232

REMARKS.

ford, with the least possible quantity of water, solutions perfectlylimpid. These solutions are to be preserved in well-closed bot-tles, to defend them from the access of air.

The greatest difficulty of this process arises from the facilitywith which the thud assumes a solid form. To obviate this in-convenience, a small portion of it may be concentrated to thepoint at which it becomes converted into a solid mass by cool-ing. The saturation of a lixivium considerably evaporated maybe ascertained by throwing small pieces of this' mass into it dur-ing its cooling. When these are no longer dissolved, it is aproof that it is at the required point.

With regard to the foreign salts which are mixed with thepotash, the greatest portion separates by crystallization after thefirst evaporation. The rest is separated during the second con-centration by the continual skimming of the pellicle. The littlewhich may remain with the potash must precipitate for want ofwater of solution, in a lixivium, wherein the alcali itself is nolonger dissolved but by its own water of crystallization.

REMARKS.

The property of alcalies to dissolve in highly rectified alcohol,with the exclusion of every foreign salt, would afford an excel-lent means of obtaining potash very pure, if their mutual actiondid not afford a new source of impurity. For when an alcali ab-solutely pure and crystallized is dissolved in spirit of wine, evenwithout heat, the fluid assumes a very brown colour, which be-comes still deeper after being decanted from the saline mass.

The crystallization of potash is very different, accordingly asthe crystals are formed with cold or heat. In the first case, thecrystals obtained are'octahedra in groups, which contain 0.43water of crystallization, and excite by their solution in water,even in the summer, a degree of cold very near the point ofaqueous congelation. In the second case, very thin crystallinetransparent blades of extraordinary magnitude are formed, which