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, Sb2S3 or Sb^Ss. 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°. Sb2S5 has also apparently 

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

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



TABLE XIII. 



Amaionium Chloride. 



red in color, very much like the red Sb2S3. 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., 



