E. F. (Sheffield). It is only in converting a positive picture into a negative one, or in increasing the powers of a feeble negative, that the bichloride of mercury is recommended to be used. A perfectly good printing negative will be procured by following the instructions we have given in our former Numbers. Dr. Diamonds's Photographic Notes will treat fully upon this subject.
Our Sixth Volume, strongly bound in cloth, with very copious Index is now ready, price 10s. 6d. Arrangements are making for the publication of complete sets of "Notes and Queries," price Three Guineas for the Six Volumes.
"Notes and Queries" is published at noon on Friday, so that the Country Booksellers may receive Copies in that night's parcel, and deliver them to their Subscribers on the Saturday.
PHOTOGRAPHY.—Collodion (Iodized with the Ammonio-Iodide of Silver).—J. B. HOCKIN & CO., Chemists, 289. Strand, were the first in England who published the application of this agent (see Athenæum, Aug. 14th). Their Collodion (price 9d. per oz.) retains its extraordinary sensitiveness, tenacity, and colour unimpaired for months: it may be exported to any climate, and the Iodizing Compound mixed as required. J.B. HOCKIN & CO. manufacture PURE CHEMICALS and all APPARATUS with the latest Improvements adapted for all the Photographic and Daguerreotype processes. Cameras for Developing in the open Country. GLASS BATHS adapted to any Camera. Lenses from the best Makers. Waxed and Iodized Papers, &c.
TO PHOTOGRAPHERS.—Pure Chemicals, with every requisite for the practice of Photography, according to the instructions of Hunt, Le Gray, Brébisson, &c. &c., may be obtained of WILLIAM BOLTON, Manufacturer of pure chemicals for Photographic and other purposes.
Lists of Prices to be had on application.
146. Holborn Bars.