POLYMORPHISM AT HIGH PRESSURES. 



139 



Further comment will be made on the behavior of these three halo- 

 gen compounds under the discussion by groups. This is the best 

 example of a thorough going isopolymorphism that I have found. 



The Antimony Sulfides. — - Antimony may form either the triva- 

 lent or the pentavalent sulfide, SboSs or SboSs. Sb2S3 exists in two 

 distinct modifications; a black form occurring in nature, and a red 

 form, said to be amorphous, which is formed chemically by precipita- 

 tion. The red modification may be changed to the black at atmos- 

 pheric pressure by heating to about 200°. SboSs has also apparently 

 two forms; the commercial form is a bright orange powder, but when 

 made in the laboratory by precipitation with H2S from solution it is 



TABLE XIII. 

 Ammonium Chloride. 



red in color, very much like the red ^ho^z. The materials used in 

 this investigation were obtained from two sources; the black Sb2S3 

 and the orange Sb2S5 were from Eimer and Amend, and the red Sb2S3 

 and red Sb2S5 were made especially for me at the Chemical Labora- 

 tory of Harvard University. 



The behavior of Sb2S3 will be first described. The black modifica- 

 tion shows no peculiarity; there is no new form to 12000 at 20° or 100° 

 or 200°. The red Sb2S3 changes to the black Sb2S3 on heating in a 

 peculiar way. Up to temperatures of 150° and pressures up to 12000 

 kgm. no change in the red is produced; this was verified by taking the 

 apparatus apart after exposure to these values.. If red Sb2S3 is heated 

 at 12000 kgm. however, some sort of change takes place between 150° 

 and 200° accompanied by a decrease of volume. If after exposure to 

 200° at 12000 kgm. the apparatus is cooled, still under 12000 kgm., 



