PHOTOGRAPHY.--XYLO-IODIDE OF SILVER, prepared solely by R. W. THOMAS, has now obtained an European fame; it supersedes the use of all other preparations of Collodion. Witness the subjoined Testimonial. "122. Regent Street "Dear Sir,--In answer to your inquiry of this morning, I have no hesitation in saying that your preparation of Collodion is incomparably better and more sensitive than all the advertised Collodio-Iodides, which, for my professional purposes, are quite useless when compared to yours. "I remain, dear Sir, "Yours faithfully, "N. HENNEMAN. Aug. 30. 1852. to Mr. R.W. Thomas." MR. R. W. THOMAS begs most earnestly to caution photographers against purchasing impure chemicals, which are now too frequently sold at very low prices. It is to this cause nearly always that their labours are unattended with success. Chemicals of absolute purity, especially prepared for this art, may be obtained from R. W. THOMAS, Chemist and Professor of Photography, 10. Pall Mall. N.B.--The name of Mr. T.'s preparation, Xylo-Iodide of Silver, is made use of by unprincipled persons. To prevent imposition each bottle is stamped with a red label bearing the maker's signature. * * * * * PHOTOGRAPHIC PORTRAITS and VIEWS by the Collodion and Waxed Paper Process. Apparatus, Materials, and Pure Chemical Preparation for the above processes, Superior Iodized Collodion, known by the name of Collodio-iodide or Xylo-iodide of Silver, 9d. per oz. Pyro-gallic Acid, 4s. per drachm. Acetic Acid, suited for Collodion Pictures, 8d. per oz. Crystallizable and perfectly pure, on which the success of the Calo-typist so much depends, 1s. per oz. Canson Frères' Negative Paper, 3s.; Positive do., 4s. 6d.; La Croix, 3s.; Turner, 3s. Whatman's Negative and Positive, 3s. per quire. Iodized Waxed Paper, 10s. 6d. per quire. Sensitive Paper ready for the Camera, and warranted to keep from fourteen to twenty days, with directions for use, 11×9, 9s. per doz.; Iodized, only 6s. per doz. GEORGE KNIGHT & SONS (sole Agents for Voightlander & Sons' celebrated Lenses), Foster Lane, London. * * * * * PHOTOGRAPHY, DAGUERREOTYPE, ETC. PURE CHEMICALS for the above Processes supplied at the following prices, by JOHN J. GRIFFIN & CO., 53. Baker Street, Portman Square.--Superior Iodized Collodion, in bottles at 2s. 6d.; Pyrogallic Acid, 4s. per drachm; Pure Crystallizable Acetic Acid, 8d. per oz.; Iodide of Potassium, 1s. 6d. per oz.; Canson Frères' Negative Paper, 3s.; Positive Ditto, 4s. per quire. Bromine, 8s. 6d. per oz.; Iodine, 2s. 6d. per oz.; Charcoal, 1s. per bottle; Rouge, 1s. per oz.; Tripoli, finely prepared, 6d. per oz. An Illustrated priced List of Photographic Apparatus and Materials, post free, 3d. Nearly Ready, the Third much enlarged Edition of Professor HUNT'S MANUAL OF PHOTOGRAPHY.