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348 THE PHOTOGRAPHIC NEWS. [July 17, 1868. a surface stain, as from the absorbent nature of marble it probably will. The stains probably consist of partly and completely reduced carbonate of silver and of carbonate of iron. Oxalic acid in strong solution would best remove the latter, and cyanide of potassium to which a little iodine has been added would best remove the silver stains; or iodide of potassium might be applied, and fol lowed by cyanide. But in each case a little soaking and scrubbing with a brush will be necessary to do any good at all, followed by well washing i n warm water. Possibly rubbing down and re- polishing will, after all, be the only effectual remedy. WM. Sturgeon.—Both the salts of which you forward us examples are really the same thing—iodide of cadmium. That labelled bromide of calcium is not a bromide at all. You may ascertain the distinction between a bromide and an iodide by a variety of tests, some of which are simple and easy. The addition of nitrate of silver will convert an iodide into iodide of silver which is yel low, whilst the bromide of silver is white, or of a cream tint. The addition of bichloride of mercury will convert the iodide into orange-coloured iodide of mercury, whilst the combination with the bromide is not so readily formed, and shows no red tint. An iodide strikes a deep blue tint with starch, but no such re action takes place with a bromide. All the iodide reactions fol lowed treatment of the salt labelled bromide of calcium. C. W.—We have never tried the process inquestion, and cannot say much about it. It is probable that with a bromide only you would not get a very vigorous print. A mixture of bromides and chlorides gives, in our estimation, the best results for printing by develop ment. A solution containing 72 grains of bromide of potassium and 4} grains of chloride of ammonium per ounce, with a 50-grain nitrate bath, will yield very good results. We have seen good results obtained with a solution containing 6 grains of iodide, 4 grains of bromide, and 2 grains of chloride per ounce. Alka line development of paper prints would probably produce discolour ation of the whites. Hot gallic acid may be used, and the expo sure may, in such case, be shortened. Young.—The fact that you fail to succeed with several processes with which others succeed suggests that there is some want of care or precision in your working. The object of filtering the syrup through charcoal is to remove certain impurities. The solu tion should not be returned to the stock bottle after being used. The want of sensitiveness and the fog must have been due to error in some part of the operations, or impurity in something used, but we cannot tell in what the error lies. The commercial collodion of which you speak has the reputation of being very good. The fact that you could not obtain an image with it in either the wet or dry process suggests that you probably used it without being iodized. The photographic soap of which you speak we have not tried, but have heard good accounts of it. The nitrate bath being "blackened by a collodion plate” we do not understand. How was it blackened ? Possibly the collodion plate had been con taminated with hypo or some other impurity, which decomposed the bath. Without knowing more details we cannot give you a remedy. A. W.—We cannot tell you when bromide of potassium was first introduced into the market. Bromine was not discovered until 1826. It was first used in photography in 1810, and there is some dis pute as to whom the honour of its introduction belongs; in this country we generally accord it to the late Mr. Goddard. Our American cousins dispute this. M. Bayard introduced it into the paper process, we believe, the same year. Bromide of potassium was one of the earliest bromide salts introduced into commerce, but we do not know the date. W. J. A. G.—It is difficult to trace the cause of your failure with morphine plates. It may be due to two or three causes. Many of the ordinary samples of commercial bromo-iodized collodion do not Contain sufficient bromide, and the addition of about 1 grain per ounce is necessary to secure good results with most dry-plate pro cesses. The soft water may have been impure : it sometimes con tains traces of sulphuric acid and other impurities collected from the atmosphere of towns. The morphine solution may have been exhausted by using over and over a few times. 2. The matt silver stain like a slug-track, extending from the edge of the plate, is generally the result of contamination of the nitrate solution on the plate, from contact with the inner frame. Constant washing of the inner frame and allowing the plate to rest on clean blotting- paper will assist you. See article in the present number; see, also, a paragraph on the use of lard on the inner frame to prevent contact ■with the silver solution. T. W. (Thornton).