ON THE PREPARATION OP COLLODION. 
233 
high price, than the acetate, and should always be pre- 
ferred to it whatever process is employed. 
That the process by iodide of calcium is most advanta- 
geous as regards the quantity and quality of the product. 
That since the two processes by iodide of iron and by 
iodide of zinc yield an equally beautiful product and in 
nearly the same amount, it is indifferent which is used. 
That the process by iodide of sodium has no advantage ; 
that by iodide of potassium is less economical, as this salt 
costs as much as the iodine, with which the other iodides 
may be readily prepared without loss and at a little expense, 
aud furnishes nearly one-fourth less for the same weight. 
In fact, when iodide of potassium and acetate of lead are 
employed, there is a loss of 10 per cent.; but the greater 
portion of this loss may be avoided by substituting the 
nitrate for the acetate of lead, or by pouring into the super- 
natant liquid a sufficient quantity of nitric acid to decom- 
pose the acetate of potash. 
Lastly, that the process by the double iodide of potas- 
sium and lead, although yielding a larger product than all 
the others, is less advantageous, in the first place from its 
requiring iodide of potassium, and secondly from the 
inferior quality of the iodide which it furnishes. — Chem. 
Gaz., from Journ. de Pharm. 
ART. L.— ON THE PREPARATION OF COLLODION. 
By J. B. Edwards, F. C. S. ; M. P. S., &c. 
Much difference of opinion appears to exist among some 
distinguished French Chemists, as regards the solubility in 
ether of the ordinary explosive gun-cotton, as described by 
Mr. Maynard, in America ; but since the discovery of M. 
Mialhe's process with nitrate of potash, I am not aware of 
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