Infusum Rosae Acidum

Every student of volumetric analysis knows that in titrating acids or alkalies certain vegetable colours are used as indicators, because they show different colours in acid, alkaline, and neutral solutions. The colour of rose-petals is not so used, but it might be : it is a beautiful red in presence of acids, and a vivid green when alkali is in excess. This should be kept in mind when compounding the acid infusion of roses, and prescribers should be warned not to prescribe alkalies with it, as in the following instance:

As soon as the magnesium carbonate is added, the sulphuric acid of the infusion begins to be neutralised, the mixture becomes blue, and eventually brown.

Infusum Serpentariae

For some reason or other doctors are fond of the following prescription:

It gives dispensers a great deal of trouble, because the mixture may be in colour like black ink, or like pale sherry, or like rich brown sherry. The inky-coloured mixtures are of course due to the infusion containing starch taken into solution from the bruised root (see page 55). Sometimes the drug contains no starch at all, but in any case it is advisable to make the fresh infusion from unbruised root, and with water at 1600 F., infusing three times longer than the Pharmacopoeia directs. Many dispensers prefer to use the concentrated preparation (liq. serpentariae cone, B.P. 1898), which is free from starch, and gives a sherry-coloured mixture with iodine.

Liquor Hydrargyri Perchloridi

Remarks have already been made regarding the readiness with which mercuric chloride combines with alkaloids. See next page.

A precipitate of mercuric iodide is formed in No. I., and of mercuric oxide in No. II.