ON RED OXIDE OF MERCURY OINTMENT. 
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in the British Pharmacopoeia, not indeed for the purpose for which it was for¬ 
merly introduced, but as an infinitely better substance than that now used for 
the preparation of the red oxide of mercury ointment. 
Oxide of mercury ointment appears always to have been prepared with the 
nitric oxide; it is so directed not only in the British Pharmacopoeia, but in the 
London Pharmacopoeias of 1851, 1836, 1824, and 1809. 
One possible reason for this preference for the nitric oxide is, that in the con¬ 
dition of scales, the oxide of mercury is less capable of adulteration, since its 
physical properties, e. g. the reflection of light from the glittering scales, enable 
it to be more readily recognized. 
But one can readily understand how the so-called binoxide should be a more 
active remedy. 
A mere comparison of the naked-eye appearance of the one with that of the 
other will suffice to show how much smaller the particles of the binoxide are: 
theirs is a paler and a duller colour. There is, in fact, just the difference that is 
seen between coarsely-pounded coloured glass and the same glass finely pul¬ 
verized. 
Under the microscope this difference is yet more clearly perceptible. An 
•examination of the precipitated oxide shows that none of its particles exceed the 
thirty-thousandth of an inch in diameter ; while the same scrutiny applied 
to the best levigated nitric oxide shows that although a great number of its par¬ 
ticles scarcely exceed the size just mentioned, many of them are as large as the 
five-hundredth of an inch. The diameter of a large proportion of the particles 
of the unlevigated nitric oxide is as much as the one-hundredth of an inch. 
The advantages of ointment made with the precipitated oxide of mercury, over 
that made with the so-called nitric oxide, are, in the first place, that supposing 
ointments of equal therapeutical value be used, greater economy is gained by 
the use of the precipitated oxide, since a less proportion of it will suffice in the 
same quantity of ointment. 
But there is a more serious objection to be urged against the use of the nitric 
oxide, and that is, that the presence of a quantity of gritty particles in an 
ointment which is to be rubbed in over a raw and irritable portion of skin, pro¬ 
duces a totally different action in it to wliat is sought for when an ointment of 
the red oxide of mercury is employed. 
One of the uses of the ointment of the flowers of sulphur in the treatment of 
scabies is, that the gritty particles of sulphur do, as it is rubbed in over the skin, 
actually ^rupture the tunnels in the epidermis in which the acarus scabiei resides, 
and so lay bare the itch-mite to the poisonous influence of the sulphur; and 
although the particles of well-levigated oxide are much less coarse than those of 
the sulphur, still it must be remembered that they are applied usually to much 
more delicate surfaces. 
This disadvantage in the use of nitric oxide I have more especially noticed in 
hospital and dispensary practice, where the oxide employed, except for ophthal¬ 
mic use, is often by no means carefully levigated, and where the introduction of 
ointment made with the precipitated oxide would ensure, irrespective of quality, 
a fine division of the particles. 
But I have also often had occasion to observe on the skins of persons for whom 
I had prescribed ointment containing the levigated nitric oxide, and whose pre¬ 
scriptions had been made up by the first chemists, very obvious glittering red 
scales. 
Here is some of the red oxide of mercury ointment of the British Pharmaco¬ 
poeia, and here again is the same preparation, except that precipitated has been 
substituted for nitric oxide ; you may observe how much “ smoother ” an oint¬ 
ment the precipitated oxide makes. 
However, although the fine state of division of the particles of the binoxide, 
