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260 THE PHOTOGRAPHIC NEWS. [May 28, 1869. advantage of being much more simple. It is prepared as follows :— Gelatine 20 grains Double sulphate of iron and ammonia 80 „ Sulphate of iron 80 „ Soak the gelatine in cold water fifteen minutes, then put the above together in a bowl with the gelatine, and pour on boiling water 10 ounces. When the gelatine and iron have dissolved, add .10 drops of concentrated ammonia and shake thoroughly; then add sufficient glacial acetic acid to dis solve the precipitate, which will be about 1 drachm, then add 20 grains of tartaric acid. This developer works the best after it is two weeks old. For a plain pyro acid deve loper, use 8 or 10 grains to the ounce of water, and 4 or 5 grains to the ounce of citric acid. I have, however, used a developer made as follows, which is very energetic, and produces beautiful wine-coloured negatives with very short exposure:— Hot water 5 ounces Gallic acid 30 grains Pyrogallic acid 30 „ Citric acid ... ... ... ... 30 „ Glacial acetic acid ... ... ... 30 drops Saturated solution of acetate of lead ... 10 ,, The glacial acetic acid dissolves the precipitate formed by the addition of the acetate of lead* Unless hot water is used, the gallic acid will dissolve very slowly, as that amount is a saturated solution in cold water. A SIMPLE DEVELOPING STAND. Ix cases where long development is necessary, or in any case where the solution is required to remain long upon the plate, a levelling or developing stand is indispensable. The fol lowing is a description of one, which almost any operator can make for himself:— Get a piece of any hard wood about one-quarter cf an inch thick, and having cut two discs, about two inches in diameter, out of it, bore a hole about one inch in diameter through the centre of each ; then take a piece of vulcanized india-rubber, about two and one-half inches square, and one-sixteenth thick (which can be procured at any dealer's in that article for a few cents), and stretch it tightly over the surface of one of the discs, keeping it in that position by tying a piece of string round the edge ; then place the other disc upon it, on the rubber side, and fasten the two together by means of three or more small screws. The superfluous rubber may then be cut away, as the binding of the screws will be found amply sufficient to keep the re mainder in position. Now procure three pieces of stout wire, and, having bored three holes at equal distances, and rather smaller than the wire near the edge of one side of the compound disc, insert the wires so as to turn up, which, by- the-by, should be about five inches long. Next take a piece of brass wire seven inches long, and about one-eighth of an inch diameter, and fasten to one end a small disc of wood into which three other pieces of wire must be inserted in such a manner as to form an inverted tripod upon which to rest the negative ; now take a buckshot, or small rifle ball, and having bored a hole of such a size as to fit tightly on the brass wire through its centre, push it up the wire to within one inch of the disc supporting the tripod. To com plete the stand, it is only necessary to make a very small puncture in the centre of the rubber disc; push the brass wire through until stopped by the buckshot coming in con tact with the rubber, and attach a leaden weight to the lower end ; this weight should, of course, be sufficient to keep the wire in a vertical position. The wires forming the inverted tripod must, of course, be cut so that the nega tive will rest in a perfectly horizontal position, and when * The addition of acetate of lead to a gallic acid developer to increase its developing power should be credited to Mr. Carey Lea. this is done the stand will be found to be thoroughly self- adjusting, and, no matter what the irregularity of the surface upon which it is placed may be, will always keep the negative perfectly level.—Humphrey's Journal. THE ALKALINE BICHROMATES: THEIR SOLU BILITY. DENSITY OF THEIR SOLUTIONS, AND MEANS OF DISTINGUISHING THEM. BY M. A. DAVANNE.* Ox account of the importance of alkaline bichromate processes, and in order somewhat to facilitate the use of these agents, I have thought it desirable to do with them as has already been done with regard to the principal products used in photography. Density.—I have prepared tables showing the density of the bichromates of potash and of ammonia usually sold in the trade at a mean temperature of 15° C. (59° F.), so that whatever solution be given, by means of the hydro meter, or Beaume’s areometer, the value of the solution may be immediately ascertained. The table of density, for the one or the other bichromate, is formed into three columns. The first column indicates the quantity of bichromate dissolved in 100 parts of water at the above temperature. I have not gone beyond 10 per cent., the solutions never being employed in a more concen trated condition. The second column indicates the degree marked by these solutions on the hydrometer. When the density of the liquid is shown on the tube of the instrument, it is only necessary to read the same and see upon the table at what point this figure corresponds with the first column, which will show the value of the solution. The third column is intended for persons who may not have, or cannot procure, an hydrometer, but who have a Beaume’s areometer. It indicates the points of correspon dence between the two instruments. I should mention that the areometer is often too short in the stem for the number of degrees inscribed ; and then it lacks the sensitiveness and precision necessary for the special case we have in view. TABLE of Densities for the Solutions of Bichromate of Potash and Bichromate of Ammonia. Bichromate of Potash. Bichromate of Ammonia. In 100 Water. Density. Degrees Baume. In 100 Water. Density. Degrees Baume. 1 1008 1-2 1 1006 0'9 15 1012 1-8 1'5 1008 1'2 2 1010 24 2 1010'5 1-6 2-5 1019-5 2-9 25 1013 1-9 3 1022-5 33 3 1015 2'2 3-5 1025'5 3-7 3-5 1017'5 2'5 4 1028 4 4 1020 3 4-5 1030 43 45 1023 3-8 5 1032-5 46 5 1026 3'7 6 1038-5 5-5 6 1030 44 7 1045 6-4 7 1035 6 8 1051 7-2 8 1040 5-8 9 1057 8 9 1045 6'4 10 1063 8-8 10 1050 7'1 Solubility.—The solubility of the bichromate of potash is that of 10 parts in a 100 of water at the temperature of 19° C., and 90 parts to one 100 of water at boiling-heat. That of the bichromate of ammonia is 31 parts to one 100 of water at the temperature of 15°, taking as the base of the experiment a hot supersaturated solution, cooled for twenty-four hours. At boiling heat the solubility is much more considerable ; and at the first glance it would be supposed that the bichromate of ammonia, like the nitrate of silver, became dissolved in any proportion. It happens, • Read before the French Phetographic Seciety.