the oxygen and hydrogen are in exactly the proportions which form water,
so that sugar may be said to be compounded of 72 parts of carbon and 99
parts of water; and it is the carbon in the sugar that combines with the
oxygen carried in by the air in the process of respiration—so making us
like candles—producing these actions, warmth, and far more wonderful
results besides, for the sustenance of the system, by a most beautiful and
simple process. To make this still more striking, I will take a little
sugar; or, to hasten the experiment, I will use some syrup, which contains
about three-fourths of sugar and a little water. If I put a little oil of
vitriol on it, it takes away the water, and leaves the carbon in a black
mass. [The Lecturer mixed the two together.] You see how the carbon is
coming out, and before long we shall have a solid mass of charcoal, all of
which has come out of sugar. Sugar, as you know, is food, and here we have
absolutely a solid lump of carbon where you would not have expected it.
And if I make arrangements so as to oxidize the carbon of sugar, we shall
have a much more striking result Here is sugar, and I have here an
oxidizer—a quicker one than the atmosphere; and so we shall oxidize this
fuel by a process different from respiration in its form, though not
different in its kind. It is the combustion of the carbon by the contact
of oxygen which the body has supplied to it. If I set this into action at
once, you will see combustion produced. Just what occurs in my
lungs—taking in oxygen from another source, namely, the atmosphere—takes
place here by a more rapid process.
You will be astonished when I tell you what this curious play of carbon
amounts to. A candle will burn some four, five, six, or seven hours. What,
then, must be the daily amount of carbon going up into the air in the way
of carbonic acid! What a quantity of carbon must go from each of us in
respiration! What a wonderful change of carbon must take place under these
circumstances of combustion or respiration! A man in twenty-four hours
converts as much as seven ounces of carbon into carbonic acid; a milch cow
will convert seventy ounces, and a horse seventy-nine ounces, solely by
the act of respiration. That is, the horse in twenty-four hours burns
seventy-nine ounces of charcoal, or carbon, in his organs of respiration,
to supply his natural warmth in that time. All the warm-blooded animals
get their warmth in this way, by the conversion of carbon, not in a free
state, but in a state of combination. And what an extraordinary notion
this gives us of the alterations going on in our atmosphere. As much as
5,000,000 pounds, or 548 tons, of carbonic acid is formed by respiration
in London alone in twenty-four hours. And where does all this go? Up into
the air. If the carbon had been like the lead which I shewed you, or the
iron which, in burning, produces a solid substance, what would happen?
Combustion could not go on. As charcoal burns, it becomes a vapour and
passes off into the atmosphere, which is the great vehicle, the great
carrier for conveying it away to other places. Then, what becomes of it?
Wonderful is it to find that the change produced by respiration, which
seems so injurious to us (for we cannot breathe air twice over), is the
very life and support of plants and vegetables that grow upon the surface
of the earth. It is the same also under the surface, in the great bodies
of water; for fishes and other animals respire upon the same principle,
though not exactly by contact with the open air.
Such fish as I have here [pointing to a globe of gold-fish] respire by the
oxygen which is dissolved from the air by the water, and form carbonic
acid; and they all move about to produce the one great work of making the
animal and vegetable kingdoms subservient to each other. And all the
plants growing upon the surface of the earth, like that which I have
brought here to serve as an illustration, absorb carbon. These leaves are
taking up their carbon from the atmosphere, to which we have given it in
the form of carbonic acid, and they are growing and prospering. Give them
a pure air like ours, and they could not live in it; give them carbon with
other matters, and they live and rejoice. This piece of wood gets all its
carbon, as the trees and plants get theirs, from the atmosphere, which, as
we have seen, carries away what is bad for us and at the same time good
for them,—what is disease to the one being health to the other. So are we
made dependent, not merely upon our fellow-creatures, but upon our
fellow-existers, all Nature being tied together by the laws that make one
part conduce to the good of another.
