"Take of common sulphuric acid, one pound. Put it into a white glass retort, and have fitted to it a receiver of the same description, and luted; distil over one twelfth of the quantity in the retort, and reject it as watery. Having again fitted the receiver, distil to dryness.

"It is necessary to place a portion of platina in the retort to prevent the boiling from becoming too vehement.

"The specific gravity of this acid should be to that of distilled water as 1845 to 1000.

"It must be kept in closely stopped vessels."

This operation is seldom requisite for the purposes of medicine. Sulphuric acid, except for pharmaceutical purposes, is always employed in its diluted state; and the addition of the water requisite throws down any sulphate of potassa, or of lead, which the strong acid may contain. If it be filtered, and boiled to expel the water, a very pure acid is procured. In this state it consists of 1 eq. of the anhydrous acid = 40.1 +1 of water = 9, making the equivalent 49.1.

Acidum Sulphuricum Dilutum. Lond. Diluted Sulphuric Acid

"Take of sulphuric acid a fluid ounce and a half; distilled water, fourteen fluid ounces and a half. Add the acid gradually to the water, and mix."

Edinburgh.

"Take of sulphuric acid, one part; water, seven parts: mix them."

Dublin.

"Take of pure sulphuric acid, one part; distilled water, seven parts. Add the water gradually to the acid. The specific gravity of this acid is, to that of water, as 1084 to 1000."

Syn. Acidum Vitriolicum dilutum, P. L. 1787. Acide Sulphurique etendu d'eau (F.), Verdilunte Schwefelsaure (G.), Verduuntes Zwavelzuur (Dutch), Acido solforico diluito (I.), Zakab (Arab.).

It is very much to be regretted, that the London College, when it altered the proportions of acid and water in this mixture, from those in the edition before the last of its Pharmacopoeia, did not adopt the proportions ordered by the two other colleges, so that, in this preparation at least, a standard strength might have been fixed for the whole kingdom. The reasons which induced it to adopt the present proportions are not easy to be conceived; for the puerile reason that "this mixture will be more conveniently made, and its dose more easily apportioned than the former one," cannot surely have operated in causing the alteration. One fluid ounce of this diluted acid of the London Pharmacopoeia contains 80 grains of the strong acid; in the Edinburgh and Dublin Pharmacopoeias it constitutes an eighth part.

Owing to the great affinity of sulphuric acid for water, and the density of the mixture being much greater than the mean of the separated acid and water1 , a very considerable increase of temperature is produced during their combination, sufficient to crack the glass vessels in which it is made, if the two ingredients be at once mixed together.2 To prevent such an accident, the acid must be gradually added in small portions to the whole of the water, and the mixture agitated after every addition. It is of importance always to ascertain the specific gravity of the acid before the mixture be made. The mixture, when it has cooled down to the temperature of the atmosphere, lets fall a white precipitate, consisting of a small portion of sulphate of lead, which the strong acid always contains, but which the diluted acid is incapable of holding in solution. The diluted acid is thus purer than the strong acid, which suffers no other alteration except in point of strength. If it be suspected to contain sulphate of potassa, this may be detected by saturating a given quantity of the acid with ammonia, then evaporating to dryness, and afterwards expelling the sulphate of ammonia by heat: the sulphate of potassa will be left behind.

Medical properties and uses. - Diluted sulphuric acid is tonic, antiseptic, and refrigerant. Its tonic and antiseptic

1 It is a curious fact that, after the mixture has cooled down to the temperature of the atmosphere, a considerable time elapses before it acquires its real density.

2 If one part by weight of sulphuric acid of 1.845 specific gravity be mixed with one fourth its weight of water, both being at the temperature of 50° Fahr., the caloric instantly evolved is sufficient to raise the thermometer from 50° to 300°, and a still greater heat is produced by mixing 73 parts of the acid with 27 of water.

powers render it extremely serviceable in low typhoid fevers, dyspeptic affections, diabetes, convalescences, and in cutaneous eruptions. It restrains the colliquative sweats which attend hectic: locally applied, it is a common and useful adjunct to gargles in cynanche, and to check salivation; and as a refrigerant it is given with certain benefit in passive haemorrhages, from whatever part they may arise. Combined with mucilages, it has been beneficially given in passive diarrhoeas, operating on the relaxed mucous coat of the intestine as an astringent. In the first-mentioned cases, the diluted acid may be combined with infusions of cinchona or other vegetable bitters and aromatics; and in the latter with infusion of roses, mucilage, or simple water sweetened with syrup. It is certainly injurious to the teeth; and, therefore, should be sucked through a quill, when taken as an internal remedy. The usual dose is from x. to xxx., but this dose may be very often repeated : in malignant erysipelas, with a tendency to haemorrhage, it has been given to the amount of f j. in twenty-four hours; and we have administered it, with evident advantage, to the same amount, in violent uterine haemorrages, and in obstinate scabies.

Officinal preparations. - Acidum Sulphuricum aromaticum, E. Infusum Rosae compositum, L. Potassae Bisulphas, L. D. Sodae Sulphas, L. E. D. Ferri Sulphas, L. E. D. Zinci Sulphas, L. E. D.

Acidum Sulphuricum Aromaticum. Edin. Dub. Aromatic Sulphuric Acid

"Take of alcohol, two pounds; sulphuric acid, six ounces. Drop the acid gradually into the alcohol. Digest the mixture in a covered vessel with a very gentle heat for three days; then add of cinnamon bark, bruised, one ounce and a half; ginger root, bruised, one ounce. Digest again in a closed vessel for six days; then filter through paper placed in a glass funnel."

This preparation is generally regarded as an imperfect ether; but we are of opinion that the reciprocal action of the acid and alcohol during the digestion is scarcely sufficient to produce such a result; and the acid, undoubtedly, very much predominates. It is, therefore, a simple alcoholic solution of sulphuric acid, holding the essential oils of cinnamon and of ginger in solution.

Qualities. - The odour is peculiar and aromatic; the taste gratefully acid. It is limpid, and of a brownish colour.

Medical properties and uses. - This is an agreeable mode of exhibiting sulphuric acid in dyspepsia, chronic asthma, and most of the complaints for which the diluted acid has been found serviceable. The dose is from x. to xxx., in any convenient fluid vehicle; and may be given three or four times a day.