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
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April 17, 1885.j THE PHOTOGRAPHIC NEWS. 251 pand from 2 to y inch after passing a tenth or an eighth of an inch inwards. I have known jets in which the narrow part of the bore was | or it inch long, but these jets do not burn as much gas nor give as much light, unless the bag is more heavily loaded. With the most careful instructions for the manufacture, you will find that scarcely two jets will agree in the amount of pressure which can be put on without producing hissing. You must, therefore, blow through the jets beforehand with the breath, and pick out the noisy ones. On taking off the nipples, and looking through them against a strong light, you will, pro bably, find that with those which work silently the small bore of 3’ inch is exactly in the middle of the larger 1 inch bore, whilst with the roaring nipples, it is one side. Failing this, all that you can do with the noisy ones will be to select a needle of the right size and polish the bore with it, after dipping it in a cream of oil and knife-polishing powder. The same may be done with good effect in the case of an old jet which has become corroded or choked up with lime dust. The Granule Safety Chamber.—I do not consider that any thing of this kind ought to be necessary; but as I usually lecture in crowded rooms and often to children, I have used the safety chambers since the Chadderton accident. They may be applied in the form of tubes attached to the taps of an ordin ary jet, or the jet may be made purposely with the safety chamber in front, immediately below the nipple. The biunial which I show to-night has a safety jet in the top lantern packed with granules of binoxide of manganese, and safety tubes in the lower lantern with granules of pumice. The safety chamber must be circular in form, }-inch wide and }- inch deep, interior measurement, with a disc of wire gauze of sixty meshes to the inch next to the granules, and a second of thirty meshes to strengthen it, both resting on the top of the chamber. These two disc must be five-eighths of an inch across, and be kept in position by a ring of wire fitting into a groove in the brass. Two other similar discs are to be pressed or screwed tightly upwards against the bottom of the chambers, but in such a way as to be easily removable for cleaning or renewal. Below the chamber thus formed, there should be an empty space holding half a fluid drachm, to serve as a mixing chamber for the gases bafore they enter the granules. Above the chamber is no cavity of any kind, but the cap screws down nearly close, leaving only sufficient room for the gases to pass freely to the nipple. The difficulty with this jet will be not so much in extinguishing the exploding gases, as in getting enough pressure with one hundredweight on the bag. Therefore no attempt must be made to economise space by contracting the diameter of the granule chamber at the top ; the upper discs of wire gauze must be as large as the lower, and all the discs must be changed if they become rusty or choked up. I have seldom had occasion to change them, but a few minutes will suffice for the operation. The safety tubes ought to be a little longer than the chamber in the safety jet, about three-quarters of an inch instead of half- an-inch, but they need not be quite so wide, say half-an-inch exterior measurement instead of interior, with discs of wire gauze, exactly as before, in the screw caps at the ends ; the whole to be made air-tight by springing a piece of vulcanised rubber over the tube and shoulders of the caps, until it is flush with the milled heads at the ends, and then securing it by tying with red silk. The Safety Granules.—I know of none superior to the pumice, originally proposed by Mr. Broughton, in its power of extinguish ing flame ; but it is inclined to be dusty, and is easily disinte grated by the action of the gases. When this happens, a flicker ing will be seen from small particles of pumice projected icto the flame, and eventually the tubes, on being opened, will be found not to be quite full. The flickering is very slight after the tubes have been a little time in use, and some persons do not observe it; but if you wish to avoid it, granules of blach oxide of manga nese may be substituted. These granules are not entirely equal to the pumice in power of arresting flame, but they are strong enough for use in the jet or tubes now described. The hardest and purest variety of the mineral should be selected, and it may be crushed in a steel mortar. This operation is somewhat troublesome, but a little goes a long way and lasts a long time. In reference to the size of the granules, wire gauze sieves of forty and fifty meshes to the inch are the best for screening ;* • Wire gauze of any size can be obtained of Messrs. Bedford & Steer, wire-workers, of Long Lane, Bermondsey, London. all that passes through the former and rests upon the latter being retained. Granules ecreened by Nos. 50 and 60 are too small to allow of a free passage for the gases, and 30 and 40 are too large to stop the flame. 