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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1285, April 20, 1883
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The photographic news
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- Titelblatt Titelblatt I
- Register Index III
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APRIL 20, 1883.] THE PHOTOGRAPHIC NEWS. 255 Clark adopted as his oxyhydrogen jets Professor Daniell’s jet, and fixed over the ends of the tubes a small chamber prolonged into the usual jet. In this way he provided the mixing chamber, and the gases emerged as mixed gases from the point of the jet. From Messrs. W. II. Oakley and Co.:—The snapping you speak of is very objectionable to an audience, and I think it could be remedied by filing away a little of the slot in the plug of the dis solving tap, so as to turn the oxygen completely off, leaving the hydrogen slightly on. In doing this you may find it necessary to cut away a trifle of the “stop ” or of the « shell ” at the point where it touches the stop to make the plug turn a little further round. From Mr. IF. Broughton :—I can add but little to your very explicit directions for the working of my ethoxo light. You say the light is suitable for audiences of 200 persons; but I have shown it to an audience of over 2,000, using a t welve-feet screen. It was ad mitted to be the best light they had seen, and was mistaken by some for the electric light in consequence of its extreme whiteness. I have made some capital transparency plates from a formula which recently appeared of gelatino-bromo-iodide. They give bare glass in the shadows, and are very slow, averaging about ninety seconds at a distance of twelve inches from a gas flame. The pumice chamber is by far the safest arrangement with the ethoxo gas. Accidents have occurred without it, and will occur again. The ether volatilises better at high temperatures ; hence the necessity, if it be under 50° Fahr., of placing the tank in a bucket of warm water, thus making it much easier and safer to work. I have no doubt, that the pumice as I use it, namely, in the mixing chamber of the mixed jet, performs another useful function—the thorough combination of the two gases. I would suggest, if a back pressure valve be used, that instead of oiled silk as in Chadwick’s valve, the diaphgram should be made of silk coated with a mixture of glycerine, gelatine, and chrome alum, or potash—bichromate glycerine to make it pliable, and the salts to render the film insoluble. The ether ought always to be tested before exhibiting. My method is as follows:—Into a glass tube graduated with U centimetres, I place first 100 centi metres of water, and then 100 of ether. The tube is now well corked and agitated, taking care to keep the finger tight on the cork. With ether of sp. gr. *720 the water absorbs about 10 per cent, of ether, and ditto of *730 about 20 per cent. The ether will be found floating on the top of the water. I use methylated ether. My reason for mentioning this is, that quite recently I had supplied to me, in mistake, spirit of ether, and which was only detected by testing it; there was no separation of ether when mixed with water. I should also advise the emptying of the tank altogether when it has been used (say) half-a-dozen times, as the action of oxygen on the ether has a tendency to turn it acid. The best light is got by pres sure and small aperture ; but size of aperture makes no difference in dissolving, provided sufficient hydrogen be left on. The poppings out and small explosions in other burners are, as a rule, due to this cause, namely, insufficient hydrogen to drive out the oxygen before the gases become explosive. I always use the mixed jet, finding it brighter, more economical, and safer. Mr. HARDWICH: I am afraid it will hardly be safe to recommend dipping the ether tank in warm water, because some persons may not be aware that ether boils at a little over 90° Fahr.; but if warm water be used, a thermometer should certainly be dipped in it to ascertain its recent temperature. My own experience of the ethoxo light has been at comparatively low pressure, because when I lecture in a very large room I usually find gas laid on. High pressure may give more light, but it requires greater care on the part of the operator to prevent accident. With reference to Messrs. Oakley and Co.’s letter, I have altered my dissolver as they suggest, filing away the hydrogen slot until I found by suction that a little of the hydrogen passed after the oxygen bad ceased. I have not since had an opportunity of trying the dissolver; but, if I have carried the correction too far for the oxyhydrogen process, I can easily cut away a little of the oxygen slot until I have hit the right point. The dissolving tap which I use has large and free passages for the two gases, and I find it is both more air-tight and more free to move when I put in the plug just as it is, and do not rub it with oil, hog’s lard, or burnt