3,32 MR. ROBERT HUNT ON THE INFLUENCE OF IODINE IN RENDERING 
with a portion of muriatic vapour, or a quantity of chlorine, sufficient to produce this 
effect, may be liberated from the preparation on the paper, to react on the sulphuret 
of silver. 
The most elaborate directions would be quite insufficient to ensure the production 
of perfectly equal papers : repeated experiments alone will ensure a certainty in the 
result. To produce a glittering metallic surface is less difficult, but the perfection 
of the papers consists in having a deep black ground to contrast with the mercurial 
deposit. No silvering on paper can be brought to the lustre of the metallic plates, 
and consequently, although the revived silver may be rendered tolerably dark by 
using very pure sulphuretted hydrogen and a strong solution of silver, yet the con- 
trasts are not sufficiently decided. With the black papers the picture is seen equally 
well in all directions, and the adhesion of the mercurial particles is closer than where 
a glittering surface has been presented to the action of its vapour. 
27 . If the paper is removed from the sulphuretted hydrogen at the moment the 
first white silver is revived, or still better, if the silver is revived by hydrogen gas, it 
maybe used to produce effects like what Sir John Herschel designates the negative 
variety of photographic drawing. 
After the drawing is produced in the usual method of the Daguerreotype, it is only 
necessary to immerse it in a warm saturated solution of common salt. The silvered 
portion gradually acquires a beautiful whiteness, while the parts covered by the mer- 
cury pass into a deep gray. All the fine effects producible by the original muriated 
photographic papers are given by this process, and the picture has the advantage of 
being absolutely permanent. 
Method of using those Papers . 
28. All the kinds of paper above-mentioned may be rendered sensitive by being ex- 
posed to the vapour of iodine, the best mode of applying which, is to spread over a 
thin board, the size of the sheet, a paste of iodine with spirits of wine. This board 
is placed in a box, and the papers being fixed in a frame about three inches above it, 
are iodidated in a few minutes. This plan is equally applicable to the plates. 
For the sulphuretted paper I recommend another plan, which has many very great 
advantages. It consists simply in drawing the surface of the paper lightly over a so- 
lution thus formed : a saturated solution of any hydriodic salt is made to dissolve 
as much iodine as possible ; and of this liquid two drachms are mingled with four 
ounces of water. 
Care is required that one side only of the paper be wetted, which is by no means 
difficult to effect, the fluid is so greedily absorbed by it ; all that is necessary being 
a broad shallow vessel to allow of the paper touching the fluid to its full width, and 
that it be drawn over it with a slow steady movement. When thus wetted it is to he 
quickly dried by a warm, but not too bright fire ; of course daylight must be carefully 
excluded. Papers thus iodidated do not lose their sensitiveness for many days. 
