48 On Change of State : Solid-Liquid. 



it does not wet. 1 think, then, we ought to expect its tempe- 

 rature to rise, as Dr. Carnelley has apparently found to be the 

 case. 



Dr. Lodge has pointed out ('Nature/ Jan. 20, 1881) that, 

 as far as we know, " there is no definite subliming-point for a 

 solid, any more than there is a definite evaporating-point for a 

 liquid." Hence, with such a mode of supplying the heat as 

 above described, the temperature might perhaps be expected 

 to rise to that of the last isothermal which reaches the line of 

 no pressure. When it has reached this point the whole will be 

 in an unstable state, and we might expect a further supply of 

 heat to cause a sudden change into water. If, however, at 

 any point in this process of raising the temperature the vapour- 

 tension is allowed to rise nearly to its maximum, it will exceed 

 that of water, which has a lower maximum ; then a layer of 

 water will be formed on the ice, and we shall have melting 

 with a tendency of the temperature towards 0°. 



The Sealing-wax Tgj?e of Melting. 



We have seen that there is some reason to suppose that ice 

 would pass gradually into water at a sufficiently low tempe- 

 rature and with sufficiently high pressure ; that is, there 

 would be no abrupt change of volume at a constant tempera- 

 ture, and no definite latent heat. But these are just the cha- 

 racteristics of the melting of substances of the sealing-wax 

 type ; and I think it exceedingly probable that we have such 

 substances at temperatures below their critical points, or at 

 least that they are analogous to water-ice below its critical 

 point. If sealing-wax have a critical point, then if we start 

 with some in the solid state at ordinary temperature, and 

 while raising the temperature we increase the pressure so as 

 always to keep it solid till above the critical point, if we 

 reduce the pressure again to a certain point and at the same 

 time a small amount of liquid sealing-wax be introduced, we 

 ought to have a liquefaction of the whole with a finite expan- 

 sion of volume ; that is to say, we should have changed the 

 ordinary sealing-wax type of melting into the ice-water type. 

 It might, perhaps, be possible to test the truth of this suppo- 

 sition experimentally. 



