1086 
In all cases Merck’s pure reagents were recrystallised and used 
in the present investigation. In order to avoid contamination of the 
isomorphous substance with germ erystais of the original substance, 
the isomorphous body was kept in a different room. 
Extreme care should be taken against the inoculation of the 
solutions with germ erystals, and in sealing off the tube care should 
be taken that no erystals are formed due to the evaporation of water. 
In all cases no erystallisation was produced with either calcium 
fluoride or strontium chloride (SrCl,, 6 H,O) though the amount of 
supersaturation was fairly high. 
Rereers (loe.eit) says, “CaF, and CaCl, are both cubic, the former 
being nearly insoluble, the latter extraordinarily deliqueseent. Mixed 
erystals, therefore, cannot be formed from an aqueous solution, yet 
the two compounds are isomorphous. It is quite possible that a 
common solvent might exist from which mixed crystals would be 
obtainable or the latter might be obtained from the fused mixture”. 
SrCl,, 6H,O is well known to be strictly isomorphous with 
CaCl,, 6H,O (cf. Roscor's Chemistry, Vol. IJ (1913) p. 596). Yet 
SrCl,, 6H,O or CaF, cannot release the supersaturation of a solution 
of calcium chloride. 
In Grotn’s “Introduction to chemical Crystallography” translated 
by MarsHarL (1903) the following statement occurs, “copper sulphate 
CuSO,.5H,O is isomorphous with sulphates of Magnesium, Man- 
ganese, Iron, Cobalt, Zine and Cadmium”. 
Pure samples of all these hydrated sulphates were tried for the 
relief of supersaturation of the solution of copper sulphate but 
crystallization began only in the highly supersaturated systems, which 
were rather unstable; in the solutions containing as much as 60°/, 
of the salt in excess, there were no cases of occurrence of crystal- 
lisation by the isomorphous bodies. lt was also observed that in the 
highly supersaturated systems, crystallisation was sometimes induced 
by such substances as (NH,),5O,, K,SO, ete., which were not iso- 
morphous with copper sulphate ; evidently these form unstable systems. 
The solubility data for cobalt sulphate are taken from the work 
of WerzeL (Zeit. Phys. Chem. 52, 395 (1905) |. In the case of 
cobalt sulphate crystals appeared with isomorphous substances only 
when the solution contains more than 70°/, of the dissolved salt in 
excess. Evidently at this stage the supersaturated solution is unstable 
holding such enormous amount of cobalt sulphate in excess. As 
long as the supersaturated solution contained about 60 °/, of the 
dissolved salt in excess, there was no induction of crystallisation 
with the isomorphous substances. 
5] 
