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

402 THE PHOTOGRAPHIC NEWS. [August 22,1862. American Journal of Photography, May, 1862).* After being thus washed with water, it is flowed with or dipped into a bath composed of fifteen grains of tannin dissolved in each ounce of pure water, the solution being carefully filtered. The plate should remain in this bath four or five minutes. It is then drained, and set up on one corner, on bibulous paper, to dry in a dark room or box. The ordi nary exposure necessary is about four times as long as a wet. Two solutions are used in the development— No. 1.—Pyrogallic acid ... ... 72 grains Alcohol (95 per cent.) ... 1 ounce. No. 2.—Nitrate of silver 20 grains Citric acid .., ... 40 „ Water, pure ... ... 1 ounce. To develop—wet the plate rapidly with pure water, when the film is thoroughly moistened, flow the plate with water, to each drachm of which has been added two drops of No. 1, and one drop of No. 2; keep this developer in motion over the plate until the details are well out; then add to it drop by drop of No. 2, until the required intensity is ob tained. Fix in hyposulphite of soda as usual. Experience in the use of this process teaches—1. That drying by artificial heat is not necessary. 2. That the amount of acid in No. 2 may be judiciously varied with the length of exposure. It is better to have an excess of acid than too little. 3. Warming the plate in a bath of water heated 90° F., but using the developing solutions at the usual temperature, as recommended by Dr. Draper, of New York, and others, shortens the time of exposure necessary, so that this process may be worked almost as rapidly as the wet. 4. By the use of honey in combination with the tannin, fifteen grains of each to the ounce of water, as re commended by Mr. England, of London, great rapidity is gained. 5. A bromo-iodized collodion is to be preferred, and an old collodion works better in my hands than a new sample. 6. The silver bath should not be neutral, but ought to be decidedly acid ; this may be done by adding one drop of nitric acid for every twelve ounces of bath. 7. This process is peculiarly adapted to the production of glass transparencies for the stereoscope, affording great beauty and richness of tone. A SHORT LESSON IN CHEMISTRY.—No.l. f The land, the water, and the atmosphere, together with animal and vegetable substance, constitute what is denomi nated the earth. All the matter of this earth, as varied as it is, as far as has been discovered, consists of sixty-three simple forms of matter, called elements, by which we mean such forms as are homogeneous throughout, and incapable of being reduced into any other simpler forms. Of these elements four, when isolated from all combination with other elements, are in the gaseous and aerifgrm state, their names are: hydrogen, oxygen, nitrogen, and chlorine. One element has never yet been isolated from its combinations, so that we do not know what may be its independent or elementary form; it is called fluorine. One of the elements, called bromine, exists in the liquid state when uncombined. The rest are solid. The sixty-three elements are divided into two groups, one of which is denominated the group of the metalloids and com prehends thirteen elements ; the rest of the elements receive the appellation of metals. The study of the metalloids is the most important for the chemist; for it is, as it were, the key to a knowledge of all the rest. The following is a list of the metalloids: hydrogen, oxygen, nitrogen, chlorine, iodine, bromine, fluorine, carbon, boron, silicon, sulphur, selenium and phosphorus. Now, although the earth contains no other sort of matter besides the metals and the metalloids, to the number already mentioned, yet there is an indefihite variety produced by their intermixture, or chemical combination. Mixture is totally different, however, from combination. Sugar dis * See letter from Mr. Thompson on p. 359 of the present Volume. t From Humphreys Journal of Photography. solved in water, and lac in alcohol, are examples of mixture, because the sugar and the lac have not changed their nature by their solution, and can be regained in their original states by evaporating the water and the alchol. Common salt and nitrate of silver are examples of chemical combi nation ; for these salts show no signs visible to the eye of the metals or acids which form them; the acids have dis appeared and so have the metals, and totally different sub stances are formed from the combination of acid and metal respectively, called chemical combinations. Since mixture and chemical combination are so different it becomes an important question to ask by what cause this difference is produced, or, which is about the same thing, to ascertain the cause or causes of chemical affinity whereby composition and decomposition are effected. Researches in this department of natural science demonstrate that there is something more than matter required to make up even an element of matter; that certain forces arc always brought into play in every formation or transmutation of matter, and that one or more of these forces form a part in the com position of all matter. The forces alluded to are denomi nated the imponderables, and are recognized in heat, light, electricity, and gravitation. There is not a single atom of matter on the earth that is, or can be isolated from all these forces, if from any of them : and not a single combination or separation in chemistry is effectuated without the appli cation or disturbance of these forces. The precise method by which all this chemical work is performed, that is, the intellectual part of this work, is as yet in a great measure a mystery. We know the effects, we can reproduce the effects, by the application of these forces as immediate causes or agents; but we cannot always give a satisfactory rationale of the varied phenomena in chemical changes. For instance, in the film of iodide, bromide, or chloride of silver, nothing is now better known than the changes that occur whenever these films are exposed either to the light of the sun, or the diffused light of day. But we arc very far from being in a condition to explain philo sophically, that is logically, as applied to cause and effect, the changes that we know must follow. We know that the chloride of silver, by being exposed to light, is changed into what is called a subchloride, which has a beautiful violet colour and is insoluble in solvents in which the chloride is quite soluble ; but neither the microscope nor any other aid in science has detected any constitutional alteration to account for the change. Sufficient however, is known to determine that these imponderable forces are the very essence of chemical science. Certain generalizations, too, in their action have been well determined; so that we know that heat, light, and electricity, in many instances compose and decompose with almost equal facility; for instance, heat changes ice into water, water into vapour, vapour into i: elements—oxygen and hydrogen ; electricity with a slight modification of application will do the same. Again, visible heat (that is flame) will recompose oxygen and hydroge" into vapour, so will electricity. Withdraw heat or apply 15 negative, that is, cold, or apply compression, which is simpl! a modification of gravitation, and vapour will be restored t0 water. Thus, then, by the co-operation of these forces, 0 by their antagonism, arise all the unspeakable and un intelligible phenomena of chemistry. Harbison’s New Lens.—The new lens, stated to include a very wide angle, has recently been patented in America. The specification runs:—“We claim the combination of two sets o cemented lenses, the exterior surfaces of which shall form pr J of the same sphere, the axes of which shall bo coincident, and the other curves of which shall be so proportioned to thefoca. distance of the combination, and to the refractive and disper sivo powers of the glass used in their construction, that ta imago found at the focus shall be achromatic, and that Si image shall bo upon, or almost exactly upon, a plane without: n. tortion of form, and including a larger visual angle, rubs a tially as before described and represented.”