CRYSTALLISATION OF WATER. G9 



CRYSTALLISATION OF WATER. 



BY W. B. GROVE, B.A. 



''Head before the Societij, vnder the title " Some Phenomena of Ice," 

 March 16th, 1880.1 



The sharp frosts of last winter and the preceding afforded us 

 nnusual opportunities of becoining acquainted with many of the 

 phenomena of ice formation. It may not be known to all the readers 

 of the " Midland Naturalist " that an amorphous, apparently structure- 

 less, block of ice is really a crystalline body ; it is indeed by no means 

 evident at first sight that such is the case. We know that, when a 

 thin film of water crystallises on our window panes, strange and 

 beautiful forms appear, amidst which we can often trace somewhat of 

 regularity and the predominance of that angle of sixty degrees to 

 which a snow-crystal owes its well-known outline, and we might con- 

 jecture (I priori that the crystals of which ice is composed, could we but 

 obtain them perfect, would be seen to be formed upon the same plan. 



It was Professor Tyndall, I believe, who first showed indirectly that 

 such is the case. Everyone who has read his lectures on " The Foi-ms 

 of Water,' or on "Heat as a ilode of Motion," will remember the 

 beautiful experiment by which the intimate structure of ice is revealed. 

 A slab of ice is cut parallel to the plane of freezing, and the concen- 

 trated beaiu of the electric lamp is sent through it. The heat melts 

 the ice in parts, within the block as well as on the surface, the greatest 

 effect being confined to a depth of about one inch. Each hquefied 

 portion in the interior begins as a minute point, which as it enlarges 

 assumes the shape of a six-petalled flower (Plate IN., Fig. 3;) the petals, 

 at first rounded, become gradually more and more pointed and serrated, 

 and at last approach some of the characteristic forms of snow-crystals. 

 These liquid flowers are evidently the cavities previously occupied by 

 those ice-crystals, which for some reason or other have yielded soonest 

 to the influence of the transmitted heat. 



If we wish to reproduce this eft'ect ourselves, we have only to take a 

 piece of clear ice, form it into a slab, the plane surfaces of which are 

 parallel to the plane of freezing, (by sawing it, or by pressing each side 

 alternately on a hot metal plate,) and then expose one of these surfaces 

 to the warmth of a glowing fire. Hold it as close as the hand can bear, 

 and in an instant the previously- transparent ice is clouded with 

 multitudes of minute bubbles (or what appear to be such) and, on 



Refeeexces to Plate IV. 



Fig. 1. Ice-crystal, formed on the sur- | Fig. 4. Hexagonal snow crystal, x 3. 



face' of still water, natural Fi^s. 5 and 6. Liquid discs in ice, x 10. 



size. I Fig. 7. Composite cavity in ice, cou- 



Fig. 2. Snow crystal, magnified. ( tamins air and water. 



Fig. 3. Ice-flowers, x 10. 1 



