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The photographic news
- Bandzählung
- 29.1885
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- 1885
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- Bandzählung
- No. 1389, April 17, 1885
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The photographic news
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Band
Band 29.1885
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- Register Index III
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252 THE PHOTOGRAPHIC NEWS. [April 1?, 1885. H tap closed, or some diffusion of ether vapour backwards might gradually take place, in spite of the pressure from the bag. In the ordinary way, nothing of this kind happens, and 1 have often smelt the residue of oxygen in the bag at the close of the lecture, without detecting any trace of ether. When the jets are lighted, put on as much pressure as you can without producing hissing. After a little while, when the lantern warms up to its work, you will be able to turn the taps a little more, and then they will need no further touohing for at least an hour and a half, if the ether be light and good. Rotate the lime about once every ten minutes. To preserve the granules from disintegration and dust, the following mode of putting out the light at the close of the lec ture may be adopted. The H tap of the jet to be turned off slowly, and the oxygen from the 0 tap allowed to blow out the flame. If you turn off both taps at once a “ snap ” will pass back, and the inside of the jet will gradually be coated with fine pumice dust. Then the next time you light up you will see quite a little shower of scintillations in the flame ; whereas when small explosions of that kind are prevented by proceeding in the way described, the surface of the brass in the safety-chamber remains bright and clean. My impression at first was that the oxygen left blowing in this way would make the lime cylinder crack and “fly,” but I have not found such to be the case. When you have completed your lecture, leave all the jet taps open, and draw air through them to suck out the ether vapour, which, if allowed to remain, would turn acid and corrode the metal. My experience of the safety-jet exhibited this evening has been principally with ether vapour. I have, however, used pure hydrogen gas, carefully freed from air, with good effect. This pure hydrogen explodes more strongly, when mixed with oxygen, than that prepared in the common way by dilute sulphuric acid and iron turnings, but it is extinguished without any difficulty in the granule chamber of the safety-jet. In segard to ether, the treatment to which I have subjected the jet may, I think, be considered exhaustive, for the chemicals were of the best quality, the gases mixed in various proportions, and the jet heated by a spirit lamp until the india-rubber washers showed signs of melting. The result, however, was invariably the same, a faint snap at the orifice, but the flame could not pass the granules to the chamber beneath. The jet would be more perfect if this mixing chamber beneath could be dispensed with, but I have not been able so far to do more than reduce it in size. In the numerous experiments I have had occasion to make, one point has struck me forcibly, viz., the very moderate amount of pressure which suffices to keep even the most explosive gases burning quietly at the mouth of the jet without passing back. The exhibitor at the Chadderton Town Hall, although he allowed ether to enter his oxygen bag from a wrong construction of the tank, would, I believe, have escaped any accident if the bag or tubing had not been touched. Hence, whilst recommending a safety-jet, I recommend also that the ordinary precautions for keeping up the pressure should be observed. The whole of th* gas used in maintaining the light in this process passes from the bag through a single tube, and it is therefore obvious that if this tube was stepped upon, the pressure would at once be taken off. A Letter from A. S. HERSCHIELL, Esq.,M.A., F.R.A.S., Professor of Physics and Experimental Philosophy in the Parham College of Physical Science. Dear Sir,—I can now confidently vouch for your jet’s perfect safety under all conditions of burning with explosive oxyhydro- gen gas, as 1 have put it to as severe a test as can possibly be applied in its normal state, and it gives way to none of them. Taking off the fine nozzle of the jet, I placed over the chamber instead of it, the tin lid of a round vesta match-box, which just fitted on the outside, so that it could slide up and down and cover the wire gauze exit of the chamber with a gas measure of variable volume between it and the escape orifice, which was a small hole pricked with an auger point in the middle of the match-box lid. A short riband of paper had to be gummed round the outside of the cylinder to make this tin cap fit it and slide on to it quite tightly. The greatest capacity of the cap above the wire gauze was