On diseases of the skin : a system of cutaneous medicine / by Erasmus Wilson, F.R.S.

  • Wilson, Erasmus, Sir, 1809-1884.
Date:
1867
Catalogue details

Licence: Public Domain Mark

Credit: On diseases of the skin : a system of cutaneous medicine / by Erasmus Wilson, F.R.S. Source: Wellcome Collection.

    982/1058 (page 900)
    eight hours. But it was left to the late Mr Bell to draw our attention particu- larly to the preservative property of the gum benjamin, of which he proposed to avail himself in the preparation of an unguentum zinci benzoatum. This pro- position was eagerly accepted, and medical men and chemists will still remem- ber Mr Bell by this, one of his last improvements in pharmaceutical chemistry— the unguentum zinci benzoatum. This ointment is made by selecting the best and most fragrant gum benzoin, the so-called benzoin in tears ; this, when comminuted, is added to good fresh lard, in the proportion of ten grains to the ounce, and the whole digested in a water bath for about forty-eight hours; this, subsequently strained, is used for the preparation of the benzoated zinc ointment. In making this ointment with two oxides of zinc, a difference of reaction will be observed between the oxide made by combustion and that made according to the Pharmacopoeia, which, slight as it may be, deserves nevertheless some attention. The buff-coloured oxide of the Pharmacopoeia seems readily and speedily to amalgamate with the benzoated lard, so much so as sometimes to impart to the whole still warm fluid a certain consistency, which in far greater degree becomes more observable when the ointment is cold. Subsequent experi- ments showed that the seemingly lighter oxide of combustion resists with greater effect the influence of weaker acids, while the dense oxide of the Pharmacopoeia is readily dissolved by them. This chemical difference is in all probability the cause of the different be- haviour of these two oxides when used for the unguentum zinci benzoatum. Ben- zoic acid is readily dissolved by fats and oils; and in digesting the gum for some time with the lard, this acid, as well as the aromatic principles, impregnates the fat, and subsequently acts on the zinc. How far this greater susceptibility to weak acids may render it a beneficial application to a wound is a surgical question; but it is a well-known fact that many of the most skilful and eminent surgeons' always prefer the buff-coloured zinc ointment to the perfectly white one made with the new oxide of zinc of combustion. Although of British origin, the unguentum benzoatum has not as yet been adopted by any British Pharmacopoeia; but the United States of America have had the wisdom to introduce it into their Pharmacopoeia of 1863, under the name of unguentum benzoini, and have given as their formula for preparing it one part of gum benzoin to sixteen of lard, with an exposure to heat in a water bath of two hours.