452 



separate into the original plates, and which may be worked, and even 

 cut with a diamond, as if the whole had originally been a single mass. 

 In some specimens which I have examined, with the surface of one 

 plate were incorporated portions of another, the surfaces of fracture of 

 which were alone exposed, its substance having been torn through in 

 the effort to separate the united plates by mechanical force*. The 

 same effect took place in some experiments by Clement Desormes. 



I assume it to be highly probable that the process by which the 

 two plates of glass become one, is, in reality, analogous to that of 

 regelation in ice, and finally dependent on the same principles, 

 whatever their true character may be conceived or shall ultimately 

 be determined to be. To this it may be objected, however, that 

 there is no evidence, in the case of the glass, of the previous lique- 

 faction, or even approach to liquefaction, of the surfaces which 

 become united so as entirely to disappear (or, more properly speaking, 

 to be altogether obliterated), and that the phenomenon is referable 

 simply to the homogeneous attraction of the molecules of one plate for 

 those of the contiguous one, the evenness of the two polished sur- 

 faces allowing them to he brought within a very minute distance of 

 one another. But two remarkable facts greatly diminish the weight 

 of this objection, if, indeed, they do not entirely remove it. First, 

 unpolished plates of glass have no tendency to unite ; the hard and 

 compact siliceous film, to which Prof. Faraday, regarding glass " as 

 a solution of different substances one in another,' 5 long ago referred 

 its power of resisting agents generally f, and which previously bound 

 together the outer molecules of each plate, must be removed by 

 grinding and polishing, so as to render the actual surfaces of contact 

 those of portions of the glass the chemical nature and condition of 

 which are such as readily to admit of their rapid mutual action and 

 union into one mass. Secondly, the polished plates sometimes have the 

 forms and configurations of the surfaces of straw and other packing- 

 materials impressed upon them (portions of straw, paper, &c. some- 

 times adhering inseparably to the glass, after having been taken to 



* These and other facts of a similar nature I adduced as illustrative of the phy- 

 sical nature of glass, in lectures on that substance delivered before the Pharma- 

 ceutical Society of London in the year 1845. See Pharm. Journ. vol. v. (Oct. 

 1845) pp. 157-160. 



t Phil. Trans. 1830 ; Exp. Res. in Chem. and Phys. p. 282. 



