326 
MR. ROBERT HUNT ON THE INFLUENCE OF IODINE IN RENDERING 
This led to many experiments, and as I consider that the results arrived at are 
of considerable scientific importance, I shall, without apology, proceed to detail a 
series of experimental observations, which, it appears to me, promise to extend the 
principles of photography to purposes of high interest and of much utility. 
1. M. Daguerre has stated, that a solid silver plate is less effective than one of 
copper plated with silver. All my experiments go to prove the correctness of this 
statement. This has been attributed, and I think correctly, to electric influence called 
into operation in the preparing processes by heat and with the acid. It will be found 
that an unprepared plate requires as long again to become properly coated with iodine 
as does a prepared one ; and a pure plate, though carefully prepared, a third longer 
time than a compound one. 
It is necessary, to produce iodidation readily, and to ensure the best effect from 
radiation, that a semi-oxidized surface be presented to the iodine. This fact will 
render obvious the superiority of the two metals ; common observation will show, 
that plated goods lose their lustre much sooner than silver articles, the process of 
oxidation being much accelerated by the compound arrangement. 
2. If an unprepared plate be iodidated and exposed to light, it darkens, and its 
superficial coat may be easily rubbed off, leaving a surface of exquisite lustre, some- 
what darker than that which results from the nitric acid process, and more susceptible 
of iodidation. Whether a film of oxide or iodide of silver is here produced, I am 
uncertain: I suspect the former*. It is, however, evident that the silver has under- 
gone some change. 
3. If a leaf of very pure untarnished silver be carefully spread upon card, ora piece 
of glass, and at once exposed to the vapour of iodine, it will be found to remain un- 
attacked for a considerable time. 
4. If a silver leaf thus spread be w r ell burnished, it will be seen that iodine acts 
upon it more readily than before. 
5. If we burnish half of a leaf, and tarnish a portion of both the dull and bright 
parts, the iodine will then attack, first, the tarnished, then the bright, and last of all 
the unpolished portion. 
6. Spreading a leaf of silver upon a piece of copper foil, and, to render the adhesion 
perfect, applying a gentle heat, a surface was formed which received the iodine 
readily. A sheet thus prepared was perfectly iodidated in five minutes, whereas a 
surface of the same extent on glass required twelve minutes. 
These results established in my mind most satisfactorily, the possibility of giving 
to paper all the properties of the silver plates. It is clearly shown, that a degree of 
oxidation is required on the metallic surface. From this fact, the necessity is sug- 
gested of examining the peculiarities of action manifested by iodine, on the oxides of 
silver produced in different ways, and their relative states of sensibility to luminous 
influence induced by iodidation. 
* See Philosophical Magazine, vol. xvi. p. 271. 
