than twice as good as common air; for when it is highly dephlogifticated, the candle burns with a crackling noife, as if it was full of fome combuftible matter.

It may be inferred, from the very great explofions made in dephlogisticated air, that, were it poffible to fire gunpowder in it, less than a tenth part of the charge, in all cafes, would fuffice; the force of an explosion in this kind of air, far exceeding what might have heen expected from the purity of it, as fhewn in other kinds of trial. But I do not fee how it is poffible to make this application of it. I should not, however, think if difficult to confine gunpowder in bladders, with the interftices: of the grains filled with this, instead of common air; and fuch bladders of gunpowder might, perhaps, be used in mines, or for blowing up rocks, in digging for metals, &c.

Nothing, however, would be easier than to augment the force of fire to a prodigious degree, by blowing it with dephlogisticated air inftead of common air. This I have tried, in the presence of my friend Mr. Magellan, by filling a bladder with it, and puffing it, through a final glafs-tube, upon a piece of lighted wood but it would be very easy to

fupply

fupply a pair of bellows with it from a large refervoir.

Poffibly much greater things might be effected by chymifts, in a variety of refpects, with the prodigious heat which this air may be the means of affording them. I had no fooner mentioned the discovery of this kind of air to my friend Mr. Michell, than this use of it occurred to him. He obferved that poffibly platina might be melted by means of it.

From the greater ftrength and vivacity of the flame of a candle, in this pure air, it may be conjectured, that it might be peculiarly falutary to the lungs in certain morbid cafes, when the common air would not be fufficient to carry off the phlogistic putrid effluvium faft enough. But, perhaps, we may alfo infer from these experiments, that though pure dephlogisticated air might be very ufeful as a medicine, it might not be fo proper for us in the ufual healthy ftate of the body: for, as a candle burns out much fafter in dephlogisticated than in common air, fo we might, as may be faid, live out too fast, and the animal powers be too foon exhaufted in this pure kind of air. A moralift, at least, may fay, that the air which nature has provided for us is as good as we deserve.

My reader will not wonder, that, after havi ing ascertained the fuperior goodness of dephlogisticated air by mice living in it, and the other tefts above mentioned, I fhould have the curiofity to taste it myself. I have gratified that curiofity, by breathing it, drawing it through a glass-fyphon, and, by this means, I reduced a large jar full of it to the standard of common air. The feeling of it to my lungs was not fenfibly different from that of common air; but I fancied that my breast felt peculiarly light and eafy for fome time afterwards, Who can tell but that, in time, this pure may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it.

air

Whether the air of the atmosphere was, in remote times, or will be in future time, better or worse than it is at prefent, is a curious fpeculation; but I have no theory to enable me to throw any light upon it. Philofophers, in fu. ture time, may easily determine, by comparing their obfervations with mine, whether the air in general preferves the very fame degree of purity, or whether it becomes more or less fit for refpiration in a course of time; and also, whether the changes to which it may be subject are equable, or otherwife; and by this means may acquire data, by which to judge both of

the

the past and future ftate of the atmosphere. But no obfervations of this kind having been made, in former times, all that any person could now advance on this fubject would be little more than random conjecture. If we might be allowed to form any judgment from the length of human life in different ages, which feems to be the only datum that is left us for this purpofe, we may conclude that, in general, the air of the atmosphere has, for many ages, preserved the fame degree of purity. This datum, however, is by no means fufficient for an accurate folution of the problem.

1

SECTION V.

Of Air procured from various Substances by Means of Heat only.

I have observed already, that, in my former experiments, I had not the use of a burning lens of any confiderable force; and, for want of it, was obliged to leave many of the experiments extremely incomplete, and many things not even attempted. But having, foon after my late publication, provided myself with a lens of fufficient force for the purpose, the first thing I did, when I began to refume my experiments, was to make ufe of it, in order to fatisfy myself what kind of air certain fubftances would yield by means of heat only, either in vacuo, or when confined by quickfilver; and it has been feen in the preceding fections, that by pursuing this method, I was led to the discovery of many new and curious facts, of fufficient importance to be confidered feparately, and at large.

In this fection, I propofe to comprize the reft of the observations that occurred to me in

that