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258 THE PHOTOGRAPHIC NEWS. [May 30,1862. men were not unprepared to hear that lumps of some ounces in weight had been reduced by this means to a liquid form; but when we inform them that 20, 30, and even 40 lbs. of it had been liquified at one operation, the figures were thought by many to have been a misprint. A few months, however, showed that we were perfectly correct in our statements, and long after philosophers were thrown into a state of scientific amazement by the full publication of Deville’s wonderful metallurgical processes. Athough devised by a French savant, the process has, we believe, met with the most ex tended application in England. Messrs. .Johnson and Matthey, the well-known metallurgists of Hatton Garden, having immediately seen the importance of the process, and made arrangements with the inventor for employing it in in their works. The crowning feat of all has just now been performed. In the presence of the inventor, and a goodly collection of English and Foreign savans, this firm accom plished an operation hitherto unparalleled in the science of metallurgy. In their lime crucibles and furnaces, and by the calorific action of ignited jets of mixed oxygen anil hydrogen, they reduced to a perfect fluid state, and then run into a mould, a mass of platinum of the astounding weight of 2 cwts. This magnificent ingot, of the value of £3,840, is now one of the most striking ornaments in the Metallurgical Depart ment of the International Exhibition. In order to show the extreme fluidity of the melted metal, the lump is purposely left in the state in which it came from the roughly con structed mould ; the metal has run into every minute crevice, between the blocks of which it was built, and illustrates in a striking manner the great adaptability of this metal for castings. The still more highly refractory metal, iridium, has also succumbed to the enormous temperature at their disposal, and is present in the same case, in the form of a perfectly fused lump, weighing 272 ounces. The manufac tured metals exhibited by this firm are also of the highest interest; they show an enormous platinum boiler, capable of rectifying three tons of oil of vitriol of full strength in twenty-four hours. This is worth’ £465. Coming to articles of more special interest to the photographer, we find some beautiful specimens of gold, both in tire metallic form, and also in the form of neutral chloride of gold, prepared espe cially for photographic purposes. There is likewise upwards of 80 worth of silver in different forms, viz., a lump of chemically pure silver, weighing 41 ounces, a bar of the same metal, melted by the combined gases, weighing 377 ounces ; nitrate of silver commercial, and fused into sticks ; and finally some beautiful specimens of fused and recrystal lized, nitrate of silver, prepared especially for photographic purposes, and hermetically sealed in glass tubes for exporta tion. Passing on to the Chemical Department of the Exhibition, after braving the difficulties of the subterranean passage, and with difficulty, and after much enquiry, finding our way through the ponderous iron forgings and mineral products into the Eastern Annexe, as it has become the fashion to de signate this remarkably ugly and ricketty shed, we find our selves amongst a collection of scientific products the inspec tion of which amply repays us for the difficulties and dangers encountered in our voyage of discovery. One of the first objects which meets the eye is the pillar of rock salt sup ported upon large square blocks of the same material. This is shown in the same state in which it was dug from the mine, and is of some photographic interest, inasmuch, as it illustrates, in a striking manner, a fact which we have taken several opportunities of impressing upon our readers. Pure chloride of sodium does not, as our readers well know, absorb moisture from the atmosphere, but the presence of small quantities of certain mineral impurities communicates to it deliquescent properties. The mass of salt in question affords a fine illustration of this fact. Close examination shows it to be always covered with a film of water collected here and there into drops, whilst the floor upon which it rests is soaking wet with brine for some distance round it. It is growing small by degrees and beautifully less," before many weeks are over the boards in that depart!® 8 will only require sprinkling with nitrate of silver solution 9 render them in a high state of photographic sensitive^ The Stereoscopic Company, who will require positnt printed by the acre, would do well to avail themselvl this interesting phenomenon. The natural tendency* this salt to absorb from the atmosphere is not diminisbd by the leakages in the roof. It is a great pity that W beautiful specimen of the product of our English mins) not better protected, it far more deserves a glass case ths many substances prettier, perhaps, to look at, but of c siderably less commercial importance. From mineral s to mineral coal is an easy transition, and the latter natnW leads us to the magnificent products derived from 16 destructive distillation. The best known of these, coal-g we shall not mention, but the splendid array of coa- colouring matters, is too important to be passed by. 0 of the first things that strikes the eye upon entering”! department is the gorgeous display of Messrs. Perkin 8 Son, as the originators of a branch of industry entirely" since 1851. These gentlemen certainly deserve promind notice. They here show us a collection illustrating th manufacture of mauve or aniline purple from the rWy coal-tar to the pure dye ; a lump of the latter, upwards of cubic foot in bulk, the product of 2,000 tons of coal, occupy ing one corner of the case, whilst the centre is filled with dyed specimens of all kinds in skeins and fabrics*’ the various mordants used in fixing the colour. The cd pleteness of the collection will give it an interest to M intelligent visitors beyond the beauty of the display, 81 will make them readily appreciate the happy intellige® which succeeded in extracting “ a thing of beauty ” ft the vilest refuse, and the skill which has adapted it to® most agreeable forms of decoration. Two specimens of yellow glass have been sent us byacon. pondent for examination in the spectroscope; they are, both*' the naked eye and in the instrument, of the same qualit rather light orange yellow. A spectrum examination sb 0 *’ that they are but ill-adapted for photographic purposss2 they allow considerable quantities of green and blue rtf to pass through. Placing one over the other effects s improvement, but even then some chemically acting R filter through. When perfectly good glass is easily o. tained for illuminating purposes, we do not counsel the ® ployment of an inferior variety. SENSITIVE DRY PROCESSES. BY U. COOPER, JUX. Dubins the last four months, I have been making exg2 ments to ascertain which is the simplest, most sensitive, % surest of the dry processes. The processes I took to es2 ment upon were the tannin, Mr. England’s modificatiota ditto, the morphine, alkaline gelatine, alkaline resin, P washed collodion, and morphine resin. The collodion " a mixture of Ponting’s, and one iodized with iodidk potassium and cadmium, and bromide of cadmium.. D bath, 35 grains of nitrate of silver, and 1 of a minipv acetic acid to the oz. I prepared six plates by each ofl above methods ; I will give a short epitome of my metlo preparing them, so that a more definite conclusion ma) drawn between the conflicting merits of each :— a 1. The Tannin.—Coated and sensitized a perfectly C plate, washed thoroughly, and coated with solution ot tann 15 grains to the oz. 1 ran a brush-full of varnish, preP as follows, round all the plates to prevent slipping d film :—The varnish : 1 drachm of shellac and 1 drach % fused gum benzoine to enough alcohol to form a s0 te about double as thick as Shne varnish. The advanv of this solution is, that it adheres firmly to the glas g can be easily removed by alcohol, to which a little nitrc has been added.
