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
• URN: urn:nbn:de:bsz:14-db-id1780948042-186300004
• 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

silver, by sensitizing. A comparatively weak nitrate bath will, of course, produce good effects upon it, provided it bo of suffi cient strength to saturate the albumen in the ordinary time of floating, as a strong bath is only necessary when the albumen is soluble, because by hastening the time when insolubility occurs, it prevents the solvent power of the water having full effect. Ever since I have known anything of photography, I have been firmly convinced that the nitrates of the base of the salting chloride, affects the colour of the print; although this lias^ been strongly denied, the belief that such is the case has been daily gaining ground, and in Mr. Towler’s “ Lessons on Photography," No. 11, published in Humphrey's Journal, I now find my statement corroborated. In allusion to plain and albu- menized paper, prepared for photographic printing, he says :— “ The chemical foundation in either, is an alkaline chloride, which by floating the paper on nitrate of silver, or ammonia nitrate of silver, becomes converted into chloride of silver, in a state of very tine division, mixed with the nitrate of the alkali employed. The latter salt modifies in a great measure the colour and intensity of the print produced. From this circumstance, we account for the different tones in different specimens of prepared paper. Some manufacturers use chloride of ammonium, others that of potassium, sodium, or lithium, in the salting of their paper ; each print, on this account, will have a different tone when it leaves the printing frame.” Under the title, “Coagulation of Albumen,” I find in the leading article of the British, for Feb. 16th, some statements of the editor’s, which require a passing notice. Alluding to MM. Devanne and Girard, he says:—“They go into another phase of the question, which has disturbed the equanimity of our an tagonist, Mr. George Price—we mean that of the amount of albuminate of silver, in comparison with the chloride, produced upon a piece of positive photographic paper, on being sensitized on the nitrate of silver bath.” Now, there is not a single word of truth in any part of this assertion; the whole of it is such pure fiction, as not to have even the shadow of a fact for its foundation. I am no antagonist of Mr. Shadbolt in any way whatever, not having as yet entered into any controversy with him; and moreover, my antagonism is against fallacies, and not against persons. I was the first person who drew attention to the erroneous ideas prevalent respecting the coagulation of dried albumen ; and I believe also, that I am the only one who has calculated from an atomic weight, the amount of albuminate of silver on a sheet of albumenized photographic paper; and how my equanimity can possibly have been disturbed by so doing, I am ut a loss to imagine, I only know that it has not been so in reality, for nothing I have ever written respecting the impossi- bilityof coagulating dried albumen, has yet been disproved, although I have publicly challenged any one to do so. Mr. Shadbolt takes an exceedingly lofty flight in the realms of fiction, when he states the subject of MM.Davanne and Girard’s investigations to be “the amount of albuminate of silver in com parison with the chloride, produced upon a piece of positive albumenized paper on being sensitized on the nitrate of silver bath ; ” the plain matter of fact being that their paper has no reference whatever to the amount of albuminate of silver in com parison with the chloride ; they investigate simply “ the action of nitrate of silver upon albumen,” without any reference to either the alkaline chloride on the paper before sensitizing, or the chloride of silver produced by its being sensitized ; and they state merely that varying strengths of the nitrate of silver solution pro duces varying degrees of coagulation of the albumen, and there fore varying compounds of albumen and nitrate of silver; a pre viously well-known fact. Because I calculated according to a particular atomic weight, it is a strange perversion of logic to assume, as Mr. Shadbolt does, when he says that its combina tion in other proportions is “ an idea apparently ignored by Mr. Price.” It happens, however, that for more than twenty years I have been well aware of the different character of the precipi tates which varying strengths of solutions of metallic salts pro duce when mixed with albumen. Mr. Shadbolt also says:—he alludes to the subject “ for the purpose of discussing the accuracy or otherwise of certain pro positions advocated and maintained by the editor of a contem porary and one of his correspondents, in opposition to certain others held by ourselves and one of our contributors.” As what I have written appeared