Silver Printing Processes 
CoLLoDIO-CHLORIDE PRINTING-OUT EmMuLsion.—The va- 
rious formulas have been calculated for a total bulk of 
1000 ccm (16 oz.). The correct method of making the emul- 
sion is to prepare the collodion by dissolving the pyroxyline 
in the alcohol and ether, by first pouring the former on to the 
pyroxyline and shaking until it is thoroughly saturated, and 
then adding the ether. Absolute alcohol should be used, and 
pure methyl alcohol may replace ordinary ethyl alcohol, but 
the alcohol must be free from pyridine bases, which cause dis- 
coloration of the coated paper. As little water as possible 
should be used to dissolve the chlorides, acid, and silver, and 
such solutions should be mixed with alcohol prior to addition 
to the collodion. It is often necessary to allow the raw col- 
lodion to stand for some time for any impurities or undis- 
solved fibers to settle down; but the best results are obtained 
with the specially prepared pyroxylines, sold under the name 
of celloidin or pyralin. The best chlorides are those of 
strontium and lithium, and only the crystalline salt of stron- 
tium should be used. The lithium chloride should be 
weighed out and dissolved in alcohol as soon as purchased, 
so as to make a 10 per cent solution, as it is very hygroscopic 
and absorbs varying quantities of moisture. These two 
chlorides are the most satisfactory in practice. Taking a 
typical formula (Hanneke), the following is the best method 
of mixing: 
Pyroxyline 26 g 200 gr. 
Alcohol 565 ccm 9 oz. 
Ether 425 ccm 634 oz. 
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