Pharmacopedia, a commentary on the British pharmacopoeia, 1898 / by Edmund White ... and John Humphrey.

  • White, Edmund.
Date:
1901
Catalogue details

Licence: In copyright

Credit: Pharmacopedia, a commentary on the British pharmacopoeia, 1898 / by Edmund White ... and John Humphrey. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    53/724 (page 29)
    double bond. The same remark applies to the isomerism o the glycende elaidin with olein. Further particulars relating to the constitution of oils will be found in the portion of the monograph on Olea, dealing with fixed oils and fats. Acidum Phosphoricum Concentratum. Concentrated Phosphoric Acid is an aqueous solution of ortho-phos- phoric acid, containing 66-3 per cent. H.PO,. It is made from phosphorus, chiefly by two methods, both of which involve oxidation of the phosphorus. In the direct oxidation process referred to in the Pharmacopoeia the oxygen is derived from the air. (i) When phosphorus is burned in air the main product is the pentoxide, PoO^, known also as phosphoric anhydride, because it combines with water to form phosphoric acid. At the same time there is always formed some of the lower oxide, P^Os, known as trioxide or phosphorous anhydride, because it forms with water phosphorous acid, thus— P2O5 + 3H2O = 2H3PO4 (phosphoric). P2O3 + 3H2O = 2H3PO3 (phosphorous). The formation of ortho-phosphoric acid, H3PO4, does not occur completely when the anhydride is merely added to water, for that body takes up>ucces- sively one, two, and three molecules of water, forming the three acids distinguished by the prefixes meta-, pyro-, and ortho-, the last being the official acid, thus— PaOg + H2O = aHPOg (meta-phosphoric). P2O5 -I- 2H.2O = H4P2O7 (pyro-phosphoric). P2O5 + 3H2O = 2H3PO4 (ortho-phosphoric). The complete hydration of the anhydride to the ortho acid is hastened by boiling, and a little nitric acid also aids the process of hydration, besides providing for the oxidation of any phosphorous to phosphoric acid. Nitric acid is one of the most commonly used oxidising agents. The products of its reduction are volatile, and any excess is easily removed by evaporation. Many other oxidising agents would convert the phosphorous to phosphoric acid, e.g., potassium permanganate. But the reduction products from that compound, viz., the potassium and manganese salts, are not volatile, and could not be easily removed from the phosphoric acid. (2) In the other process for the preparation of phosphoric acid the phosphorus is oxidised by boiling it with fairly strong nitric acid in a vessel connected with a reflux condenser, so that the nitric acid and water which are driven off are con- tinually returned to the flask. The first product of oxidation, phosphoric anhydride, does not actually appear in this process, because it unites at once with the water present to form phosphoric acid. The nitric acid is reduced to nitric oxide, and when all the phosphorus has disappeared the excess of nitric acid left in the fluid is removed by concentration in an open dish. The equation given for this reaction— 3P + 5HNO8 + 2H.,0 = 3H8PO4 + 5NO.