154 MOLECULAR GROUPING 



tion despite prevailing isomorphism. The following measure- 

 ments of Topsoe furnish an example ; all the compounds 

 are hexagonal : 



a:c 



t = (CH 3 ) 3 H 



R 4 =(C 3 H 7 ) 3 H 

 R 4 = (C 2 H 5 ) 2 



: I-I075 

 : i -ioo2 

 : 1-0855 

 : 1-0512 

 : 1-029 

 : 1-025 



4 = (C 2 H 5 ) 3 H ......... i 1-017 



R, = (C 2 H 5 )H 3 ......... 1:0-9955 



Deeper changes are observed in the following cases T : 



PtCl^.2NR i Cl System Axial ratio /3 



R 4 = (CH 3 ) 4 ...... regular 



R 4 --=(CH 3 ) 3 C 2 H 5 .... ,, 



R 4 = (CH 3 ) 2 (C 2 H 5 ) 2 . . . tetragonal 1:1-0875 



R t = (CH 3 )(C 2 H 5 ) 3 ... i : 1.0108 



R 4 = (C 2 H 5 ) 4 ..... monoclinic 0-9875:1:0-9348 90 46' 



Here the influence affecting the form of the crystal has 

 changed its system, yet without much alteration in the 

 axial ratio or angle. Here plainly we have to do with di- 

 or tri-morphism, and the morphotropic action has modified 

 the transition temperatures, so that, e. g., with the tetra- 

 methyl derivative at the ordinary temperature the regular 

 form, but with the dimethyl-diethyl derivative the tetragonal 

 form, is the more stable. 



The new researches of Tutton 2 and Muthmann 3 carry us 

 still further in the direction of an insight into the position 

 of the molecules in a crystal. From the latter work we 

 may take some results relating to the tetragonal phosphates 

 and arsenates, whose isomorphism was observed by Mit- 

 scherlich : 



Substance Molecular volumes a : c a c 



KH 2 P0 4 ...... 58-246 1:0-6640 i 0-664 



KH 2 AsO 4 ...... 62-822 1:0-6633 1-026 0-683 



NH 4 H 2 PO t ..... 64-170 1:0-7124 1-009 0-719 



68-842 i : 07096 i 031 0-732 



1 Arzruni, 1. c. 233. 



2 Journ. Chem. Soc. Trans. 1893. 337, 1894. 628, 1896. 344. 



3 Zeitschr.f. KrystaUographie, 1894. 