in the News long before the British took any notice of the subject, I cannot have stated opinions " tn opposition to certain others held by its editor and one of its contributors; moreover, Mr. Shadbolt is the only person who has written in the British on the subject, and then it was only in reply to a letter of mine, when, amidst much misrepresenta tion and personal abuse of myself, he denied that this contributor entertained the opinion I had attributed to him in that letter. What I wrote respecting the non-possibility of coagulating dried albumen was corroborated by Mr. Simpson before this ; and it must be borne in mine! that I commenced writing about albumen two years ago, although it is only lately that I have succeeded in arousing attention. Mr. Shadbolt also says :—“ It has been contended by one or both of our opponents that albumen, in contact with nitrate of silver and some other metallic salts, does not undergo coagula tion, but merely combination with the metallic base.” I am sorry to say that there is also not a word of truth in this state ment ; neither Mr. Simpson nor myself have ever said or written anything of'the kind ; and as Mr. Shadbolt has not ventured to gainsay aught that I have advanced, and has not published his opinions upon the subject of albumen, we cannot bo his “ oppo nents." He proceeds to say:—“We, on the contrary, main tained that there was no evidence to show that coagulation did not come about contemporaneously with combination, and cited several authorities in support of this view.” This statement of what he himself wrote in his own former leader, is also pure fiction-, Mr. Shadbolt maintained nothing whatever of the kindhe now says he did, nor did he cite any authorities to the purport he states ; in what he did say on the subject he merely attempted to show that coagulation and insolubility were considered as synonymous terms, and to prove it he cited an authority who said nothing upon the subject. I have reluctantly felt compelled, in justice to myself, to take this notice of Mr. Shadbolt, and much regret to find that such gross misstatements and fictions can emanate from the editor of a scientific journal which claims to hold high rank amongst its contemporaries. With an apology for the extra length of time my addendum has claimed your attention, I now leave the pro posed questions in your hands, to discuss in whole or part, or not at all, as you think best. • ON THE ELECTRICAL THEORY OF PHOTOGRAPHY. By John Johnstone.® I stand before you, this evening, with much diffidence; and, if I should fail in imparting information to recompense you for the time devoted to me, I trust you will vent your dissappoint- ment on your fellow-member, my friend Mr. J. E. Mayall; but, should the contrary be the case, he is no less entitled to your vote of thanks for his importunity in inducing me to appear before you. The subject announced is the electric theory of photography. It might possibly have been better if announced as an electric theory of photography, as several others have been nibbling at the same bait; but, so far as I know, no one has as yet developed a great principle as a foundation upon which to build with certainty. It is my intention this evening, if possible, to lay a firm foundation on which scientific workmen may build a superstructure sound in all its parts. I have had some doubt in my mind as to the best mode in which to introduce the subject, being aware that many of you are well versed in every department of knowledge bearing on photography; yet, from my own experience, in conversing with photographic friends, I have found a great difficulty in making them clearly comprehend the nature of electrical polarisation. If you will bear with me a short time, I will lay before you a few facts in connection with my own impressions as to the nature of heat, electricity, and light. When a boy at school, it was a habit with some of the more mischievous to cut a metal button from their coat, rub it on the desk, and then apply it to the cheek or back of the hand of their neighbour. This produced a startling effect, often eliciting a retort not very pleasing to the offender. But simple as this experiment may seem, it lies at the basis of electric phenomena. Let us vary the experiment a little by drawing the button rapidly, with a certain amount of pressure, over about eighteen inches of the surface of the facia of a painted architrave of a door. We find that adhesion of the button is the consequence. How is this to be accounted for? In the first instance we have heat generated between a conductor and a partial non-conductor of electricity by friction or abrasion. In the second case wo have the same thing, a little modified; in drawing the button along, we generate heat, but the two bodies are not equal con- * Bead at a meeting of the Photographic Society (London), March 2nd, 1863