There is another little point which I must mention before we draw to a
close—a point which concerns the whole of these operations, and most
curious and beautiful it is to see it clustering upon and associated with
the bodies that concern us—oxygen, hydrogen, and carbon, in different
states of their existence. I shewed you just now some powdered lead, which
I set burning[18]; and you saw that the moment the fuel was brought to the
air, it acted, even before it got out of the bottle—the moment the air
crept in, it acted. Now, there is a case of chemical affinity by which all
our operations proceed. When we breathe, the same operation is going on
within us. When we burn a candle, the attraction of the different parts
one to the other is going on. Here it is going on in this case of the
lead; and it is a beautiful instance of chemical affinity. If the products
of combustion rose off from the surface, the lead would take fire, and go
on burning to the end; but you remember that we have this difference
between charcoal and lead—that, while the lead can start into action at
once, if there be access of air to it, the carbon will remain days, weeks,
months, or years. The manuscripts of Herculaneum were written with
carbonaceous ink, and there they have been for 1,800 years or more, not
having been at all changed by the atmosphere, though coming in contact
with it under various circumstances. Now, what is the circumstance which
makes the lead and carbon differ in this respect? It is a striking thing
to see that the matter which is appointed to serve the purpose of fuel
_waits_ in its action: it does not start off burning, like the lead and
many other things that I could shew you; but which I have not encumbered
the table with; but it waits for action. This waiting is a curious and
wonderful thing. Candles—those Japanese candles, for instance—do not
start into action at once, like the lead or iron (for iron finely divided
does the same thing as lead), but there they wait for years, perhaps for
ages, without undergoing any alteration. I have here a supply of coal-gas.
The jet is giving forth the gas, but you see it does not take fire—it
comes out into the air, but it waits till it is hot enough before it
burns. If I make it hot enough, it takes fire. If I blow it out, the gas
that is issuing forth waits till the light is applied to it again. It is
curious to see how different substances wait—how some will wait till the
temperature is raised a little, and others till it is raised a good deal.
I have here a little gunpowder and some gun-cotton; even these things
differ in the conditions under which they will burn. The gunpowder is
composed of carbon and other substances, making it highly combustible; and
the gun-cotton is another combustible preparation. They are both waiting,
but they will start into activity at different degrees of heat, or under
different conditions. By applying a heated wire to them, we shall see
which will start first [touching the gun-cotton with the hot iron]. You
see the gun-cotton has gone off, but not even the hottest part of the wire
is now hot enough to fire the gunpowder. How beautifully that shews you
the difference in the degree in which bodies act in this way! In the one
case the substance will wait any time until the associated bodies are made
active by heat; but in the other, as in the process of respiration, it
waits no time. In the lungs, as soon as the air enters, it unites with the
carbon; even in the lowest temperature which the body can bear short of
being frozen, the action begins at once, producing the carbonic acid of
respiration: and so all things go on fitly and properly. Thus you see the
analogy between respiration and combustion is rendered still more
beautiful and striking. Indeed, all I can say to you at the end of these
lectures (for we must come to an end at one time or other) is to express a
wish that you may, in your generation, be fit to compare to a candle; that
you may, like it, shine as lights to those about you; that, in all your
actions, you may justify the beauty of the taper by making your deeds
honourable and effectual in the discharge of your duty to your fellow-men.
LECTURE ON PLATINUM.
