The photographic news

• Bandzählung: 24.1880
• Erscheinungsdatum: 1880
• 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-id1780948042-188000001
• PURL: http://digital.slub-dresden.de/id1780948042-18800000
• OAI: oai:de:slub-dresden:db:id-1780948042-18800000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Exemplar unvollständig: Seite 1-82 in der Vorlage nicht vorhanden
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

374 THE PHOTOGRAPHIC NEWS. [August 6, 1880. whose duties are to “take cognizance of all differences arising at any meeting of the Association among the mem bers that may be referred to them and not coming within the reach of these byelaws.” It is satisfactory to find that this Board of Honour had no power to impose any “ monied fine ”; but as to whether they could impose any penalty not “monied,” we are altogether in the dark, Article 13, relating to “ order of business and rules and order of debate,” is a most stupendous affair. It contains no less than nine directions for the order of business, four rules for the conduct of the debatea, the fourth rule being further subdivided into seven alternatives, and nine mis cellaneous orders to meet any possible contingency which may arise during the progress of the meeting. Article 12 is so unique in its way we cannot forbear quoting it. It is headed “ Funeral Honours,” and says: “ On the death of a member, it shall be the duty of any member having cognizance thereof to report the same immediately to the standing committee, that such measures as may be advisable may be entered into.” With all this elaborate paraphernalia, what a dreadful responsibility it must have entailed to have been a member of the “ American Daguerre Association! ” ON THE USE OF COAL GAS IN PHOTOGRAPHY BY AN OCCASIONAL CORRHSPONDENT. The use of coal gas for lighting the sitter by Mr. Laws, of Newcastle, appears to us to constitute a new epoch in photography, and to be one of the most important improve ments which has been made since the introduction of gela tine plates, of which, indeed, it is a direct consequence. The use of the electric light rendered the professional photographer independent of solar radiation, but at what a cost for the installation and maintenance of the substitu- tute! Here we have solar light superseded without the expensive magnetic-electric engine in the motive power. Our source of force is already within our reach, and we have only to find the best method of utilising it. Our efforts must be directed to obtaining from the gas the whitest—or, more properly speaking, the most actinic— flame which it is capable of yielding, and there are, at least, two chemical methods of greatly enhancing the light of pure coal gas, which do not appear to have occurred to Mr. Laws, both of which, we think, are applicable to his apparatus at a very slight cost. To make this apparent, let us consider the principles involved in the operation of burning gas for illuminating purposes. The ordinary flame of burning hydrogen—by which we mean that emanating from the combustion of this gas and atmospheric air—is scarcely visible, notwithstanding the great heat produced thereby. We may, however, render that flame highly luminous by the introduction within it of a coil of platinum wire ; by causing it to impinge upon a solid refractory body, such as a piece of calcium- or magnesium-oxide ; or, still better, by previously passing the hydrogen through, or over, the surface of a liquid hydro-carbon, such as benzine, in which case it takes up a volume of the highly carbonaceous compound, and white light is the immediate result of its combustion. A comparison of experiments of this nature has led to the conclusion that the light obtained by combustion, under ordinary circumstances, is due to the presence of solid matter in the flame, heated to a very high temperature—or, as it is called, to a state of incandescence—and that the intensity of the light bears some direct relation to the degree of heat which the apparatus used enables us to attain. In the first case the solid incandescent matter is plati num ; in the second, lime, or magnesia; and in the third, unconsumed carbon. Coal gas is chiefly composed of hydrogen, and light- carburetted hydrogen or marsh gas; but these alone would yield us very little light in combustion, It also contains some olefiant gas, and a small quantity of what are called the heavy hydrocarbons, in a state of vapour; and although but a comparatively small per centage of these latter substances are present, they and the olefiant gas are the real sources of the illuminating power. It is obvious, therefore, that if we treat ondinary coal gas as we treated hydrogen in the third case, we shall very greatly increase its efficacy for lighting purposes, for atmospheric air itself becomes combustible and luminous when similarly treated. Formerly, and before Perkins’ great discovery of his aniline dye, the precursor of so many other tinctorial com pounds derived from coal-tar, the burner of the street lamps in many parts of London might be seen with a small conical vessel intervening between the supply-pipe and the burner, and this contained a bit of sponge or bundle of cotton wool, partly saturated with naphtha, distilled from coal tar, thus utilising an article for which but little other use was then made, and thereby greatly diminishing the quantity of gas consumed by the Company in carrying out their contract for lighting the streets. Now, this is the suggestion which we venture to make for the purpose of enhancing Mr. Laws’ light, unless, indeed, he has already adopted the well-known expedient. In applying it, however, there are some precautions to be taken by those who may adopt our hint. To derive the maximum effect from gas, a definite quantity of air must be used, and as the quantity is usually regulated by the draught of the chimney, this must be of a specific length for a specified quantity of gas consumed. It must, in fact, be neither too long nor too short. If it be too short, the flame will smoke—that is, give off unconsumed carbon; if it be too long, the air will be in excess, and the quantity of gas consumed will not yield all the light it is capable of yielding when the quantity of air is properly adjusted. If, therefore, these conditions have been fulfilled with the gas as it issues from the main, and before being passed over the benzine, a murky smoky flame will be the conse quence of such passage, and the supply of air must be greatly increased by increasing the draught, in order to ac commodate the supply of air to the increased quantity of carbon. The phenomenon referred to is familiar to all who use a Bunsen’s burner; when the gas burns mixed with air, asit is intended to be, the flame is blue, thin, andnon-lumin- ous ; but when the air-holes of the outer tube are stopped, or when the gas by accident becomes lighted as it issues from the jet unmixed with air, an offensive smoky flame is seen, unconsumed carbon and hydro-carbons being evolved. The light of combustible matter, unlike its heat, cannot be measured by the amount of oxygen consumed, for heat is the result of the most perfect combustion, whereas light results from imperfect combustion. Probably the best way of obtaining this adjustment between the atmospheric air and gas, if our suggestion be acted on, will be to employ a chimney long enough to obtain nearly perfect combustion of the gas, and upon the end of it, or within it, to place a damper or valve for regulating the draught, and to gradually close this until the flame begins to smoke, or to show by its deepened colour that this point is near; then again open the valve till the best result is attained. The second method of increasing the illuminating power of coal gas to which we alluded is to greatly increase the temperature of the incandescent carbon, by heating the air before it is brought in contact with the gas. It was the use of this expedient, under the name of the • • hot blast,” by which Neilson, of Glasgow, so greatly improved the manu facture of iron, reduced the cost of its production, and for which, after protracted litigation, he secured more than one hundred thousand pounds from the combined iron masters, who had largely adopted his process. We believe that the principle was first applied to illuminating purposes by Dr. Frankland, the eminent chemist; and it has lately been adopted for increasing the heat of the blow-pipe flame by Mr. Fletcher. Wo have not space to describe its application to lighting purposes in our present number, but may refer to it on a future occasion.