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Дата написания1970-01-01
Язык книгиen
Возрастное ограничение0+
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зарубежная образовательная литератураобщая химия

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You now see the action of the heat upon the piece of platinum—heat so great as to break in pieces the plate on which the drops of metal fall. You perceive, then, that we have sufficiently powerful sources of heat in nature to deal with platinum. I have here an apparatus by which the same thing can be shewn. Here is a piece of platinum, which is put into a crucible of carbon made at the end of one pole of the battery, and you will see the brilliant light that will be produced. There is our furnace, and the platinum is rapidly getting heated; and now you perceive that it is melted, and throwing off little particles. What a magnificent philosophical instrument this is. When you look at the result, which is lying upon the charcoal, you will see a beautifully fused piece of platinum. It is now a fiery globule, with a surface so bright, and smooth, and reflecting, that I cannot tell whether it is transparent, or opaque, or what. This, then, will give you an idea of what has to be done by any process that pretends to deal with thirty, or forty, or fifty pounds of platinum at once.

Let me now tell you briefly what Deville proposes to do. First of all, he takes this ore, with its impurities, and mixes it (as he finds it essential and best) with its own weight of sulphuret of lead—lead combined with sulphur. Both the lead and the sulphur are wanted; for the iron that is there present, as you see by the table, is one of the most annoying substances in the treatment that you can imagine, because it is not volatile; and while the iron remains adhering to the platinum, the platinum will not flow readily. It cannot be sent away by a high temperature—sent into the atmosphere so as to leave the platinum behind. Well, then, a hundred parts of ore and a hundred parts of sulphuret of lead, with about fifty parts of metallic lead, being all mingled together in a crucible, the sulphur of the sulphuret takes the iron, the copper, and some of the other metals and impurities, and combines with them to form a slag; and as it goes on boiling and oxidising, it carries off the iron, and so a great cleansing takes place.

Now, you ought to know that these metals, such as platinum, iridium, and palladium, have a strong affinity for such metals as lead and tin, and upon this a great deal depends. Very much depends upon the platinum throwing out its impurities of iron and so forth, by being taken up with the lead present in it. That you may have a notion of the great power that platinum has of combining with other metals, I will refer you to a little of the chemist's experience—his bad experience. He knows very well that if he takes a piece of platinum-foil, and heats a piece of lead upon it, or if he takes a piece of platinum-foil, such as we have here, and heats things upon it that have lead in them, his platinum is destroyed. I have here a piece of platinum, and if I apply the heat of the spirit-lamp to it, in consequence of the presence of this little piece of lead which I will place on it, I shall make a hole in the metal. The heat of the lamp itself would do no harm to the platinum, nor would other chemical means; but because there is a little lead present, and there is an affinity between the two substances, the bodies fuse together at once. You see the hole I have made. It is large enough to put your finger in, though the platinum itself was, as you saw, almost infusible, except by the voltaic battery. For the purpose of shewing this fact in a more striking manner, I have taken pieces of platinum-foil, tin-foil, and lead-foil, and rolled them together; and if I apply the blowpipe to them, you will have, in fact, a repetition on a larger scale of the experiment you saw just now when the lead and platinum came together, and one spoiled the other. When the metals are laid one upon the other, and folded together and heat applied, you will not only see that the platinum runs to waste, but that at the time when the platinum and lead are combined there is ignition produced—there is a power of sustaining combustion. I have taken a large piece, that you may see the phenomenon on a large scale. You saw the ignition and the explosion which followed, of which we have here the results—the consequence of the chemical affinity between the platinum and the metals combined with it, which is the thing upon which Deville founds his first result.

When he has melted these substances and stirred them well up, and so obtained a complete mixture, he throws in air upon the surface to burn off all the sulphur from the remaining sulphuret of lead; and at last he gets an ingot of lead with platinum—much lead, comparatively, and little platinum. He gets that in the crucible with a lot of scoriæ and other things, which he treats afterwards. It is that platiniferous lead which we have to deal with in our future process. Now, let me tell you what he does with it. His first object is to get rid of the lead. He has thrown out all the iron, and a number of other things, and he has got this kind of compound indicated in the table. He may get it as high as 78 per cent. of platinum, and 22 of lead; or 5, or 10, or 15 of platinum, and 95, or 90, or 85 of lead (which he calls weak platinum), and he then places it in the kind of vessel that you see before you. Suppose we had the mixture here; we should have to make it hot, and then throw in air upon the surface. The combustible metal—that is, the lead—and the part that will oxidise, are thoroughly oxidised; the litharge would flow out in a fused state into a vessel placed to receive it, and the platinum remains behind.

Here is the process which Deville adopts for the purpose of casting off the lead, after he has got out the platinum from the ore. (Having made use of your friend, you get rid of him as quickly as you can.) He gets his heat by applying the combination of oxygen and hydrogen, or of carburetted fuel, for the purpose of producing a fire. I have here a source of coal-gas; there I have a source of hydrogen; and here I have a source of oxygen. I have here also one of the blowpipes used by Deville in his process for working platinum in the way I have spoken of. There are two pipes, and one of them goes to the source of coal-gas, and the other to the supply of oxygen.

By uniting these we obtain a flame of such a heat as to melt platinum. You will, perhaps, hardly imagine what the heat is, unless you have some proof of it; but you will soon see that I have actually the power of melting platinum. Here is a piece of platinum-foil running like wax under the flame which I am bringing to bear against it. The question, however, is whether we shall get heat enough to melt, not this small quantity, but large masses—many pounds of the metal. Having obtained heat like this, the next consideration is what vessel is he to employ which could retain the platinum when so heated, or bear the effects of the flame? Such vessels are happily well supplied at Paris, and are formed of a substance which surrounds Paris; it is a kind of chalk (called, I believe, by geologists, calcaire grossière), and it has the property of enduring an extreme degree of heat. I am now going to get the highest heat that we can obtain. First, I shew you the combustion of hydrogen by itself. I have not a large supply, because the coal-gas is sufficient for most of our purposes. If I put a piece of lime obtained from this chalk into the gas, you see we get a pretty hot flame, which would burn one's fingers a good deal But now let me subject a piece of it to the joint action of oxygen and hydrogen. I do this for the purpose of shewing you the value of lime as a material for the furnaces and chambers that are to contain the substances to be operated on, and that are consequently to sustain the action of this extreme heat. Here we have the hydrogen and the oxygen, which will give the most intense heat that can be obtained by chemical action; and if I put a piece of lime into the flame, we get what is called the lime-light. Now, with all the beauty and intensity of action which you perceive, there is no sensible deterioration of the lime except by the mechanical force of the current of gases rushing from the jet against the lime, sweeping away such particles as are not strongly aggregated. "Vapour of lime" some call it; and it may be so, but there is no other change of the lime than that under the action of heat of this highly-exalted chemical condition, though almost any other substance would melt at once.

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