HKB
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.