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[March 20, 1863. THE PHOTOGRAPHIC NEWS. 136 must have been registered, and a copy deposited, in London, within three, months after such first publication. Considering the beauty of, and the immense demand for, many photographic works produced both in France and England, the existing state of those international relations to which we have called attention seems calculated largely to enhance the value of original productions of that descrip tion by French and British artists.—Athenceum. CHEMICAL EXPERIMENTS. Formation of Nitrate or Silver from an Impure Source, with Separation of Impurity ; the same from Pure Silver, with Proof of the Atomic Theory.—Paper Relative to the above, comprisino General Remarks on the Sensitizing Bath. By John Kibble.* In the present advanced stage of our Society, it will doubt less appear to many of you a retroceding, on my part, in entering into a subject with which all of you are supposed to be familiar. Such an opinion, to a certain extent, will really be correct; yet, from the numerous queries put to me by photographers and others, many practical difficulties must exist —not so much, perhaps, in the preparation of the new silver baths as in the reduction of the old solutions, which have become unfit for use by general deterioration, such as acidity, foreign matter getting admittance into it by some unknown means, or from any accidental cause whatever. I think it will best forward the object I have in view to com mence with the preparation of nitrate of silver from an impure source, such as the silver alloy of commerce, which will not only show the formation of nitrate of silver, but the very simple manner in which the copper or any other impurity can be separated and a pure salt obtained, and, if desired for instantaneous work, brought to its greatest state of alkalinity by fusion. Before doing so, I will enterinto a few particulars regarding the tendency which all bodies have to combine in definite proportions with each other when entering into chemical union. So fixed and invariable is this, when all circumstances aie alike, that the term “ law ” has been adopted to express the fact. The chemical atom must not for one instant be confounded with the atom of the philosopher, or that infinitesimal portion of matter supposed to be indivisible. The latter is purely imaginary, and, although affording a wide field for ingenious speculation, is of very little conse quence to the present purpose; the former is an absolute fact, proved by gravitation, and visibly demonstrated through the medium of the finely-adjusted balance. Until such an instrument was resorted to, chemistry, that matter-of-fact science, had in it much that was hypothetical. Oxygen—that body which plays so important a part in the economy of the universe in which we dwell—exists in combination with hydrogen in the proportion of eight of the former to one of the latter by weight, forming that well known and absolutely necessary fluid, water. Assuming the combining proportion or atom of hydrogen as unity, it necessarily follows, the atom of oxygen being eight times heavier than the former, when they enter into chemical union with each other the resulting atom of water must be nine. For example : take eight grains, by weight, of oxygen, one of hydrogen, and having ready a glass tube of the requisite capacity, sealed at one end, filled with water, place it on a shelf in the pneumatic trough, the open end a little below the line of the water. Having done so, pass into it the gases in tho above proportions. Pass an electric spark through the tube: chemical union will at once take place, accompanied by detonation and light—simple manifestations of combina tion. Tho water from the trough will rush into this tube, filling it, showing that the gases no longer exist. Repeat this experiment, say with ten grains of oxygen to one grain * Read at a meeting of the Glasgow Photographic Association, March 5th, 1S63. of hydrogen. Upon the electric spark being applied, the gases will again combine in their atomic proportions; but, in this instance, it will be observed that the water does not fill the tube, but leaves a space equivalent to the vacuum occupied by two grains of oxygen. Upon a quarter grain of hydrogen being added, and the electric spark applied, the water will rush into and fill the tube as in the first instance, proving the gases will only combine in the ratio of eight to one, or their atomic proportions; could they be forced to combine in any other proportions tho result would be no longer water. Let me now take the metal iron. If fifty-six grains of it in a very finely divided state, bo enclosed in a bulb tube of the following shape, the exact weight of which is known —having fixed it to some support so that the flame of a spirit lamp, or better still, if at command, a Bunsen’s gas burner, can be applied to the bulb containing ths iron until such time as the mass is ignited to redness—the flame of an additional lamp must now be applied to the flask containing water, attached, as you observe, to the end of the tube, until the water undergoes ebullition, keeping a continual stream of vapour passing over the red hot iron. The affinity of the metal for oxygen will cause decomposition of the vapour, the oxygen thereof uniting with the iron forming the peroxide: the released hydrogen passing off with the superfluity of vapour can be collected, if means be used for that purpose. Allow the glass vessel to cool, and, after ascertaining that there is no adhering moisture, the whole can be care fully weighed. It will now be found to have increased exactly twenty-four grains in weight ; two atoms of oxygen which have attached themselves to the metal form ing the peroxide of iron = eighty grains. This is in chemistry termed a synthetic experiment, or the forma tion of a compound from the elements of which it is com posed. Now comes rather a paradoxical point. Detach the flask containing the water and add thereto some iron filings and a small quantity of sulphuric acid : replace it again: this, by the decomposition of water will yield hydrogen, which, as it passes over the heated oxide will rob it of the oxygen, the pure metal being left the same as at the start ing point. This is called an analytical experiment, or the resolving of a compound into the elements of which it is composed—the exact converse of the former. This is an exceedingly interesting experiment. In the first instance, iron under the influence of heat decomposes the vapour of water, becoming itself an oxide, the hydrogen passing oft free. In the second instance, the oxide of iron under heat parts with its oxygen to the hydrogen, the two gases com bining to form water, the pure metal coming into existence once more. There is something very singular here. In the first experiment the iron tears the oxygen from the hydrogen: in the second, the hydrogen tears back the oxygen from the iron. This can only be explained by quantity ; that is, the great volume of hydrogen passing over the heated oxide, every atom of which is struggling for its atom of oxygen, the joint force empowers the affinity existing between the metal and oxygen, which, in the act of splitting up, is seized upon by the hydrogen in atomic proportion—the result being water, the iron left pure. You will also observe that when these two gases are presented to each other in the nascent state—that is, immediately on being let loose from other combinations —they at once enter into chemical union; whereas, if col lected in separate vessels and allowed to get into a state of repose, and then presented to each other, they will mix
