Ether

In regard to mixing with water, see the paragraph on volatile ingredients (page 306). It is worth bearing in mind respecting ether that it generally liberates iodine from potassium-iodide solutions, owing to the fact that on exposure to sunlight ether develops a trace of ozone, which reacts with the potassium iodide. Mixtures containing iodide and ether should therefore be made alkaline with potassium bicarbonate.

Extractum Ergotae Liquidum

Reference has already been made to the fact that this preparation is apt, on dilution with aqueous fluids, to undergo the viscous fermentation (see page 248). This experience is based upon the old preparation made by exhausting the drug with water, evaporating to three-quarters of the drug bulk, and adding alcohol to preserve. Any preparation made in vacuo which is not sterile before evaporation, and is not sterilised by boiling before the preservative is added, contains micro-organisms and their spores. The preservative may destroy the micro-organisms, but it seldom affects spores, so that when suitable conditions arise, the spores revivify, and fermentation of mixtures may result. Liquid extracts generally are prone to yield somewhat copious precipitates on dilution with water, especially in presence of acids; e.g. :

A heavy precipitate forms. Pharmaceutical ethics does not permit dispensers to make such mixtures elegant by filtration, which is to be regretted, for rarely are such precipitates of the slightest therapeutic value. Of course, when the precipitates are resinous, it would be wrong to remove them by filtration, but not so when inert extractive matter is the cause of turbidity.

Ferri Sulphas

Solutions of ferrous salts, if neutral, soon lose their brightness through oxidation of the salt, some ferric hydroxide giving a rusty appearance to the solution. This appearance is prevented by acidifying the solution; thus in the case of ferrous sulphate, dilute sulphuric acid is used, and the fact appeared to be known to the writer of the following prescription, who, however, was 'no chemist':

Here the aromatic spirit of ammonia neutralises the free acid and precipitates some green ferrous carbonate. Yet the mixture was dispensed clear by two chemists, who probably added sufficient acid to dissolve the ferrous carbonate, which, in the circumstances, is the wisest thing on the whole, considering that the therapeutic properties of the aromatic spirit are extinguished in the combination.