Properties : Sodium phosphate occurs as large, colorless, monoclinic prisms, or a granular, crystalline salt, odorless, and having a cooling saline taste. It is freely soluble in water (1 :5.5), but practically insoluble in alcohol.

Action and Uses: Sodium phosphate is used as a saline cathartic, and its mode of action has much in common with magnesium sulphate and sodium sulphate. It is less disagreeable, but is less active. The acid phosphate NaH2PO is used for the purpose of rendering the urine acid. When the official phosphate is used for this purpose the equivalent amount of an acid, such as dilute hydrochloric or phosphoric, may be administered at the same time to convert it into the acid sodium phosphate.

Dosage: 2 gm. or 30 grains dissolved in warm water. To render urine acid, from 1 to 2 gm. or from 15 to 30 grains of acid sodium phosphate may be given every two or three hours, for five or ten doses until the urine is acid.

It may also be administered in liquid form by adding 4 parts of sodium nitrate, 13 parts of citric acid and a little water to 100 parts of sodium phosphate.

Sodii Phosphas Effervescens.—Effervescent Sodium Phosphate, U. S. P.

A mixture of exsiccated sodium phosphate, sodium bicarbonate, tartaric acid and citric acid, representing approximately 50 per cent, of sodium phosphate described above.

Dosage: 8 gm. or 120 grains.