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

JAXUARY 9, 1885.] THE PHOTOGRAPHIC NEWS. 27 the enlargement. If it be desired to make a small enlargement, the lens is drawn away from the negative or slid forward ; if the reverse, the lens is pushed back nearer the nearer the negative. I omitted to say that the upright focussing-board can be folded down horizontally for convenience in packing, or to put on and take off the sheet of sensitive paper. Having described the work ing of the apparatus, I will proceed to make an enlargement with it. I have a peculiar vignetting device, which consists of a stand with a long, slender wire bent at right angles, and suspended upon its horizontal portion is a vignetting banner. The least motion given to the stand sets the wire in a rapid vibratory motion, which produces the vignetting effect during the exposure. I have a sheet of Morgan and Kidd’s argentic bromide gelatine paper, which I will pin to the board. I now remove the rest cap from the lens, which, as you saw, enabled me to place the paper in position before exposure, and will expose for twelve minutes. The size of the head on the negative is about half an inch. We will enlarge it. Regarding the development of gelatine enlargements, some little skill is required, in view of the fact that the print is to be looked at by white light. It is oftentimes deceptive, but, as a general rule, it is better to carry the development up a trifle further than would appear right for the red light, in order that the picture may look strong and vigorous by white light. Allow ance should also be made for the darkening of shadows, or black portions, by the fixing ba'h. Careful and cleanly manipulation is important, and the experience of a few preliminary trials necessary in order to acquire success. Practice with small sheets, until the right time of exposure is obtained, is advisable. The developer which I recommend and employ is that used by Morgan and Kidd, and consists in making two saturated solutions, one of sulphate of iron, and one of oxalate of potash. To the iron is added a few drops of sulphuric acid, and the neutral oxalate is acidified with sulphuric acid until blue litmus paper turns red, after which are added 1 ounce of loaf-sugar to each 16 ounces of solution. The function of the sugar appears to be to give deeper and blacker tones. If the exposure has been right, I add 1 ounce of the iron to 6 ounces of oxalate, and also 9 minims of a 60-grain solution of bromide of potassium. If the development hangs back, I increase the quantity of iron until it is in the proportion of 1 part to 4 of oxalate. After development, the print is slightly washed by soaking in changing water, and then fixed in a fresh hypo bath—1 ounce of hypo to 6 of water. This usually occupies four minutes’ time. The print is next well washed by soaking in water for two or three hours. Should the whites have a tinge of yellow colour, this may be removed by soaking for a few minutes in a bath of sulphuric acid 1 dram, water 80 ounces. The tem perature of all the solutions should be about 60° F. Through the kindness of Mr. H. V. Parsell, I have for use hero to-night a series of large rubber trays adapted to take in a sheet 18 by 22; each is marked “Developer,” “Water,’’ “Hypo,” which you see is an excellent plan. The enlargement I have made I will develop along with that to be made by the rapid method as illustrated by Mr. T. C. Roche’s improved enlarging camera-bcx, which requires the use of a condenser. Mr. Roche’s camera is quite unique for the purpose of enlarging; it has a bellows attached to the front of the lamp-box, and is worked from the rear by a sliding bar underneath the bottom, which, you will notice, adjusts the distance between the negative and lens. The interior of the lamp-box is provided with a single condenser, with the convex portion toward the light, and in front of the condenser is placed the negative held in a frame. A red pane of glass is inserted at one side of the box, to permit the use of the light for developing. A hinged or lid cover at the top of the box allows easy access for the purpose of adjusting the position of the con denser and negative. Mr. Roche will operate the instrument, and APPATATUS WOxKIXG ACROSS a PARTITIOX. has brought a sample of his new gelatine-albumen paper to show its ease of working and freedom from fog. Lastly, I desire to call your attention to the third arrangement of apparatus for enlarging. It consists in the use of two rooms, the dark room and an outer room. A square aperture is cut through the partition of the dark room, and in it is inserted, in this case, a box open at both ends. The end projecting into the outer room is fitted with vertical grooves, arranged to hold frames adapted to retain in position different sized negatives. On a shelf in front of, and close to, the negative, is placed a double 6 j-inch achromatic condenser, and behind that, at the proper focal distance, is located the light. In the dark room I have arranged a sliding-box, which takes the place of a camera-bellows, on which is fixed the lens (in this case a Rapid Rect. Dalmeyer, 8 by 10), 18 inches focus. By sliding the box in or out, the size of the image on the screen is increased or diminished. It is important that the light be near the centre of the con denser, and in line with the centre of the lens. Upon the front of the camera are slides arranged to accommodate different sized lenses. Prior to the insertion of the negative, the light should be arranged in such a position behind the condenser as will cause the cone of light coming from the condenser to just cover the rear of the lens, allowing the rays to cross each other at the dia phragmed centre of the lens-tube. MEASURING THE ABSOLUTE SENSITIVENESS OF PHOTOGRAPHIC DRY PLATES. BY WILLIAM H. PICKERING.* Within the last few years the subject of dry plate photography has increased very rapidly, not only in general popularity, but also in importance in regard to its application to other depart- ’ A communication to the American Academy,