162 
HYDRARGYRUM CUM CRETA. 
tion, and consequently the value of the product will depend 
on the judgment or patience of the operator. Three or four 
weeks' rubbing is necessary, in order to reduce it to that 
minute state of subdivision in which the globules will not 
cohere on the addition of a small portion of tinct. opii, 
which is frequently prescribed with it. 
The cheapness of labor in England, or the use of steam 
power in their large chemical manufactories, has enabled 
them to prepare our best samples of Hyd. c. Cret. and blue 
mass. The foreign mercurial ointment has for some time 
been excluded from our market, owing to the facility with 
which mercury is divided, in 15 or 20 minutes, by a small 
quantity of lard rendered viscid by exposure to the air. It 
has been ascertained that other viscid substances will accom- 
plish the same object: resinous extracts, for instance. This 
power, I imagine, depends not only on the separation of the 
minute globules, but also on the electrical condition which 
is excited by the friction employed, and being preserved by 
the resin, renders them repulsive to each other, thus facili- 
tating their further subdivision. Upon this principle, I 
propose to make use of pure resin in the following formula 
for Hyd. cum Cret.: 
P. Hydrargyri giij. 
Re si nag §vj. 
Cretse ppt. §v. 
Alcohol is q. s. 
Rub the mercury with the resin for three hours; add the 
chalk, and triturate one hour; transfer the powder to a glass 
jar; treat it with Oij. alcohol; pour off the solution of resin, 
and replace it with Oss. of alcohol ; repeat the washing until 
the resin is removed, and dry the powder on bibulous paper; 
when perfectly dry, mix it intimately in a mortar. Three 
hours are sufficient to make a preparation in which the glo- 
bules are not visible with a very powerful lens. 
