12 Strom EYKR, TJi-: Formation of Minerals in Granite. 



surface tension, and, although an estimate as to the 

 internal pressure in one of these water globules, if only one 

 hundred thousandth of an inch in diameter, could not 

 account for a material lowering of freezing temperature, 

 it must be remembered that surface tension is a misnomer 

 when a[)plicd to very small bodies, and that in a small 

 globule of the above size the molecular forces tending to 

 compress it do not act only on its surface but also across 

 its diameter.* In any case it is evident that when water 

 is reduced to drops of very small diameter it behaves as if 

 it were subjected to an enormous pressure, and lowers its 

 freezing point considerably. We thus have a means of 

 obtaining some information as to the influence of pressure 

 on the melting temperature of minerals; all that is necessary 

 is to measure the differences of the melting temperatures of 

 small but different sized beads of minerals, and then 

 ascertaining their diameters and shapes when cold. 

 Possibly, too, the difference of density of the original 

 specimens of minerals and of the resultant beads will 

 show itself b\' affecting the melting temperature. All 

 this could be done in Prof Joly's Meldometer. 



The determination of the latent heat of melting, 

 another necessar\' element, should not be a very difficult 

 matter, but it is unnecessary unless there is a good 

 prospect of finding the changes of volume. The following 

 concluding considerations as to the bearing of this sug- 

 gestion will show its importance to geologists and 

 mineralogists. 



There exist amongst the porphyretic granites, quartz- 

 porphyry in which the (juartz crystals are large and the 



•Clerk Maxwell, in his article on " Capillary Action," in the Eticy. 

 Brit., mentions that the molecular pressure for water is 5,cxx) atmospheres. 

 If correct, then infinitely small water globules would not freeze until 4o''C. 

 has been reached. 



