A dispensatory, or commentary on the phgarmacopoeias of Great Britain.

  • Robert Christison
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: A dispensatory, or commentary on the phgarmacopoeias of Great Britain. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

    75/1058 page 25
    cyanide of potassium I have invariably found to keep remarkably well. A specimen of medicinal strength continues still colourless, though it has been exposed to diffuse light for thirteen years; and I once kept for thirteen months unaltered a specimen which con- tained forty per cent of real acid. It has appeared to me, as it has also done to others, that those diluted acids keep best which con- tain a trace of some mineral acid; and in most of the specimens just referred to a trace of sulphuric acid was present. But at the same time I have known medicinal hydrocyanic acid from ferrocya- nide of potassium keep perfectly well, although nitrate of baryta did not produce in it the slightest muddiness. Those which con- tain cyanide of ammonium are very prone to decomposition, but the addition of a trace of sulphuric acid renders them permanent [Thaulow]. The change is accelerated by exposure to light, espe- cially to the direct rays of the sun. It is scarcely necessary to mention, that, on account of the volatility of this acid, it must always be kept in well-closed phials, otherwise its strength quickly dimi- nishes : Glass stoppers however are not absolutely necessary for its preservation, as many suppose. Adulterations and their Tests.—The medicinal hydrocyanic acid of the shops frequently contains impurities; and it is exceedingly apt to vary in point of strength. On these accounts great care has been taken by the Edinburgh and London colleges to guard the practitioner and druggist against its irregularity and adulterations. The ordinary impurities are sulphuric or muriatic acid, derived from these acids having been allowed to pass over in the process of distillation ; and sometimes, when hydrocyanic acid is prepared by decomposing bicyanide of mercury with sulphuretted-hydrogen, there is a trace of that salt in consequence of the gas not having been supplied in excess. The presence of either acid is shown by the precipitate with nitrate of silver being not entirely dissolved by boiling nitric acid; or, as the London College indicates, by a red precipitate of biniodide of mercury being produced by the double salt of iodide of potassium and bicyanide of mercury (Geoghegan.) In regard to these impurities, however, it must be remarked, that a trace of some inorganic acid is not objectionable, as it prevents the hydrocyanic acid from undergoing decomposition. The pre- sence of bicyanide of mercury is proved, according to the London directions, by the action of sulphuretted-hydrogen on the mercury; but the test is unnecessary as this salt is almost abandoned now for making medicinal acid. The effects of heat on the acid and of the acid upon litmus, which have been added by the London College to the tests of its purity, are likewise superfluous.— A more impor- tant subject than the adulteration of hydrocyanic acid is its irregu- lar strength. At one time the acid in the shops of London and Edinburgh varied in strength in the ratio of one to four; and even still the variation is considerable. A great deal has been written on this head, and numerous attempts have been made to render
    digitised image 1
    digitised image 2
    digitised image 3