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528 THE PHOTOGRAPHIC NEWS. [October 30, 1868. with sulphuric acid, and then mixes the trisulphate obtained I with three equivalents of chloride of sodium or other convenient I chloride. Upon heating the mixture in dry air the chloride of I sodium yields all its chlorine.—Chemical News. Manufacture of Permanganate of Potash.—Some facts I worthy of attention concerning the manufacture of perman-1 ganate of potash have been pointed out by M. Staedeler. In I the preparation of this salt, by heating a dilute solution of the I manganate, a third of the manganic acid is reduced to the I state of peroxide without taking part in the reaction; the I case is the same when hydrochloric acid is used to effect I the transformation, notwithstanding that this process permits I of the use of concentrated solutions. Things happen differ-1 ently when chlorine is employed. The following is a con venient method of operating:—The crude pulverized man ganate is abandoned in its own weight of water for several days; then a similar quantity of water is added, and a current of chlorine transmitted until the liquid becomes red; the solution is frequently agitated, diluted with four times its volume of water, filtered through coarsely powdered glass, and reduced to one-fifth of its original volume. At this point the permanganate crystallizes; it can be obtained in a state of purity by recrystallizations. The yield is 90 per cent, of tho weight of peroxide of manganese employed.— Ibid. UD Oorresponents, Bab.—Where two solutions have to be used in succession on the plate in developing or intensifying, they should each contain the same amount of alcohol, or such amount as will make each flow evenly without causing greasy-looking marks, caused by the im perfect mixture of the two liquids of different densities. See a short article on the subject for fuller explanation. A. B.—The enquiry you make is a very important and useful one, and the answer, fully given, would be very instructive, but would, unfortunately, require several pages of our Journal, as it would involve an explanation of the difference between good work and imperfect work in almost every detail. The Bristol pictures are good examples of good workmanship throughout: well lighted, well posed, developed properly, printed and toned with taste, and, finally, well mounted and well rolled; whilst the others arc faulty in all these particulars. In the Pontypool pictures the figure is, in the first place, taken on much too large a scale, giving an effect of clumsiness to the figure. The camera requires moving further from the sitter. The figure is not well lighted, too much top-light being used. The negatives are a little under-exposed and over- intensified, causing black shadows and chalky lights without de tail. They are toned a little too black; not neatly mounted, and not well rolled, if rolled at all. The backgrounds and accessories are not good. The background screen should be more even and free from marks, and should be further from the figure. W. ADREWS.—The number of the News containing the descrip tion you require has been forwarded. You cannot do better than follow out the instructions in all respects. 2. Yes; let the bath into the bottom of the box. 3. It is customary to mount stereo scopic pictures so that any two points (say the centres of each pic ture) shall be about 24 inches apart. Of course, if the centres are that distance apart, there will be also that distance between any two points in the pictures. The best and truest effect is obtained by leaving on a little more of the right-hand side of tho subject in the right-hand picture, and of the left-hand side of the subject in the left hand picture. A .Seeley, who seems a little inclined to indulge in badinage, sends us the following :—" Now that so much is being said about photo engraving, I enclose two specimens of a process to be called photosketchitblackvarnishengraving, and shall be glad of your remarks thereon. It is not patented.” The specimens enclosed are examples of a process introduced seven or eight years ago as photographic etching. A plate of glass is covered with an etching ground, either of black varnish or other suitable substance, and a drawing is then executed with an etching-needle, by which means an etched negative is produced, from which a print may be ob tained on excited paper by the ordinary photographic printing process. The specimens enclosed, which are good examples of what may bo termed the slate and pencil school of art, appear to have been executed by such a process. GULIELMUS (Sheffield).