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tions of air were found to be as nearly as possible of the fame dimensions, and of the same degree of purity.'

From these and other experiments the Author at first concluded, that mice would not live in dephlogisticated air till they had completely phlogisticated it, which happens when they die in common air ; though they lived longer in the former than might be expected from its purity, as indicated by the nitrous test. He neglected then, however, to put other mice into the remaining dephlogisticated air. Attending to this circumstance afterwards, he found that when the second mouse died in this remaining air, it was as completely phlogisticated, as common air is generally found to be, when mice have died in it; and that the death of the first mouse, long before the complete phlogistication of the air, was principally occafioned by its long continuance in the cold, after having pafied through water,

In a subsequent section the Author satisfactorily shews the fale lacy of the new method of ascertaining the purity of common air by means of nitrous air, proposed by the Abbé Fontana, and described by Dr. Ingenhoulz in the work above referred to *. From the Author's experiments and reasonings, it appears, that philosopbers ought to be as attentive as ever to the strength of the nitrous air, employed as a teft of the purity of common air.

Many new obfervations follow respecting that peculiar modi. fication of nitrous air, formerly discovered by the Author, which he is now induced to call dephlogisticated nitrous air ; and which possesses the peculiar properties of admitting a candle to burn in it, though it still continues as fatal to animal life as any of the most noxious species of air ; and sometimes will diminish common air as much as fresh made nitrous air, though at other times it is noc pofseffed of this power. The Author has now found an easy method of producing this singular species of air in great abundance, merely by putting iron into a solution of copper in nitrous acid.

Some curious and fingular experiments are next related, in which the Author treats more particularly than he had before done, of the production of a genuine inflammable air; merely in consequence of repeatedly transmitting electric 1parks, or explofions, through a given quantity of alcaline air confined by quicksilver. He carried on this process, as he supposed, to its maximum; or till he judged that the electric explosions made no addition to the bulk of the air : and he found that the space finally occupied by the air was, as nearly as poffible, three times as great as that which the alcaline air alone had originally occupied.

See the same volume of our Review, pag. 349.

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This air exploded in the same manner, and appeared in every other respect to be of the faire nature as that procured from iron or zinc, by means of the vitriolic or marine acids. And though water was admitted to it, and frequently agitated with it, during two whole days; no sentible part of it was absorbed, nor had the water acquired a smell of volatile alcali. When, however, this air was made to explode, the Author, on instantly applying his noftrils to the mouth of the veffel, perceived a very evident alcaline smell: from which he infers, that the whole of the volatile al ali had not been completely incorporated with this air ; though the combination was fufficiently intiniate, to deprive the volatile alcali of irs property of being absorbed by water.

This curious experiment undoub.edly deserves to be repeated on a larger scale, and the process to be carried on, till the operator be perfectly affured that no additional explosions will prom duce any

further effect on the alcaline air. The water after. wards added to it should likewise be striétly examined. There appears here to be either an actual decomposition of the volatile alcali; or a new combination formed of it with some additional fubilance. The questions, accordingly, that naturally occur here are-Is its own abundant phlogiston only feparated from the alcaline air, by the electric explotions, so as to constitute inflammable air; and in that cale, what becomes of its other principle or principles?-or does the electric matter conduct, from other substances, or itself furnith, more phlogiston, to the alcaJine air; so as to constitute a kind of neutral compound, infoluble in water !-or lastly, is there, in this case, a disunion of principles, and an increase of dimension, effected merely by the intense heat of the electric explosions; as is hinted at pag. 385?-We ought to have premised a conjecture of the Author's that inflammable air in general consists of phlogiston combined with some basis, which is of an alcaline nature; and that the phlogiston of this inflammable air is principally supplied by the electric matter.

The next lection contains an account of some singular experiments, thewing the remarkable volatility of that ponderous metallic substance, quicksilver, under certain circumstances. The evaporation of mercury in vacuo, or rather its subsequent condensation into globules, in the upper part of a barometer, had been before oblerved. The Author 100 had formerly taken police of a black matter lining the cavity of the upper part of a glats lyphon, containing vitriolic acid air confined by mercury, when he tent (lectric explofions through ic : but at that time he entertaines no fufpicion that this matter came from the quickfilver; imagining that it was altogether forir.ed from the vitriplic acid air,

Without Wi.bout mentioning his previous experiments relative to this subject, we shall only observe, that he made the electrical explosions, in vitriolic acid air, not from the surface of the mercury itself, but between two wires, placed at the great distance of ihree feet above it; and he found that the black matter was, to all appearance, produced quite as readily, as when the explofions had been taken ever so near to the surface of the mercury. As this black matter on applying heat to it, was found to be mercury ; it seems that the mercurial vapour must have completely and previously pervaded the whole space, filled with vie triolic acid air ; and that the electric matter found it already difpersed throughout this air, and did not produce any proper evaporation, or mechanical trusion, of the mercury, by its immediate action upon that fluid. It even appears, from other experiments of the Author's, that mercury exilts in the form of vapour, in common air : for here too the black matter is produced, though not so plentifully, and only at a finall distance above the surface of che mercury

To these experiments succeed others-on the nitrous acid existing in metallic calces;-on the extraordinary volatility given to the nitrous acid, on its admixture with the vitriolic, from which it entirely escapes ;-and on the marine acid, depblogisticated by means of manganese: a discovery, we believe, of Mr. Scheele's. The experiments made with the acid in this new State (in which it will, singly, dissolve gold) confirm the opinion which the Author had always entertained ; that a certain portion of phlogiston is necessary to all substances, and especially acids, assuming the form of air.' The marine acid, thus deprived of phlogiston, is actually brought into a state very nearly resembling that of the nitrous acid; being now, like it, incapable of assuming the form of a permanent air, that is, of an air that can be confined by quicksilver ; which substance it immediately corrodes, forming probably with it a kind of corrosive fublimate. Mr. Watt, in a subsequent note, properly observes that this is perhaps an easier, as it certainly is a more direct, way of making that preparation, than the common process.

