172 ANNUAL OF SCIENTIFIC DISCOVERY. 



gravity at the same time diminishes ; that of the transparent being 

 about 3.7, and that of the opaque 3.5. The hardness, also, is sub- 

 ject to change ; the glass becoming somewhat pulverulent, so that its 

 fracture is earthy, and the lustre quite wanting. Fuchs, in his work 

 on Amorphism, has thrown out the conjecture that the glassy arse- 

 nious acid loses its transparency by virtue of a gradual change into a 

 crystalline mass. Hauseniann has, however, published the result of his 

 examinations, in which he was unable to detect any trace of crystal- 

 line structure, even when examined under a magnifying power of 400. 

 Professor Jameson, in the Edinburgh Philosophical Journal, April, 

 states that he has recently become satisfied of the truth of Fuchs' con- 

 jecture in the most convincing manner. Masses of transparent arse- 

 nious acid selected for examination, were found, on assuming the porce- 

 lainous structure, to have become highly crystallized, " the sides of the 

 masses being studded with great numbers of distinct, octohedral crys- 

 tals, some of which were half a French line in diameter." Such a 

 transformation of arsenic glass, says Professor Jameson, into a mass of 

 well-formed crystals, is a most remarkable instance of molecular change 

 in a rigid body, and is the more striking, since, apparently, it is not 

 caused by any exterior circumstance, nor is attended by any change 

 of constitution. It would seem that the molecules were put in motion 

 by a tendency of the amorphous mass to pass from the condition of 

 tension to that of repose and equilibrium, which is the characteristic 

 condition of crystallization. This remarkable change also proves that 

 nature can accomplish, in time, what she cannot effect in a shorter 

 space ; a truth deserving to be remembered in all physical inquiries, 

 and especially in geology. Professor Jameson also observes, that in 

 similar masses of arsenic glass there are differences of aggregation, 

 which cause them to differ in their progress towards becoming opaque. 

 On this it may depend, as well as on other determining causes, that 

 generally the amount of change is independent of the length of time 

 elapsed. 



Similar changes in structure are observed to take place in calca- 

 reous minerals, and probably changes of the same description occur in 

 many of the minerals, and also in rocks. Among artificial substances 

 exhibiting such changes, we may particularize the confection called 

 barley-sugar. This substance, when newly prepared, has a pale wine- 

 yellow color, and is more or less translucent. Its fracture is conchoidal, 

 with a shining vitreo-resinous lustre. If kept for a time, its trans- 

 lucency diminishes, and gradually the conchoidal fracture disappears, 

 and in its place the whole mass of the substance assumes a beautiful 

 stellular radiated structure. Geologically considered, this topic is 

 of great importance. Edinburgh Philosophical Journal. 



ARTIFICIAL MARBLE. 



THE following is an account of the experiments and theories of a Mrs. 

 Marshall, of Edinburgh, who has been engaged, with success, in the 

 production of artificial marble, sandstone, conglomerate, &c. 



So far back as 1840, Mrs. Marshall was struck with the odd idea, 



