I have been making some experiments in preparing the iodized paper in the
following manner, more especially in consideration of the present price of
iodide of potassium:--60 grains of nitrate of silver; 60 ditto of iodide of
potassium, cleaned and prepared as before described, by the addition of
three ounces of water,--that is 3 oz. altogether; 60 grains of cyanide of
potassium; add a little of this at a time, and shake it up; and I generally
find that this quantity is sufficient to redissolve the 60 grains of iodide
of silver. Brush the paper over with the above, and when the wet surface
disappears, dip it into cold water containing one drachm of dilute
sulphuric acid to one quart of water; and then into water for half an hour,
changing the water once: pin up to dry. I have not had an opportunity of
trying this for negatives, but I have taken some good positives with the
paper so prepared.
N.B.--I find that if the paper is allowed to dry with the cyanide of
potassium, or that it is allowed to remain in the dilute sulphuric acid
water too long, it weakens the paper so much as to be very absorbent. I
would therefore wish to know from any of your correspondents whether this
arises from taking away the size, or injuring the fibres of the paper? and,
if so, whether a paper prepared with starch, instead of size, would be
better? as it appears to me that this mode of iodizing might be an
improvement. At all events, it is an enormous saving of iodide of
potassium; as, for instance, to redissolve the 60 grains, it would take 1½
oz. of iodide of potassium (about four shillings); whereas 60 grains of
cyanide would not cost more than one penny or twopence.