liquid; and this also has a beneficial effect in washing off
any little particles of collodion, dust, oxide, or any foreign matter
which, if adherent, would form centres of chemical action, and cause
spottiness in the negative.

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I find that the plate is more sensitive also, if not exposed before all
the exciting fluid that can be _drained off_ is got rid of; that is,
while still quite moist, but without any _flowing_ liquid.

As to redipping the plate before development, it is, I believe, _in
general_ useless; but when the plate has got _very_ dry it may be dipped
again, but should be then _well drained_ before the developing solution
is applied.

MR. F. MAXWELL LYTE (p. 364.) quotes the price of the purest iodide of
potassium at 1s. 3d. per oz. I should be glad to know where it can
be obtained, as I find the price constantly varies, and upon the last
occasion I paid 4s. per oz., and I think never less than 1s. 8d.

MR. L. MERRITT will probably succeed in applying the cement for a glass
bath thus:--Place the pieces of glass upon wood of any kind in an oven
with the door open until he can only just handle them; then, with a roll
of the cement, melting the end in the flame of a spirit-lamp, apply it
as if for sealing a letter. This should be done as quickly as possible.
The glasses may then be passed over the flame of the lamp (in contact
with it), so as to raise the temperature, until the cement is quite soft
and nearly boiling (this can be done without heating the parts near the
fingers); and while hot the two separate pieces should be applied by
putting one down on a piece of wood covered with flannel, and pressing
the other with any wooden instrument: metal in contact would cause an
instantaneous fracture.

MR. MERRITT's difficulty with the developing solutions depends most
probably in the case of the pyrogallic acid mixture not having enough
acetic acid. The protonitrate of iron, if made according to DR.
DIAMOND's formula, does _not_ require any acetic acid, and flows quite
readily; but the protosulphate solution requires a bath, and the same
solution may be used over and over again.

GEO. SHADBOLT.

London, April 9, 1853.

_Economical Iodizing Process._--MR. MAXWELL LYTE is probably as good a
judge as myself, as to where any weak point or difficulty is found in
iodizing paper with the carbonate of potass: if any chemical is likely
to be the cause of unusual activity, it is the carbonic acid, and n