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The photographic news
- Bandzählung
- 29.1885
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- 1885
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1405, August 7, 1885
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The photographic news
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Band
Band 29.1885
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- Register Index III
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Band 29.1885
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E AvGUsT 7, 1885.J THE PHOTOGRAPHIC NEWS. I Bee the picture is coming out under the action of the ferrous oxalate developer. After fixing, we see that we have the photo graphed spectrum on the plate. This is the text on which I have to hang my lectures. We have three things to consider. First of all, we have got the light, then we have the apparatus, and then the sensitive material on which the spectrum is taken. The white light from the carbon poles, in passing through the apparatus, is spread out into a coloured baud, which we called the spectrum ; and the spectrum has effected a change in the sensitive salt of silver, as is shown by the blackening on the application of what is called a developer. The cause of the change in the sensitive material is what I first address myself to. To conceive a right notion of photographic action we must first of all conceive, in the most elementary manner, the struc ture of matter. The structure is beyond our actual visual acquaintance, but we may be able to visualise it from the way it behaves; we have to draw our conclusion about it from evidence of an experimental nature. What we want to get is a mental picture of matter. Physicists have come to the conclusion that homogeneous matter is composed of molecules, or small masses which are altogether similar one to another, i.e., they have the same com position. In different matter, these molecules have different weights. Further, it is believed that the molecules, or the small particles of matter, are themselves composed of atoms, which we take to be the fundamental unit of matter. Now, from experimental data, Sir William Thomson and others have come to conclusions as to the limits of the size of these mole cules, and also as to their distribution in space. From the kinetic theory of gases, it is concluded that the diameter of a molecule lies somewhere between one twenty- five millionth part of an inch and one two hundred and fifty millionth part of an inch. Further, in gases it is conceived that the molecules are free to move in straight lines in any direction, the direction , being altered only when the molecules collide ; that is to say, when they strike one against another. In a liquid, the particles are bonded much more closely together, and the free path of the molecules is very much shorter; that is to say, that they can not go from one place to another without very much more fre quently coming into contact with other molecules ; and the molecules pass from place to place at a very much slower rate than they do in gases. A solid, such as is our silver salt, is con ceived to be such that the molecule has no free path, but is con fined in a limited space in which it can oscillate, moving round a mean centre. As to the distribution of these molecules in liquids and solids, Sir William Thomson has arrived at very definite conclusions also. In a lecture at the Royal Institution, he said that he concludes that in every ordinary liquid, or trans parent solid, or seemingly opaque solid, the mean distances between contiguous particles is less than one twelve millionth of an inch, and more than one two thousand five hundred millionth part of an inch. Those are big figures, but still the distance apart is very small. “ To form a conception of this,’’ he says, “ imagine a globe of water as large as an ordinary foot ball to be magnified to the size of the earth, each constituent molecule being similarly magnified. The magnified structure would be more coarse-grained than a heap of small shot, but probably less coarse-grained than a heap of footballs.” So you see that, by magnifying to this extent, you have a coarse-grained ness v. hich, of course, is only relatively coarse-grained after such an enormous magnification. Or you may put it in a different sense. If you magnify eight thousand diameters by an ordinary microscope—and that is about the limit to which a microscope will magnify—and if you magnify that eight thousand diameters again eight thousand times, you would be able to see the mole cular structure of water. So much, then, for molecules. We will now turn to the atoms. These will not bear such a very large disproportion of size to the molecules as do the mole- cules to the smallest visible particles. We must, however, I think, conceive that every atom (and this is an important point) is charged with energy very much in the same way that the magnet is charged ; ouly, instead of two poles, as a magnet has, each atom has only one pole. It is unipolar. Now, suppose that this energy is something like electrical energy. We know that positive repels positive, and that nega tive repels negative. And further, we know that the positive energy will attract what is called negative energy ; and if the two be exactly equal when they combine, of course there will be a neutral state. But in the case of the atoms of matter, circum stantial evidence tells us that the amount of electrical energy which is upon a given atom of matter—if you like to put it in that way—is never the same as it is upon another atom of matter ; that is to say, there is always a surplus of one over the other. Thus we may have an atom charged with what we may call plus 2 of energy, and another one charged with minus 1 of energy. Those two atoms, on coming together, give you a result of energy of plus 1, and this would again be capable of attract ing another atom of matter which was charged with a negative energy, and so on. From chemical considerations, it would appear that plus and minus energies of different atoms, as I have said before, are never exact multiples of one another, and that when they are bonded together there is always an excess one over the other. A good example of the energy of the combina tion of atoms together may be shown by the combination between a gas, chlorine, which we have here, and the metal antimony, and you will see that when the latter, as powder, is thrown into the former, the two combine with an evolution of heat, showing that a vast amount of energy is given out. The chlorine aud the antimony form chloride of antimony; that is to say, five atoms of chlorine and one of antimony. [A small quantity of finely-powdered antimony was dropped into a jar of chlorine.] You see the evolution of heat between those two ; so much, in fact, that the chloride of antimony, as it was formed, was at a perfectly bright white heat. The case immediately before us is the silver salt. Let us experiment with that in a similar way. Into the chlorine I will throw some powdered silver, and I wish you to notice the difference between the re sults in the two cases. [A small quantity of the powdered silver was dropped into a jar of chlorine.] You see that the combina tion between the silver and the chlorine only produces a red heat, whereas antimony produced a white heat. In other words, the combination between antimony and chlorine is much more vigorous than the combination between silver and chlorine. If you had to separate the atoms of chlorine from those of the antimony, you would have to use very much greater force than if you had to separate the atoms of silver from the atoms of chlorine. When two electrified bodies attract one another, they attract one another inversely as to the square of the distance ; that is to say, if there is a distance of one foot between them, they attract one another with a force of say—1. If they are two feet from one another, they only attract one another with a quarter that amount. Supposing atoms attracted one another according to the same law, then of course they being so very close to one another, the attraction would be considerably greater than if they were visibly apart. But besides this attraction between atoms comprised in the molecules, there also seems to be a repulsive action, into which I will not enter more fully now, because that would be almost beside my subject; but I may say that besides the atoms attracting one another (we will take chloride of silver, for instance) when they get within a certain distance of one another, they repel one another, and so there is a continual oscillation between the atoms composing those molecules. (To be continued.) Uorrespondente. DR. EDER’S NEW SULPHITE OF AMMONIA DEVELOPER. Sir,—As nearly every week sees the publication of a new developer, or some modification of an old one, it seems to me possible tint the above may fail to meet the attention which it merits, especially cs the new light, which is to render all others needless, published the formula with the trilling omission of the ammonia, and which, of course, disppointed those who followed its leading. I think this new developer contains all the advantages, with none of the defects, of those which have preceded it. It comes up rapidly, giving brilliant and well-graded pictures, without a trace of fog or frilling. It does not discolour on the plate, and the same solution may be used two or three times, although I do not think such close economy desirable ; and it shares with the sulphite of soda the advantage of not staining the fingers. As the original formula was published in the French fashion of
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