SOLIDS, LIQUIDS, AND GASES. 297 



A rather complex theory has been propounded to explain this 

 change the theory of revelation i.e. re-freezing ; a theory which 

 assumes that the pressure first thaws a film of ice at the surfaces of 

 contact, and that presently this re-freezes, and thus effects a healing 

 or general solidification. Faraday found that two pieces of ice with 

 moistened surfaces united if pressed together when at just about the 

 temperature of freezing, but not if much colder. Tyndall has further 

 illustrated this by taking fragments of ice and squeezing them in a 

 mould, whereby they became a clear, transparent ball, or cake. 

 Schoolboys did the like long before, when snowballing with snow at 

 about the thawing point. Such snow, as we all remember, became 

 converted into stony lumps when firmly pressed together. We also 

 remember that in much colder w r eather no such cohesion occurred, 

 but our snowballs remained powdery in spite of all our squeezing. 



I am a sceptic as regards this theory of regelation. I believe that 

 the true explanation is much simpler ; that the crystals of snow or 

 fragments of ice in these experiments are simply welded, as the smith 

 unites two pieces of iron, by merely pressing them together when they 

 are near their melting point. Other metals and other fusible sub- 

 stances may be similarly welded, provided they soften or become 

 sufficiently viscous before fusing. 



Platinum is a good example of this. It is infusible in ordinary fur- 

 naces, but becomes pasty before melting, and, therefore, one method 

 adopted in the manufacture of platinum ingots or bars from the 

 ore is to precipitate a sort of platinum snow (spongy platinum) 

 from its solution in acid, and then compress this metallic snow in 

 red-hot steel moulds by means of pistons driven with great force. 

 The flocculent metal thus becomes a solid, coherent mass, just as the 

 flocculent ice became coherent ice in Tyndall's experiment or in 

 making hard snowballs. 



Wax, pitch, resin, and all other solids that fuse gradually, cohere, 

 are weldable, or, in very plain language, " stick together, " when near 

 their fusing point. 



I have made the following experiment to prove that when this so- 

 called regelation of snow or ice-fragments occurs, the ice is viscous 

 or plastic, like wax or pitch. A strong iron squirt, with a cylindrical 

 bore of half an inch in diameter, is fitted with an iron piston. This 

 piston is driven forth by a screw working in a collar at one end of 

 the squirt. Into the other end is screwed. a brass nozzle with an 

 aperture about one twentieth of an inch diameter, tapering or open- 

 ing inward gradually to the half-inch bore. 



Into this bore I place snow or fragments of ice, then holding the 

 body of the squirt firmly in a vise, I work the lever of the screw, and 

 thus drive forward the piston and crush down the snow or ice-frag- 

 ments, which presently become coherent and form a half -inch solid 

 cylinder of clear ice. Applying still more pressure, this cylinder is 

 forced like a liquid through the small orifice of the nozzle of the squirt, 

 and it jets or spouts out as a thin stick of ice like vermicelli, or the 

 "leads" of ever-pointed pencils, for the moulding of which the 

 squirt was originally constructed. 



I find that ice at 32 can thus be squirted more easily than bees- 

 wax of the same temperature, and such being the case, I see no 

 reason for imagining any complex operation of regelation in the case 

 of the ice, but merely regard the adhesion of two pieces of ice when 



