25. Some Notes on Mineralogy: Isomorphism between 
Anthydrite and Barites. 
By Proressor E. SoMMERFELDT, PH.D., F.C.S., F.G.S. 
There had been doubts up to the present, if the mineral 
barites and anhydrite are isomorphous, as the crystallographic 
symmetry of both is the same, but as the difference of corres- 
ponding anglesis very great. The artificially made crystals may 
e is no doubt that mixed crystals of the two sulphates 
are to be found, and if all such two substances are called isomor- 
phous then anhydrite and barites are isomorphous. But one 
must not rely on this condition alone. 
The supersaturation of a solution can be removed by a 
trace of the dissolved substance and by a trace of any isomor- 
phous substance: that gives a method investigated by Ostwald 
for recognising isomorphism, I made experiments by adding 
a trace of anhydride to a supersaturated solution of barites 
in sulphuric acid and watched the time necessary for crystallisa- 
tion, but no acceleration could be found if such nuclei were 
added or not. 
) 
perhaps another modification of lime sulphate, unknown yet, 
may be isomorphous with barites. 