—The markings you describe are very suggestive of over-iodizing. Collodion, when over-iodized, is very apt to yield just such markings as you indicate. If this be the cause in your case, the addition of a little plain collodion to the sample in use will effect a cure. Somewhat similar markings will sometimes proceed, however, from other causes. The use of a very old bath is sometimes a cause. The immersion of the plate before it has well set is often a cause, especially at this period of the year. Moving the plate rapidly the moment it is put into the bath, and keeping it moving for half-a-minute or a minute after, proves a cure when the defect arises from other causes than over- iodizing. 2. It is a somewhat difficult task for us to say when a certain article appeared, of which you can only tell us that it was a good developing process, without giving us tho title, as we have published so many, and are so frequently publishing such processes. You will find one in the present number of the News. W. J. A. G.—By care and perseverance in tho plan you describe you cannot fail of success. 2. Mr. Rejlander’s address is 129, Malden Road, Haverstock Hill. You are right in your conjecture as to the “authority” it was necessary to correct, and also in your estimate of its character. New Subscriber.—With the dimensions you propose the arrange ment generally is good; but we should prefer at least three feet more glass at the north side, and one or two feet more in tho north roof. In some respects No. 2 would be tho best form, but the sun would trouble you in summer, so that on the whole No. 1 will be attended with the fewest troubles. Old Developer.—You can obtain a solar camera through most dealers. Mr. Atkinson, of Liverpool, will certainly supply you, and general instructions for its use will accompany the instru ment. We shall have pleasure in assisting you through any specific difficulties which you may find on trying it. Henry Lamb.—The stereoscope described by Mr. Blanchard is of American manufacture. Whether it has yet been made by any one in this country or not, and if so at what price, we have not yet learnt. The amount of magnifying power in the instrument Mr. Blanchard exhibited was pretty good; but that is a point depending on the lenses with which the instrument is fitted; within a suitable range, any power of lens might be employed. The great advantages of the stereoscope in question were perfect illumination of tho slide, convenience for use, facility in adjusting the focus to any sight, and some other mechanical advantages not usually possessed by existing and more expensive forms of box stereoscope. We think it will very probably be taken up by some manufacturer, in which case it will doubtless be noticed and advertised in these pages. F.—Any chloride soluble in alcohol may be used. We have not noticed any special difference in the results of different chlorides. We prefer citric acid to any organic substance for the purpose which we have tried. We saw the letter to which you refer. Tho name was, as you conjecture, an interpolation, to cause a false suggestion. Wo had a letter from the writer of tho letter a few days after it appeared. R. N. F.— You will seo some further explanations of the method of masking in question on another page. B. F.—Very dilute sulphuric acid (say one part acid and four parts water) may be employed to clean lenses. Tako care to rinse well afterwards, and dry thoroughly. 2. No. 3 of your list is preferable. M. D.—The simplest mode of ascertaining tho equivalent focus of a portrait combination is that which wo suggested some years ago. Focus an engraving sharply on the ground glass, getting tho image precisely the same size as the original. Then remove the lens, and measure the distance exactly between tho ground glass and the engraving. Ono-fourth of that distance is the equivalent focus of your lens. Thanks for your good wishes. Silex.—The proportions of the room certainly present some diffi culty, but such as may, wo think, b overcome. The greatest is the great height of the wall—twelve feet—in which you can have no side-light. There is a method, however, of dealing with this. If you raise the floor of the room three or four foot, and so bring the sitter nearer the skylight, you will be able to submit him to a much larger volume of light, and avoid slowness. If the premises answer well in all other respects, we should bo tempted to try this method. We should put in a good length of skylight, broken up with as few sash-bars as possible on tho north side, and a smaller skylight, for use in dull weather, on the south side. Thanks for the paragraph, which we shall use. E. Sawyer.—We have written to our correspondent, and will lot you know the result next week. Stereo.—Received. Thanks. Several Correspondents in our next. 3hotographs Aegistere. Mr. J. Stuart, Glasgow, Photograph of Prince of Wales laying Foundation Stone of Glas gow University. Photograph of Foundation Stone of ditto. Mr. P. A. F. VILLIERS, Newport, Mon., Photograph of Sir J. Ramsden. Photograph of Mr. Rees Jones. Mr. J. Milton, Newcastle, Stafford, Photograph of Map of Borough of Newcastle, Stafford.