distilled into pure water contained in a platinum dish. 

 The precipitate was washed thoroughly, collected upon a pure washed 

 tiller paper, separated from the filter paper while moist, and finally dried 

 in a platinum dish upon the steam hath. The lumps of dried hydrate 

 were crushed in an agate mortar and finally ignited tor Beveral hours in 

 a current of pure dry air. During the latter operation the weighed 

 platinum boal with the oxide was contained in a large porcelain tube 



* These Proceedings, 26. ^V2 (1891). 



: Richards, These Proceedings, 26, ^si (1891). Kichanls and lingers, ibid., 28, 

 200. 



