Should contain 95 per cent. of pure bicarbonate, which it resembles in appearance and tests.

U.S.P. Mistura Rhei et Sodae. Mixture of Rhubarb and Soda. - Bicarbonate of sodium 3, fluid extract of rhubarb 3, spirit of peppermint 3, water q.s. to make 100.

U.S.P. Pulvis Effervescens Compositus. Compound Effervescing Powder. - Bicarbonate of sodium 8, tartrate of potassium and sodium 24, mixed to make a powder of 160 grains; tartaric acid, in separate powder, 35 grains.

Uses. - Bicarbonate of sodium has a slight local irritant action. It may be used as a wash in cases of itching skin-diseases, e.g. prurigo, and as a lotion to eczema. The strength is 2 grains to the ounce, and it is applied like water-dressing.

A solution of this strength when used to rinse the mouth sometimes relieves the pain of toothache, and also relieves headache, either temporal or occipital, depending on decayed teeth, even though no pain should be felt in the tooth itself.

It may also be used to prevent injury to the teeth from acid tonics.

Mixed with tincture of opium, and introduced into the cavity of a decayed tooth by means of a pledget of cotton-wool, it will often arrest the pain of toothache. When swallowed it stimulates the secretion of gastric juice, and is a most efficient remedy when given from ten minutes to half an hour before meals, in cases of atonic dyspepsia, where the patient complains of weight or pain at the pit of the stomach, pain between the scapulae, and much flatulence unaccompanied by constipation. In such cases it is often advantageous to combine it with a bitter tonic and some carminative. As dyspepsia often occurs in persons engaged in business who cannot carry mixtures about with them, the lozenges (B.P.) are very useful, for they can be easily carried about and taken when necessary.

It also relieves frontal headache, unaccompanied by constipation, where the headache is situated just at the junction of the forehead with the hairy scalp. Frontal headache, lower down, just above the eyebrows, is better treated by nitro-hydrochloric acid (p. 576). In persons who suffer from great acidity after meals, it may be used as an antacid. A solution of 1/2 or 1 grain to the ounce of water or milk is exceedingly useful in the diarrhoea and marasmus of infants.

It is also serviceable in cases of diabetes, to lessen the amount of sugar. It renders the bronchial secretion less tenacious, but is not so useful as bicarbonate of potassium. The lozenges are very convenient in such cases.

It seems to have less tendency than potash to produce catarrh of the stomach, and may be used for a longer time (p. 606).

As sodium naturally exists in large quantity in the blood, the amount we can add is but a small fraction of that quantity, and its alterative action is very slight. It will increase the alkalinity of the blood, and has been given instead of bicarbonate of potassium in acute rheumatism, but it is perhaps not so good. The urate of sodium is not so soluble as that of potassium, so sodium is not so good in the uric acid diathesis (Garrod), and its diuretic power is also less.