ON EMPLASTRUM PLUMBI. 
177 
in the preparation of it is, that less time is required for the 
accomplishment of the same object, than where the direc- 
tions of the Pharmacopoeia are strictly followed. A receipt, 
then, for lead-plaster that might be preferable to that of the 
Pharmacopoeia, would be, — lard, eight pounds; litharge, 
four pounds ; water, a pint. When the water is all evapo- 
rated, suffer the mixture to attain a temperature at which 
fuliginous vapours arise, — remove it from the fire and 
gradually add water-— constantly stirring until ebullition 
ceases, and if the plaster be not perfectly formed, repeat the 
operation. When the lard was boiled with water, some- 
thing was taken up, and the remaining lard acting on the 
litharge much quicker than ordinarily would prove Chev- 
reuii's view to be correct. The specimen of neutral plaster 
obtained by boiling the officinal article with caustic potassa, 
appeared to be margarate of lead. On thirty grains being 
treated with warm diluted nitric acid, and precipitated with 
iodide of potassium, it yielded twenty-six grains; from 
which take the iodine, and twelve grains of lead would re- 
main ; to which add sufficient oxygen to make the equiva- 
lent of litharge thirteen. Take this from thirty and seven- 
teen remains, which corresponds nearly with an equivalent 
of margaric acid and water. 
16* 
