198 



Analogous results were obtained by Steinmetz with isopropyl- 

 amine-platinichloride l ): (iso-C 3 H 7 .NH 2 ) 2 PtCl 6 , which is a mono- 

 clinic, but pseudo-rhombic substance, and which at 32 C. is changed 

 into an apparently true rhombic individual, without measurable 

 heat-, or volume-effects. Something of the same kind was found 

 by Gossner 2 ) in the case of glaserite: K 3 Na(S0 4 ) 2 , and of the 

 corresponding chr ornate: K 3 Na(CrO^) 3 ; here too, neither heat- nor 

 volume-effects were found when the monoclinic, pseudo-hexagonal 

 crystals passed into such of apparently true hexagonal symmetry. 



Beautiful examples were also found by Gossner 3 ) in the case 

 of the tri-alkali-hydrosulphates: K 3 H(SO^) 2 , (NHJ 3 H(SOJ 2 , and 

 T1 3 H(SO^) 2 , and in that of the corresponding selenate: K 3 H(SeO^) 2 . 

 The ammonium-, and potassium-hydrosulphates are monoclinic and 

 pseudo-trigonal; the thallo-salt is really ditrigonal, with approxi- 

 mately the same angular values. On heating the monoclinic salts, a 

 system of three sets of lamellae, crossing at angles of 60, becomes 

 visible, which at increasing temperatures get gradually more nume- 

 rous, until finally apparently a perfect ditrigonal crystal is pro- 

 duced. The transformation is completely reversible, and according 

 to Gossner, a continuous one. Fischer 4 ), however, demonstrated, 

 that in reality in the case of the ammonium-salt a ^continuous 

 change may be present between 124 and 135 C., so that a true 

 polymorphic change seems to immediately follow the first one. 



From this it appears that the phenomenon of poly symmetry 

 must be distinguished from the case of true polymorphism 5 ) ; and 

 for the explanation of the latter, Mallard's theory cannot serve. 

 It must, however, be remarked, that pseudosymmetrical substan- 

 ces can often be changed at higher temperature into new, true 

 polymorphic modifications 6 ) : potassium-sulphate is a wellknown 

 example of this, it being suddenly changed at about 650 C. into 

 a new, really hexagonal modification. 



1 ) A. Ries, Zeits. f. Kryst. 36. 329, 360, (1902); H. Steinmetz, Zeits. f. phys. 

 Chemie, 52, 449, (1905). 



2 ) B. Gossner, Zeits. f. Kryst., 39, 155, (1904). 



3 ) B. Gossner, Zeits. f. Kryst., 38, 110, 159, 161, (1904). 



4 ) P. Fischer, Dissertation Gottingen, (1911), p. 10, 25. 



5) J. Beckenkamp, Zeits. f. Kryst., 34, 633, (1901). The author suggests 

 to adopt Mallard's theory in all cases of so-called polymorphism, where both 

 modifications have the same or only unappreciably different specific gravities. 



6 ) P. Groth, Einleitung in die Chemische Krystallographie, (1904), p. 6. 



