ANNUAL OP SCIENTIFIC DISCOVERY. 



rarely preserved, and Ehrenberg has detected infusoria in fire-stone with 

 their forms uninjured. Powdered quartz, or fire-stone, resists the action of 

 boiling hydrate of potash, or, after prolonged exposure, is only slightly 

 dissolved, while amorphous siliea is dissolved in considerable quantity. 

 Experiments to produce crystallized silica have only succeeded when the 

 humid method has been tried: among others, Daubree produced well- 

 formed crystals of quartz by decomposing glass by the action of water at 

 a high temperature and under pressure. But no one has obtained crystal- 

 lized silica by the method of fusion, and quartz which has been melted has 

 si specific Gravity of 2.2. Davy, Clarke, Stromcyer, Marcet, and others 

 fused quartz into a clear globule; and more recently, Gaudin and St. Claire 

 Deville have melted considerable quantities of quartz, which they formed 

 into buttons and drew out in threads; but although the quartz had a 

 specific gravity of 2.6 before fusion, after it, its density was reduced to 2.2. 

 M. Rose observes, that it is not likely that the quartz of the granite crys- 

 tallized during a slower cooling, or by the prolonged action of an elevated 

 temperature, because, if such an action had taken place, it would have been 

 irregular in its operation, and where the cooling was accelerated we should 

 expect to find silica with a density of 2.2, which, however, never occurs in 

 any sort of granite. 



Different modifications of silica were exposed to an elevated temperature 

 in a porcelain furnace at Berlin (estimated at two thousand Centigrade 

 degrees) for eighteen hours, and then cooled very slowly. The specimens 

 of silica were placed in platina crucibles, which were in turn placed in larger 

 crucibles of the same metal, contact being prevented by the interposition 

 of magnesia. A rock crystal thus treated was unchanged, except that some 

 small fissures occurred in the side nearest the platina, and which was con- 

 sequently cooled quickest. By exposing a second time some quartz crystals 

 to the action of the furnace, the lower portions of which exhibited a few 

 cracks, the latter were after exposure reducible to a granular state by the 

 action of the fingers. The grains thus obtained were for the most part 

 transparent and crystalline, but some of them were opalized and easily 

 reducible to powder. The coarse powder had a specific gravity of 2.613, 

 thus showing that some weight had been lost. The second portion of these 

 crystals remained uninjured. Rock crystal, reduced to as fine a powder as 

 possible, was then placed in a furnace, and its density was found to be 2.394. 

 By a second exposure it was reduced to 2.329. Black fire-stone, with a 

 density of 2.591, preserved its form after the action of the furnace, but thoso 

 portions in contact with the platina were cracked, and the mass was ren- 

 dered completely white and easily reducible to powder in a mortar. The 

 specific gravity of the whole was 2.218, and of the powder 2.237. By these 

 experiments it was shown that the prolonged action of a high temperature 

 produced different results, according to the mechanical condition of the 

 crystalline silica, and that a temperature insufficient for fusion enabled the 

 crystalline silica to pass into the amorphous state. 



The modification of siliea which has a density of 2.2 is obtained not only 

 by fusion or heating the crystalline form, but when it is melted with alka- 

 lies and precipitated in a gelatinous form. When the gelatinous silica is 

 thorn;: -hly dried, it becomes pulverulent with a density of 2.2 to 2.3. No 

 r!go;o;H line of demarcation can be drawn between the silicates which we 

 sec in li.-miro. and which resist the action of acids, and those which are 

 ;; ; ;>.^i by them. In fact, many of those which huv b-.-oij ranged 



