410 Transactions.— Chemistry. 
a useful contribution to those who have taken this question as an especial 
subject for research. 
These results are : — 
lst. That crystals of the common hydrated sulphate of copper, epsom 
salts, nitrate of baryta, borax, and glauber salts, after being sluiced with 
water, and while still wet all over, do not act as nuclei in a super-saturated 
solution of sodic acetate when applied thereto. 
2nd. That on the other hand a crystal of sodice acetate similarly treated ` 
(as above) does act as a nucleus with such solutions. 
9rd. That chloride of sodium does not when sluiced and mixed while 
wet with a super-saturated solution of alum, aet as a nucleus thereto, but 
that a crystal of alum similarly treated does. 
4th. That the formation of solid sulphate of baryta formed in any of 
the super-saturated solutions of a sulphate (by adding baric-chloride thereto) 
is not attended or followed upon by the erystallization of such solution. 
5th. That the electro-deposition of copper in a super-saturated solution 
of either sodie acetate or alum (charged feebly with cupric sulphate) is also ` 
unattended by crystallization in either case. 
These results show that only those salts* which are of the same kind as 
that of the super-saturated solution, are nuclear thereto, and they also tend 
to show that solids having no affinity for water have not any nuclear effect 
in such solutions, not even when applied thereto as freshly prepared, per- 
haps I may correctly say in a nascent state. ; 
It will be seen, therefore, that so far as these results are indicative of 
anything at all, their general character is such as to sustain De Gernez1 
in his assumption that ** sudden crystallization of a super-saturated solution 
is in all cases induced only by contact with a crystal of the same salt" 
(allowing, of eourse, that he excludes from his cases those of the oils and 
alcohols, also salts, having notable affinities for water); and so far they are 
antagonistic to the results of J eannel, as stated in the same work, viz., that 
any solid substance applied to such a solution of sodic-acetate causes crystal- 
lization, and so tends to upset the theory by which he seeks to explain the 
phenomena in question. 
À due consideration of all whieh has been now advanced on this subject 
will, I think, have the effect of inclining you strongly to the following 
general deductions which I draw therefrom :— 
l. That the only substance which acts directly upon a super-saturated 
solution as a nucleus, is a salt of the same kind as that of such solution, 
* Only those salts are indicated here which have feeble affinities for water; it is 
always understood, I believe, that those having strong affinities for it are left out of the 
t Watts’ Dictionary of Chemistry, Vol. V., p. 350. 
