APPLICATION OF YELLOW AMORPHOUS OXIDE OF MERCURY. 335 
lsf. The crystalline, or red oxide, prepared by the dry method, and commonly known 
as red precipitate, constituting the very common remedy ; and 
2nd. The amorphous, or yellow oxide, prepared by the wet method by precipitation ; 
up to within a few years unknown to the pharmacopoeia, although it is indubita¬ 
bly preferable to the first. 
The common red precipitate is rendered applicable to practice by being triturated in 
a porcelain mortar till no more brilliant crystalline points can be perceived : a powder 
is thus obtained, which is quite soft, and when rubbed between the fingers no longer 
imparts any gritty feel. If this, after being prepared in the most careful possible way, 
is submitted to the microscope, it may, under a magnifying power of even 120 diameters, 
be recognized as a mass of broken crystals. The point up to which the trituration should 
be continued, which forms the measure of the fineness of the division, is in this method 
uncertain and inconstant. Thus this preparation occurs in different degrees of fineness 
in different shops; and as its efficacy is intimately connected with its fineness, the sur¬ 
geon gets preparations which act with unequal strength. 
For obtaining, therefore, a preparation uniform in its effects, and in the finest possible 
state of division, the yellow precipitate, which is thrown down, is highly to be recom¬ 
mended. Thinking this would also prove a far more energetic preparation, I, in 1850 for 
the first time, prepared some, and recommended its use to Dr. Pagenstecher in his eye- 
practice, instead of the common precipitate, and found my anticipation most gratifyinglv 
confirmed. The mode of preparing the yellow precipitate, although well known, may¬ 
be still worth mentioning. Care must be taken in the precipitation to obtain a pure 
oxide, and not any of its compounds, to which precipitates of mercury have a great 
tendency—a fact which might detract from the efficacy of the preparation. The pre¬ 
cipitation is effected by adding a solution of the chloride of mercury to a solution of 
potash, in such a way that there is always an excess of the latter. After the precipitate 
has deposited itself, the supernatant fluid is at once poured off, the precipitate thoroughly 
washed with distilled water, and dried by a gentle heat, with exclusion of daylight. 
Thus prepared, the yellow precipitate has a light-yellow (that of the yolk of egg) colour, 
and is exceedingly fine powder, which, even under the microscope, appears completely 
amorphous. In addition to both the above-signalized properties, it differs from the ordinary 
precipitate in its chemical behaviour, being much more quickly acted on by reagents. 
A solution of oxalic acid, which acts on the red oxide only after boiling, very quickly 
changes the yellow oxide, even at the ordinary temperature, into the white oxalate. The 
preparation of hypochloric acid gas depends on the property the yellow oxide of mercury 
possesses of decomposing in contact with chlorine gas; the results being hypochloric 
acid and chloride of mercury; whereas the red oxide undergoes, with chlorine gas at 
the ordinary temperature, hardly any change. This difference of chemical behaviour 
of the two oxides constitutes a different degree of resistance to the various agents they 
are submitted to, and is explained by their different states of cohesion. In respect to 
the use of the yellow precipitate for eye-ointments, I may be allowed to say a few words 
on the vehicle of the ointment. The most perfect vehicle for an eye-ointment must be 
very soft, without, however, being too fluid, lest the heavy oxide sink to the bottom; 
but when in contact with a moderate heat of the body, it must completely melt, so that 
the preparation it contains may become quickly and uniformly diffused over the eye. 
Besides this peculiarity of consistence, the vehicle must be, as far as possible, indifferent 
in its behaviour to the oxide, and exhibit the least possible tendency to rancidity, which 
might exert a deoxidizing, reducing action on the oxide. Numerous experiments with 
hog's-lard, butter, glycerine, glycerine ointment, and mixed fats, have led me to give the 
preference to the last; and I recommend either the mixture of spermaceti, wax, almond- 
oil, and rose-water, known as “ cold cream,” only omitting the water, as this favours 
rancidity, and substituting for it quantities of almond-oil, varying according to the heat 
of the weather; or a mixture of butter, of cocoa, and almond-oil, likewise proportionate 
to the temperature. In both compounds the almond-oil must be as fresh as possible, 
and had best be prepared by the apothecary himself.* 1 
* As regards the strength of the ointment, I generally use one drachm of oxide to one 
ounce of fat. This may appear very strong to some, but experience amply shows that, ap¬ 
plied in proper cases, it does not in any way irritate too much. Idiosyncrasies may, of 
course, be observed, as in every remedy; and if the ointment in a given case irritates too 
much, its strength may be reduced to 30 grs. of oxide to the ounce. I may further remark. 
