858 Prof. J. Joly on the 



substances examined. I may add that the state o£ comminu- 

 tion of the powder is not, within limits, important. I have 

 tried the effects of re-grinding a substance already tested but 

 have not obtained any notable alteration of the sublimation 

 temperature. 



The sublimation temperature is not arrived at on a single 

 experiment. It is necessary to approximate to it on pre- 

 liminary experiments made at neighbouring temperatures. 

 As it is approached it is essential to put fresh powder (three or 

 four milligrams) upon the hob for each observation of three 

 minutes' duration. The reason for this is that a powder which 

 has rested on the hob for some time becomes slower in its rate 

 of evolution of sublimate owing to the exhaustion of those 

 lower particles which most perfectly take up the temperature 

 of the ribbon. A deceptively high temperature must be 

 maintained to affect those particles which are out of contact 

 with the platinum. The slower rate of sublimation which 

 arises after a certain time of exposure to a particular tempe- 

 rature also, doubtless, involves the fact that the larger particles 

 are at first only superficially affected, and a higher vapour- 

 pressure is required to maintain the evolution of vapour from 

 their interior. 



Antimony. 



The observation of the sublimation of antimony is ren- 

 dered easy by the definite characters presented by its oxides. 

 These are either JSb 4 6 or Sb 2 4 . Both are pure white and 

 very well defined sublimates, appearing nearly always in 

 streaks on the upper glass transverse to the length of the 

 ribbon. The commencing sublimate reproduces the distri- 

 bution of the powder on the hob with a fidelity which shows 

 that there is but little diffusion and suggests electrical repul- 

 sion. The streaky deposition is solely due to the vortical 

 air-currents prevailing between the glasses when the hob is 

 heated. Neither of these oxides is volatile, and at no con- 

 venient temperature can they be driven off the glasses if 

 these are held over a bunsen flame. The sublimed Sb 4 6 is 

 instantly soluble in cold HC1; the sublimate Sb 2 4 is only 

 soluble in the hot acid. The first faint white streak indicates 

 the commencement of sublimation. 



A large number of antimony-bearing minerals carry the 

 antimony in the stibnite or antimonite molecule, Sb 2 S 3 . 

 The mineral stibnite sublimes first at about 480°. The 

 following minerals possessing this molecule have been 

 examined : — 



