The photographic news

• Bandzählung: 6.1862
• Erscheinungsdatum: 1862
• 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-id1780948042-186200003
• PURL: http://digital.slub-dresden.de/id1780948042-18620000
• OAI: oai:de:slub-dresden:db:id-1780948042-18620000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite 1-72 fehlen in der Vorlage. Vorlagebedingter Textverlust.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

photograph. In this series, Mr. England has produced some very fine interiors. In. speaking of them we accord them very high praise when we state that we think some of them are equal to Wilson’s interiors. Several views of the interior of the church of St. Etienne du Mont, which we believe presents some considerable difficulties as regards the question of lighting, are exceedingly fine. The magni ficently carved pulpit, which, though nearly black and dimly lighted, is here secured with the most perfect defini tion, detail, and gradation. There are also some fine pic tures of scenes in the Bois de Bologne, which are very per fectly executed. ♦ ON THE MANUFACTURE OF COLLODION. BY THOMAS SEBASTIAN DAVIS.® Thebe are few investigations in connection with modern pho- tography that possess greater theoretical, chemical, and prac tical interest than those associated with the manufacture of collodion. The interest and importance of the subject are not exclusively derived from scientific considerations, but are inti mately associated with the greater or less facilities that the compound is capable of affording for the production of artistic effects. It is true that the pictorial merits of a photograph can only partially constitute the standard for a just estimation of the exact value of a collodion or process ; yet it is equally undeniable that the conceptions of a cultivated taste may be fairly expected to realize a nearer approximation to its senti ments, when aided by the more appropriate agents. Regarded in this aspect, the manufacture of collodion, and the character istic results dependent thereupon, constitute a theme of recur rent interest, and one which, from time to time, should be brought under our notice in order to adapt its qualifications to the current requirements of the artistic photographer. The preparation of collodion embraces the consideration and realization of two especial qualifications ; the one the produc tion of a medium that will possess the necessary physical pro perties of yielding a homogeneous and even film after evapora tion from a smooth surface, and the other the power of giving an image possessing the nearest approximation to a true re presentation of the varied gradations of light and shade as seen in nature. The former requirement directs our primary attention to the constitution of the plain collodion, and the latter to the nature of the salts best adapted for receiving the actinic impression. I purpose, in the present paper, detailing the methods by which the above conditions may bo most satis factorily attained according to the result of my own varied ex periments in connection therewith. It may be well hero to re mark that the special formula which I am about to advocate is the one which I have especially found advantageous to adopt in working the wot collodion process with iron developers, and the washed collodion albumen dry plate processes generally. It is one by which a collodion may be prepared in every respect adapted for yielding the best results with pyrogallic acid development; but under such circumstances the necessary impression of the latent imago is received with less rapidity than upon films pre- pared with one or two commercial collodions particularly dis tinguished in this respect. It may bo judged, therefore, from the latter observation, that I neither advocate or recommend the practical or artistic photographer to make his or their own collodion ; but this I would emphatically urge, that no modi fied form ot development, or any description of a dry plate method of preparation should be esteemed of scientific value unless it be capable of being successfully practised in combi nation with a colodion of known chemical composition. To turn, in the first instance, to the consideration of the manufacture of the PYroxyline, we may notice that its intro duction into photography primarily resulted from the discovery of M. Schonbein, that the elements of nitric acid are capable of combining with certain vegetable fibres, and that the com pounds resulting therefore . ssess hew and remarkable pro perties. The development ot the fact led to the knowledge of the practical value of gun-cotton, and consequently to the specification of a patent taken out in our country in the year 1846 by a Mr. John Taylor, of the Adelphi, for the manufac ture of explosive compounds. In this specification wo have a * Bend nt the South London Photogray hio Society on the evening of Thursday, February 13th. detailed description of the means by which gun-cotton of the most explosive character may be successfully prepared. I shall venture to make one or two extracts therefrom, inasmuch, as they will contain some practical hints equally applicable to the manufacture of photographic pyroxyline. “ The vegetable matter,” it states, “ which is found best suited for the purpose is cotton, in the state in which it comes to this country, but cleared from any extraneous matter, it being desirable to ope rate only on the clean fibre of the cotton, which should bo dry. C The acids which I employ are nitric acid of from 1-45 to 150 - , specific gravity, and sulphuric acid of 1-85 specific gravity. As far as my experience goes the best mode of using them is to mix them in the proportion of one measure of the nitric, acid with three measures of the sulphuric acid, in a convenient vessel of glazed earthenware or other material not acted on by acids. By this mixture great heat will be produced. The mixture will be allowed to cool until it reaches a temperature of from sixty to fifty degrees of Fahrenheit. It should bo introduced as open as practicable. And in order to ensure the cotton being fully impregnated with the acids, and every part equally and fully subjected to the action thereof, tho cotton when in the acids is to be moved or stirred by means of a rod or glass, or other matter not acted on by the acids. The acids are then to be poured or drawn off. * # * Tho cotton is afterwards to be washed, opened out and dried, which may be conveniently done by spreading it thinly on surfaces in a room heated by steam or otherwise to about 150° Fah., and when dried it is fit for use. I would remark that nitric acid alone produces on cotton an effect similar to that produced on cotton by the mixture of acids above mentioned ; but in carry ing out the invention with nitric acid alone the cotton should be removed and washed immediately after it has become soaked with the acid, but I believe that so good a result cannot be obtained by the use of nitric acid alone, and the product is more costly.” It will be gathered from the above extract that tho principle of the manufacture of gun-cotton is not dependent upon the relative proportions of the mixture of tho acids, although tho preference is given by the patentee to the three to one ratio, as more recently advocated by Mr. Hardwich. The explosive cotton made in acids of tho above strengths is unsuited for the manufacture of collodion, inasmuch as the pro duct is insoluble in a mixture of alcohol and ether. If, how ever, wo only dilute tho acids to a suitable extent, or, what is analogous thereto, take acids of a less specific gravity, and act upon the cotton therewith, we shall obtain a pyroxyline soluble in an ethereal mixture of alcohol, and distinguishable from tho former when saturated with water by a semi-transparent appearance, and a tendency to partial disintegration. Pro vided we carry the dilution of the acids to too great an extent tho texture of the cotton will be entirely destroyed; if to tho extreme degree it will be completely dissolved as soon as im mersed in the acid mixture. Tho disintegrating, or solvent power of tho dilute acids increases with an elevation of their temperature, so that it happens that an acid mixture, in which the fibre of tho cotton would be scarcely altered at a low tempe rature, might entirely dissolve tho whole at a higher one. As it is found that a more fluid collodion can be manufactured from a pyroxyline made at elevated temperatures, it follows that the strength of the acids must bo correspondingly less diluted when used at higher temperatures, in order to produce a given action upon tho same vegetal fibre. The essential element for consideration, therefore, in the manufacture of pyroxylino adapted to moot tho requirements of the photographer, is tho proportionate dilution of the acids, that will give tho best re sults when brought into union with the normal cotton at some fixed temperature, ranging between 130° and 150° Fahr. Tho above rule will equally apply to the case whether the nitric acid bo used in its free condition or be liberated from nitrate of potash by tho chemical action of the sulphuric acid thereupon. As far as my own experience has led me to a preference between the use of free nitric acid, or the employment of nitrate of potash, I must confess that I consider a slight advantage in respect to uniformity and suitability is gained by tho combination of the two. Without, however, dwelling upon this point I must now proceed to the statement of the means by which I manufacture a pyroxyline equally adapted for tho production of collodion to bo used for tho wet ad dry plate processes. (To bi continued.) 4