SOME RECENT RESEARCH UPON THE 
BIRTH AND: AFFINITIES OF CRYSTALS? 
By PROFESSOR H. A. MIERS, D.Sc., F.R.S. 
Tue main facts concerning the growth of crystals are familiar 
to all, and do not require more than the briefest statement. A 
saturated liquid solution of any substance, A, in any other, B, 
is a mixture of A and B in the liquid condition, such that if a 
solid crystal of A be immersed in it the crystals will neither 
grow nor dissolve. If the solution be ever so slightly weakened 
by addition of B, the crystal will begin to dissolve till equilibrium 
is restored ; the same effect is in general produced by slightly 
warming the solution. If, on the contrary, the liquid be ever so 
slightly supersaturated by removal of B (e.g. by evaporation), 
the crystal will begin to grow till equilibrium is restored ; 
the same effect is in general produced by slightly cooling the 
solution. 
The solubility or freezing-point curve, SS (fig. 1), gives the 
temperature at which a series of the solutions of different 
strengths are saturated. It may be experimentally determined by 
immersing a minute crystal fragment of A in each solution as it 
cools, and noting the temperature at which the fragment neither 
grows nor dissolves. If the solution be cooled below the 
saturation temperature without the insertion of A, and if it be 
protected from agitation and from exposure to the air, it may 
often be preserved for a long time in the supersaturated con- 
dition without crystallising. Its behaviour is in this respect 
similar to that of a simple liquid supercooled below its freezing 
point ; the latter can also be preserved for a long time in the 
supercooled condition without crystallising. The insertion of 
a fragment of the solid crystalline substance in either at once 
1 This paper embodies the substance of two lectures delivered at the Royal 
Institution on April 11 and 18, 1907. 
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