154 BRIDGMAN. 



as to be imperceptible. In view of this known fact it did not seem 

 worth while to make an examination under pressure. The result 

 would in all probability be negative as for AgoS. 



HgS has two modifications ; a very unstable black modification, cubic, 

 and a stable red one. It is known that under pressure the black form 

 changes to the red. I made trial on the red modification over the usual 

 range without result; a negative result is not surprising. 



The antimony sulfides have already been extensively commented 

 on, and the other sulfides seem to require no special mention. In the 

 only two cases where the phase diagrams of sulfides have been meas- 

 ured, they have been found to be simple and quite normal in type. 



SuLFOCYANiDES. — KSCN, II rhombic; NH4SCN, I rhombic, II 

 monoclinic. 



Although the phase diagrams of these two substances differ in 

 appearance, it has been shown in the discussion of individual data that 

 the substances probably are isopolymorphic when modifications in the 

 same crystalHne system are put into correspondence. Each substance 

 probably has three modifications instead of two, and the appearance 

 of difference in the phase diagrams is to be explained by the different 

 temperatures of transition. 



It is known that RbSCN, CsSCN, and TISCN also have other 

 modifications. It would be interesting to try them. 



Halogexates.^KCIOs* monoclinic; KBrOs trigonal; KIO3 mono- 

 clinic; NaClOs cubic, trigonal, rhombic; KCIO4, rhombic. 



The relation between the first three potassium salts is not simple. 

 The ordinary form of KCIO3 is monoclinic, and that of KBrOs is trigo- 

 nal pseudo-cubic. KBrOs is, however, isodimorphous with KCIO3, 

 forming a series of niLxed crystals with a gap. It is possible that 

 the ordinary form of KBrOa is the high pressure form of KCIO3. If 

 the usual form of KCIO3 corresponds to the second unstable form of 

 KBrOs, the latter might be expected to have three modifications under 

 pressure, but no new one was found. KIO3 is monoclinic, but will not 

 form mixed crystals with either KCIO3 or KBr03. NaClOs is cubic, 

 and shows no isomorphism with KCIO3. It is known, however, to 

 have two unstable forms, one trigonal and one rhombic, and might 

 on this account be expected to have other forms under pressure. 



It would be interesting to try RbClOs and CsClOs, since these are 

 probably isomorphous with KCIO3. 



The first one of this group of substances which I investigated was 

 KCIO3, my reason was simply that its well known chemical instability 

 seemed to suggest the possibility of readily taking new groupings. 



