265 



However Barker and Marsh 1 ) have recently drawn attention 

 to the fact that among these substances there are a number, 

 which ^li.mld have binary helicoidal axes, especially those belong- 

 ing t> tin rhombic and monoclinic system. Such assemblages 

 should only exhibit true enantiomorphism if the constituting 

 units of the structure have themselves a non-superposable sym- 

 m<tiv 2 ). According to these authors, this will apply to such cases 

 as sodium-chlorate and -bromate, because their heteropolar ternary 

 axes are always combined in pairs. They conclude from their 

 reasonings that molecules such as NaCl0 3 , Mg S0 4 -f 7 H t O, etc., 

 must themselves have an enantiomorphous configuration. 



To gain such a conception of the stereometrical configuration 

 of inorganic salts such as the above mentioned, the authors take 

 into account Werner's co-ordination-schemes. As might be expected 

 in advance however, they only succeed in finding such stereo- 

 chemical formulae in a few cases ; thus in the case of magnesium- 

 sulphate (+ 7# 2 0), and of sodium-chlorate, while in far the most 

 cases too little is known about the true constitution of the salts 

 considered, to make such an attempt successful. Even in the 

 case of the two salts mentioned, their suppositions seem rather 

 hypothetical: thus for magnesium-sulphate + 7 H Z 0, one of the 

 seven molecules must be considered as ,, constitution "-water, and 

 the oxygen-atom is thought always to take the place of two 

 co-ordination-loci, being in their opinion a substitute of a dyad 

 character. When the atom is thought to be in the centre of eight 

 co-ordination-places, divided in space as the corners of a cube, 

 they demonstrate that of the three possible arrangements for 

 the atom -complex : (SO 4 , H 2 O)", two will have the symmetry C% 

 and S, (I and //: fig. 169) but only one that of the axial group 

 D 3 ; III in fig. 169. 



In their opinion, to (MgSO^,H z O) + 6 H.f) could therefore only 

 be attributed the configuration ///; and in an analogous way 

 they deduce for the C10 3 -, resp. BrO' 3 -ion a configuration quite 

 analogous to that of Werner's tri-ethylenediamine-sa\is (D 3 ), in 



apparently the same way as the binary system built up from the components: 

 solvent + sodium-chlorate. This is valid, however, only for that one, singular 

 point of the system, and only for a definite temperature and pressure. 



1) Th. V. Barker and J. E. Marsh, Journ. of the Chem. Soc. London 103. 

 837. (1913). 



2) Cf.: St. Kreutz, Elemente der Krystallstruktur, /. p. 83,90. (1915). 