1 succeeded with this size when crushed slate was used, but on trying pulverized glass the flame passed easily through them. The granules of binoxide of manganese are in appearance like coarse grains of gunpowder, and being very heavy they sink by their own weight and keep the chamber closed, in filling the chamber, it should be tapped gently, and the granules scraped to a level surface ; but they must not be pressed tight together, or the flow of gas will be impeded. As regards the relative merits of the safety-jet and safety tubes, the jet is a neater and more compact arrangement, the granules being readily accessible, and well secured in position ; it also has an advantage in the chamber being upright. On the other hand, the tubes are available for a jet already in use, and although the volume of the exploding gases is larger, the granules, being in a cool place outside the lantern, are better able to with stand the shock of an explosion. The upper jet in a biunial becomes strongly heated by the hot air from the lower lantern, and it is well known that heat facilitates the passage of flame through fine tubesand orifices. What you gain in one direction; therefore, by using the jet, you lose in another, and it is hard to say to which side the balance of advantages belongs; practically, either jet for tubes will answer the purpose, if kept in working order. Supposing the safety-tubes to be used, with pumice, they must be opened from time to time to see that they are full ; for, not being vertical in position, the granules, in wasting away, and sinking down, will eventually leave an empty space, along which the flame might travel. The India-rubber Tubing. — }, must repeat the caution given in a previous paper, not to use any but the best and thickest quality of tubing. The ether softens the thin kinds, and speedily makes them rotten. Red rubber is very elastic, but I have found it sticky, and apt to cut with the string used in tying. The pure grey vulcanised rubber is far tougher, and will last a long time. Half-an-inch outside diameter, and a quarter of an inch in the bore, is a good size for carrying the ether vapour. I object to putting the ether-tank on the floor, because it involves the use of a long tube between it and the lantern ; and this tube absorbs a quantity of ether, as you may prove by drawing air through it when the lecture is over. With the tank on the table close to the lantern, you have only a short piece of tubing, of nine inches or so, to look after, or two pieces if you use a biunial. These pieces of rubber must be examined from time to time, because if they were to give way, there would be a rush of vapour, liable to ignite at the nearest flame, and to run down the tubing, burning fiercely. I consider this danger more real and obvious than that of ether passing back into the bag, or forming an explosive mixture in the tank, neither of which could easily happen with good ether and a tank properly constructed. Setting up the Apparatus.—The lime cylinder ought, un doubtedly, to be a little further off from the tip of the jet with ether than with hydroden gas, because ether, being rich in car bon, deposits it on the lime if you bring it too near. A quarter of an inch from the orifice to the point where the burning gases impinge upon the face of the cylinder is an average distance; but all depends upon the angle of incidence of the flame. Mr. Lewis Wright mentions 35° as the nearest to a right angle obtainable without risk of throwing a shadow on the screen, and this agrees with my own experience ; but if the angle is less than 35°, then the lime may be brought nearer. You can tell when it is right by looking at the lime itself; it should be worn away into a depression of an oval or elongated form ; if a small round hole is drilled by the flame, then the cylinder is too near. The weight on the oxygen-bag should be about a quarter more than you are in the habit of using with an ordinary jet. I sel dom find it necessary to exceed a hundred-weight, unless with a very large bag and a biunial lantern, in which case a hundred weight and a-quarter may be put on. Turn the taps in a regular order, beginning with the bag, and ending with the taps of the jet. In the old form of ether-tank, it was recommended to relieve the pressure of ether by opening the H tap of the tank first; but in the tank described in this paper, it is comparatively immaterial which tap you open first, provided that you open them both at the same time. You must not, however, open the oxygen-tap of the tank, and leave it for a long time with the