60 
MERCURIAL OINTMENT AND VAPOR OF MERCURY. 
but the younger Mitscherlich rendered it again doubtful. The 
two former even believed that a fifth part of the mercury was oxi- 
dized, which proportion appears far too great in accordance with 
my experiments ; it is moreover possible, that, in addition to keep- 
ing, finer trituration might increase the amount of oxide consider- 
ably. Guibourt, on the other hand, arrived at the result that only 
the one five-hundredth of the mercury was oxidized, that it did not 
exist in a free state in the ointment, but was combined with an 
acid. To decide this question I tested the etherial solution, which 
contained the fatty matter of the ointment, by means of a single 
pair of plates. A strip of sheet copper and of zinc were soldered 
together at one end in such a manner as to represent in form a 
tuning fork. When this simple apparatus is immersed in a liquid 
containing mercury in organic combination, in consequence of the 
galvanic decomposition the metal is thrown down upon the copper 
pole in the form of a gray film, which when rubbed upon the cop- 
per colors it white. This method has been recommended several 
times, and is so delicate that it detects one-tenth of a grain of 
corrosive sublimate in an ounce of a solution of albumen. But no 
mercury could be separated from the blue ointment by this 
means. 
We must therefore undoubtedly consider the oxide as the active 
ingredient of the blue ointment. But even the oxide cannot be 
taken into the body without the aid of a solvent; and this solvent 
is, in ail probability, the free acid of the cutaneous secretion. Both 
the perspiration and the fatty secretion of the sebaceous follicles 
exhibit an acid reaction ; and, according to Anselmino, the perspi- 
ration contains a considerable amount of free acetic acid. The 
acetic, acid dissolves the oxide, and this solution readily transudes 
through animal membranes and the cells of the epidermis. 
If this explanation be true, the greater part of the mercury con- 
tained in the blue ointment is perfectly inactive, and we ought to be 
able to form a far more active ointment from the pure protoxide. 
This can, in fact, be done. An ointment containing 3j- of the black 
oxide of mercury to 3ij. of fatty matter, hence as much as the blue 
ointment contains of metallic mercury, acts as an active poison to 
animals upon which it is rubbed in, and a scruple of it killed a cat 
in four days, and a rabbit in twenty-four hours. From some experi- 
ments which I made upon some patients with an ointment contain- 
