The more important soluble salts are the acetate, bromide, chloride, iodide, nitrate, sulphate; the scale salts-the citrate, soluble phosphate, pyrophosphate, iron and ammonium citrate, iron and ammonium tartrate, iron and potassium tartrate, iron and quinine citrate, soluble iron and quinine citrate, iron and strychnine citrate, and the double crystalline salt iron and ammonium sulphate. Particular care should be exercised against the formation of the insoluble hydroxide or carbonate.

Silver

The nitrate is the only inorganic salt often used in solution, and should be employed alone or with nitric acid or some other nitrate.

Organic combinations, as argyrol, protargol, etc., are frequently used in solution, but are prescribed alone.

The nitrate and sulphate are soluble.

Lead

Seldom prescribed in solution except as the acetate, which is not usually associated with other agents except the tincture of opium or zinc sulphate, the resulting precipitate to be suspended by shaking before using.

The acetate and nitrate are soluble.

Bismuth

With the exception of the double salt, bismuth and ammonium citrate, none of the common salts of bismuth are soluble. They are frequently prescribed in liquids to be suspended by shaking when used.

Antimony

The only salt of much interest to the prescriber for use in solution is the soluble double salt antimony and potassium tartrate. The quantity used is comparatively so small that it is not often a source of trouble from a chemical standpoint. The simple salts of antimony may be regarded as generally insoluble.

Arranged by Acids.

Acetates And Nitrates

Generally soluble except bismuth sub-nitrate; so the prescriber need not worry about an acetate or nitrate being precipitated.

Bromides, Chlorides, And Iodides

Generally soluble except silver, mercurous, lead, and bismuth; with these exceptions the prescriber need not expect a precipitate from the metallic agents in common use. It should be remembered that iodides and bromides precipitate alkaloidal salts.

Sulphates

Generally soluble except barium, calcium, lead, and strontium.

Tartrates And Citrates

Mostly soluble.

Lactates, Hypophosphites, And Nitrites

Soluble or slightly soluble.

Arsenates. Arsenites.

Borates. Carbonates.

Hydrates. Oxides.

Oxalates. Phosphates.

These are mostly insoluble, or sparingly so, except those of ammonium, potassium, and sodium. Those of lithium are soluble or slightly soluble.

Salicylates. Sulphates. Valerates.

These salts that are in more common use are soluble, but they arc seldom prescribed in solution with other chemicals. Mercury salicylate is insoluble and is often prescribed in suspension.

Tannates may be considered as generally insoluble, though the tannic acid in vegetable drugs is not a common source of trouble except with ferric and some alkaloidal salts.

(B) Precipitation Of Alkaloids And Alkaloidal Salts By Chemical Action

As a general rule alkaloids should not be prescribed with hydroxides, carbonates, iodine, iodides, bromides, borates, or tannic acid. The presence of glycerin or alcohol in sufficient percentage (10 to 50) will prevent precipitation in the majority of instances. With a few exceptions it is not often that a prescriber will want to combine an alkaloid with these chemicals.

The alkaloids in the various tinctures need seldom be considered as possible factors in precipitation.

Morphine or codeine may sometimes be desirable with the bro mides. The hydrobromides of these are soluble; so these mixtures seldom precipitate.

Cocaine is sometimes ordered with boric acid or borates. The presence of glycerin will prevent precipitation.

Compound tincture of cinchona is prescribed with potassiomer-curic iodide. The alcohol present prevents the precipitation of the small amount of quinine.

(C) Precipitation Due To Other Causes

There are some instances of the precipitation of other than metallic and alkaloidal substances by chemical action, but they are seldom encountered in the regular course of prescription writing. Gelatinous precipitates will be treated elsewhere.

The majority of the trouble coming in this division of the subject results from adding to a solid in solution a liquid in which the solid is insoluble.

Gums

These are soluble in water, but insoluble in alcohol. A most common instance is adding an alcoholic liquid to acacia in aqueous solution.

Resins

These are soluble in alcohol, but insoluble in water. Common examples are adding aqueous liquids to tincture of asafetida, tincture of guaiac, tincture of myrrh, etc.

A large percentage of fluidextracts will precipitate either gums or resins when treated with a liquid of materially different alcoholic strength.

Among the drugs soluble in alcohol and insoluble or sparingly soluble in water are: acetanilide, acetphenetidin, benzoic acid, betanaphthol, camphor, monobromated camphor, iodine, menthol, methyl salicylate, phenyl salicylate, terpin hydrate, thymol, alkaloids.

Care should, therefore, be used in prescribing alcoholic solutions of these substances with aqueous liquids.

Salts, both of metals and alkaloids, are usually much more soluble in water than in alcohol.

Among those soluble in water and almost entirely insoluble in alcohol are: alum, tartar emetic, arsenic trioxide, double salts of iron, iron phosphate, iron sulphate, lithium citrate, magnesium sulphate, potassium bicarbonate, . potassium carbonate, potassium chlorate, potassium citrate, potassium and sodium tartrate, sugar, milk sugar, sodium borate, sodium carbonate, sodium chloride, sodium citrate, sodium nitrite, sodium phosphate, sodium sulphate, zinc sulphate.

It should be remembered that considerable water can usually be added to an alcoholic solution or alcohol to an aqueous solution without precipitation.