These substances all possess distinctly acid properties, that is, they neutralise alkalies, and turn blue litmus red.

Acidum Sulphuricum. - Sulphuric Acid. H1SO4 98 per cent., = 79 per cent. SO3, in water.

Source. - Obtained by the combustion of Sulphur, and oxy-dation by nitrous fumes.

Characters. - A colourless, oily-looking, intensely acid liquid.

Impurities. - Nitric acid, lead, and arsenic, organic matter; detected by colour.

Preparatiotis.

1. Acidum Sulphuricum Dilutum

Acidum Sulphuricum Dilutum. 1 to about 11 of Distilled Water. Dose, 5 to 30 min.

From Acidum Sulphuricum Dilutum is prepared: Infusum Rosae Acidum. 1 of Diluted Acid in 80.

2. Acidum Sulphuricum Aromaticum

Acidum Sulphuricum Aromaticum. 1 to about 13 of Spirit, with Cinnamon and Nutmeg. Dose, 5 to 30 min.

3. Many Sulphates and other preparations.

Acidum Nitricum. - Nitric Acid. HNO3, 70 per cent by weight, in Water.

Source. - Prepared from Nitre by distillation with Sulphuric Acid and Water.

Characters. - A colourless, intensely acid fuming liquid.

Impurities. - Sulphuric and hydrochloric acids; mineral matter; excess of water; peroxide of nitrogen; known by yellow fumes.

Preparations.

1. Acidum Nitricum Dilutum

Acidum Nitricum Dilutum. 1 to fully 4 of Distilled Water. Dose, 10 to 30 min.

2. Acidum Nitrohydrochloricum Dilutum

Acidum Nitrohydrochloricum Dilutum. 3 to 25 of Distilled Water, with 4 of Acidum Hydrochlo-ricum. Dose, 5 to 20 min.

3. Many Nitrates and other preparations.

Acidum Hydrochloricum. - Hydrochloric Acid. HC1, 31.8 per cent. by weight, dissolved in Water.

Source. - Obtained by the action of Sulphuric Acid upon Chloride of Sodium, and the solution of the resulting fumes.

Characters. - A nearly colourless, very acid liquid, with pungent odour.

Impurities. - Sulphuric and sulphurous acids, arsenic, and water; detected by ordinary tests.

Preparations.

1. Acidum Hydrochloricum Dilutum

Acidum Hydrochloricum Dilutum. 1 to 2 1/4 of Distilled Water. Dose, 10 to 30 min.

2, Acidum Nitrohydrochloricum Dilutum. - 4 to 25 of Distilled Water, with 3 of Acidum Nitricum. Dose, 10 to 30 min.

3. Many Chlorides, and other preparations.

Acidum Phosiilioricum Dilutum. - Diluted Phosphoric Acid. H3PO4 dissolved in Water =10 per cent. P2O5.

Source. - Made by distilling Phosphorus with Nitric Acid and Water, heating, and diluting.

Characters. - A colourless sour liquid, with a strongly acid reaction.

Impurities. - Arsenic and lead; detected by H1S. Sulphuric, nitric, hydrochloric, and pyro- and meta-phosphoric acids; detected by usual tests.

Incompatibles. - Lime-water, calcareous salts, and carbonate of soda.

Dose. - 20 to 30 min.

Diluted Phosphoric Acid is used in preparing Syrupus Ferri Phosphatis, and Ammoniae Phosphas.

Acidum Aceticum. - Acetic acid. Anhydrous Acetic Acid, C4H6O3. 28 parts in Water.

Source. - Prepared from Wood by destructive distillation and purification.

Characters. - A colourless liquid, with a pungent odour and strong acid reaction.

Impurities. - Lead, copper; sulphuric, hydrochloric, and sulphurous acids.

Preparations.

1. Acidum Aceticum Dilutum

Acidum Aceticum Dilutum. 1 volume to 7 of Water. Dose, 1 to 2 fl.dr.

2. Oxvmel

Oxvmel. Acetic Acid, 1; Water, 1; Honey, 8.

Dose. - 3 to 6 dr.

Acetic Acid is also used in preparing Acetum Can-tharidis, Acetum Scillae, Extractum Colchici Aceticum, Linimentum Terebinthinae Aceticum, Liquor Epispas-ticus, and many Acetates.

Acidum Aceticum Glaciale. - Glacial Acetic Acid. C4H6O3, 84 per cent. in Water.

Source. - Made by distillation from Acetate of Soda and Sulphuric Acid.

Characters. - A colourless acid liquid, with a powerful acetic odour.

Impurities. - Sulphurous acid; and water.

Glacial Acetic Acid is used in preparing Acetum Cantharidis, and Mistura Creasoti.

Acetum. - Vinegar.

Source. - Prepared from Malt and Unmalted Grain by acetous fermentation.

Characters. - A brown-coloured acid liquid, with a characteristic odour.

Impurity. - Excess of sulphuric acid; detected volumetri-cally.

Dose. - 1 fl.dr. and upwards.

Vinegar is used in preparing Emplastrum Cerati Saponis.

Acidum Citricum. - Citric Acid. H3(C6H5O7)H1O.

Source. - Obtained from the juice of the Lemon (Citrus Limonum), or of the Lime (Citrus Limetta), by neutralising it with Chalk, decomposing the Citrate of Lime thus formed by Diluted Sulphuric Acid, purifying, and crystallising.

Characters. - Colourless crystals, in the form of right rhombic prisms. Very soluble in water. 17 gr. in 1/2 fl.oz. of water make a solution resembling lemon juice in strength and acidity, and exactly neutralise 25 gr. of Potassae Bicarbonas, 20 gr. of Sodae Bicarbonas, or 15 gr. of Arnmoniae Carbonas.

Impurities. - Copper, sulphuric acid, mineral matters. Tartaric acid, detected by precipitate with acetate of potash.

Dose. - 10 to 30 gr.

Citric Acid is used in preparing Ferri et Ammonias Citras, Ferri et Quiniae Citras, and Vinum Quiniae.

Acidum Tartaricum. - Tartaric Acid. H1(C4H4O6).

Source. - Obtained from Acid Tartrate of Potash by neutralising its solution with (1) Chalk and (2) Chloride of Calcium, (3) decomposing the Tartrate of Lime thus formed by Sulphuric Acid, and purifying. (1) 2KHC4H4O6 + CaCO3 = CaC4H4O6 + K2C4H4O6 + H1O + CO2. (2) K2C4H4O6 + CaCl2 = CaC4H4O6 + 2KC1. (3) 2CaC4H4O6 + 2H1SO4 = 2H1C4H4O6 + 2CaSO4.

Characters. - Colourless oblique rhombic prisms, with a strongly acid taste, readily soluble in water. 20 gr. exactly neutralise 27 gr. of Potassae Bicarbonas, 22 gr. of Sodae Bicarbonas, or 15 1/2 gr. of Ammoniae Carbonas.

Impurities. - Lead, oxalic acid, lime, mineral matter, acid tartrate of potash.

Dose. - 10 to 30 gr.

Tartaric Acid is used in preparing Sodas Citrotartras Effervescens.

Carbonic Acid. - Although not officinal as such, carbonic add gas is extensively used in medicine, being obtained from Bicarbonates and Carbonates, commonly of Soda, Potash, or Ammonia, by decomposition with Citric or Tartaric Acid. The process is known as effervescence. The reaction may be thus represented: