A Manual Of Photography

THE USE OF ALBUMEN ON GLASS PLATES AND ON PAPER. 283 of silver. This property of the fluorides is calculated to give very valuable results, and will probably cause, in this branch of photographic art, a change equally as radical as that effected by the use of bromine on the iodized silver plates of Daguerre.” A process published in the author's Researches on Light, in 1844, and named the Eluorotype, sufficiently establishes my claim to priority in the use of the fluorides. Messrs. Boss and Thompson, of Edinburgh, at the meeting of the British Association in that city, exhibited some positive images on glass plates : these were backed up with plaster of Paris, for the purpose of exalting the effects, which were exceed- ingly delicate and beautiful. Messrs. Langenheim, of Philadelphia, have, however, recently introduced into this country specimens, which they term Hyalotypes. These are positive pictures, copied on glass from negatives, obtained upon the same material. Their peculiarity is the adaptation of them for magic-lantern sliders. The process by which they are produced is not published, but judging.from the effects obtained, the probability is that a very slight variation only from the processes described has been made. The idea is an exceedingly happy one, as by magnifying those images which are of the utmost delicacy and the strictest fidelity, perfect reflexes of nature are obtained. There can be no doubt but other means of coating glass with sensitive materials may be employed. Certainly the use of albumen is a ready method, but this medium appears to interfere with the sensibility which it is so desirable to obtain. As stated, by using combinations of iodide and fluoride salts, there is no doubt but the sensibility may be most materially improved, and we find many of the continental photographers using honey and grape sugar with much advantage. I would, however, venture to suggest that films of silver pre- cipitated from the solution of the nitrate by grape sugar, aldehyde, or gun-cotton dissolved in caustic alkali, upon which any change could be afterwards produced, appear to promise many important advantages. Section V. _Positive Photographs from Etchings on Glass Plates. A very easy method of producing any number of positive photocranhs from an original design is in the power of every one having some slight artistic talent. The merit oi having