FOREIGN CORRESPONDENCE. 
399 
solution of common salt (chloride of sodium) and, after having slightly 
dried it, heats it to a good red heat in a platinum crucible. Soon 
vapours of hydro-chloride acid are given off (showing that the salt is 
decomposed) and silicate of soda is found to have formed in the kaolin. 
This experiment is repeated three, four, or five times, until the kaolin 
no longer decomposes the salt, when the earth is seen to have become a 
granular mass of crystals, easily fusible, and so hard as to scratch glass 
with facility. The same experiment was tried with chloride of calcium 
and chloride of magnesium instead of salt, and with similar results. 
Chloride of magnesium and proto-chloride of iron act with far greater 
ease than common suit. But, as a remarkable exception, chloride of 
potasium gives no result at all. This becomes an extremely interesting 
fact, since M. Delesse has shown formerly that those feldspars, which 
seem to have been produced by metamorphism, are never found to 
contain potassa. 
Sandstones. — One experiment is alone recorded : — The author took a 
piece of sandstone, essentially quartzose, and containing little or no ad- 
mixture whatever — it was the gres cV Orsay, with which the streets of 
Paris are paved. He soaked it alternately with a solution of chloride 
of magnesium and a solution of chloride of calcium, and then submitted 
it to a red heat. Aftei- a certain number of successive imbibitions and 
calcinations, the sandstone was observed to become spungy ; it absorbed, 
without difficulty, a considerable quantity of liquid, and was easily 
pulverized in an agate-mortar. Thus pulverized, it was heated in a 
crucible to a white heat, when it melted, and was transformed into a 
milky mass, composed of numerous long crystalline needles. It had a 
specific gravity of 3 00, was insoluble in acids, and did not contain a 
trace of chlorine. When, analyzed, it gave the composition of amphi- 
bolite or pyroxene, of which it showed the specific gravity. 
Hydrophane is opal (hydrated silica), which has the remarkable 
property of becoming transparent or translucid when placed in water, 
and losing its transparence again when taken out of the liquid. M. 
Langlois* has just produced artificial hydrophane in the following 
* We remember having read in the Comptcs Rend^cs, of the Paris Academy of 
Sciences, a memoir published many yeai-s ago by Ebelman, late chemist of the 
porcelain manufactory of Sevres, where he describes a process by which he produced 
hyalite ; and, if we are not mistaken, hydrophane also. We will turn again to 
this memoir at the first opportunity. — T. L. P. 
