Volltext Seite (XML)
280 THE PHOTOGRAPHIC NEWS. [TEKE 13,1862. I the substance of the paper, and this resinate is very sensitive to light. It is the same with resinate of gold. Another curious compound is the chloro-succinate of silver. This salt is produced in the paper by double decomposition, and is very slightly sensitive to the light of the sun ; but if the paper be placed on a sheet of glass heated to 212° Pah., the action of the light becomes very active, and the salt decomposes rapidly and turns black. Moist nitrate of silver is very sensitive, but dry, it is dis coloured very slowly. All the salts of silver are not white; some arc red, green, yellow, brown, &c. The picrimate is of a very beautiful red colour, and unchanged by light; the phloroziate is blue; the nitrophiauilate is orange, &c. We shall give hereafter a summary of the general pro perties under the influence of light of a great number of salts of silver, from which the experimentalists will pro bably derive very useful suggestions: as to the means of procuring these substances, most of them will be found in commerce. It is evident that with regard to greater sensitiveness under the influence of direct light, there is little to be hoped from the substitution of new salts of silver for the iodide now employed. It is not the same, however, with regard to the substitution of soluble salts of silver for the nitrate of silver, of which negative baths are composed. It is well ascertained at the present day, that it is not the sensitiveness to light of iodide of silver which gives rapidity in our present processes, but rather the singular property possessed by this substance of being the motive of the local decomposition of the nitrate of silver by the developing agent. Thus pure iodide of silver is not of itself sensitive to light, but it fixes the molecules of silver set at liberty wherever they have been struck by light. This is perhaps a physical property, and not a chemical one, of the iodide. But according as we mix sulphate of iron or pyrogallic acid with a more or less stable salt of silver, the reduction takes place more or less quickly; it is also very probable that other salts of silver may be substituted for the nitrate now employed. Our task in this place is to give a list of these salts, such as arc easily prepared and quickly reduced. In the first place we name the cldorate of silver. This salt behaves exactly like the nitrate. The sulphoglycerate, the ethyl sulphate, which is also very soluble in alcohol, the amyl sulphate, the amyl citrate, and the lactate, arc the salts best adapted to these researches, and to which we shall recur in another article. Such is the list of the organic salts of silver, or, at least, of such as possess properties which cannot be doubted, and upon which experimenters will, doubtless, be glad to obtain some details. Our aim, it must not be forgotten, is not to dilate upon the researches wc have accomplished in this direction, but rather to aid experimentalists by condensing the most striking properties of these organic salts of silver. The enquirer in this direction will, probably, find many useful hints; it is our intention to publish our researches upon these salts at an early date. • Scientitir Gossip. Japanese Crystal Spheres ; Danger of Fire at the Inter national Exhibition Building—Paraffin and American Oil, their Dangers and Methods of Testing—Fusion of Platinum—Injury to M. Deville by the Fumes of Osmic Acid. A curious accident lately happened at the International Exhibition, by which, had it not been for the promptness with which it was discovered, the building might by this time have been reduced to ashes in a very scientific manner. Among the most noteworthy objects in the Japanese court were two spheres of rock crystal, about five inches»I diameter, ground and polished with mathematical accurT; I They were exhibited by Messrs. Baring Brothers, S® I attracted very little attention from the general visitos I One very sunny day, however, a person rushed into t I superintendent’s office with the alarming intelligence ® I “ the two glass globes had caught fire.” On hastening tot® I spot it was found that the spheres had acted the part 4! burning glasses, and had concentrated the rays of thes which was shining full upon them, on to the mahogan! I stand, which was then in a blaze. These globes have w* I been removed to the Chinese Court, where the curious visitt I may see two holes in the stand large enough to insert t I top of the finger. These holes are of some interest, as W I are each double, showing in a very perfect manner t I double refracting properties of the quartz. A very important report on paraffin oil has just b I made by Mr. Charles O’Neill. This oil is now so general” I used for illuminating purposes, and on account of the p® 1 ! I of its light is of somewhat frequent employment for mie", I scopic photography, that a knowledge of the properties 11 1 the multitudinous liquids sold under this name, and of t I simple methods of ascertaining whether their employme. I would be attended with danger, cannot be too general made known. In deciding whether a sample of oil is do I gerous or not, reference must always be had to the lamp” I which it is used ; some of the dangerous oils might beud I with safety in lamps of a different construction, and t I most harmless of them would be dangerous, if used in • I moderator or carcellamp. Special lamps are now constructd for burning this oil in, and Mr. O’Neill’s report must . considered as referring to the oil when burnt in these lamP) From his experiments, it results that the chances of accidel. from the use of these oils may be referred almost exclusive! to their greater or less proneness to form an explosive 10 turc with the air contained in a partly-filled bottle, or laP reservoir. Nearly all the accidents arising from the 0 the new illuminating oils have been primarily caused by t ignition of the explosive mixture of combustible vapour" air, either in the bottle in which the stock of oil is kept 0 in the reservoir of the lamp. Thirty-two samples of oil, fr as many different establishments, were examined, chielt with a view to ascertain whether any of the oils would fo an explosive mixture with air at a mean temperature AI 00° Fah. ; this representing the average temperature ’ I domestic rooms where the bottles of oil are kept. To a80 1 tain this point, about a quarter of an ounce of the oil" put into a six-ounce stoppered bottle, the stopper inserta and the bottle shaken and moved about, so as to facilit the escape of vapour from the oil; in three or four min" the stopper was taken out, and a lighted match held to C mouth of the bottle : if there was a rush of pale blue fo through the bottle, the oil was said to give off an exploshi vapour at the ordinary temperature of the atmosphere, 4 to be highly dangerous. Only two out of the thirty" samples exploded when tested in this way. This temperst can, however, be only considered as the lowest limit of Pa sible danger; the actual limit of danger being the hig temperature to which, under all ordinary circumstances E oil is likely to be exposed, either in storing or while b ing in the lamp. A temperature as high as 85° to 90° 10 be calculated upon as often existing in the cistern ofalal this high temperature being produced by a long-contilu burning in a warm room, and on a table near the fire- 'J oil, therefore, giving off combustible vapour, and formilsy explosive mixture with air at this temperature, mus sir looked upon as unsafe for ordinary use. Out of the reCte ing thirty samples, three were found which were dangd |J at a temperature of 85°. With these five, therefore, itwQed require the constant exercise of skill and care to PE of serious accidents. The remaining oils were then successtt o tested at temperatures of 100°, 120°, and 150°. Ft (b them were dangerous at the first, three others 4 p second, and the remaining twenty at the highest t
