SOME RECENT RESEARCH UPON THE 

 BIRTH AND AFFINITIES OF CRYSTALS 1 



By PROFESSOR H. A. MIERS, D.Sc ., F.R.S. 



The 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. i), 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 u and 18, 1907. 



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