The following more or less insoluble salts will be formed whenever the materials of which they are composed are brought together in solutions: the Hydrates, Carbonates, Phosphates, Borates, Arseniates and Tannates of most earthy and heavy metals and alkaloids, and the metallic Sulphides; the Sulphates of Calcium, of Lead, and of the subsalts of Mercury; the Chlorides, Iodides, and Bromides of Bismuth, Silver, Lead, and subsalts of Mercury; the Iodides of Quinine, Morphine and most alkaloids.

Instances are-Limewater or Aromatic Spirit of Ammonia with Tincture of Chloride of Iron, or solutions of Mercury salts, or neutral solutions of Quinine or Morphine salts.

Ammonium, Potassium and Sodium carbonates or bi-carbonates with Lime

water.

Solutions of Magnesium Sulphate, Alum, Zinc Acetate or Sulphate with solutions of salts of Iron, Manganese, Bismuth, Antimony, Lead, and of most alkaloids.

Ammonium or Sodium Phosphates with solutions of Iron salts, with Limewater, solution of Magnesium Sulphate, of Alum, etc.

Liquor Potassii Arsenitis with Lime-water, with solutions of basic salts of Iron, and of neutral salts of Quinine and Morphine, etc.

Solutions, decoctions, tinctures and extracts containing Tannic Acid with solutions of salts of Iron, Mercury, Antimony, Lead (as also with solutions containing albuminous substances and Gelatin).

Lime-water with solutions of Quinine or Morphine Sulphates.

Solutions of Lead Acetate with Zinc Sulphate or Alum.

Sodium Chloride with Silver Nitrate.

Morphine Hydrochlorate with Lead Acetate.

Alkaline iodides or bromides with Bismuth Carbonate or Sub-nitrate, with Lead Acetate, with Sub-chloride of Mercury, or with neutral solutions of Quinine, Morphine or Strychnine salts.

Explosive Compounds result from the admixture of powerful oxidizing agents with substances which are readily oxidizable. The most important members of these two classes are as follows:

Oxidizers.

Chromic Acid.

Potassium Chlorate.

Potassium Permanganate.
Nitric Acid.

Nitro-hydrochloric Acid.

Oxidizable or Combustible.

Glycerin, Sugar and other Alcohols.
Oils and Ethers

Sulphur and Sulphides.

Phosphorus.

Dry Organic Substances.

Explosions have resulted from mixing Fluid Extract of Uva Ursi with certain samples of Spirit of Nitre, Chromic Acid with Glycerin, Permanganate of Potassium with Glycerin, Nitric Acid with Glycerin, Nitrate of Silver with Creasote, Oxide of Silver in pill with Extract of Gentian, Potassium Chlorate with Glycerin and Tincture of the Chloride of Iron. Chloride of Lime triturated with Sulphur in a mortar has exploded, so also has Calcium or Sodium Hypophosphite when triturated alone. Tincture of Iodine with Ammonia forms the Iodide of Nitrogen, which is highly explosive, especially if tritu

rated in the presence of water. Catechu and Potassium Chlorate in a dentifrice have exploded in the mouth from the friction produced by a dry toothbrush.

Poisonous Compounds may be formed by the admixture of many substances in solution, such as

Potassium Iodide with Potassium Chlorate, in solution together do not react at ordinary temperatures, but in the system they evolve a poisonous agent, probably the Iodate of Potassium.

Dilute Hydrocyanic Acid or Potassium Cyanide, with Calomel, forms the Bichloride and Bicyanide of Mercury, both virulent poisons;-with metallic hydrates, carbonates, sub-nitrates or sub-chlorides, cyanides of the metals are formed which are even more poisonous than the acid itself in its usual diluted form.

Pharmaceutical Incompatibility differs from chemical incompatibility in the absence of chemical action, and is generally produced by adding one substance to another which, through differences in solubility, causes a precipitation of solid matter or a separation of part of the liquid. The constituents separated may be active and hence important, or inert and therefore unimportant.

Instances of this are the addition of an acid to a Quinine and Liquorice mixture, resulting in precipitation of the Glycyrrhizin (relied on to cover the taste of the Quinine) by the acid;-or the use of Quinine, Tincture of Ferric Chloride and Liquorice together;-or the prescribing of solutions of Chloral and Potassium Bromide with an alcoholic preparation, the Chloral separating to the top as an alcoholate, and therefore dangerously in excess for the first few doses; or the neglect to prescribe Acacia or some other emulsifier in mixtures of an alcoholic fluid extract of a resinous body with an aqueous preparation, which would result in the separation of the resin to the surface and an overdose with the first teaspoonful.

When the fluid extracts are diluted with liquids differing in composition from those used in the fluid extracts, the gum, albumen, resin, and mucilage are often separated. In such a case as Fluid Extract of Cannabis Indica the active resin would be thrown out of solution, and floating on top might cause serious symptoms; but in many other instances the precipitate would be inert and filtration would be in order. Water is the solvent for albuminous, gelatinous, gummy, and saccharine bodies and for a large number of inorganic salts; while Alcohol is the solvent for volatile oils and resins, gum-resins, resinoids, balsams, and all drugs containing these as their active principles. The solvent power of either Alcohol or Water for their particular substances decreases in proportion to the amount of the other added.

Instances of Pharmaceutical Incompatibility.

Resinous tinctures or fluid extracts with aqueous solutions.

Tincture of Guaiac with Spirit of Nitric Ether.

