Saline Mixtures

In many prescriptions chemical action is intended, as in the case of saline mixtures, which are extemporaneously prepared solutions of the alkaline acetates, citrates, or tartrates. For example:

Here the prescnber intends the mixture to contain carbonic-acid gas in solution. To get this, powder the carbonate of ammonium and dissolve it and the bicarbonate of potassium in the mortar in 5 ounces of water; add the acid, stir, allow the effervescence to pass off, strain the solution into the bottle, add the syrup to the bottle, make up, and quickly cork. The mixture will not effervesce, but it will have the fresh taste of the free carbonic acid which it contains.

1 Experiments by Greenish and Beesley on solutions of sodium salicylate and sodium bicarbonate tend to show that the presence of sodium sesquicarbonate in sodium bicarbonate is the cause of the coloration, also that absorption of oxygen acts by forming some sesquicarbonate. A grain of sodium hyposulphite per oz. of mixture prevents coloration, and sodium sulphite and bisulphite are equally effectual, as also is formaldehyde. - C. & D. 1915, 1. 231.

Effervescing Mixtures distinct from the foregoing are frequently ordered by medical men, the usual method being to prescribe an alkaline mixture and acid powders, although there are cases in which an alkaline and an acid mixture are sent out together. It is important that the directions should be quite explicit. It sometimes happens that the prescriber leaves the dose of acid to the discretion of the dispenser; if this should occur, the dispenser may put in a slight excess of acid: it improves the taste in most cases. The following are examples of this class of mixture:

One tablespoonful of No. 1 to be taken with two tablespoonfuls of No. 2 twice a day, etc.

It may appear that the prescriber has erred in placing the syrup of lemon in the alkaline mixture, thereby neutralising it, but it will be observed that there remains after the doses are mixed a slight excess of citric acid- viz., 1 1/2 grain in each dose. Prescribers of effervescing mixtures occasionally err in regard to compatibilities, as the following example shows:

of No. 1, with of No. 2, to be taken effervescing at 12 noon and 4 P.M.

To avoid strychnine being precipitated as hydrate in No. 1, the dispenser put the liquor in No. 2 mixture. Alkaloids should always be put in the acid mixture, and if the acid is prescribed in powders in such cases and the alkaline bicarbonate in solution, the dispenser should reverse the order and indicate the change on the prescription.

The directions should be:' Two tablespoonfuls (by measure-glass) every four hours, in water. Add one of the powders, and drink during effervescence.'

The following mixture is an unusual one, and gave rise to some trouble:

The Acid Mixture. The mixture was taken every two hours the first day, and was all right, but on standing over night the last dose had practically lost all its effervescence. The repeat mixture was given twice a day, and after about two doses the same thing occurred- viz., effervescence had ceased. Compound traga-canth powder 3ss. was used to suspend the bismuth subnitrate. The acid mixture is on the lines of a process for making bismuth citrate. The citric acid enters into combination with the bismuth, which, suspended in the mixture by means of compound powder of tragacanth, is in a condition most favourable for obtaining completion of the reaction in a short time; hence the rapid deterioration in the production of effervescence. A little free nitric acid is liberated, but it is insignificant and equivalent to the citric acid. The prescriber was recommended to order bismuth carbonate and put it into the alkaline mixture.

Saturation Equivalents. In round numbers, for purposes of prescribing and dispensing.

This table (compiled by the late Dr. John Attfield, F.R.S.) is read thus: 20 grains of citric acid will saturate 29 grains of bicarbonate of potassium; 20 grains of bicarbonate of sodium will saturate, or be saturated by, 18 grains of tartaric acid; 11 grains of tartaric acid = 8 grains of carbonate of ammonium; 20 grains of bicarbonate of sodium is equivalent to, or will do as much work as, 34 grains of carbonate of sodium; 14 grains of citric acid is as strong as 15 grains of tartaric acid. It is occasionally convenient to double the numbers, halve them, or take some other proportion; also to employ them in weights other than grains.

Lemon-juice contains, on an average, 35 grains of citric acid in 1 fluid ounce, or 4 1/2 grains (nearly) per fluid drachm.

Chlorinated Solutions containing chlorate of potassium, hydrochloric acid, and water are frequently prescribed for scarlatina, and other disorders in which the throat is affected. The object is to make a solution of chlorine according to the old method of the late Mr. Beamish, Covent Garden, viz.:

After the chlorine has been developed, it is well to add about a fluid ounce of the water and shake well to absorb the chlorine.

If the water be poured in right away, a large quantity of the gas is simply displaced and escapes from the bottle. The chlorine is likewise liberated in a dilute solution, but, of course, more gradually, and for this reason it used to be thought that it is intended that chlorine should be slowly liberated.