S. L. Penfielcl and G. S. Jamieson — Tychite. 223 



for the stability of the compounds. It is possible also that 

 the assumed symmetrical arrangement of the atoms in the 

 molecule is the cause of the crystallization of these compounds 

 in the isometric system, for, as a rule, salts of a highly com- 

 plex nature crystallize in some system other than the isometric. 

 Moreover, if the above formulas are correct, it might be 

 expected that tychite would be more difficultly soluble in 

 water than northupite, for the S0 4 radical uniting the two 

 magnesium atoms would serve, as we might say, to protect the 

 latter from attack, while the sodium atoms could not be taken 

 away without disturbing the equilibrium of the molecule. 

 Perhaps also the union of the magnesium atoms by the S0 4 

 radical in tychite is more difficult to establish than the com- 

 bination of the two chlorine atoms with magnesium in north- 

 upite, which may account for the greater length of time 

 required to make the sulphate compound artificially. 



In these compounds, two chlorine atoms in the one and a S0 4 

 radical in the other play the same role, and are isomorphous 

 with one another in the broader sense of the term, namely, that 

 different constituents may enter into similarly constituted mole- 

 cules without changing the crystalline form. In simple chemical 

 compounds, it is contrary to all experience that a chloride and 

 a sulphate should have the same crystalline form, or be isomor- 

 phous with one another. In the salts under consideration, 

 however, it is assumed that some definite arrangement of the 

 large number of sodium, oxygen, carbon and magnesium atoms, 

 by virtue of mass effect* determines the crystalline form of 

 the compounds, and that the roles played by two chlorine 

 atoms in the one and a S0 4 radical in the other are relatively 

 so unimportant that either of these constituents may enter into 

 the molecule without changing the crystalline form. Whether 

 it is possible to obtain a single crystal containing both the two 

 chlorine atoms and the sulphate radical replacing one another 

 as isomorphous constituents, or to obtain a single crystal with 

 a nucleus of one salt and an external growth, in parallel posi- 

 tion, of the other, we are not as yet able to state, but experi- 

 ments along these lines, to determine to what extent the prin- 

 ciples of isomorphism may be applied to so widely different 

 radicals as Cl 2 and S0 4 under the influence of mass effect action, 

 will be carried on and form the subject of a later communica- 

 tion. In one experiment, in which the attempt was being 

 made to obtain a product containing both Cl 9 and the S0 4 

 radical, a small crop of octahedral crystals was formed which 

 reacted for neither chlorine nor sulphate. In appearance 



* Compare mass effect action as applied to tourmaline (Penfield and Foote, 

 this Journal (4), vii, pp. 122-124) ; also to the alunite-jarosite group of min- 

 erals (Hillebrand and Penfield, this Journal (4), xiv, pp. 216-220). 



