176 
ON EMPLASTRUM PLUMBI. 
7th was melted with resin in the proportion directed for 
adhesive plaster; it made a harder plaster than the result of 
experiment 5th, in which case olive oil was used. I account 
for this from the fact that the stearate is firmer than the 
oleate of lead. There was a slight difference in the fracture 
of the adhesive plaster, that made from the olive oil having 
a more shining fracture, than that from the lard. When 
applied to the skin the sticking qualities appeared the same. 
The combining weight of stearine being much greater 
than that of olein, a less quantity of litharge would be re- 
quired to convert it into a plaster, and there may be some 
advantage in using a plaster of this kind ; as there is upon 
record a case of lead-cholic, as having occurred from the 
use of lead plaster, it might be desirable to use that which 
contains the smallest proportion of lead. 
9th. A small quantity of officinal lead plaster was boiled 
with carbonate of soda, and was decomposed, forming a 
soap of soda, and carbonate of lead. When boiled with 
caustic potassa, a soap of potassa and oil was formed, and 
neutral margarate of lead was thrown down, which consists 
of one equivalent of margaric acid 140, and one equivalent 
oxide of lead 111.6 combined with one equivalent of water 
9 = 260.6. 
From these experiments it would appear first, that a plas- 
ter cannot be formed directly by the oxides of iron ; and 2d, 
the specimen of American litharge used consisted of a prot 
and suboxide of lead, and when acted on by the oily acids 
it was reduced to a protoxide and metallic lead, the change 
of colour would indicate that oxygen is absorbed by a part, 
while that which parts with its oxygen is reduced ; and 
3dly, as the lead assumes a floculent form, and thereby im- 
proves the appearance of the plaster, it is an advantage ; 
and 4th, it proves that lard is equal to olive-oil in all respects 
for making plaster, and perhaps advantageous on account 
of less litharge being required ; and also another advantage 
