INCOMPATIBILITY.

Incompatibility may be Chemical, Pharmaceutical or Therapeutical, according as the prescribed combination results in chemical decomposition, physical disassociation or antagonistic action. In the first case the incompatibility may be unintentional or intentional on the part of the prescriber, for in many cases the result of the chemical action affords the substance desired.

Instances of intentional incompatibility are the mixtures of Calomel and Corrosive Sublimate with Lime water, producing the Black and Yellow Oxides of Mercury respectively, and commonly known as Black Wash" and "Yellow Wash." Such combinations should not be filtered (as a novice might suppose), but should be dispensed with a "Shake-label," that the precipitate may be uniformly distributed before using.

Chemical Incompatibility generally results from neglect on the part of the prescriber of the most common chemical reactions, such as1. Acids tend to combine with bases and to form salts.

2. Weak acids or bases are displaced from their combinations by stronger ones, so that salts in solution when brought together generally exchange their radicles, especially if by doing so an insoluble compound can be formed.

3. A salt in solution is easily decomposed by a strong alkali if the salt is one having a weak or volatile base.

4. A substance in solution may be decomposed by another without precipitation, the product being soluble in the solution.

5. Alkaloidal salts are precipitated from their solutions by the addition of fixed alkalies, their salts or salts which produce insoluble compounds. Oxides of the fixed alkalies decompose salts of the metals proper, and those of the alkaloids, precipitating their bases; but the base may be soluble in an excess of the alkali.

6. Tannic or Gallic Acids and vegetable substances containing them precipitate albumen, alkaloids and most of the metallic oxides, and form inky solutions when brought into contact with the persalts of Iron. Tannic Acid precipitates gelatin.

7. Glucosides are incompatible with free acids or Emulsin.

Examples of the neglect of these principles are seen in the prescribing of Quinine Sul. phate in mixture with Potassium Acetate, resulting in a voluminous precipitate of Quinine Acetate which could not be poured from the bottle;-Vinegars or Syrups containing Acetic Acid (Syr. Allii, Syr. Scilla) added to a solution of alkaline carbonates, causing decomposition of the latter with evolution of CO2;-the addition of Liquor Potass to a solution of Ammonia-alum, setting free gaseous ammonia;-the mixing of Strychnine Sulphate and Potassium Bromide in solution, causing the decomposition of the alkaloid sulphate and precipitation of Strychnine; -preparations of Cinchona with salts of Iron, forming an inky tannate of iron; Elixir of Chloral with alkalies, causing the elimination of Chloroform and its subsequent evaporation, etc., etc.

The following table shows the most important instances of solutions.

which mutually precipitate each other, the letter P meaning "forms a precipitate with "

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, and of Lead, and 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 Limewater. Solutions of Magnesium Sulphate, Alum, Zinc Acetate or Sulphate with solutions of silts 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 Limewater, 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).

Limewater 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.

Nitric Acid. Chromic Acid.

Free Hydrochloric Acid.

Nitro-hydrochloric Acid.

Potassium Chlorate.

Potassium Permanganate.

Oxidizable or Combustible.
Glycerin, Sugar, Alcohols.
Oils and Ethers.
Sulphur and Sulphides.
Dry Organic Substances.
Phosphorus.

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 triturated in the presence of water. Catechu and Potassium Chlorate in a dentifrice have exploded in the mouth from the friction produced by a dry tooth-brush.

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

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

Potassium Chlorate with Syrup of Iodide of Iron, liberates Iodine from the Iodide in the warm stomach, causing severe gastric irritation, perhaps gastritis of dangerous degree.

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 emuisifier 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,

Saponin,-Digitalin.

Strychnine,-Alcohol, Chloral, Hydrocyanic Acid, Nicotine, Nitrite of Amyl.
Thebaine,-Chloral-hydrate.

The Dangers of Incompatibility may in a great measure be avoided by the use of the utmost simplicity in prescribing. The subject can only be glanced at within these pages, but the following simple rules may help the burdened memory of the student and the practitioner. (1). Never use more than one remedy at a time, if one will serve the

purpose.

(2). Never use Strong Mineral Acids with other agents, unless you know exactly what reaction will ensue. They decompose salts of the weaker acids, and form ethers when combined 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 of water for their respective substances decreases in proportion to the quantity of the other added.

(4). Generally do not combine two or more soluble salts; for such salts in solution, when brought together, usually exchange their radicles, thereby forming an insoluble compound.

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 the subsalts of Mercury; the Chlorides, Iodides, and Bromides of Bismuth, Silver, Lead, and Mercury; the Iodides of Quinine, Morphine and most alkaloids.

(5). Never order a drug in combination with any of its Tests or Antidotes.

(6). Never prescribe a Glucoside, (as Santonin, Colocynthin, etc.), in combination with free acids or with a substance containing Emulsin, as these agents will decompose it.

(7). Aconite should be ordered in water alone, Mercuric Chloride by itself in water or in simple syrup. The latter drug is incompatible with almost everything, even the Compound Syrup of Sarsaparilla being said to decompose it.

(8). Iodide of Potassium decomposes most of the metallic salts, and is one of the drugs which are best administered alone.

(9). 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 :