[_Delivered before the_ ROYAL INSTITUTION, _on Friday, February 22,
1861._]
Whether I was to have the honour of appearing before you this evening or
not, seemed to be doubtful upon one or two points. One of these I will
mention immediately; the other may or may not appear during the course of
the hour that follows. The first point is this. When I was tempted to
promise this subject for your attention this evening, it was founded upon
a promise, and a full intent of performing that promise, on the part of my
friend Deville, of Paris, to come here to shew before you a phenomenon in
metallurgic chemistry not common. In that I have been disappointed. His
intention was to have fused here some thirty or forty pounds of platinum,
and so to have made manifest, through my mouth and my statement, the
principles of a new process in metallurgy, in relation to this beautiful,
magnificent, and valuable metal; but circumstances over which neither he
nor I, nor others concerned, have sufficient control, have prevented the
fulfilment of that intention; and the period at which I learned the fact
was so recent, that I could hardly leave my place here to be filled by
another, or permit you, who in your kindness have come to hear what might
be said, to remain unreceived in the best manner possible to me under the
circumstances. I therefore propose to state, as well as I can, what the
principles are on which M. Deville proceeds, by means of drawings, and
some subordinate or inferior experiments. The metal platinum, of which you
see some very fine specimens on the table, has been known to us about a
hundred years. It has been wrought in a beautiful way in this country, in
France, and elsewhere, and supplied to the consumer in ingots of this
kind, or in plates, such as we have here, or in masses, that by their very
fall upon the table indicate the great weight of the substance, which is,
indeed, nearly at the head of all substances in that respect. This
substance has been given to us hitherto mainly through the philosophy of
Dr. Wollaston, whom many of us know, and it is obtained in great purity
and beauty. It is a very remarkable metal in many points, besides its
known special uses. It usually comes to us in grains. Here is a very fine
specimen of native platinum in grains. Here is also a nugget or ingot, and
here are some small pieces gathered out of certain alluvial soils in
Brazil, Mexico, California, and the Uralian districts of Russia.
It is strange that this metal is almost always found associated with some
four or five other metals, most curious in their qualities and
characteristics. They are called platiniferous metals; and they have not
only the relation of being always found associated in this manner, but
they have other relations of a curious nature, which I shall point out to
you by a reference to one of the tables behind me. This substance is
always native—it is always in the metallic state; and the metals with
which it is found connected, and which are rarely found elsewhere, are
palladium, rhodium, iridium, osmium, and ruthenium. We have the names in
one of the tables arranged in two columns, representing, as you see, two
groups—platinum, iridium, and osmium constituting one group; and
ruthenium, rhodium, and palladium the other. Three of these have the
chemical equivalent of 98½, and the others a chemical equivalent of
about half that number. Then the metals of one group have an extreme
specific gravity—platinum being, in fact, the lightest of the three, or
as light as the lightest. Osmium has a specific gravity of 21.4, and is
the heaviest body in nature; platinum is 21.15, and iridium the same; the
specific gravity of the other three being only about half that, namely,
11.3, 12.1, and 11.8. Then there is this curious relation, that palladium
and iridium are very much alike, so that you would scarcely know one from
the other, though one has only half the weight of the other, and only half
the equivalent power. So with iridium and rhodium, and osmium and
ruthenium, which are so closely allied that they make pairs, being
separated each from its own group. Then these metals are the most
infusible that we possess. Osmium is the most difficult to fuse: indeed, I
believe it never has been fused, while every other metal has. Ruthenium
comes next, iridium next, rhodium next, platinum next (so that it ranks
here as a pretty fusible metal, and yet we have been long accustomed to
speak of the infusibility of platinum), and next comes palladium, which is
the most fusible metal of the whole. It is a curious thing to see this
fine association of physical properties coming out in metals which are
grouped together somehow or other in nature, but, no doubt, by causes
which are related to analogous properties in their situation on the
surface of the earth, for it is in alluvial soils that these things are
found.
Now, with regard to this substance, let me tell you briefly how we get it.
