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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
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- Public Domain Mark 1.0
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- urn:nbn:de:bsz:14-db-id1780948042-186200003
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- http://digital.slub-dresden.de/id1780948042-18620000
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- oai:de:slub-dresden:db:id-1780948042-18620000
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- Fotografie
- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
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- Seite 1-72 fehlen in der Vorlage. Vorlagebedingter Textverlust.
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- Bandzählung
- No. 201, Juny 11, 1862
- Digitalisat
- SLUB Dresden
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- Ausgabe
- Parlamentsperiode
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- Wahlperiode
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Zeitschrift
The photographic news
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Band
Band 6.1862
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- Ausgabe Ausgabe 73
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- Register Index 619
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Band
Band 6.1862
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328 THE PHOTOGRAPHIC NEWS. [July 11, 1862. of gases, these several constituents of of coal gas, would diffuse into the atmosphere through leakage or any large opening in the pipe, with different velocities, and thus it is possible that when gas is escaping into a room, the mixture may have different igniting points, close to, and at some distance from the pipe. A great many experiments were tried by Dr. Frankland on the igniting points of different mixtures of the gases : thus, a mixture of carbonic oxide with about three per cent of bisulphide of carbon vapour, issuing from a jet into the air was readily ignited on the approach of a glass tube containing oil heated to 410° F. ; hydrogen and bisulphide of carbon igniting when the temperature of the oil tube was 420°. Fortunately, however, it was found that the presence of a minute trace of olefiant gas, instantly raised the igniting point of the mixture, and neutralized the ill effects of the bisulphide of carbon. The Doctor therefore concludes that under the most favourable circumstances, coal gas cannot be inflamed at a temperature below that necessary to render iron percep tibly red hot by daylight, in a well lighted room ; this high igniting point being due to the presence of olefiant gas and other similar hydro-carbons. A mixture of coal gas and air is however more easily ignited than the explosive mixtures in coal mines, and therefore the safety lamp in ordinaiy use in mines is not considered safe in a mixture of coal gas and air; this latter being also readily inflamed by sparks struck from metal or stone. Thus, an explosion may arise from the blow of a tool of a workman against iron or stone, from the tramp of a horse upon pavement &c. as a scum, and cau be easily removed. The liquid is then heated to dull redness, and kept at that temperature during the night. In the morning the mass appears per fectly transparent, the sides and bottom of the vessel being coated with cauliflower-shaped masses of crystals, consisting of silicate of alumina, with chloride and sulphate of sodium, and a little lime. The clear fused liquid is ladled off in® these crystals, and when cooled is ready for use. The sow prepared in this way is perfectly free from alumina; a small quantity of the soda was fused in a platinum crucible and some pure alumina added. This remained undissolved in the fused mass, swimming about like a precipitate in the red bot liquid. On cooling, water was added to this fused mass,al the alumina was found to dissolve completely. If the com mercial soda contains oxide of iron, this also separates out completely during the process of fusion. Lime, on the other band, is dissolved in large quantities by the caustic soda,W it is completely separated by solution in water. The cans'* soda prepared in this way is hard and brittle, and can easily be obtained as a fine powder by attrition in an iron mortar It contains only a trace of carbonate of soda. We have devoted more space than we intended to a de scription of this body, but it is before long destined to pla! an important part in many manufactures, and will prove 0 invaluable adjunct to the photographic laboratory, for ne! tralising acidity in the bath or other solutions, which it w do in a manner at once certain and unexceptionable. Thegrd difficulty has hitherto been to get it pure; now this is accot plished, its uses will be manifold. Uhe Jnternationul Exhibition. PHOTOGRAPHIC CHEMICALS. One of the most important chemical manufactures of the country, and one also which is indirectly of the utmost im portance to photographers, is that