Scale preparations are not difficult of solution, tartarated iron and sulphate of beberine being among the least soluble. Do not shake scale preparations with a solvent, as an abundant and persistent froth is in most cases formed. The following examples of mixtures containing scale preparations show the difficulties which may arise and how to deal with them:

Dissolve the fern et quininae cit. in 2 ounces of water, and the other ingredients, with 2 drachms of acacia mucilage, in the remainder; mix with gentle agitation.

The solution of the ferri et am. cit. is troublesome; it should be dissolved in a test-tube, with a drachm of water, over a spirit-lamp. If the mixture is not wanted immediately, the ammonio-citrate will dissolve if added last to the other ingredients contained in the bottle, this being laid on its side; with an occasional shake, in less than half an hour it will be dissolved. Ferri et quin. cit. is sometimes prescribed in this form, and the same procedure is to be adopted.

Ferri et ammonii citras varies considerably in solubility- that is to say, some specimens give perfectly bright solutions which show no deposit after standing for days, while others show a deposit in a few hours. This is due to the heat of scaling, and it is entirely avoided by using the solution of the compound unscaled, so that 4 fluid parts represents 1 part of the scaled compound. The scales also vary in reaction, sometimes being so acid as to give a solution which effervesces briskly with bicarbonates. In effervescing mixtures containing ammonio-citrate the acid should be put with the scale compound. If citric acid is prescribed, it is advisable to heat the mixture containing it until the brown colour changes to green. This change occurs in a few days, and might alarm the patient, so that it is as well to carry it out before the mixture is dispensed. Tartaric acid does not act in this way. The varying reaction of ammonio-citrate of iron is well exemplified in the following:

Sometimes this has in it quite a copious precipitate of ferric hydroxide, which dissolves on the addition of a few grains of citric acid. With a markedly acid scale there is no precipitate.

Even with perfectly neutral citrate of potash there is a considerable deposit of quinine citrate in this mixture. The addition of a few grains of citric acid produces a perfectly clear mixture, but even with that quinine citrate gradually crystallises out, adhering to the sides of the bottle. This phenomenon is now known to dispensers as 'salting out,'which is a convenient phrase for.explaining that some salts neutralise the solvent action of ammonium citrate on quinine citrate, which per se is a feebly soluble salt(1 in 1,000). Perhaps the 'salting-out' process is not observed by the dispenser, as it takes some time, but prescribers should be advised to omit alkaline citrates from such mixtures.

The liq. amnion, acet. in I. should be distinctly acid, otherwise quinine hydrate will be precipitated. If II. is compounded in the order of the ingredients-the citrate being dissolved in a little of the infusion-the tincture precipitates a little of the quinine as tannate, and the phosphoric acid throws out a portion of the iron as phosphate.

No plan can be adopted for preventing precipitation of the quinine in III. The best results are obtained by dissolving the citrate in 1/2 ounce of water, and mixing it with the tincture. Dissolve the ammonium carbonate in the rest of the water and mix the two solutions, pouring the citrate solution into the ammonia one. The addition of a little mucilage to the ammonia solution before mixing prevents the quinine adhering to the bottle. Compounded in different ways, IV. varies in colour each time, the precipitate varying in bulk according to the methods of compounding; it also varies in character, being fine, coarse, or curdy. The more bulky the precipitate the lighter in colour is the mixture when shaken up. The bulky precipitate, however, is not the finest. The finest is obtained in this way: Rub up the ferri tart. and quinine sulphate together, add the syrup of lemon gradually with trituration, then the solution of strychnine and the water, lastly the spirit of chloroform.

In the case of a, rub down the tartrate to powder in a mortar and stir with 3 ounces of the peppermint-water. By attempting to dissolve it along with the bromide an insoluble coating is formed on its surface, and solution is very much retarded. Prescription b yields a precipitate of cream of tartar contaminated with iron.