2. Solution in Hot Water.-This method is founded upon the fact that most of the volatile oils are much more soluble in hot water than in water of ordinary temperature: hence, if the volatile oil is thoroughly agitated with hot water in a metallic vessel, such as a tin can or a bottle, and allowed to stand until the excess has separated, if care is used, the water will be found to be saturated: it may then be decanted and filtered.

3. Filtration through an Absorbent Powder is the process which has been most frequently employed: the object of using the powder is to divide thoroughly the oil, or volatile liquid, and expose a greater surface, so that the water in filtering through it may become completely saturated. The powder most frequently used is magnesium carbonate, but this is sometimes objectionable on account of being slightly soluble in water. Calcium phosphate, kaolin, powdered glass, silica, powdered pumice-stone, charcoal, paper pulp, precipitated chalk, sugar, etc., have been suggested as substitutes, but there are quite as forcible objections to be urged against these as against the magnesium carbonate. Where solutions of alkaloids or of silver nitrate are needed, distilled water alone should be used. The present official method directs the use of precipitated calcium phosphate, but purified magnesium carbonate is preferable.

4. Percolation through Cotton impregnated with the Substance. This was the process directed to be used in the U. S. P. 1880; it was abandoned in the revision of 1890 on account of its inconvenience and wastefulness. The oil or volatile liquid is distributed upon the fibres of cotton, which are then pulled apart in order to secure thorough division; the saturated cotton is packed in a funnel, and the water poured upon it. In its passage downward the water dissolves the oil and passes out impregnated with the odorous substance. The presence of undissolved floating oily drops in the finished preparation has constituted one of the greatest objections to this process. It is an improvement to insert a plug of dry cotton in the throat of the funnel. before placing the saturated cotton in position: this prevents the oily drops which may escape solution from being carried down by the water as it percolates through. Too much care cannot be exercised in selecting the volatile oils, which should be fresh and of the best quality.

Official Waters made by Filtration through an Absorbent Powder.

5. Distillation. This is the best process for preparing medicated waters, and should be used wherever practicable. If the fresh drug can be procured, it should always be used in preference to that which has been dried, because in the process of desiccation there is usually a loss of the agreeable volatile constituents. Metallic distillatory apparatus is preferably employed (see page 166). If the drug containing the oilcells has a loose structure and is quickly penetrated by hot water, so that the oil-cells are easily ruptured, the drug may be introduced without previous contusion or grinding: it will usually be found, however, most economical to cut or grind the drug coarsely. Most distilled waters acquire an unpleasant empyreumatic odor as soon as they are distilled; this passes off gradually upon exposure to air, if care has been taken not to expose the drug to the action of direct heat during distillation. If no precautions are taken to protect the drug from partial burning, the odor of the carbonized substance will always be noticeable in the distilled water, rendering the product worthless. Fig. 182 shows a copper wire cage contrived by the author to obviate the difficulty just described the surface of the cage is hemispherical; it rests, after being partially filled with the drug, upon the flat bottom of the still, and thus the contact of the substance with the heated surface is avoided: the meshes of the cage are coarse enough to permit the free passage of vapors and the boiling water through them. Although distillation by the use of steam may be most convenient upon the large scale, Vuaflart and Machet have shown that rose and orange-flower waters distilled over a naked fire keep better than those distilled by steam heat.

Preservation.-Distilled waters should not be made in larger quantities than can be used within a reasonable time, because they deteriorate when long kept, a flocculent precipitate forming in them, and ultimately they lose all traces of their usually agreeable odor. Microscopic plants belonging to the order Confervoidea will often be found in medicated waters. These are usually tufts of articulated filaments, propagated by very minute spores from the atmosphere which have found lodgment in the water. Their presence renders the medicated water unsightly, and when in large proportion they must be regarded as injurious. If the aromatic water is heated and introduced into a bottle with a side opening near the bottom (like a douche-bottle) to which a rubber tube with a pinch-cock is attached, and a tuft of cotton pushed into the neck of the bottle, any spores originally present in the water will be killed by the heat, and the future growth of confervæ will be prevented by the interception of the spores by the cotton. It usually suffices, however, to heat the medicated water and introduce it at once into small bottles, which are to be completely filled, tightly sealed, and kept in a cool, dark place. Alcohol is sometimes added as a preservative, but this generally serves its purpose only a short time, as it cannot be added in sufficient quantity to preserve the water permanently, on account of its interference with the therapeutic action. The small percentage of alcohol in the medicated water is converted into acetic acid when long kept, and thus the preparation is soured. Glycerin and syrup have been suggested as preservatives. In the writer's experience they are not of much value unless used in large and inadmissible quantities.

