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THE PHOTOGRAPHIC NEWS, Vol. XXVII. No. 1300.—August 3, 1883. CONTENTS. PAGE Testing for Hypo 481 Fixing Bath containing Alum 481 Lantern Slides 482 The Tourist Photographer 483 Mewcastle-on-Tyne Photographic Association 481 Does the Amount of Gelatine affect the Rapidity and Quality of the Negative. By A. L. Henderson 485 The Eclipse Party 485 Practical Aids to' Instantaneous Photography. By R. Crowe... 486 PA GF. Notes • Patent Intelligence A Trip to Kilauea. By C. Ray Woods.. A Dictionary of Photography Solid and Liquid Illuminating Agents. Correspondence Proceedings of Societies Talk in the Studio To Correspondents 487 489 489 491 By L. Field, F.C.S 492 494 494 495 """2.,. 490 TESTING FOR HYPO. It is probable that not one hand-book out of every twenty which has been written on the subject of photography during late years could be found that does not contain the method of determining the presence of thiosulphate or hyposulphite of soda by means of iodide of starch. This subje ct having been well ventilated in these columns from time to time, also by various authors of treatises on chemis try, we may take it as a pretty (occlusive fact that the average photographer is thoroughly well acquainted with the re-agent spoken of, and the reactions which take place. Assuming such to be the case, we take this opportunity of pointing out just how one little error might upset the calcu lation, and render the experiment valueless. There is very little doubt that the blue colour of starch iodide, when diluted with pure (or comparatively pure) distilled water, may be retained fcr sometime if kept in a closed tube in the dark room ; but as the photographer does not always possess a very pure sample of water, it is customary to pre pare the comparing liquid at the time of performing the experiment. Suppose we place a given quantity of the starch iodide into a clean test-tube, and fill it up with dis tilled water, and into another clean test-tube of the same dimensions put a similar quantity of starch iodide, and fill it up with the liquid to be tested, the difference in colour, if any, when examined over a sheet of white paper, denotes the bleaching action of sodium thiosulphate; this is all very well so far as it goes, but it does not for a moment prove that other bleaching agents are not present in the water besides the one named. To prove that such bleaching agents do exist in ordinary water, the following experiments were undertaken :—Three test-tubes of the same capacity were marked in a similar position as regards quantity, and filled to the mark with A, distilled water; B, ordinary tap-water drawn from the main, and containing lime ; C, distilled water, to which was added an equal quantity of lime water; also carbonic acid gas, until the mixture became turbid. To each A B and C we delivered by means of a pipette a quantity of the starch iodide solution, equal to five cubic centimetres ; each tube was then shaken, and placed vertically against a sheet of white paper with the light arranged from the top, so as to examine the colour in the most satisfactory manner ; and to be very exact, a piece of litmus paper of the same shade was used for comparison. A retained its colour ; B vety gradually became lighter; C bleached instantly. 50 cubic centimetres more starch was added to C; but the colour dis appeared within a few minutes, clearly showing the unrelia bility of this substance under certain conditions. . A, remaining constant, two more tubes were filled in a similar manner with distilled water, sodium carbonate being added to one, and sodium sulphite to the other; upon shaking up with a similar quantity of starch iodide as previously used, the colour was destroyed in both cases. The next experiment consisted in pouring acetic acid on chalk, so as to obtain a plentiful supply of carbonic acid gas, the mouth of the tube containing CO, being held over the mouth of another tube containing lime water to saturation ; this gas, which is heavier than air, naturally flows from the upper tube into the lower one, and carbonate of lime was rapidly deposited, so that this experiment may be considered as an intensified copy of C. To this mixture two drops of strong nitric acid were added, which cleared the turbidity, and five cubic centimetres of starch iodide solution delivered from a pipette, as before, coloured the mixture a delicate blue, similar to A, the tube we had taken as our standard. After a lapse of twenty-four hours the colour was unaltered ; but one drop of fixing solution (sodium thiosulphate) sufficed to destroy the colour instantly. From these experiments we glean that, when it is desired to adopt the iodide of starch method in testing for hypo in mounts previous to taking them into stock, silver prints, gelatine negatives, or either of their respective washing waters, it becomes a matter of some importance that the liquid should be acidified; and nitric acid is suitable for tho purpose, because, as we have shown that in the presence of unmistakable bleaching agents a very small proportion of the powerful oxidizing acid so controls or retards their action, that their presence may be considered inert. FIXING BATH CONTAINING ALUM. In many ways the mixed alum and hyposulphite bath has proved to be a valuable and important improvement upon the old fixing bath made up with sodium hyposulphite alone ; and we recommend a trial to those readers who have not yet employed the composite bath. As far as our own experience goes, the simple mode of mixing recommended in the Formulary answers ex tremely well, and either no sulphur is deposited when one volume of a saturated solution of sodium hyposulphite is mixed with two volumes of a saturated solution of alum, or the amount of sulphur deposited is extremely small; so small, indeed, as to correspond with the decomposition of so minute a proportion of sodium hyposulphite as not to perceptibly affect the working strength of the fixing bath. The Marquis de Ferronnay recommends a somewhat novel method of mixing the hypo and alum bath, his plan being as follows. One litre of warm water is poured on a mixture of 150 grammes of hyposulphite of soda and 40 grammes of alum, the whole being well stirred ; apiece of wood being more convenient for this purpose than a glass rod. A small proportion of sulphur is deposited, I but after this has been removed by filtration the solution