india-rubber. Mr. Wood speaks of a large area of ignition being likely to give a less sharply-defined picture. Such in theory is no doubt the case, but practically we do not find any complaint made of a want of sharpness in pictures shown by the blow-tbrough jet. I have seen the original jet of the late Professor Daniell, of King’s College. It is not of the exact form which we now consider to give the best light ; but Mr. Wood is right in saying that the honour of the invention of the blow-through jet belongs to him, and that all those which have since appeared are but modifi cations. In my own opinion the most simple and economical “interchangeable jet” is an old form which has been in the market for many years, slightly altered. It consists of a circular plate of brass about an inch in diameter, with three loose cups of two inches high screwing down upon it with a leather washer, the oxygen brass pipe entering the circular plate in the middle, and the hydrogen on one side. In using the jet for the blow-through, you screw on a small oxygen tip, with an aperture of one-twentieth of an inch, and a quarter of an inch shorter in length than the outside hydrogen cap, which has an aperture of one-eighth of an inch. Be careful to ascertain by means of a needle that the stream of oxygen blows exactly through the centre of the hydrogen hole. For the mixed gases you take off the inside oxygen tip, and use only cap No. 2, with an aperture of one-twentieth of an inch; and for the ethoxo light you employ No. 3, having an aperture of one-twenty-fifth or one thirtieth of an inch. The inside of the caps should be sufficiently hollowed out to hold one and a-half drachm of water, otherwise you will be annoyed by a roaring noise in the oxy- hydrogen burner when the gases are not quite pure. The lime should be upright, turning from the back of the lantern, and sliding along the horizontal brass tubes as they lie side by side. An angle of 30° to 35° will be sufficient in the general way to prevent a shadow being thrown on the upper part of the screen. An exhibition of lantern slides then took place. Slides were lent for this occasion by Messrs. Hardwich, I’Anson, Stuart, Mounsey, Blyth, Kimmish, Mawson and Swan, and Morgan and Templeton. Mr. Allison, of Monkwearmouth, kindly lent his lantern and screen, and gave his valuable assistance. The Chairman proposed a vote of thanks to these gentlemen, which was carried unanimously, and the meeting terminated. About six hundred persons were present. Sheffield Photographic Society. The seventh ordinary meeting of this Society for the present year was held on Tuesday evening, April 2nd. Mr. J. D. Leader F.S.A., and subsequently the President, Dr. Morton, occupied the chair. Minutes of preceding meeting were read and confirmed. Mr. W. Bark was elected a member. It was arranged that the first excursion should be to Hardwick Hall on the 25th inst. Mr. Foxon exhibited several effective views printed from gelatine negatives produced by contact with a positive, secured in a similar manner from the original, which was very thin, but full of detail. Dr. Morton observed that it was satisfactory to know that a secondary gelatine negative could by careful development be made denser and better than the first one by adopting a process not unknown to collodion workers, and would no doubt prove a superior plan to the ordinary intensification of a thin plate. On the motion of Mr. Hatfield, it was decided to purchase apparatus for class demonstrations, and to test value of different developers, &c. Mr. LEAMAN showed some good examples of instantaneous work. Other contributions were handed round, and discussion followed. Photographic Society of Ireland. The usual monthly meeting of the above was held in the Royal College of Science, Stephens Green, on Friday, 13th inst., Mr. George Mansfield in the chair. The minutes of the previous meeting having been read and confirmed, The Chairman called upon Mr. Conan to demonstrate the Platinotype method of printing. ' In the course of his remarks, Mr. Conan drew attention to the advantages to be derived from the absolute permanency of the finished prints ; he also exhibited a collection of prints on fabrics kindly sent over by the Platinotype Company, as well as several specimens on paper, some of which he developed before the audience. There was a well sustained discussion. Mr. J. V. Robinson exhibited several specimens of photo- filigrane, and a new single dark slide. The Society’s new albums were also laid on the tables for inspection. The next meeting is intended to be held Friday, May 11th. London and Provincial Photographic Association. At the meeting held at Mason’s Hall Tavern, on Thursday, the 12th inst., Mr. W. E. Cooke occupied the chair. Mr. A. Haddon showed some negatives on plates prepared according to Mr. Burton’s formulae ; exposure four seconds stop, „4 ; Debenham’s system. They were very clear in th shadows, and full of sparkle.
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