The process used to be this. The ore which I shewed you just now was
taken, and digested in nitro-muriatic acid of a certain strength, and
partly converted into a solution, with the leaving behind of certain
bodies that I have upon the table. The platinum being dissolved with care
in acids, to the solution the muriate of ammonia was added, as I am about
to add it here. A yellow precipitate was then thrown down, as you perceive
is the case now; and this, carefully washed and cleansed, gave us that
body [pointing to a specimen of the chloride of platinum and ammonium],
the other elements, or nearly all, being ejected. This substance being
heated, gave us what we call platinum sponge, or platinum in the metallic
state, so finely divided as to form a kind of heavy mass or sponge, which,
at the time that Dr. Wollaston first sent it forth, was not fusible for
the market or in the manufacturers’ workshops, inasmuch as the temperature
required was so high, and there were no furnaces that could bring the mass
into a globule, and cause the parts to adhere together. Most of our metals
that we obtain from nature, and work in our shops, are brought at last
into a mass by fusion. I am not aware that there is in the arts or
sciences any other than iron which is not so. Soft iron we do not bring
together by fusion, but by a process which is analogous to the one that
was followed in the case of platinum, namely, welding; for these divided
grains of spongy platinum having been well washed and sunk in water for
the purpose of excluding air, and pressed together, and heated, and
hammered, and pressed again, until they come into a pretty close, dense,
compact mass, did so cohere, that when the mass was put into the furnace
of charcoal, and raised to a high temperature, the particles, at first
infinitely divided—for they were chemically divided—adhered the one to
the other, each to all the rest, until they made that kind of substance
which you see here, which will bear rolling and expansion of every kind.
No other process than that has hitherto been adopted for the purpose of
obtaining this substance from the particles by solution, precipitation,
ignition, and welding. It certainly is a very fine thing to see that we
may so fully depend upon the properties of the various substances we have
to deal with; that we can, by carrying out our processes, obtain a
material like this, allowing of division and extension under a rolling
mill—a material of the finest possible kind, the parts being held
together, not with interstices, not with porosity, but so continuous that
no fluids can pass between them; and, as Dr. Wollaston beautifully shewed,
a globule of platinum fused by the voltaic battery and the oxyhydrogen
blowpipe, when drawn into a wire, was not sounder or stronger than this
wire made by the curious coalescence of the particles by the sticking
power that they had at high temperatures. This is the process adopted by
Messrs. Johnson and Matthey, to whose great kindness I am indebted for
these ingots and for the valuable assistance I have received in the
illustrations.
The treatment, however, that I have to bring before you is of another
kind; and it is in the hope that we shall be able before long to have such
a thing as the manufacture of platinum of this kind, that I am encouraged
to come before you, and tell you how far Deville has gone in the matter,
and to give you illustrations of the principles on which he proceeds. I
think it is but fair that you should see an experiment shewing you the way
in which we get the adhesion of platinum. Probably you all know of the
welding of iron: you go into the smith’s shop, and you see him put the
handle of a poker on to the stem, and by a little management and the
application of heat he makes them one. You have no doubt seen him put the
iron into the fire and sprinkle a little sand upon it. He does not know
the philosophy he calls into play when he sprinkles a little sand over the
oxide of iron, but he has a fine philosophy there, or practises it, when
he gets his welding. I can shew you here this beautiful circumstance of
the sticking together of the particles up to the fullest possible
intensity of their combination. If you were to go into the workshops of
Mr. Matthey, and see them hammering and welding away, you would see the
value of the experiment I am about to shew you. I have here some
platinum-wire. This is a metal which resists the action of acids, resists
oxidation by heat, and change of any sort; and which, therefore, I may
heat in the atmosphere without any flux. I bend the wire so as to make the
ends cross: these I make hot by means of the blowpipe, and then, by giving
them a tap with a hammer, I shall make them into one piece. Now that the
pieces are united, I shall have great difficulty in pulling them apart,
though they are joined only at the point where the two cylindrical
surfaces came together. And now I have succeeded in pulling the wire
apart, the division is not at the point of welding, but where the force of
the pincers has cut it, so that the junction we have effected is a
complete one. This, then, is the principle of the manufacture and
production of platinum in the old way.