about half a cubic inch (or a trifle less), and it could, when necessary, be pressed down close upon the chamber top. In no position of this cap could I make the gas flash back, though in order to strengthen the violence of its explosion, I narrowed the touch-hole orifice by forcing a taper glass tube into it, with a very small opening at its point, and lit the gas at the large open end of the tube, so that its flame blew back into the cap. Even with this assistance, I could not get a violent enough explosion in the tin cap to throw it off its fitting on the chamber (although it was just knocked off once or twice), and on pressing the balloon nearly empty with the hand, I could feel the pujf of the tin cap explosion quite strongly, making it probable that backward escape through the pumice was at least a con siderable cause of the weakness of the explosions. Feeling satisfied that half a cubic inch of gas on the front side of the wire gauze was insufficient to drive back the flame through the pumice, I then proceeded to use the body instead of the lid of the tin match-box. This held about one cubic inch, and could not be slid down to less than that, but was easily packed and tied down tightly to the top of the chamber, It had also a small pin-hole pricked through the lid. The “puff” of this, as before, did not injure or move the box, but the very first ignition passed through the pumice and inflamed the balloon, bursting it with a pistol sound. Finding that the large box of one cubic inch always blew up the balloon, I next tried the effect of varying the rate of egress of the gas by holding the short india-rubber tube, leading from the balloon to the jet, between the finger and thumb, and pinching it. In this way, with the small r inch cap, I was able to burn the explosive gas either at the mouth or inside the cap, on the surface of the wire gauze with a fizzing sound. The tin cap being raised to 3 inch above the chamber, and the chamber filled with copper filings instead of pumice, the simple snap-explosions were not effective in driving back the flame, but left it kindled on the gauze inside, making a rushing noise from escaping steam, and after a little while, as the copper became heated, firing through into the balloon. I then took out the copper filings, and tried the same experi ment with pumice sand in the chamber. Here neither “ puff ” nor “ fizz ” would take any effect, although the steam formed and rushed out copiously. On looking at the wire gauze after it was over, I found that it had fused into pinholes in places, and had melted itself up with the pumice, which actually formed a semi-vitrified cap of ? orinch deep on the top of the sand ; and this sand came out whole, and was partly solid and consistent. Yet, in all this violent heating, the gas did not tiro back through into the balloon, so that the pumice appears to be a safer material to use than the copper filings. The tin-box experiments were preliminary to a concluding trial with the jet itself ; and, therefore, putting in new pumice sand, I proceeded to raise the nozzle to a good height from the gauze by means of a thick leather washer round the screw. The “fizzing” and “snapping” phenomena could then be got at pleasure, in turns, by varying the rate of gas flow, But, as I ex pected, no continuation of this process would make the gas fire back into the balloon, and the gauze and sand, after a trial of some time, were quite unharmed. Of course, with the nozzle screwed close down on to its thin washer, as in the jet you sent me, the security against ignition will be still greater, and I do not see how it could, by any possi bility, be made in that state to burn injuriously. The pumice sand is evidently sansparicl—an intercepting material of first-rate excellence. ON PLATINOTYPE. BY J. S. POLLITT.* The platinotype process, though of comparatively recent origin, is by no means a stranger amongst us, as it has been rather ex tensively practised in various parts of the country, and very successfully by some members of this Society. It is a process which, for many kinds of work, has much to recommend it, the results being characterised by a quiet beauty which invariably pleases an artistic taste ; and its freedom from the meretricious glaze of albumenised paper affords a sensation of repose to the eyes ; but the great value of the process is still further enhanced by the supposed permanent nature of the printed proofs. It is now, I believe, a matter of history that the late Roger Fenton, who went out to the Crimea during the Russian war about 1854, and took a large series of fine photographs, which were afterwards exhibited in the Exchange of this city, gave up photography because, as he said, there was no future before him, so many of his photographs having faded. Such a complaint, however, cannot be made against platinotype, and the knowledge • Abstract of a communication to the Manchester Photographic Society
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