64 PROCEEDINGS OF THE AMERICAN ACADEMY. 



a high temperature in air, but that reoxidation of the mom 

 place while it v ling. He showed tin* by igniting in air a crucible 



containing the black < » x i . 1« - and cooling ihe crucible suddenly by plunging 

 it into cold wain-. Under these conditions a film of black oxide was 

 formed on the surface only, while the lower portions remained in the 

 form of brown monoxide. Evidently, to prevent reoxidation i I was only 

 necessary to keep the oxide away from contact with oxygen. '1 he tn< thod 

 adopted by Russell was to heat the oxide in a current of an inerl gas until 

 constant weight was established, and then to reduce the compound in 

 hydrogen, thus obtaining an indirect ratio between oxygen and cobalt. 



This method of procedure, which was adopted by all subsequent experi- 

 menters on the oxide, seemed open to two Berious disadvantages. I 



Erst, the difficulty of preparing nitrogen or carl dioxide free from 



traces of oxygen, is our which can be surmounted, although not easilv. 

 The possibility that small quantities of liberated oxygen may become 

 mechanically entangled i' 1 the oxide, in Buch a way as not to !»■ Bpeedily 

 removed by the current of gas, is a danger even less easily avoided. 

 This oxygen would of course reunite with the monoxide upon cooling, 

 thus making it- weight too great. 



As an alternative to heating in a current of inert nition in a 



vacuum suggested itself as offering distinct advantages, since neither of 

 the dangers just mentioned would be incurred. For thi> purpose a 



ed porcelain tube, of twenty-eight millimeters internal diamel 

 similar to that used for [using silver in a vacuum, was employed.* The 

 tube was closed as usual with Hernpel hollow brass stoppers and heated 

 in a perforated Fletcher furnace by means of a large Mast lamp, while 

 an ordinary Sprengel air-pump served to exhaust thi from the tube. 



Very pure cobalt, which had been prepared by various methods during 

 the previous work, was converted into the oxide as follow-. From the 

 solution of the metal in pure nitric acid the pink granular coball 

 hydrate was precipitated by adding an excess of pure freshly redistilled 

 ammonia, and subsequently digesting the mixture upon the -team bath 

 in a platinum bowl. This precipitate was collected upon a Gooch cru- 

 cible in which a circular piece of hardened filter paper was used instead 

 of an asbestos mat. After drying and converting the ma>s into the Mack 

 oxide bj ignition with an alcohol lamp this material was used directly 

 Eor analysis. The metal which Berved as the source of this oxide was 

 known to be free from alkalis and -ilica.t and as neither the nitric acid 



* Richards and Parker, These Proceedings, XXXI] 16). 



t These Proceedings, XXXIII. 120 (1897). 



