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OBSERVATIONS ON COLLODION. 
able time to the air, should be boiled to free it from ab- 
sorbed water. I have found the neglect of this precaution 
the most fruitful source of failure in making the prepara- 
tion. The officinal acid has the specific gravity of 1.84, 
which is fully as strong as necessary. 
3d. The materials and vessels employed in the process by 
either method must be dry. The ether must be undiluted 
with water. The presence of a small portion of alcohol 
facilitates the solution, though in excess it injures the pro- 
duct by rendering it less volatile. The officinal ether pos- 
sesses the requisite proportion. 
4th. In drying the prepared cotton, care should be taken to 
apply diffused heat to thin layers only, otherwise the part 
in contact with the heating surface will become dry before 
the remaining portion, and be very liable to take fire on 
any sudden elevation of temperature. 
5th. Collodion must be put into vials previously dried, 
well stoppered either with glass or cork stoppers. In 
applying it, the parts should be carefully wiped to free 
them from moisture, and where a permanent plaster is de- 
sired, the solution should be repeatedly painted over the 
surface. 
Collodion, as thus prepared, is a clear, colorless liquid, 
of a syrupy consistence, which, when applied to a dry 
surface, evaporates spontaneously, yielding a transpa- 
rent plaster without whiteness, possessed of remarkable 
adhesiveness and contractility. 
Composition of Collodion. 
Notwithstanding the difference of opinion which exists 
as to the chemical nature of this body, it may not be amiss 
in this place to give some general statements on the subject, 
with a view to encouraging its further investigation. 
There appear to be three substances produced by the 
action of nitric acid on cotton, Xyloidine, Pyroxyline, 
and Etheroxyline. Xyloidine was discovered by Bracco- 
