4208. Carbonate of Soda

4208.    Carbonate of Soda. The carbonate of soda of commerce is cither prepared by lixiviating the ashes of sea - weed, or from sulphate of soda. Tho ashes of marine plants have been long an article of commerce, under the names of barilla, barilla ashes, kelp, blanquette, etc., but the carbonate made from them is of a very impure description. That made from tho sulphate is much purer, and, when tho process is well managed, merely contains a trace of sulphuric acid. The sulphate of soda is mixed with an equal weight of chalk and about half its weight of coal, each being previously ground to powder, and the mixture is exposed to a great heat in a reverberatory furnace, and during the calcination is frequently stirred with a long iron rod. The dark grey product usually contains about 22 or 23 per cent, of carbonate of soda. This is now lixiviated with tepid water, and the solution, after defecation, evaporated to dryness, mixed with a little sawdust, and roasted in a reverberatory furnace at a heat not exceeding 700° Fahr., until all the sulphur is expelled. Tho product now receives tho name of soda-ash, or soda-salt, and contains about 50% of alkali. It may bo purified by solution in water, defecation, evaporation, and crystallization; it then becomes commercial crystallized carbonate of soda, consisting of large transparent crystals, which effloresce by exposure to tho air, crumbling into a white dry powder. Tho carbonate used in medicine is prepared from tho commercial crystals by dissolving, filtering, and careful crystallization.

4209. Bicarbonate of Soda

4209.    Bicarbonate of Soda. This may bo prepared from a solution of carbonate of soda treated in tho same manner as for bicarbonate of potassa. (See No. 4183 (Bicarbonate of Potassa).) The U. S. Pharmacopoeia directs carbonate of soda in small pieces to be enclosed in a box (having an air-tight lid, and an inner bottom perforated with holes), and thus subjected, until saturated, to a stream of carbonic acid gas previously passed through water.

Cooley recommends the following process : Mix together 1 part carbonate of soda with 2 parts dried carbonate of soda, both in powder, and suiTound them with an atmosphere of carbonic acid gas, under pressure. Let tho action go on till no more gas is absorbed, which will generally occupy 10 to 14 hours, according to tho pressure employed, then remove the salt and dry it at a heat not above 120° Fahr.

4210. Phosphate of Soda

4210.    Phosphate of Soda. Mix 10 pounds powdered bono ashes with 44 fluid ounces sulphuric acid; add gradually 6 pints water, and digest for 3 days, replacing the water which evaporates; then add 6 pints boiling water, strain through linen, and wash the residue on the filter with boiling water. Mix the liquors, and, after defecation, decant and evaporate to 6 pints; let the impurities again settle, and neutralize the clear fluid, heated to boiling, with a solution of carbonate of soda in slight excess; crystals will be deposited as tho solution cools, and by successively evaporating, adding a little soda to tho mother liquor till it is feebly alkaline, and cooling, more crystals may be obtained. Keep it in closed vessels. (Ed. Ph.)