416 Intelligence and Miscellaneous Articles. 



chemists to examine the specific gravity of other oxides at different 

 temperatures, since these changes have an important influence on 

 the atomic volume. This however has not happened, with the ex- 

 ception of a very interesting investigation of Count Schafgotsch, on 

 the specific gravity of silicic acid, in which he has shown that opal 

 heated to redness has so low a specific gravity, that it floats on oil 

 of vitriol ; but that the specific gravity is so increased by heating to 

 redness, that it equals that of chemically-prepared silicic acid (2*2), 

 but which is still considerably lighter than quartz and rock-crystal 

 (2-6). 



The changes which the three metallic acids under consideration 

 experience by heating to redness are far more remarkable. When 

 the hydrate of pelopic acid is deprived of its water by a gentle red 

 heat over a spirit-lamp, just sufficient to produce the phenomenon 

 of incandescence, and then exposed to a strong red heat in a 

 charcoal fire, its specific gravity is considerably increased. If we 

 examine the ignited acid under the microscope, we see that it con- 

 sists for.the greater part of amorphous granules, in which some small 

 crystals are perceptible. The ignited acid was then exposed to the 

 most intense, and at the same time continuous heat that a platinum 

 crucible is capable of bearing, that of tne porcelain furnace of the 

 Royal Berlin Manufactory. The acid was not melted by it, but was 

 converted into a coarse sandy powder, which, examined under the 

 microscope, consisted of large perfect crystals. The specific gravity 

 of the acid however was thereby considerably diminished ; curious 

 enough, it had become still lower than that which the acid pos- 

 sessed after the hydrate had been exposed to a gentle heat over a 

 spirit-lamp in order to expel its water. 



On repeating this experiment, the specific gravity of the crystal- 

 lized acid, which had been ignited in the porcelain furnace, was 

 found to be constant, while by no other temperature could the acid 

 be brought to a constant specific gravity. 



These experiments are in so far remarkable as they prove pre- 

 cisely the contrary of what has hitherto been frequently admitted. 

 . Crystalline bodies, such as vesuvian, epidote and garnet, fuse at a 

 high temperature, become amorphous, but of lower specific gravity. 

 It is evident that what applies to these substances cannot be advanced 

 as a general rule. 



Niobic acid has a far lower specific gravity than pelopic acid. 

 It exhibits a similar behaviour. The acid, exposed to the tempera- 

 ture of the porcelain furnace, appears under the mici'oscope per- 

 fectly crystalline. 



Tantalic acid behaves very different to the other two acids. It is 

 the heaviest of all, and, by heating to redness in a charcoal fire, in- 

 creases considerably in specific gravity, from 7*0 or 7"1 to 8*2. In 

 the fire of the porcelain furnace it is likewise converted into a coarse 

 powder, but which does not appear distinctly crystalline under the 

 microscope. Its specific gravity is thereby only slightly lessened. 



In all these experiments no alteration in the absolute weight was 

 perceptible. — From the Chemical Gazette for September 15, 1846. 



