Experiments in Photography. - 327 



made to the photographic art." It is nevertheless true, as stated 

 by Sir David Brewster, that " the first pubHc 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. Brayleyl 

 attribute the sensitiveness of my process to the formation of a gal- 

 late or tannate of silver. I need scarcely say, that among various 

 experiments I tried gallic and tannic acid in their pm-e state, both 

 separately and mixed ; but the colom- of the pictures thus ob- 

 tamed mth the solar microscope was at that time less pleasing 

 to my eye, than the rich warm tone which the same acids pro- 

 duced when in their natural connexion with solutions of vege- 

 table 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 jn 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 

 dra^\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 suffi- 

 cient to reply, that though gallic acid is largely formed by a 

 long exposure of an infusion of gall-nuts to the atmosphere, as 

 first proposed 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 la 

 conducted 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 admi- 

 rable 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 sen- 

 sitiveness of the preparation. 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. 



