The photographic news

• Bandzählung: 7.1863
• Erscheinungsdatum: 1863
• 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
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• PURL: http://digital.slub-dresden.de/id1780948042-18630000
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• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

the photographic news. Vol. VII. No. 248.—June 12, 1863. CONTENTS. PAGE Formic Acid as an Accelerator Bromide in Potassium Iodized Collodion Scientific Gossip Formic Acid in the Developer. By II. Cooper, Jun Developing and Intensifying. By T. C. Leake, Jun Art in Photography. By M. Blanquart Evrard The Influence of Photography 277 278 278 279 280 281 282 PAGE The Glass-House 283 Instantaneous Pictures 284 Correspondence—Double Printing, &c 285 Proceedings of Societies 286 To Correspondents 288 Photographs Registered during the past Week 288 FORMIC ACID AS AN ACCELERATOR. A singular discrepancy of opinion and experience seems to prevail regarding the use of formic acid in the developer. The first record we have of its use appeared some ten years ago in the Society’s journal, when it was proposed by the Rev. J. Lawson Sisson, for addition to the protonitrate developer, to secure good tones in collodion positives. We tried it about that time, for that purpose, without perceiving any advantage. Since then its use has occasionally been suggested from time to time. About a couple of years ago considerable discussion was caused by a somewhat indefinite allusion to its use as an aid to instantaneous photography. by MM. Ferrier and Soulier, some charming stereoscopic street scenes of Paris having been, it was stated, produced by its aid. The matter was, however, very ambiguously stated, and the photographic public were not much enlightened at the time. Shortly afterwards a communi cation appeared in our columns from Col. Stuart Wortley, who gave a definite formula for the use of formic acid with iron, and spoke in high terms of its value. His large instantaneous pictures produced by its aid were strongly corroborative of the statement. It was urged, however, by some that the brilliant light of Italy might have produced the results without the formic acid affecting the matter. In the course of last summer a group of two figures, portraits of the Secretaries to the English and French Photographic Societies, on a 12 by 10 plate, was exhibited in the Inter national Exhibition. The negative of this picture, which was delicate, soft, and perfectly exposed, was produced in the studio of M. Claudet with a lens of long focus and small aperture in a very dull light, with an exposure of nine seconds. Mr. H. Claudet communicated to us the process by which this unusual rapidity was obtained, claiming for formic acid the accelerating properties. Since the publica tion of this communication in our own and some other journals, a more extended discussion of the subject has arisen. Many experimentalists have tried formic acid in the developer, and with, as we have said, singularly dis crepant results. Amongst those who have derived no advantage from its use is Dr. Van Monckhoven, a good authority, both as chemist and photographer. Several other photographers, upon whose opinion we could place reliance, have found similar results, and made similar reports. Our own engagements have precluded hitherto a careful and systematic examination of the subject. A few days ago we went, at the courteous invitation of M. H. Claudet, to his studio in Regent Street, for the purpose of witnessing his operations and verifying the results of formic acid in his hands. We must confess at the outset we were altogether unprepared for the amazing rapidity we witnessed. We will simply and briefly state the details of what we saw. M. Claudel's admirably appointed studio is, like many studios in London, somewhat unfortunately placed as regards light, the best light being cut off by a dark brick building which rises high above the studio, so that it is to a large extent, as M. Claudet phrased it, in a well. Added to this, the sun shines directly into the room at mid-day, rendering it imperative to use a large surface of blinds. The lenses used for card portraits are of long focus by Voigtlander; the equivalent focus was 9} inches, the diameter of the lenses 22 inches. We stood for a negative about mid-day, surrounded by blinds to shut out the direct sunlight. So far as we can judge without direct comparison, an exposure of ten seconds would have been requisite with good bromo-iodized collodion and an iron developer. To our unbounded surprise the lens was closed with exposure of barely two seconds. We then went into the dark room to watch the development. The image flashed out rapidly and in less than a minute was completely developed, the result being clean and brilliant without the slightest trace of fog. Another plate was now prepared, and the sun having retired behind some grey clouds, a portion of the blinds were withdrawn. The exposure this time was one second, and the results in the dark room similar. Perhaps the negative might have borne the fraction of a second longer exposure, but certainly not another second. We unhesitatingly affirm that we have not seen at any time such rapid working in a studio in so dull a light. The materials were, for the most part, such as M. H. Claudet described on a former occasion, but we may describe them again here. The nitrate bath contains— Nitrate of silver (commercial) ... 700 grains Strong nitric acid 3 drops Distilled water ... ... ... 1 pint prepared in the usual manner. This works better when first used, a slight deterioration in sensitiveness being observed after it has been used a short time. When this becomes too definitely marked the bath is laid aside and thrown down. The collodion used is simply iodized, and contains equal portions of cadmium and potassium. A stock of Thomas’s ready iodized cadmium collodion is kept on hand. The ordinary negative collodion of the same maker, with the potassium of salt, is iodized about ten days before it is re quired for use. Equal portions of these two collodions are then mixed for use. The developer we saw used was prepared as follows :— Pyrogallic acid ... 20 grains Formic acid (Morson’s) ... ... 1 ounce Water 7} „ Alcohol, quantum suff. The points upon which M. Claudet laid especial stress were care and exactitude in the formula generally. Regard ing the formic acid the exact degree of purity and strength are not yet satisfactorily determined, and the proportion to be used has to be decided at present somewhat empirically by actual experiment with each fresh stock. The proportions given answer with the sample in hand. Of another sample, prepared by Mr. Hockin, of alleged absolute purity, one fourth of the proportion given in the formula was sufficient.