POLYMORPHISM AT HIGH PRESSURES. 141 



now, however, that the subcooled red Sb2S3 cannot be a glass, but is 

 another crystalline modification formed from the subcooled melt. 



The system of the two modifications of SboSs now becomes strikingly 

 like that of red and white phosphorus. Red SboSs corresponds to 

 white phosphorus, and black Sb2S3 to red phosphorus. Red phos- 

 phorus and black Sb2S3 are both the absolutely stable forms, but there 

 is frictional resistance to change so that the unstable forms will not 

 change to the stable forms, even when inoculated, at low temperatures. 

 The unstable white phosphorus and the red SboSs furthermore each 

 have a second modification, and the transition curves to these new 

 modifications are very similar in location for the two substances. A 

 careful study of the system Sb2 S3 would be interesting, both for its 

 own sake, and for the light which it might throw on the vexed question 

 of the relation of the forms of phosphorus. 



The results obtained with the two forms of Sb2S5 are curious and 

 interesting, but have little real value because it is not possible to 

 produce an Sb2S5 which is even approximately pure; the pure sub- 

 stance probably does not exist, but spontaneously decomposes into 

 other sulfides and free sulfur. I have found the statement that under 

 usual chemical methods of manufacture 40% of Sb2S5 is a high pro- 

 portion. The behavior of the two specimens of Sb2S5 becomes intel- 

 ligible from this point of view. The red modification is one in 

 which there is a large proportion of red Sb2S3. At low temperatures 

 it shows the same transition as the red Sb2S3, but with corners con- 

 siderably more rounded, and the transition is at a somewhat higher 

 pressure. This is as one would expect as the result of an increased 

 proportion of dissolved impurity. On heating to 200° under a pressure 

 of 12000 kgm. and then releasing pressure at 200°, decomposition takes 

 place of what SbsSs there is to black Sb2S3 and free S. At approxi- 

 mately 4000 kgm. and 200° the melting point of the free S is reached. 

 This gave the appearance of some sort of a new transition until the true 

 nature of the effect was discovered. The presence of free sulfur may 

 be easily proved by digesting with CS2, or in some cases acicular crys- 

 tals of sulfur several mm. long were formed. The melting point of 

 the sulfur is much rounded, showing that the Sb2S3 is soluble in sulfur, 

 as one might expect. The appearance of the SboSs remaining after 

 the decomposition is black, exactly like that of red Sb2S3 subjected 

 to the same treatment. It is noteworthy that the decomposition in 

 two stages, particularly the decrease of volume at 10000 kgm. at 200° 

 could not be detected. 



The orange Sb2S5 behaves as if it contained a larger proportion of 



