ON EMPLASTRUM PLUMBI. 
173 
After it had cooled sufficiently, the mixture was transferred 
to a bottle, and allowed to stand undisturbed for twenty- 
four hours, at which time the oxide of iron had entirely 
separated from the oil, which was as clear and transparent 
as before being submitted to the operation. 
2d. The same quantity of olive oil as in experiment 
1st, was treated in the same manner with half a pound of 
anhydrous sesquioxide of iron, the result being the same as 
in experiment 1st. 
3d. One pint of olive oil was boiled with a half pound 
of protoxide of iron (prepared fresh, and added to the oil 
with the water, that it should not become peroxidized before^ 
being mixed with the oil) for the same length of time as in 
experiment 1st. After the water in which the protoxide of 
iron was added was driven off, the mixture was kept over 
a regular fire for a half hour, when it rose considerably 
above the boiling point of water ; it was then removed from 
the fire, and water gradually added to reduce the tempera- 
ture to 212°. Upon cooling, the oxide separated as in the 
former experiments; it being now black, it was probably in 
the state of a black oxide ; the oil had a dark colour, caused 
probably by its being raised to too high a temperature, and 
slightly burnt. These experiments I think prove satisfac- 
torily that the oxides of iron will not combine directly with 
the oily acids to form a plaster. 
4th. Being in possession of an article of American lith- 
arge, which on former occasions had thrown down a pre- 
cipitate of metallic lead, during the process of forming lead 
plaster, I determined to add a portion of red lead (oxid i 
plumb : rub :) with a view of supplying oxygen to the me- 
tallic lead. I therefore in this experiment took of litharge 
nine parts, of red oxide of lead one part • five pounds of 
which was added to one gallon of olive oil and two pints 
of water. The mixture was placed over a regular fire, and 
as it rose to the boiling point of water, and was continued 
VOL. XIII. — NO. III. 16 
