This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
Concentrated phosphoric acid, 3 parts mixed with water up to 20 parts; forming a solution corresponding to 10 per cent. by weight of phosphoric anhydride, P2O5, B.P.
Phosphoric acid 20 parts with 80 of water, U.S.P.
reactions. - With ammonio-nitrate of silver it gives a canary-yellow precipitate, soluble in ammonia and in diluted nitric acid. Evaporated, it leaves a residue which melts at a low red heat, and upon cooling exhibits a glassy appearance.
Tests. - It is not precipitated by sulphuretted hydrogen (no metals), chloride of barium (no sulphuric acid), nitrate of silver acidulated with nitric acid (no hydrochloric acid), nor by the solution of albumin (absence of metaphosphoric acid which coagulates albumin). "When mixed with an equal volume of pure sulphuric acid, and then introduced into solution of sulphate of iron, it does not communicate to it a dark colour (absence of nitric acid). Mixed with an equal volume of solution of perchloride of mercury and heated, no precipitate is formed (no pyro-phosphates). Its strength is estimated gravimetrically by ascertaining the increase in weight which occurs in oxide of lead when phosphoric acid is poured on it, evaporated and ignited.
Dose. - 10-30 minims.
Uses. - Phosphoric acid may be used to allay thirst, like other dilute acids, in febrile states, and in diabetes. It may be given in larger doses than other mineral acids without deranging digestion, and is therefore to be preferred to them in cases where it requires to be given for a length of time, as in diabetes and alkalinity of the urine. It is said to be useful in scrofula, and to diminish the growth of bony tumours.