Temperature of Sublimation. 11 



(2) With native bismuth and some samples of chemically 

 prepared bismuth as well us with some mineral compounds 

 o£ bismuth, there appears a whitish-buff or yellowish-buff 

 sublimate, very nebulous and diffusive, at temperatures 

 which seem variable but are always lower than that of the 

 formation of the normal sublimate of Bi 2 3 . It may be 

 evolved at the moment of sudden decomposition when the 

 internal temperature of the particles is unknown. 



This body seems to be undoubtedly an oxide of bismuth ; 

 the test with SnCl 2 in every case giving the characteristic 

 blackish-brown precipitate. A borax bead fed with the 

 scraped-up sublimate is yellow hot and colourless cold in the 

 oxidizing flame. 



The distinctive feature of this oxide is its volatility. It is 

 readily volatile off the glasses. Heated between them it 

 forms smoky clouds which may condense to minute colour- 

 less and transparent regular octahedra. In general the 

 sublimate is merely granular, as seen under the microscope. 

 It is heavy and often falls into the lower glass. 



It is instantly soluble in dilute HC1, in aqua regia, and in 

 solution of KHO. It is slowly or doubtfully soluble in 

 HN0 3 . With elemental bismuth it has been obtained at 245° 

 to 345° : soon ceasing to come off. With native bismuth it 

 w T as obtained from 470° to 630° ; more generally near the 

 latter temperature. By raising the temperature very 

 gradually it was found — at least in the case of elemental 

 bismuth — that the formation of this oxide was preventable ; 

 the stable bismuthous oxide being formed on the hob and 

 ultimately sublimed. From aikinite this volatile oxide was 

 got at 600° and 820°. From bismuthenite it was obtained 

 at 510°-600°. 



The observations do not indicate that any importance 

 attaches to this oxide in quantitative work, as, relatively to 

 the stable, high-temperature oxide, it is small in amount. 

 In many cases it does not appear to be formed. I have 

 not identified it with any recorded oxide of bismuth of which 

 I am aware. 



(3) The bismuthine oxide; Bi 2 5 (?). Along with the high- 

 temperature sublimate of Bi 2 3 , reddish and pink streaks 

 are sometimes observed. This is a non-volatile sublimate : 

 insoluble in HOI, so that it remains after the accompanying 

 Bi 2 3 is dissolved. It may be the oxide Bi 2 5 . It is said to 

 pass to Bi 2 3 if heated in air at 305°. This has not been 

 observed in the present case. It is not important in analysis, 

 being very small in amount. 



(4) Hypobismuthous oxide, Bi 2 2 . The black oxide is 



