June 3. 1854.] 



NOTES AND QUERIES. 



525 



solution to be more readily acted upon when applied 

 to the leather, suggested my application of the tanning 

 solution to paper. 



" In your own history of the photographic process," 

 says Mr. Reade, addressing Mr. Hunt, " you say, ' the 

 discovery of the extraordinary property of the gallic 

 acid in increasing the sensibility of the iodide of silver 

 was the most valuable of the numerous contributions 

 which Mr. Talbot has made to the photographic art.' 

 It is nevertheless true, as stated by Sir David Brewster, 

 that 'the first public use of the infusion of nut-galls, 

 which is an essential element in Mr. Talbot's patented 

 process, is due to Mr. Reade ; ' and in my letter to Mr. 

 Brayley I attribute the sensitiveness of my process to 

 the formation of a gallate or tannate of silver. I need 

 scarcely say, that among various experiments I tried 

 gallic and tannic acid in their pure state, both sepa- 

 rately and mixed ; but the colour of the pictures thus 

 obtained with the solar microscope was at that time less 

 pleasing to my eye, than the rich warm tone which the 

 same acids produced when in their natural connexion 

 with solutions of vegetable matter in the gall-nut. 

 This organic combination, however, was more effective 

 with the solar microscope than with the camera, though 

 the lenses of my camera were five inches in diameter. It 

 is probable enough that the richer tone was due to the 

 greater energy of direct solar rays. In using the solar 

 microscope, I employed a combination of lenses which 

 produced a convergence of the luminous and photogenic 

 rays, together with a dispersion of the calorific rays, 

 and the consequent absence of all sensible heat enabled 

 me to use Ross's cemented powers, and to make draw- 

 ings of objects inclosed in Canada balsam, and of living 

 animalcules in single drops of water. The method I 

 employed was communicated to the Royal Society in 

 December, 1836, and a notice of it is contained in the 

 ' Abstracts.' 



" You inform me that some persons doubt whether 

 I really obtain gallate of silver when using an infusion 

 of gall-nuts, and that one of Mr. Talbot's friends raises 

 the question. It is sufficient to reply, that though 

 gallic acid is largely formed by a long 'exposure of an 

 infusion of gall-nuts to the atmosphere, as first pro- 

 posed by Scheele, yet this acid does exist in the gall- 

 nut in its natural state, and in a sufficient quantity to 

 form gallate of silver as a photogenic agent ; for M. 

 Deyeux observes, that ' when heat is very slowly 

 applied to powdered gall-nuts, gallic acid sublimes 

 from them, a part of which, when the process is con- 

 ducted with great care, appears in the form of small 

 white crystals.' M. Fiedler also obtained gallic acid 

 by mixing together a solution of gall-nuts and pure 

 alumina, which latter combines with the tannin and 

 leaves the gallic acid free in the solution ; and this 

 solution is found, on experiment, to produce very ad- 

 mirable pictures. But what is more to the point, Mr. 

 Brayley, in explaining my process in his lectures, showed 

 experimentally how gallate of silver was formed, and 

 confirmed my view of the sensitiveness of the prepara- 

 tion. It is therefore certain that the use of gallate of 

 silver as a photogenic agent had been made public in 

 two lectures by Mr. Brayley at least two years before 

 Mr. Talbot's patent was sealed. 



" 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 be- 

 lieve 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 1 employed it as 

 well to form iodide of lead on glazed cards as an ac- 

 celerator. 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 lord- 

 ship's possession. I subsequently made drawings of 

 sections of teeth ; and one of them, a longitudinal sec- 

 tion 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 con- 

 struction 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, evi- 

 dently 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 en- 

 tirely useless. Lately also the glass corners for col- 

 lodion 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 pho- 

 tographic 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 



