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PREPARATION OF COLLODION. 
effect due probably to the deposition of moisture from the 
atmosphere, condensed by the cold surface from which eva- 
poration was taking place: the addition of even a minute 
quantity of water to collodion, being well known to produce 
immediate precipitation of a white insoluble substance. 
Sheets of this material of any thickness may be prepared 
as before mentioned, by drying the solution upon glass 
plates. From a number of experiments upon this form of 
collodion, it was found that a slight increase in the quantity 
of Venice turpentine produced a more transparent and flex- 
ible film, resembling oiled silk closely in some of its proper- 
ties ; for which in certain cases it might advantageously be 
substituted. It is inferior to the silk in strength, nor can it 
be sewed, as the stitches give way immediately ; but it 
possesses a great superiority in the absence of lead, which is 
largely present in the former, and which blackens upon the 
discharge of pus or other matters containing sulphur, from 
wounds, ulcers, &e. With this material no change is pro- 
duced by any discharge, the number of substances affecting 
its sensible properties being very small. 
If for a plate of glass be substituted a block of marble, the 
pellicle will present a beautiful crystalline structure resem- 
bling closely the film, which forms upon the surface of a sa- 
line liquid, when crystallizing. A temporary substitute for 
ground glass can thus be procured in a few moments. 
The singular results afforded by every new experiment 
upon this interesting and curious substance, induce a be- 
lief that other characteristic properties will yet be discover- 
ed belonging to it, rendering it of great value and importance 
to the arts. 