of soda. The process of preparing the pure caustic alkali from sea salt is a triumph of scientific ingenuity, and is well illustrated in many cases in the British chemical department. Leblanc’s process for making carbonate of soda is scarcely of sufficient interest to our readers to merit a detailed account; but we will just glance at the principal operations as a preliminary to the manufacture of caustic soda, which is an entirely novel branch of manufacture, and one which, before long, will be of con siderable importance for household and manufacturing purposes. Sea salt or chloride of sodium is first of all to be converted into sulphate of soda. For this purpose it is necessary to have large quantities of sulphuric acid, and as this is not an article which can be carried about safely, it is always prepared at the soda works. Either pyrites (bisulphide of iron) or sulphur is burned in a furnace with proper arrangement for oxydizing the resulting sulphurous acid into sulphuric acid, which is condensed in enormous leaden chambers, the bottoms of which are covered with water. This acid is then allowed to act on the salt, when hydrochloric is evolved and sulphate of soda is produced. The crude sulphate is then mixed with coal and chalk, and the whole heated together in large reverberatory- furnaces, when the so-called black ash is produced. This is exhausted with water and yields a solution containing con siderable quantities of caustic soda. The old process was to convert this by successive steps into carbonate of soda, but now caustic soda is prepared in a great measure from it. The crude alkali has lately been converted into an almost absolutely pure product by a very ingenious plan, carried out by Dr. Pauli, of the Union Alkali Works, St. Helen’s. He takes the commercial caustic soda, in quantities of about three tons at a time, containing excess of water, alumina, and all the impurities which commonly occur in this substance, and fuses them in a cast iron pot. During the evaporation nearly all the carbonate, and by far the larger quantity of the other salts separate out on the surface BRITISH PHOTOGRAPHIC DEPARTMENT. The contributions of coloured photographs to the Exhibit]® do not call for extended notice, especially in a photograpl point of view. Such interest as the coloured portion o'*" Exhibition did possess is now materially diminished. T majority of the contributors concerned have taken our In as to the dampness and removed their pictures. Almost, the water-coloured specimens are gone; some also of ta yellow and fading plain pictures have been removed, so tn- bare walls in many cases meet the eye instead of pho graphs. The most noticeable coloured pictures, or certat those which will attract the most attention, are the colotte enlargements of M. Claudet. Strictly speaking, these " not photographs at all, that is, they are not drawing] 3 light. M. Claudet recently described the method by W"’ they are produced by projecting the image of a small W tive on to canvas by the aid of a solar camera and artis light, and then tracing the principal features on the ca’ by means of a crayon. The general outline, chief shas &c., are thus secured in their due proportion as a basis the further operation of the skilled painter, who is fura aided by a print from the small negative to serve as a80 ( j We know that exception has been taken to the presendju these pictures amongst photographs; but we scarcely tjja the exception is just. They are at least valuable APBar tions of photography ; they are produced from small Pa v graphic negatives, and the enlarged image is produce • photographic appliances. As the final image is 1101 "o duced by the chemical action of light, they Arewon as we have just said, in the strict sense ot the i photographs ; but they are so nearly related to the aa tiao the result of such an interesting and valuable aPP"thios of it to the purposes of portrait painting, that We (J . there is no more legitimate place for them than the Pberd graphic department; and it must be, distinctly remet tbe that they arc not put forward as photographs, Some of method by which they are produced is described. Xcelled’ those exhibited are very admirably painted, and c] is likenesses. The portrait of Mr. Chance, of Birpinl, ye a very fine piece of painting, vigorous and forabourd withal, quiet and low in tone, free from the ,, tet smoothness of finish which is generally known 4s bd 1 boardincss.” Several other of M. Claudet’s pict Jun enlarge painted 're ma have rei consist Portrait Photog 'lie othi graphy, specime the Ex desired images likeness are per Hend ’ the sub Mr. 1 bntes s which I almost Mr. ‘ apecimt fheygi s inde ngag apparel lady a tad err Mr.Wi Mr. W Beryge Photog coloure vhich Ielhui also Lt Very p Bassan Viry li Mr. T Bowen Messrs Picture Messrs Mil but wi are f a Bme e folour to the of all Sober obtai “nd i vigou good. to"d artist wefe " prei Th cause migh but i woul exhil of th than
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