_Economical Way of Iodizing Paper._--The extravagant price of the salt
called iodide of potassium has led me to experiments as to whether paper
could not be iodized in another form; and having been successful, I offer
the process to the readers of "N. & Q." Having verified it three times, I
can safely say that it is quite as effectual as using the above salt.
The first solution to be made, is a saturated solution of iodine. Put about
sixty grains of iodine (the quantity is not of importance) into an ounce
bottle, and add proof spirits of wine; set it near the fire "on the hob;"
and when it is nearly boiling, agitate, and it will soon become a
concentrated essence: take now a bottle of clear glass, called a quart
bottle, and put in it about two ounces of what is called carbonate of
potash (nothing more than purified pearlash); fill up with water to within
an inch of the neck, and agitate; when it is dissolved, add any of the
other approved sensitives, in discretionable doses, such as fluoride or
bromide of potassa, ammoniac salt, or common salt--it may have about sixty
grains of the latter; and when all are dissolved, add the iodine. This is
added by degrees, and shaken; and when it is a pale yellow, it may be
considered to be ready for iodizing: from some experiments, I am led to
believe that a greater quantity of iodine may, if necessary, be added, only
the colour should not be dark. And should the operator reach this point, a
few drops of solution of cyanide of potassium may be added, until the pale
colour returns. Bromine water I believe may be added, but that I have not
used hitherto, and therefore cannot answer for its effects. The paper then
having its usual wash of nitrate of silver, is then floated on the solution
about one minute, and the accustomed process gone through as described by
most photographers. It is only disposed to require a pretty strong solution
of silver, say thirty grains to the ounce of water. This I attribute to the
potash being in a little more caustic condition than when recrystallised
with iodine. And the only difference in the above formula between the two
states is, that the iodine in the medical preparation is incorporated by
means of iron filings with the water, which I only interpret into being a
cheaper method; which makes its high price the more scandalous, and I hope
this method will save photographers from the imposition: the price of a
quart of iodide of potassium would be about six shillings, by the above
about ten-pence. And I can safely say, it is quite as effectual:
theoretically, it appears to be better, because iodine is exceedingly
difficult to preserve after being dissolved and recrystallised. And much of
it is lost in the preparing iodized paper: as, for instance, the usual way
generally requires floating on free iodine at the last; and with the
formula here given, after using once, some small quantity of tincture of
iodine should be added before putting away, as the silver laid upon the
surface of the paper absorbs more of the iodine than the potash. Therefore,
a very pale yellow may be its usual test for efficiency, and the equivalent
will be maintained.
N.B.--Potash varying much in its alkaline property, some samples will
remain colourless with addition of iodine; in which case the judgment must
guide as to the quantity of iodine. It should not exceed the ounce of
tincture: about two drachms may be added after using it for paper.