OCR Text |
Show PRICKLY SALTWORT. PRICKLY SALTWORT. 952 over it Then put the concrete potash into a jar, and pour in it; the sulvery strong alcohol; the potash alone dissolves and phate and muriate of potash, with the portions of earth whichit or , retains ately even of carbonic acid, which it obstin mayhave acquired fromthe air during the evaporation, remain at the bottom of the solution. Afterwards decant the pureliquor, anddistil it in a retort till it becomes colourless. It must then be evaporated in a silver bason. On cooling, it crystallizes in white lamine, which are sometimes three-tenths of aninch in length: or, instead of suffering it to crystallize, it may be evaporated to dryness. 2. Lowitz has given another method*. According to this chemist, the whole ofthe operation for obtaining potash ofthe greatest purity, and without the least colour, consists in this ; A lixiviumof potash, freed from carbonic acidin the usual manner, is evaporated to a thick pellicle. After the cooling, the foreign salt which has crystallized is to be separated, and the evaporation of the lixivium continued in anironpot. During this second evaporationthe pellicle of foreignsalts, particularly of carbonate of potash, which continues to be formed, must be carefully taken off with an iron skimmer. Whenno more pellicle is formed, and the matter ceases to boil up, it is removed fromthe fire andsuffered to cool, continually stirred with aniron spatula. It is then to be dissolved in double the quantity of cold water, and the solution filtered, and evaporated in a glass retort, till it begins to deposit regular crystals. If the mass should consolidate ever solittle by cooling, a small quantity of water is to be added, and it must be heated again to render it fluid, After the formation of a suflicient quantity of regular crystals, the fluid, which is very brown, is to be decanted, and thesalt, after being suffered to drain, must be redissolved in the same quantity of water. The decanted fluid must be kept in a well-closed bottle, and suffered to become clear by subsiding during several days. lt must then be decanted for a second eva= poration and crystallization. The process must be repeated as 253 The greatest difficulty of this process arises from the facility with which the fluid assumes asolid form. To obviate this inconvenience a small portion of it may be concentrated to the point at which it becomes converted into a solid mass by cooling. Thesaturation of a lixivium considerably evaporated may be ascertained by throwing small pieces of this mass into it during its cooling. When these are no longer dissolved, it is a proof that it is at the required point. With regard to the foreign salts which are mixed with the potash, the greatest portion separates bycrystallization after the first evaporation. The rest is separated during the second con- centration by the continual skimming of thepellicle. The little which may remain with the potash must precipitate for want of water of solution, in a lixivium, wherein the alkali itself is no longer dissolved but by its own water of crystallization. Potasu, AND SiLex (Flint), rorm Gass. If potash and silex are fused together, a combinationis obtained known underthe name of glass. This product differs according to the quantities of silex and potash of which it is composed. If three or four parts of potash be fused with one of silex, the result will be a soft brittle kind of glass, which is soluble in water. This solution is called liquidsiliceous potash, or improperly liquid of flints. To prepare this liquid, take one part of silex, reduced to a fine powder (or pure sand), and three or four parts of potash ; put these two substances into a crucible, which must be onlyhalf filled, and place the crucible in the fire. As soon as the matter enters into fusion it puffs up considerably, and continues to swell till the alkali has dissolved the silex. The crucible is to be kept Uncovered as Jong as the effervescence lasts; but whenit is over cover the crucible, and augment the heat till the whole fuses quietly. The contents are then poured out ona dryiron plate or stone; the matter as it cools becomes hard, and assumes the appearance of glass. long as the crystals afford, with the least possible quantity of wae ter, solutions perfectly limpid. served in well-closed bottles, ‘hese solutions are to be pre- to defend them from the access of air. pat * Nicholson's Journal, yol. i, p. 14. Naturay History oF Sona. The name of soda is given to the next alkali, which greatly resembles potash. Hitherto we are not better acquainted with the nature of soda than with that of potash, being equally uneer- |