975 
crystallization but also, in the ease of crystals belonging to other 
than the holohedral elass of any system, that is, crystals showing 
less than the full symmetry of the system, the particular variety 
must be the sanie. 
J. M. Thomson (Zeit, für Kryst. 1881 6, 94) showed that strict 
isomorphism was essen tial in the erystal gerrn and that the internal 
structure of the germ must be similar to that of the dissol ved 
substance. 
Up till now this has been accepted by all scientists. Thus Tutton 
in his large volume on Crystallography (1912) States: — “The state 
of supersaturation can be removed not only by the agency of solid 
germs (excessively minute crystals) of the dissolved substance itself, 
but also by the action of solid germ crystals of a substance isomorphous 
with it and possessing close similarity of molecular volume and of 
the molecular distance ratio”. 
Moreover, the power of the release of supersaturation has been 
adopted as one of the tests tbr the determination of isomorphism. 
In this investigation on many isomorphous substances it will be 
shown that the above test is not generally applicable. 
Hydrated calcium chloride (OaCl a , 6 H 3 0) is well known to be 
isomorphous with stronfium chloride (SnCl 3 , 6 H 2 0) but the release 
of a supersaturated solution of calcium chloride cannot be effected 
by strontium chloride. 
Also Rhtgers (Zeit. Phys. Chem. 1889, 3, 289, 497 ; 4, 599) from 
other evidences has shown that calcium fluoride is isomorphous 
with calcium chloride but it will be seen that calcium fluoride 
cannot release the supersaturation of a solution of calcium chloride. 
Experimental Procedure. 
A bulb was blown at one end of a clean piece of soft glass 
tubing of length of about 12 cms. and of interna! diameter of about 
10 mms. A little constriction was made near the open end of the 
tube in order to facilitate its sealing off. The bulb tube was carefully 
cleansed and well steamed and then dried in an air oven. Now the 
tube was weighed (coj and then a weighed arnount of the substance 
(u) 2 ) in question was poured upon a small funnel held at the open 
end of the tube. By small additions of water the salt was completely 
dissolved and the funnel was washed. 
The tube was now heated to boiling of the solution over a Bunsen 
flame for some minutes and by some trials it could be ascertained 
that a supersaturated solution is obtained. 