PRACTICAL PROCESSES FOR OFFICIAL WATERS.
AQUA AMYGDALÆ AMARÆ. U. S. Bitter Almond Water.

Dissolve the Oil in the Distilled Water by agitation, and filter through a well-wetted filter.

Triturate the Oil of Anise with the precipitated Calcium Phosphate, add the Water gradually, under constant trituration, and filter.

AQUA AURANTII FLORUM. U. S. Orange Flower Water.

[AQUA AURANTII FLORUM, PHARM. 1880. TRIPLE ORANGE FLOWER WATER.]

Water saturated with the volatile oil of fresh Orange Flowers, obtained as a by-product in the distillation of the Oil of Orange Flowers. It should be kept in loosely-stoppered bottles, in a dark place.

Stronger Orange Flower Water should be neutral to litmus paper, and possess a strong odor of fresh orange flowers.

It should be colorless and clear, or only faintly opalescent, not mucilaginous, and give no reaction with hydrogen sulphide T.S. or ammonium sulphide T.S. (absence of metallic impurities).

Triturate the Camphor with the Alcohol and Precipitated Calcium Phosphate, then with the Water gradually added, and filter.

AQUA CHLORI. U.S. Chlorine Water.

An aqueous solution of Chlorine [Cl=35.37], containing at least 0.4 per cent. of the gas.

Metric.

10 Gm.

35 C.c.

75 C.c. 400 C.c.

Old form.

146 grains.

9 fl. dr.

2 fl. oz. 34 fl. dr. 12 fl. oz. 6 fl. dr.

Place the Dioxide in a flask connected by a suitable tube with a small wash-bottle containing 50 C.c. [old form 1 fl. oz. 5 fl. dr.] of Water, and connect this with a bottle having a capacity of 1000 C.c. [old form 2 pints], and containing 400 C.c. [old form 12 fl. oz. 61 A. dr.] of Distilled Water which has previously been boiled and allowed to cool. Add to the Dioxide in the generating flask the Hydrochloric Acid, previously diluted with 25 C.c. [old form 63 fl. dr.] of Water, and, by means of a sand-bath, apply a gentle heat. Conduct the generated Chlorine through the Water contained in the wash-bottle into the bottle containing the Distilled Water, which should be loosely stopped with cotton and kept, during the operation, at a temperature of about 10° C. (50° F.). When the air has been entirely displaced by the gas, disconnect the bottle from the apparatus, and, having inserted the stopper, shake the bottle, loosening the stopper from time to time, until the gas ceases to be absorbed. If necessary, reconnect the bottle with the apparatus, and continue passing the gas and agitating until the Distilled Water is saturated. Finally, pour the Chlorine Water into small, dark amber-colored, glass-stoppered bottles, which should be completely filled therewith, and keep them in a dark and cool place.

Chlorine Water, even when kept from light and air, is apt to deteriorate. When it is required of full strength, it should be freshly prepared.

A clear, greenish-yellow liquid, having the suffocating odor and disagreeable taste of Chlorine, and leaving no residue on evaporation.

It instantly decolorizes dilute solutions of litmus, indigo, and other vegetable coloring matters.

When shaken with an excess of mercury until the odor of Chlorine has disappeared, the remaining liquid should be at most but faintly acid (limit of hydrochloric acid).

On adding 17.7 Gm. of Chlorine Water to a solution of 1 Gm. of potassium iodide in 10 C.c. of water, the resulting deep-red liquid should require for complete decoloration not less than 20 C.c. of decinormal sodium hyposulphite V.S. (corresponding to at least 0.4 per cent. of Chlorine).

Chloroform,

AQUA CHLOROFORMI. U. S.

Distilled Water, each, a sufficient quantity.

Chloroform Water.

Add enough Chloroform to a convenient quantity of Distilled Water, contained in a dark amber-colored bottle, to maintain a slight excess of the former, after the contents have been repeatedly and thoroughly agitated.

When Chloroform Water is required for use, pour off the needed quantity of the solution, refill the bottle with Distilled Water and saturate it by thorough agitation, taking care that there be always an excess of Chloroform present.

Triturate the Oil of Cinnamon with the Precipitated Calcium Phosphate, add the Distilled Water gradually, under continued trituration,

Agitate the Creosote vigorously with the Distilled Water, and filter through a well-wetted filter.

Distil the Water from a suitable apparatus provided with a blocktin or glass condenser. Collect the first 100 volumes [old form 2 pints], and throw this portion away. Then collect 800 volumes [old form 8 pints], and keep the Distilled Water in glass-stoppered bottles, rinsed with hot Distilled Water immediately before being filled.