Compound Infusion of Gentian with Infusion of Wild Cherry.
Compound Infusion of Cinchona with Compound Infusion of Gentian.
Essential oils with aqueous liquids in quantities exceeding I drop to 3j.
Fixed oils and Copaiba with aqueous liquids (except excipients).
Tinctures made with Alcohol with those made with Diluted Alcohol.
Alcoholic tinctures and fluid extracts with aqueous preparations.
Spirit of Nitric Ether with strong mucilages,
Infusions generally with metallic salts.

Therapeutical Incompatibility arises when two agents are administered together which oppose each other in their action on the human system, -as for instance Belladonna in any form with Physostigma. But in many cases physiological antagonists are designedly prescribed together, one as a guard against the action of the other, as in the hypodermic administration of Morphine guarded by Atropine. The antagonists to each of the active medicinal agents may be found in the section on Materia Medica under their various titles; but they may be well summarized as to the most important ones in the following list.

PHYSIOLOGICAL ANTAGONISTS.

Aconitine,-Atropine, Digitalin, Strychnine.
Alcohol,-Strychnine.

Ammonium Chloride,-Chloral-hydrate.

Atropine,-*Aconitine, *Bromal-hydrate, Chloral-hydrate, Hydrocyanic Acid, Jaborandi, Muscarine, *Morphine, Physostigmine, Phytolacca, Pilocarpine, Quinine. [Those marked * will not prevent death from a lethal dose of Atropine, though the latter will prevent death from a lethal dose of either of them.] Barium,-Sodium Sulphate, Potassium salts.

Bromal-hydrate,-Atropine.

Brucine, Chloral-hydrate.

Calabarine,-Chloral-hydrate.

Carbolic Acid,-Chloral-hydrate.

Chloral-hydrate,-Ammonium Chloride, Atropine, Brucine, Calabarine, Carbolic Acid, Codeine, Physostigma, Picrotoxine, Strychnine, Thebaine. Chloroform,-Amyl Nitrite.

Cocaine, Morphine.

Codeine,-Chloral-hydrate.

Digitalin,-Aconitine, Muscarine, Saponin.

Gelsemium,-Opium, Atropine.

Morphine,-Atropine, Caffeine, Chloroform, Cocaine, Daturine, Hyoscyamine,

Nicotine, Physostigma.

Muscarine,-Atropine.

Opium, -- Atropine, Gelsemium, Veratrum Viride.

Physostigma,-Atropine, Chloral, Morphine.

Saponin,-Digitalin.

Strychnine, Alcohol, Chloral, Hydrocyanic Acid, Nicotine, Nitrite of Amyl.

Thebaine, Chloral-hydrate.

Good Rules to follow in order to avoid the dangers of incompatibility are the following,

1. Never use more than one remedy at a time, if one will serve the purpose.

2. Never use Strong Mineral Acids in combination with other agents, unless you know exactly what reaction will ensue. They decompose salts of the weaker acids and form ethers with alcohol. Never combine Free Acids with hydrates or carbonates.

3. Select the simplest solvent, diluent, or excipient you know of, remembering that the solvent power of Alcohol and Water for their particular substances decreases in proportion to the quantity of the other added.

4. Generally do not combine two or more soluble salts.

5. Never prescribe a drug in combination with any of its Tests or Antidotes.

6. Do not order Glucosides (as Santonin, Colocynthin) in combination with free acids or in emulsions.

7. Prescribe Aconite only in water, and Mercuric Chloride alone in water or simple syrup. The latter is incompatible with almost everything, even the Compound Syrup of Sarsaparilla is said to decompose it.

8. Iodide of Potassium decomposes nearly all metallic salts, and is one of the drugs which is best given alone.

9. Acacia or some other emulsifying agent should always be added to prescriptions containing resinous tinctures or fluid extracts (e. g., Tinct. Cannabis Indica) with aqueous solutions, to prevent the separation of the resin.

10. Silver Nitrate, and Lead Acetate and Subacetate, although incompatible with almost everything, may be combined with Opium; the latter forming with Opium a compound which, although insoluble, is therapeutically active as a lotion.

11. The following-named substances are incompatible with so many others that it is best to always prescribe them alone; they are best given in simple solution:

12. Tannic Acid may be prescribed with the proto-salts of Iron, but not with its per-salts. Calumba is the best vegetable tonic to prescribe with Ferric salts, as it contains neither Tannic nor Gallic Acids.

LIQUID EXTEMPORANEOUS PREPARATIONS.

Mixtures (Mistura),-in official pharmacy are aqueous preparations containing some insoluble ingredients held in suspension by an appropriate vehicle. In extemporaneous pharmacy, however, the term Mixture is applied to every fluid compound intended for internal use, except a few which bear distinctive titles, such as Emulsions, Draughts, Enemas, Elixirs and Drinks. The simplest form of mixture in this extended sense is that in which two or more liquids are mixed together; but a great variety of substances may be prescribed in this form, chief among which are most of the soluble salts, light insoluble powders, salts which may be diffused by agitation, extracts, gum-resins, and the fixed and essential oils. They are generally ordered in 2, 3, 4, 6, 8, 10 and 12-ounce vials.

The substances suitable to the mixture-form, properly so called, are those which, though more or less insoluble in water, will mix with it by agitation, trituration, etc. Those most frequently ordered are as follows:

Best suspended by the aid of a fixed oil or yolk of egg:

Ext. Cannabis Indicæ.

Camphora.

Oleum Terebinthinæ.
Chloroformum.

Solutions intended for internal administration are classed as Mixtures in extemporaneous pharmacy, for the reason stated