d with the use of the air-pump, as recommended by Mr. Stewart, I
have met with much trouble and little success; and I am inclined to
attribute the very beautiful specimens which he has produced to his own
good manipulation under a favourable climate.[6]

To excite the paper take 10 drops (minims) of solution of aceto-nitrate of
silver, and 10 drops of saturated solution of gallic acid, mixed with 3
drachms of distilled water.

The aceto-nitrate solution consists of--

Nitrate of silver 30 grains.
Glacial acetic acid 1 drachm.
Distilled water[7] 1 ounce.

If the weather is warm, 6 drops of gallic acid to the 10 of aceto-nitrate
will suffice, and enable the prepared excited paper to be kept longer.

This exciting fluid may be applied either directly {599} by means of the
glass rod, or by floating, as before, and then the glass rod. But if
floating is resorted to, then a larger quantity must be prepared. As soon
as it is applied the paper should be blotted off by means of blotting-paper
(which should never be used more than once in this way, although preserved
for other purposes), and put into the dark frames for use.[8] It is not
requisite that the paper should be perfectly dry. This exciting should be
conducted by a very feeble light; the paper is much more sensitive than is
generally supposed; in fact, it is then in a state to print from by the aid
of gas or the light of a common lamp, and very agreeable positives are so
produced by this negative mode of printing.

I would advise the aceto-nitrate of silver and the solution of gallic acid
to be kept in two bottles with wooden cases differing in their shape, so
that they may not be mistaken when operating, in comparative darkness. A
1/4 of an ounce of gallic acid put into such a 3-ounce bottle, and _quite_
filled up with distilled water as often as any is used, will serve a very
long time.

I would also recommend that the paper should be excited upon the morning of
the day upon which it is intended to be used; no doubt the longer it is
kept, the less active and less certain it becomes. I have, however, used it
successfully eight days after excitement, and have a good negative produced
at that length of time. The general medium time of exposure required is
five minutes. In the negatives exhibited, the time has varied from three
minutes to eight, the latter being when the day was very dull.

The pictures should be developed by equal quantities of the