L'NG

H3

cury exists iq two different conditions,—in the state of metal, mechanical-ly mixed,Jts asserted by Vogel, and in that of an oxide, chemically combin-ed with the lard, and that the medicinal activity of the ointment exclusive-ly "resides in this latter portion, the presence cf metallic mercury not onlybeing useless but injurious, by obstructing the absorption of the activecompound of the oxide. Mr. Donovan accordingly formed a direct chemi-cal combination, by continually agitating together lard and black oxide ofmercury at the temperature of 350° Fah: for two hours. At the end ofthe process it appeared that every ounce of lard had dissolved, and com-bined with 21 grains of oxide ; and from the trials which have been maderespecting its activity, it would seem to be as efficient as the officinal oint-ment, and moreover that it may be introduced by inunction in one third ofthe time. The investigation is highly important, for it not only offers themeans of preparing a mercurial ointment more ceconomically, but onemore active and manageable, and less liable to that want of uniformity instrength, which must always attend a preparation in which so much labouris required for its completion ; for independent of that variation in strengthwhich will arise from imperfect triture, it is by no means an uncommonpractice to use chemical means, which are not admissible, to facilitate theprocess, such as the addition of Sulphur, which is found to abridge veryconsiderably the labour requisite for the extinction of the mercury, but itconverts a portion of the metal into a Sulphuret, and diminishes the powerof the unguent. There is however a method of facilitating the process,which is not liable to any apparent objection, but the theory of its opera-tion is obscure; it consists in adding to the half-prepared ointment a por-tion of that which has been long kept: which appears to act as a leaven tothe whole mass.

The following table exhibits the relative quantity of mercury contain-ed in each of the different ointments directed by the British Pharmaco-poeia;, and in that prepared according to the process of Donovan.

One drachm C stronger ointment contains of Mercury, 30 grs.

oftheLond: £ weaker ointment ...........10 —

of the Edinb : common ointment ...........12 —

f tti D * S s ^ ron 8 er 0 i n t men t ...........30----

£ weaker ointment ...........20----

of that prepared according to Donovan........2J —

Mercurial ointment furnishes the most prompt, and least exceptionablemode of impregnating the system. The external method of adminis-tering mercury, says Mr. John Hunter, is always preferable to the internal,because the skin is not nearly so essential to life as the stomach, andtherefore is capable in itself of bearing much more than the stomach.The inunction is generally performed by rubbing 3ss to 3j on some partof the body where the cuticle is thin, generally on the inside of the thigh,except perhaps in cases of chronic hepatitis, when it is more usually ap-plied to the region of the liver, care being taken that the friction is con-st 212°, when it separated into two distinct strata, viz. the upper one which was lightgrey, and exttemely active as a medicine, and the under one, which upon being tritu-rated with magnesia, yielded a large proportion of metallic mercury, and which wasnot found to possess any activity.

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