The photographic news

• Bandzählung: 29.1885
• Erscheinungsdatum: 1885
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-188500006
• PURL: http://digital.slub-dresden.de/id1780948042-18850000
• OAI: oai:de:slub-dresden:db:id-1780948042-18850000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite I-II fehlen in der Vorlage. Paginierfehler: Seite 160 als Seite 144 gezählt.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

738 THE PHOTOGRAPHIC NEWS. [November 20, 1885. plate makers are far too thin. Actual halation, as it is generally understood, does not in all cases arise from thin ness of films, but merely a degradation of dark portions where they are near to bright lights, as, for example, in the case of foliage when adjacent to a bright sky. We noticed in connection with the late exhibition the large number of pictures which showed this defect. It is also to be noticed sometimes in the case of portraits, the eyes especially being rendered less brilliant than they should be. It would of course be entirely out of place to name particular makers here ; but we may state that in more than one case a test has shown that not more than half the amount of bromide of silver that was, four years ago, is now used. Our last word is one to plate makers, warning them that unless they bethink themselves in this matter, they are doing all in their power to aid the enterprising firms who are pushing the sale of paper films as a thing better for negative-making than glass. ALGIN AND OTHER SUBSTANCES FROM SEA WEED. Reference to algin compounds having lately been made in the Photographic News (Notes, page 648) as likely to be of use in photography, it may be interesting if we give a short description of their properties and mode of pre paration. It should be mentioned that we are principally indebted to papers read by E. O. C. Stanford, before the Chemical Society in 1883, and before the Society of Chemical In dustry on April 8, 1884, for our information on the sub ject. Algin much resembles gelatine in many of its properties, and, as its name implies, it is produced from seaweed. The principal British algae, which yield this body in con siderable quantity, are the Fuciand Laminarias. Formerly these seaweeds were collected, and burnt so as to yield kelp, which was not long ago the principal source of iodine; but this being an expensive and wasteful process, has been abandoned almost entirely, owing to cheaper sources of this halogen having been found. It is, by the inventor of the algin process, proposed to extract the soluble salts from the weed by maceration with water, all the iodine salts being thus obtained in solution, to be afterwards treated by suitable means for the extraction of iodine. The residual weed, unaltered in appearance, and containing the peculiar principle named Algin, is next macerated with dilute hydrochloric acid, whereby it becomes greatly swollen through the setting free in the interior of the plant of alginic acid, in the form of a colourless jelly. The next process consists in soak ing the weed in cold solution of caibonate of soda. In twenty-four hours the whole plant disintegrates, and forms a thick gelatinous mass, the cellular fabric of the plant being completely broken up. This mass, containing only about two per cent, of solid matter, is too thick to pour out. It is heated, if necessary diluted, and then filtered through linen sacking. The cellulose, which constitutes 10 to 15 per cent, of the original air-dry plant, remains in the filtering bags, and is said to yield a tough, transparent paper, the qualities of which at once suggest its being of use for flexible negatives. The solution running from the filters contains, in addi tion to the algin, in the form of alginate of soda, some mucilage and dextiine. Hydrochloric or sulphuric acid is added, and the algin separates in albuminous flocks as alginic acid, and this is easily washed in a filter press. If the product is required colourless, a little bleaching pow der is added during the precipitation. Algin forms salts with the metals, those of the alkalies and magnesium being soluble in water ; most others are in soluble. The silver salt is very sensitive to light, being rapidly darkened by it, which suggests this second pro duct being in some photographic processes substituted for gelatine, but aS to the comparative sensitiveness of algin silver compounds, we at present have no information. Algin is also acted on in the same way as gelatine by bichro mates, which render it insoluble when exposed to light With shellac, algin forms a compound somewhat resem bling gutta-percha in physical properties, and numerous important applications may be expected. In the soluble forms (alginate ot soda, potash, &c.) it forms in solution a viscous fluid much resembling gum-arabic, which, when dried by suitable means—that is, in the same way as gela tine—yields a transparent, elastic film, much more flexible than gelatine in the same condition. It is precipitated or coagulated by alcohol and the strong mineral acids, also by citric, tartaric, oxalic, and some other organic acids, and by most metallic salts except those of the alkaline metals and magnesium ; but not by ether, glycerine, starch, or sugar ; nor by acetic, tannic, pyrogallic, carbolic, and some other organic acids. The solution of algin is extremely viscous, a two per cent, solu tion being semi-solid. Alginic acid dries to a hard body, very much resembling horn. Surely these bodies possess abundance of properties which should render them of great service to photography, and probably before long we shall hear of their being utilised by photographers; especially from the descriptions we have of it, does algic cellulose paper seem likely to aid those who are seeking for a substance to replace glass for negat ives—a tough paper without fibre. Is not that just the substance we are in search of ? WITH A CAMERA IN MEXICO. BY E. ERNEST BILBROUGH. It may be taken for granted that a traveller whose only hobby was photography, would not choose Mexico as the best field for its pursuit. To the geological traveller, how ever, such an assertion could not apply, for the country is so rich in old ruins of a deeply interesting nature, that to take away representations of them would surely be the second best (though a very long second best) thing to transporting the ancient stones themselves. But though Mexico might not be chosen as the best ground for work with the camera to other individuals than those deep in the lore of ancient relics, yet, when once there, there is no lack of subjects on which to uncap the lens. True it is that the almost vertical sun is at times exceed ingly unmanageable, and militates against that pleasant chiaroscuro which we can get here in our much-vilified climate ; but from this drawback comes unmixed joy on such occasions as the sun is balked in its flaring intrusive ness, or done without, through the kindly offices of a passing cloud. Clearer air than that which fills the heavens over Mexico city could not be had, and therefore such things as instan taneous street pictures—which are not the easiest subjects to reproduce, satisfactorily—come up exceedingly well, and distinct in all details. I It might be almost called the resident “ Photographers Paradise,” as far as nature is concerned ; for the studio lighting is of course of the best, since the sun, even during the “rainy” season, shines brightly every morning; and advantages for rapid printing are likewise equally great And, judging by the exhibit sent by Valleto and Co. (the chief photographers in the Repullic) to the New Orleans Exhibition, these advantages are fully taken advantage ot. In their hands, photography is treated as an art; whenens with others in the city and elsewhere it is too often only “ profitable business, worked by rule-of-thumb. Althoug devoting themselves chiefly to portraits, Don Julio-ia prior of the firm—indulges in landscape for pastime; on it is owing to his kindness in the free use of his dark ro0m! and in many other ways, that I have been enabled to P