PHOSPHORIC ACfD.

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acid as fast as it is formed. To fulfil the first of these indications,large quantities of mild demulcent liquids are to be exhibited, so as toenvelop the phosphorus and exclude it from the air contained in thealimentary canal. Magnesia should be given, in order to neutralize thephosphorous and phosphoric acids. Parts burned with phosphorus are tobe washed with a weak alkaline solution, to remove any adhering acidwhich might serve to keep up irritation.

Ac'idum Phosphor'icum. — Phos'phoric Ac’id.

History. —Phosphoric acid was first distinguished by Marggraf , in1740.

Natural History. —(See Phosphorus).

Preparation. —In the London Pharmacopoeia, dilute phosphoric acid(the only officinal form of phosphoric acid) is ordered to be prepared byadding an ounce of phosphorus to four fluidounces of nitric acid, mixedwith ten fluidounces of distilled water, in a glass retort placed in a sand-bath; then apply heat until eight fluidounces are produced. Let thesebe again put into the retort that eight fluidounces may distil, which areto be rejected. Evaporate the remaining liquor in a platinum capsuleuntil only two ounces and six drachms remain. Lastly, add to the acid,when it is cold, as much distilled water as may make it accurately mea-sure twenty-eight fluidounces.

In this process six equivalents or 96 parts of phosphorus react on fiveequivalents or 270 parts of real nitric acid, and abstract fifteen equiva-lents or 120 parts of oxygen, with which they form six equivalents or216 parts of phosphoric acid, while five equivalents or 150 parts of thebinoxide of nitrogen are evolved.

INGREDIENTS REACTING. RESULTS.

r 5 eq. Nitrogen 70?.

5 eq. Nitric Acid 270 } 10 eq. Oxygen . 80S

115 eq. Oxygen . ] 20?

6 eq. Phosphorus. 90S

5eq. Binox. Nitrogen . . 150

•6 eq. Phosphoric Acid . . 216

If strong nitric acid be employed, instead of the dilute acid ordered inthe Pharmacopoeia , the re-action is so energetic that an explosion andcombustion are sometimes the consequence. In such cases some nitrateof ammonia is usually developed: the ammonia being formed by theunion of the nitrogen of the acid with the hydrogen of the water.

Properties. —The aqueous solution of phosphoric acid ( acidurn phos-phoricum dihitum, Ph. L.) prepared as above, is a colourless and odour-less liquid. It possesses the usual characteristics of an acid; that is, itis sour to the taste, reddens litmus, and neutralizes bases. Its sp. gr.,according to Mr. Phillips, is P064. By evaporation it acquires the con-sistence of treacle ( hydrated phosphoric acid) : and when exposed to ahigher temperature, it loses water and becomes pyrophosphoric acid.At a dull red heat a further evolution of water takes place, and a compoundis formed, called metaphosphoric acid: this is fusible, and by cooling con-cretes into a transparent solid, called glacial phosphoric acid.

Characteristics. —If phosphoric acid be saturated with an alkali(soda) so as to form a soluble phosphate, it may be distinguished from all