"I employed hyposulphite of soda as a fixer. Mr. Hodgson, an able practical chemist at Apothecaries' Hall, assisted me in the preparation of this salt, which at that time was probably not be found, as an article of sale, in any chemist's shop in London. Sir John Herschel had previously announced the peculiar action of this preparation of soda on salts of silver, but I believe that I was the first to use it in the processes of photography. I also used iodide of potassium, as appears from my letter, as a fixer, and I employed it as well to form iodide of lead on glazed cards as an accelerator. Iodide of lead has of itself, as I form it, considerable photographic properties, and receives very fair impressions of plants, lace, and drawings when placed upon it, but with the addition of nitrate of silver and the infusion of galls the operation is perfect and instantaneous. Pictures thus taken were exhibited at the Royal Society before Mr. Talbot proposed his iodized paper. The microscopic photographs exhibited at Lord Northampton's in 1839 remained in his lordship's possession. I subsequently made drawings of sections of teeth; and one of them, a longitudinal section of a tooth of the Lamna, was copied on zinc by Mr. Lens Aldous for Owen's 'Odontography.' I may say this much as to my own approximation to an art, which has deservedly and by universal consent obtained the name of Talbotype."
Photographic Cautions.—Diffused light being one of the most common causes of photographic failures, I beg to call the attention of your readers to the construction of their cameras. Working with a friend, and taking the same localities, using the same paper and chemicals, his pictures have proved comparative failures, a general browning pervading the whole, evidently the effect of light. Every inspection failed to discover it, until the mode was adopted of putting one of the paper-holders in its position as for taking a picture, then removing the lens, and, with the aid of the focussing-bag, looking through the hole where the lens is applied, when light became visible in many spaces, entirely accounting for these failures. As many such cameras are now becoming made upon the same sliding construction, every one should test his apparatus before he commences, for such a one is entirely useless. Lately also the glass corners for collodion plate-holders in the dark slides, have been by some makers replaced by a sort of silver looking wire, but possessing little of that metal. The most minute portion of the copper in this wire coming in contact with the excited collodion, produces a decomposition sufficient to spoil any picture. These may appear trivial things to "make a note of," but as they have caused much vexation to one who has had some photographic experience, they may still more perplex a novice; and as you have done so much towards making the science plain, I hope you will give them space in your forthcoming Number.
Lux in Camera.
A Query respecting Collodion.—I have been making some collodion by Mr. Tery's process, and have iodized it with a very sensitive medium. The collodion is very clear and properly diluted. The ether I used had a very powerful smell of sulphur, and was likewise very strong and volatile. I diluted it with an equal
volume of alcohol. The ether was then still very strong. The cotton dissolved freely. On mixing the iodizing medium, the colour of the collodion turns immediately to nearly a port-wine colour, but still remains very clear. I obtain a very good film of iodide of silver from the bath, but cannot produce a picture under five or seven minutes, whereas with the same lens, and the same iodizing medium, viz.
| Alcohol | 8 drms. |
| Iodide of potassium | 8 grs. |
| Iodide of ammonium | 4 grs. |
| Iodide of silver | ½ gr. |
I have obtained beautiful pictures in less than one second with collodion prepared by the same (Archer's) process. As I have made a quantity of it, and am unwilling it should be wasted, I have taken the liberty of asking your opinion on the subject. Do you think the collodion is too new, or the ether not good? On pouring the developing solution on the plate (protosulphate of iron), the plate has the appearance of having ink poured on it; but this appearance is removed on the application of the hyposulphite of soda, and the plate remains as clear as when it was taken from the nitrate of silver bath.
J. Cook.
The Céroléine Process.—Have any of your photographic correspondents made such experiments on the céroléine process as to enable them to communicate the results to "N. & Q."?
Is Mr. Crooke's process for preserving the sensitiveness of collodion applicable to all collodions? If not, what collodion is best suited for it?