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XLVI. On some Effects of small Quantities of Foreign Matter on 

 Crystallization. By Chaeles Tomlinson, F.R.S., F. C.S.* 



I WAS interested in reading an account of a lecture by 

 Professor Judd, delivered at the Royal Institution on 

 January 30 last, on some phenomena of crystallization. I 

 was present at the same Institution on one of the Friday 

 evenings upwards of forty years ago, when Professor Faraday 

 performed an experiment which greatly impressed me. He 

 poured water into a test-tube, and added to it an intense 

 colouring-matter, such as sulphate of indigo, and then placed 

 the tube in a freezing-mixture : the water in freezing drove 

 the whole of the colouring-matter into the axis of the tube, 

 so that it could be poured away, and, the cavity being rinsed 

 out, a plug of pure transparent ice, entirely free from colour- 

 ing-matter, was withdrawn. A similar experiment was tried 

 with the addition of sulphuric acid to the water, and in a 

 third experiment of ammonia ; and in these cases also, the 

 water in freezing expelled both the acid and the alkali, so 

 that the ice in each case on being melted could be tested for 

 either with negative results. In order to free the resulting 

 ice from air particles, the contents of the tube were gently 

 stirred with a feather, and reference was made to the rapidity 

 with which melting ice reabsorbs air, a useful provision in 

 the case of aquatic plants and animals, as was recently pointed 

 out, when referring to the necessity of breaking the ice in 

 fish-ponds. 



A few years later, it was noticed that a large block of 

 Wenham Lake ice, when illuminated by the electric light, 

 presented a banded structure, which Faraday explained 

 with reference to the experiments above noticed. Suppose 

 the first layer of water in a still lake to freeze, it would reject 

 any saline or other foreign matter into the layer of water 

 below, and should the temperature continue to fall, the second 

 layer would be unable to reject the particles derived from the 

 first in addition to its own, and so this double set of particles 

 becoming entangled in the ice, would so far alter its structure 

 that it may be called amorphous, while the first layer would be 

 crystalline. As the freezing proceeded, the third layer would 

 be in an analogous position to the first, and the fourth layer 

 would be in a similar condition to the second. In this way 

 we might have alternate bands of crystalline and amorphous 

 ice to a considerable depth. 



Among the Finchley gravels we may sometimes pick up 



* Communicated by the Author. 



