244 
MINUTE DIVISION OF MERCURY. 
tion, the oxide remaining on the surface of the cuticle,, after 
the unctuous matter is absorhed. Dr. Paris justly remarks, 
that this is owing to its being a mechanical mixture, instead 
of a chemical combination; aiVopinion, however, which is ren- 
dered doubtful, by the experiments made to prove the non- 
oxidation of the mercury in the preparation of the mercurial 
ointment." 
Dr. Thomson mentions that, 
" M. Roux triturated mercury and maltha, a species of 
pitch, in a vacuum, and produced the extinction of the metal 
as well as if the operation had been performed in the air. 
Thence he concludes that the metal is not oxidized, but merely 
mechanically divided in the ointment. There are still, how- 
ever, some difficulties in deciding this point. Whatever tends 
to favor oxidation, as, for instance, a slight degree of rancidity 
in the lard or oil of eggs, shortens the time, and lessons the 
labor required for the preparation of the ointment." 
Dr. Pereira qualifies his statement as follows : — 
Hydrarg. cum Greta. {Dr. Pereira 9 s Materia Medica, 
1839.) — " It consists of mercury and chalk, with perhaps a 
little protoxide of mercury. 7 ' 
The following is Professor Mitscherlich's explanation : — 
( Lehrbtich der Chemie. Berlin, 1840.) — "When quick- 
silver is triturated with fat and other substances, in contact 
with air, there forms ultimately a black powder, which con. 
sists of metallic particles only. This can be readily ascer- 
tained by muriatic acid ; because protoxide of mercury affords 
with muriatic acid, calomel, which is easily recognized by 
sublimation. 
" It can be easily shown that in the common mercurial 
ointment (ung. hydrarg.), only finely divided quicksilver is 
contained, by removing the fat with ether, or by saponifying 
it, and then removing the soap with alcohol ; the residuum, 
treated with a little muriatic acid and sublimed, affords only 
metallic quicksilver. 
"If an ointment be prepared, on the other hand, quite in 
the same way, only using the protoxide instead of quicksilver, 
then the residuum, treated with muriatic acid, affords calomel," 
