OBSERVATIONS ON COLLODION. 291 
Thoroughly saturate the cotton with the acids previously- 
mixed, and allowed to become cool, and macerate for 
twelve hours. Wash the nitrated cotton in a large quan- 
tity of water, pick it out into thin layers, and dry it 
thoroughly by artificial heat : then dissolve it in the ether. 
No. 2. Take of Nitrate of Potassa, thoroughly dried 
and reduced to fine powder, 5 oz. 
Sulphuric Acid (concentrated) 4i fluid oz. 
Clean Carded Cotton, - - 15 grs. 
Sulphuric Ether, - 2\ fluid oz. 
Alcohol, 30 minims. 
Mix the nitre with the sulphuric acid in an open glass or 
porcelain vessel, then add the cotton and agitate the mass 
by means of two glass rods for three minutes; then pick it 
out into a thin layer and dry it thoroughly by artificial heat ; 
lastly, dissolve the prepared cotton in the ether, adding the 
alcohol. 
By both these processes we have repeatedly made Collo- 
dion of excellent quality. We have also made it by a pro- 
cess more nearly resembling that of J. B. Edwards, pub- 
lished in the last number of this Journal, (which accident- 
ally we did not see till since commencing this essay,) al- 
though the result of our experience is, that in order to in- 
sure the complete alteration of the cotton, it is preferable to 
macerate it for from six to twelve hours in the acids, and 
it is certainly less troublesome than the method of plunging 
it in very small quantities in the acids for the space of one 
or two minutes. 
The following precautions, however, must be observed 
in its preparation in order to insure success. 
1st. The nitric acid employed in No. 1 must be free from 
chlorohydric acid, a common impurity; it must be of the 
specific gravity named, or not less than 1.45. The officinal 
acid is 1.5. 
2d. The sulphuric acid employed in both formulae should 
be recently prepared, or if it has been exposed a consider- 