The treatment which Deville proposes to carry out, and which he has
carried out to a rather large extent in reference to the Russian supply of
platinum, is one altogether by heat, having little or no reference to the
use of acids. That you may know what the problem is, look at this table,
which gives you the composition of such a piece of platinum ore as I
shewed you just now. Wherever it comes from, the composition is as
complicated, though the proportions vary:—
Platinum, . . . . . 76.4
Iridium,. . . . . . 4.3
Rhodium,. . . . . . 0.3
Palladium,. . . . . 1.4
Gold, . . . . . . . 0.4
Copper, . . . . . . 4.1
Iron, . . . . . . . 11.7
Osmide of Iridium,. 0.5
Sand, . . . . . . . 1.4
—————
100.5
This refers to the Uralian ore. In that state of combination, as shewn in
the table, the iridium and osmium are found combined in crystals,
sometimes to the amount of 0.5 per cent., and sometimes 3 or 4 per cent.
Now, this Deville proposes to deal with in the dry way, in the place of
dealing with it by any acid.
I have here another kind of platinum; and I shew it to you for this
reason. The Russian Government, having large stores of platinum in their
dominions, have obtained it in a metallic state, and worked it into coin.
The coin I have in my hand is a twelve silver rouble piece. The rouble is
worth three shillings, and this coin is, therefore, of the value of
thirty-six shillings. The smaller coin is worth half that sum; and the
other, half of that. The metal, however, is unfit for coinage. When you
have the two metals, gold and silver, used for coinage, you have a little
confusion in the value of the two in the market; but when you have three
precious metals (for you may call platinum a precious metal) worked into
coin, they will be sure to run counter to one another. Indeed, the case
did happen, that the price of platinum coin fixed by the Government was
such, that it was worth while to purchase platinum in other countries, and
make coin of it, and then take it into that country and circulate it. The
result was, that the Russian Government stopped the issue. The composition
of this coin is—platinum, 97.0; iridium, 1.2; rhodium, 0.5; palladium,
0.25; a little copper, and a little iron. It is, in fact, bad platinum: it
scales, and it has an unfitness for commercial use and in the laboratory,
which the other well-purified platinum has not. It wants working over
again.
Now, Deville’s process depends upon three points,—upon intense heat,
blowpipe action, and the volatility of certain metals. We know that there
are plenty of metals that are volatile; but this, I think, is the first
time that it has been proposed to use the volatility of certain
metals—such as gold and palladium—for the purpose of driving them off
and leaving something else behind. He counts largely upon the volatility
of metals which we have not been in the habit of considering volatile, but
which we have rather looked upon as fixed; and I must endeavour to
illustrate these three points by a few experiments. Perhaps I can best
show you what is required in the process of heating platinum by using that
source of heat which we have here, and which seems to be almost
illimitable—namely, the voltaic battery; for it is only in consequence of
the heat that the voltaic battery affects the platinum. By applying the
two extremities of the battery to this piece of platinum-wire, you will
see what result we shall obtain. You perceive that we can take about this
heating agent wherever we like, and deal with it as we please, limiting it
in any way. I am obliged to deal carefully with it; but even that
circumstance will have an interest for you in watching the experiment.
Contact is now made. The electric current, when compressed into thin
conducting-wires offering resistance, evolves heat to a large extent; and
this is the power by which we work. You see the intense glow immediately
imparted to the wire; and if I applied the heat continuously, the effect
of the current would be to melt the wire. As soon as the contact is
broken, the wire resumes its former appearance; and now that we make
contact again, you perceive the glow as before. [The experiment was
repeated several times in rapid succession.] You can see a line of light,
though you can scarcely perceive the wire; and now that it has melted with
the great heat, if you examine it, you will perceive that it is indeed a
set of irregularities from end to end—a set of little spheres, which are
strung upon an axis of platinum running through it. It is that wire which
Mr. Grove described as being produced at the moment when fusion of the
whole mass is commencing. In the same manner, if I take a tolerably thick
piece of platinum, and subject it to the heat that can be produced by this
battery, you will see the brilliancy of the effect produced. I shall put
on a pair of spectacles for the experiment, as there is an injurious
effect of the voltaic spark upon the eyes, if the action is continued; and
it is neither policy nor bravery to subject any organ to unnecessary
danger; and I want, at all events, to keep the full use of my eyes to the
end of the lecture.
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.