The commercial bicarbonate above mentioned, contains, of course, all the impurities of the carbonate from which it is made, this being an inevitable consequence of the method by which it is manufactured, which, as described in Knapp’s Chemical Technology, is simply to expose commercial crystals of carbonate of soda to the action of carbonic acid gas, which it takes up to the extent of one equivalent, falling into a fine powder, with evolution of heat and loss of water of crystallization. These impurities, in the case of the specimen operated upon by {37} me, were, besides considerable silica, sulphate of soda, chloride of sodium, a trace of phosphoric acid detected by monohydrate of ammonia, and a little organic matter which imparted to the mass a soapy smell.
The sulphate, phosphate and chloride are easily removed by washing with water by decantation, with a loss, however, of at least one half of the material. When the washings, after addition of excess of nitric acid, no longer react with nitrate of silver, or with chloride of barium, the mass is introduced into porcelain dishes, and dried on the sand bath; when dry it is exposed to a high sand bath heat, though not to a red heat, for two or three hours. By this treatment, not only are one equivalent of carbonic acid, and one equivalent of water expelled, but the greater part or the whole of the silicate is decomposed and converted into carbonate, so that a solution of the mass in water will now be found full of flakes of silica.
The filtered solution should now be tested for silica, and if not yet entirely free from it, must be evaporated again to dryness, with addition of lumps of carbonate of ammonia, exactly as proposed by me, in the last article, to separate silica from carbonate of potash. The residue of this last evaporation, on solution in water, filtration and evaporation in platinum, silver, or even clean sheet iron (never in glass or porcelain) dishes, will give pure carbonate of soda, from which may be prepared the pure hydrate of soda, observing the precaution of using lime which is free from silica.
{38}
REMARKS UPON SOME OF THE PREPARATIONS OF THE PHARMACOPŒIA OF THE UNITED STATES, 1851. BY GEORGE D. COGGESHALL.
The Pharmacopœia of the United States is, or should be, to the Pharmaceutist of the United States, his text book and standard. In making its preparations he should not vary from the letter of its directions, unless a change of process effects a quicker, more uniform, or more elegant result; in regard to strength he should not vary at all, except upon distinct understanding with the physician prescribing, or with his customer. It is much to be regretted that perfect conformity throughout the United States, with our National Pharmacopœia should not prevail, so that our citizens, traveling or removing with prescriptions, or copies of them, might not be subjected to inconvenient, and even in some cases to dangerous alterations, impairing confidence in the medicine relied upon, or involving the safety of the patient in using it. With these important considerations in view, the apothecary should, as far as circumstances permit, conform strictly to the acknowledged standard, giving up his own opinions, if need be, for the general good. But strict adherence to the formulæ of our Pharmacopœia seems not to be practicable in all cases, in all localities. When there is such diversity of practice in the City of Philadelphia and in New York, within five hours of each other, with intercommunication five times a day, in each of which the formation and subsequent revisions of the Pharmacopœia have been of such especial interest and attention, how can it be expected that in our widely extended country, in communities diversified almost as much as those of different nations, with many local habits, set by time and many prejudices, a full and uniform compliance with the official standard should prevail.
In New York it would disappoint the physician to put
ss of the officinal Solution of Sulphate of Morphia into a {39} prescription of