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THE PHOTOGRAPHIC NEWS, Vol. XXVII. No. 1287.—^fay 1883. CONTENTS. A New Guillotine Shutter 273 The Effect of the Temperature at whicn Plates arc Dried in Modifying their Sensitiveness 273 The Explosive Substances Act, 1883 274 The Studio Turn-Table 275 Half-a-Dozen Portraits 275 The Eclipse Expedition. By C. Ray Woods 277 Photo-Lithography and Photo-Zincography. By Major J. Waterhouse, B.S.C 278 Notes 280 Patent Intelligence 28- PAGE Twelve Elementary Lessons on Silver Printing Notes on Photography. By E. Howard Farmer Astronomical Photography Emulsion Processes for Beginners. By M. Lockett Apparatus for Printing by the Blue Process. By Channing Whitaker Correspondence ............ Proceedings of Societies Talk in the Studio To Correspondents Registrations 282 284 284 284 285 285 287 288 288 288 A NEW GUILLOTINE SHUTTER. A SHUTTER, which has recently been adopted in Austria, and which is the design of Herr Czerni, of Vienna, deserves to have a few words devoted to it, since it has come under the favourable notice of the Vienna Photo graphic Society. The instrument, of which we give a sketch, is made of ebonite; and one of the advantages claimed for it is that it acts more quickly than the simple drop-shutter, which, we believe, is usually associated in this country with the name of Mr. England. The Czerni shutter is not very complicated, although it may at first sight appear so. It is set in action by a steel spring, and the rapidity of exposure claimed for it is that of 3 of a second ; moreover, we are told, the spring, when set in action, being to a certain extent neutralised by other springs, there is little or no vibration. The action of the shutter will be apparent from our sketch. The falling portion, or shutter itself, is shown at B, moving in grooves in the frame-work, AA. The shutter is pushed up by means of the button, a, and thus the steel spring, b, is bent. This spring presses upon a, giving the shutter a downward pressure. A. little catch at the side of the apparatus at c holds the shutter in its place when it has been slid upwards; and as soon as this catch, c, is forced back pneumatically, the shutter at once rapidly falls. We may further mention that the “ cut-out,” or aperture, of the falling shutter is square, and to prevent vibration, or, rather, to neutralise it, two cheeks or projections, e e, are fitted on the upper part of the shutter, and these, on falling, press against the spiral springs, ff. A pneumatic arrangement of the ordinary nature is attached by means of a brass ring, as shown in the wood-cut, g being the pear to be squeezed by the photographer, and d the little bellows that acts upon the catch, c. Altogether the apparatus will be seen to be exceedingly ingenious, and should not be very expensive to construct. THE EFFECT OF THE TEMPERATURE AT WHICH PLATES ARE DRIED IN MODIFYING THEIR SENSITIVENESS. It has been observed at various times that some difference in the sensitiveness of different plates prepared from the same emulsion may arise from the method employed in drying; but how great this difference may be is, we believe, by no means generally known. Mr. Warnerke, a short time since, somewhat indefinitely stated that plates dried slowly were more rapid than those dried rapidly ; but no very great attention appears to have been paid to his remarks. Some little time ago our attention was forcibly drawn to observe the matter in the following manner. W e are in the habit, after we have completed an emulsion, of coating a few small trial plates. This we generally do the last thing at night, and, so that the plates may be dry by next morning, we apply a somewhat high temperature. In ccating afterwards with the bulk of the emulsion we use a much lower temperature, as we are not anxious about the result. It has always happened that the last batch has proved considerably more sensitive than the trial plates ; but this we put down to the effect of the ripening of the emulsion ; and it was only when on one occasion the we reversed operation that we came to see that we had some quite other cause to take into account. We had not quite used up a batch of emulsion which gave very rapid plates, and coated a few quarters with the remainder as for trial plates, our object being to give them to a friend to let him see what very quick plates we could make ; they were dried rapidly, and, to our no small surprise, turned out several times less sensitive than the bulk of the plates coated with the same emulsion. Here was something quite new to us. Our first impres sion that the emulsion had become slower appeared an un likely one, and the only other cause which presented itself as a probable explanation was the temperature or the speed of drying. We determined to institute some experiments. We need not detail all of these, but shall give such as may be taken as typical. We dried plates without artificial heat at a temperature below 50° F., the time taken being about forty-eight hours. Others we dried at the highest temperature short of that which would melt the gelatine, the time taken being only three to four hours. The plates were tested side by side with a result both remarkable and (to us) unexpected. The plates dried slowly, developed in a quarter of the time which those dried quickly took, and were enormously more rapid. According to sensitometer readings they were six times quicker—by the camera four times. The difference in time taken to develop was not only due to difference in sensitiveness. When the slower plates were