DRY COLLODION PROCESS IN PHOTOGRAPHY. 320) 
perty capable of bringing about the union of small pieces of ice floating freely 
under water: and the mode of growth of ground-ice is, he believes, as yet com- 
monly regarded as an unsettled point, no opinion offered having received very 
decisive or general assent.—Proceedings of the Belfast Natural History and 
Philosophical Society, May 7, 1862. 
——_—— 
DRY COLLODION PROCESS IN PHOTOGRAPHY. 
Mr. Sutton claims to have discovered a process with dry plates which gives 
all the rapidity and keeping properties of the well-known trade secret of Dr. 
Hill Norris. The following account is extracted from the “ Photographic 
Notes” Oct. 15, 1862. ‘ 
The problem which has most interested photographers of late years has been 
the discovery ofa dry collodion process, by which plates can be prepared as 
‘sensitive as with wet collodion. In the wet process the negative has to be taken 
and finished upon or near the spot from which the view is taken, and with wet 
collodion the tourist is therefore obliged to work in a van or tent, and. carry a 
load of paraphernalia about with him, which is of course both expensive and 
inconvenient. To avoid this he is compelled to work with dry plates, and 
hitherto no process has been published by which dry plates can be made as 
sensitive as wet ones. A rapid dry process has therefore been an important 
subject of investigation to photographers, because during a long exposure ofa . 
plate the shadows move, and figures sometimes alter their position. A man or 
horse, for instance, are likely to remain still for a few seconds, but not for ten 
minutes. 
Ihave lately solved this problem of rapid dry collodion, and produced dry 
plates as sensitive as wet ones, which will moreover preserve their sensitiveness 
and good qualities for several weeks, and perhaps indefinitely. This process, 
and the principles upon which it is based, I will now briefly describe. : 
The rapidity of this dry process depends upon the accelerating effect of 
bromine in dry collodion, and in this respect an anology exists between the 
Daguerreotype and dry collodion processes. In the former a silver plate simply 
iodized is extremely insensitive, but when submitted to the fumes of bromine its 
sensitiveness is increased a hundred-fold. The same thing happens in those 
collodion processes, wet or dry, in which the free nitrate of silver is washed out 
of the film. A collodion film simply iodized, and without free nitrate, is as 
insensitive as an iodized Daguerreotype plate, but a bromo-iodized collodion 
film without free nitrate may be rendered as sensitive as a bromo-iodized silver 
plate. In the wet collodion process the most exalted sensibility is conferred 
upon a simply iodized film by the presence of free nitrate of silver; but you 
cannot retain free nitrate in a dry collodion film because it not only crystallizes 
on drying, but by becoming concentrated as the water.evaporates, dissolves the 
iodide of silver, and forms a curious and interesting double salt, the exact pro- 
perties of which have not yet been fully’ investigated. You cannot even retain 
a perceptible trace of free nitrate entangled in a dry collodion film without 
‘introducing an element of instability, and consequent uncertainty in your work. 
The principle therefore of preparing a rapid dry collodion plate consists in using 
