force: this is one extreme. We have it again showing its tremendous energies in the phenemena of combustion, rushing with violence into other forms-displaying the most glorious manifestations of light and heat-generating combinations of characters diametrically opposed;

from the extreme of alkalinity on the one hand, to the most violent acidity on the other:—and, finally having gone through its metamorphic phases, assuming its appointed place of rest in the world's economy. But though extraordinary as are these glorious manifestations of power displayed by oxygen in its active state,beautiful to view-admirable in their results,—there is yet another state it may assume more extraordinary still;—a state in which it is neither fully active nor fully passive, but intermediate between the two; a state in which the activity possessed is not only less in amount but different in quality. This is a state which may be designated as the semi-active or ozonised condition, and the discovery of which, as well as the chief investigations which have been made respecting it is due to the sagacity of M. Schönbein of Bâle.

Before entering upon the investigation of ozone, or ozonised oxygen, and showing its distinctive qualities, let us introduce it by a slight historical sketch.

Those who have operated with an electric-machine will not have failed to notice the peculiar smell which occurs in an apartment where the machine is in action. This has been denominated the electric smell, and it presents a marvellous field for philosophic contemplation. What is this smell? Does it depend on the presence of a substance formed? Does it depend on a substance modified? Such are the two questions which first present themselves for consideration. Numerous secondary questions then rise involuntarily up for solution in

the mind of a thinking philosopher. Is the smell consistent with any other manifestation? Yes; for, if a piece of paper be moistened with a solution of starch and iodide of potassium, the paper is tinged blue. Now, this tinging blue is an indication of the liberation of iodine; and this liberation of iodine is an indication of the agency of oxygen; hence, thus far has been established a connection between oxygen in an active condition and-the electric smell.

It remained for Professor Schönbein, of Bâle, to develope the germ of knowledge conveyed by the electric smell;-to expand and generalise it; to show that the same smell and its corresponding agency might be generated at pleasure, by various means, which it is the object of this lecture to set forth; to demonstrate other properties besides that of acting on the test-paper described; to render manifest qualities of bleaching, of intense oxidation, of deodorisation; to show that the agent on which all this depends is constantly generated in the stupendous laboratory of the physical world; and, lastly, to prove that the mysterious gaseous agency is neither more nor less than oxygen-oxygen gas existing in an allotropic form! Oxygen gas, that is to say, under a masked aspect. At least the present state of our knowledge warrants us in saying no more than this: but the philosopher, once led into this train of speculation, ends involuntarily by asking himself the questions-in what does chemical identity consist? in what will these wonderful developments of allotropism end? whether

the so-called chemical elements may not be, after all, mere allotropic conditions of fewer universal essences ? whether, to renew the speculations of the alchemists, the metals may be only so many mutations of each other, by the power of science mutually convertible? There was a time when this fundamental doctrine of the alchemists was opposed to known analogies; it is now no longer opposed to them, but only some stages beyond their present development.

As we possess in the nitric oxide gas, or bin-oxide of nitrogen, a test of the presence of oxygen gas-so we also have a test of the specific condition of oxygen gas characterised by the name of ozone. A mixture of iodide of potassium and starch solution constitutes this test, and it may be conveniently applied by imbuing bibulous paper with it, and allowing the paper to dry. Slips of this paper I here have already prepared, and let us see to what deductions we arrive:-I first dip a slip of the paper moistened into a bottle filled with oxygen gas as just prepared from the chlorate of potash and black oxide of manganese. The result is negative, you will observe, the colour of the paper undergoing no change. I now dip it into a bottle of gas which is also oxygen, but it has been subjected to the remarkable change of ozonisation, by a process which we shall presently go through. This slip of paper, observe, becomes tinged blue, demonstrating a very remarkable quality to be possessed by this gas-very different to those manifested by oxygen gas, as we have seen it

hitherto. The ozonised gas, moreover, has a peculiar smell, whilst ordinary oxygen gas is totally devoid of all smell; moreover, it has other properties quite distinctive, as we shall presently see. Into a bottle containing it I now pour this blue solution-a solution of sulphate of indigo, and you will observe with what rapidity the solution becomes bleached: if I take a bottle of common unozonised oxygen, and pour into it a portion of indigo solution, no bleaching result supervenes, thus manifesting a remarkable difference also in this respect. Ozonised oxygen, moreover, exercises a remarkable influence over certain odours-thus, if a piece of tainted meat

be immersed in this gas the effluvium is instantaneously destroyed; and if sheets of silver foil be plunged into it, the metal soon crumbles into dust the oxide of silver. In point of fact, although ordinary oxygen gas exert no agency upon the metal silver,

yet ozonised oxygen attacks it so readily and so violently, that silver, under the operation of the latter, can no longer be regarded in the light of a noble metal. The result of the operation of ozonised oxygen upon silver not only illustrates the peculiar agency of ozone,