—The yellow stains are spots of imperfect fixa tion, most probably caused by the formation. of small air-bubbles on the prints on immersing them in the fixing bath, the hypo being so prevented from acting perfectly where each bubble is formed. The result of imperfect fixation is the formation of insoluble hyposulphate of silver at each point, which decomposes and causes a yellow stain when the print is removed from the washing water and brought into full daylight; sometimes it becomes decomposed, and causes the stain on applying warm water. The remedy is to examine each print carefully after im mersing in the fixing bath, and remove any air-bubbles which are formed. Some samples of paper arc more prone to such bubbles than others. J. S.—You will find an article on enlarging by the magnesium light in our pages a few months ago, in which a good formula is given for the preparation of the paper. See answer above to C. W. As a rule, developed prints do not require toning, the deve loped image generally acquiring a deep brown or black colour. A fully exposed and rapidly developed print is generally warmin tone; one requiring long development generally passes to a black tone. The best developer is a saturated solution of gallic acid. You will find many articles on the subject on referring to the indexes of back volumes. Articles on pages 247 and 253 of our fifth volume will give you useful information. B. L.—First apply a solution of iodine to the stain (made by dis solving 1 grain of iodine and 2 grains of iodide of potassium in an ounce of water), then apply the cyanide solution, which will remove the stain ; finally, wash well. Z. H. A.—The scrap of untoned and unfixed print was too much discoloured when it reached our hands to enable us to form much opinion of the marking; but we should judge from its appearance that it was from a defect in the negative. If it is not, we should require a larger example, or two or three of them, to enable us to form an opinion. No Chemist.—When the albumen is diluted in Mr. England’s process the ammonia is still added: about 8 or 10 drops of liquid ammonia to an ounce of albumen solution. 2. The excited plate is washed, then coated with albumen solution, then washed, and then the silver solution is applied. 3. The collodion you mention will answer; but it will be better if you add to each ounce an additional grain of bromide of cadmium. 4. The edges of the plates may be varnished with the varnish you name. 5. Your 30-grain bath strengthened will serve. If it possess great excess of nitric acid, add a little oxide of silver to neutralize a portion of it. 6. Better make anew toning bath. We are glad to learn that our advice helped you so satisfactorily. Thomas STOTHARD.—The addition of a little more soluble cotton will probably assist you in obtaining vigorous images more effec tually than will the addition of an iodide; or you may try the gelatino-iron developer. W. II. W.—Thanks for your letter. We arc quite of one mind on the subject named. We will speak to the Publisher as to the neglect in question. Thomas Collins.—We do not know of any stereoscopic slides of the statuary in the Vatican; but, if they are to be had, Messrs. Marion and Co., of Soho Square, will most likely be able to supply you. Specimens of the work of the lens you mention can doubt less be obtained of the manufacturer. W. H.—Vignetting opal-glass pictures produced in the camera is effected by placing a piece of card with an oval aperture between the lens and sensitive plate, or by placing a vignette glass in con tact with the negative. 2. Patent plate flashed opal answers best. T. Martin.—Received. Thanks. J. Stuart. —We have very carefully examined the spots on the prints, which are singular and puzzling. We find that they are of three sorts: bright yellow spots, grey and transparent, and black and opaque. We are disposed to believe that the cause is in the mounting board; the origin of the latter class certainly is. On soaking and removing the print wo find the spots chiefly on the board, and not on the print. They suggest the idea of a fun goid growth, the consequence of the boards having remained some time damp. The boards contain a great deal of starch, and more hypo than is desirable. Enamel.—On careful examination and testing of the cards sent we find a trace of hypo, but much less than in most commercial samples of cards we meet with. The amount is insufficient to cause serious injury. Several articles in type arc again compelled to stand over. Several Correspondents in our next. Photographs Aegistere. Mr. A. Paul, Putney, Photograph of Regatta Prize Cups. Mr. J. Spark, Stoke-on-Trent, Photograph of Bust of Alfred Tennyson. Mr. F. Downer, Watford, Photograph of St. Alban’s Abbey. Messrs, W. and D. Downey, Newcastle, Photograph of Sir R. Napier. Mr. W. Tonks, Birmingham, Seventeen Photographs—Composition Pictures. All Communications for the Editor to be addressed to 15, Gough Square, Fleet Street, London, E.C.