the Amorphism of Solid Bodies. ggy 



change into both conditions. Of some, especially of those ex- 

 isting in a state of powder, we cannot with certainty say to 

 which class they belong. Uncrystalline bodies are produced 

 by the dry as well as by the moist method. All, however diffe- 

 rent they are in regard to material substratum, have, like all 

 liquids, nearly the same appearance, in whichever of the two 

 modes they may have been produced. All possess only sino-le 

 refraction. The formation of bodies having a regular figure has 

 for a long time been termed crystallization. In the production 

 of bodies without form, we can distinguish the vitrification when 

 they are produced in the dry way, and the coagulation when in 

 the moist way. These expressions have been long in use, but 

 no correct and clear ideas were connected with them. Opal is 

 one of the bodies formed by coagulation, and is often met with 

 quite soft in the beds in which it occurs. I Avill now mention 

 the most remarkable amoi-phous bodies, and at the same time 

 make the necessary observations. 



Common glass deserves to be first noticed, as a perfectly 

 formless body. It is equally devoid of traces of crystal- 

 lization as the opal, and has, in common with that mineral, 

 single refraction. Most glass, however, is also capable of crys- 

 tallization, and then usually forms a crystalline mass, which 

 is no longer transparent, but is only more or less translu- 

 cent, since it consists of a mass of innumerable minute crys- 

 tals. It is only necessary for me to mention here Reaumur's 

 porcelain. This alteration of glass, termed devitrification (ent- 

 glasung), occurs not unfrequently in the manufacture of glass, 

 and often causes great difficulty. It happens especially when 

 the mass of glass has a very complicated composition, and is 

 very easily rendered liquid. The separate crystals sometimes 

 met with in glass, are generally needle-shaped ; but I have seen 

 some of them having distinctly the form of four-sided prisms 

 and square pyramids. The name of glass is no longer proper 

 for such crystalline masses : our never-to-be-forgotten Frauen- 

 hofer named them glass-stones ; and generally they are called 

 devitrified glass. The glass-aone is distinguished from glass, 

 not only by possessing form, but also by other properties, ha- 

 ving a greater degree of hardness than common glass of the 

 same compo.sition, a different specific gravity. Sec. 



We may assume that glass and glass-stone differ in the same 