In the following sections are contained-Observations on the lateral electrical explosion, formerly printed in the Philosophical Tranfactions, and some miscellaneous experiments in electricity. These are succeeded by others relative to sound, in different kinds of air ; and by a few experiments of a miscellaneous nature,

Towards the end of this volume, the Author has added a methodical Index, or a summary view of all the more important facts contained in this and the four preceding volumes, under distinct heads ; with relerences to those parts of the work in which they are more largely treated of. This recapitulation will be found to be exceedingly useful and instructive. A section is added too, containing explanations or corrections of various passages in the four former volumes; suggested by sublequent experiments or observations. An Appendix to this volume contains – An Extract of a Letter from Mr. Arden, describing a very fingular appearance produced by artificial electricity ;--some observations on different parts of this volume, by Mr. Watt, and Mr. Bewly;-a description, accompanied with a drawing, of a new apparatus for impregnating water with fixed air, invented by Dr. Withering;- and an account, by Mr. Warltire, of a very curious experiment made by him ; from which it seems to follow, that the latent heat in bodies adds to their weight, or that fire is actually beavy. At least, the fact is, that on firing inflammable air, by the electric spark, in a copper flask holding three pints, perfectly closed, and accurately weighed before the explosion; it was found, after the explosion, that the vessel weighed less (generally two grains) than before.

We shall only add our wishes, that the Author, now entering,' as he observes, 'on a new period of life,' (at Birmingham) may have it in his power to realise the hopes, which he expresses in his Preface, that, in his new situation, he shall be enabled to devote bimself, as much as in any former period of his life, to philosophical pursuits.' In these withes every friend to philosophy will, we doubt not, heartily concur with us.

B...y

I S.

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ART. IV. A Régifer of the Going of Mr. Mudge's firft Time-keeper,

from April 18in, 1780, to May zeh, 1781 : with two or her Regilters of the fame Time-keeper. 46o.

Cadell. 1781. N our Review for September last, we gave a very particular

account of a watch of Mr. Arnold's making. Justice to both artists requires, from the Reviewer, as particular an account of the going of this Time-keeper.

The publication before us contains, as the title expresses, three several registers of the going of the same watch, at three (somewhat diftant) periods of time.

The first in point of time, though not placed so in the pamphlet, was kept by the Rev. Professor Hornsby at Oxford, from June 20th to October 31st. The year is not mentioned; but there are some reasons for supposing it was in 1776. In this trial, the greateft difference between the rates of the watch, on any two days in that time, was 4" 35; namely between its rate on July 4th, when it loft 2" 57, and its rate on July 30th, when it gained 1'78.

The difference between its rate on any one day and the next day to it, was 3"76; namely between July 30th, on which day it gained 1"78, and July the 31st,

when

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when it loft 1"98. In this time Fahrenheit's thermometer was never higher than 68 }, nor lower than 48 1.

When the watch was carried down to Oxford, in June, it gave the difference of longitude between that place and Greenwich 5' 3"{ in time. When it was brought up from thence, the ist of November following, it made the difference of longitude between those two places 5' 1" 8 the mean of the two is 52" }; and the true longitude of Oxford, as determined by. astronomical observations, is 5' 2" W.

It was next tried at Greenwich, under the inspection of the Rev. Dr. Maskelyne, Astronomer Royal, from November the 12th 1770, to November the 30th 1777. The watch appears under rather less favourable circumstances in this trial than it did in the last; but its going here was by no means bad. For the first month, or more, its rate of going was very near mean time ; but towards the latter end of February it began to acceJerate, and before the end of March gained rather more than 5" on a day : but at the end of this month it fell off again to 3 conds and a fraction, and continued to go at that rate, with most amazing regularity until the latter end of Sep?ember, when it began to accelerate again, and was gaining s". nearly when the journal is closed.

The greatest difference between its rates on any two days in these thirteen months was 7" 2; namely, between its rates on January the ist, on which day it loft 1" 46, and November the zoth, when it gained 5" 74.' The greatest difference between its rates of going on any one day and the next following is 3" 06 ; namely, between its rate of going on January the gth and its rate on January the roth. The greatest height of the thermometer during this trial was 70, and the least 26 degrees.

After this trial, we are told, that Mr. Mudge endeavoured to discover and remove the cause of the irregularities which were observed in the watch's going; and the success of his endea, vours will be beit seen from the following account of the last of the three trials which are here given.

It is to be observed, that the account before us is totally filent as to the place where, as well as the person by whom this last trial was made *. li must also be acknowledged, that the comparer laboured under another disadvantage, in not being able to regulate his clock by astronomical observations, but to be obliged to fetch the time from Dr. Heberden's clock, by means of watches.

On these two accounts, the authority of this trial may want weight with some persons, who will not be able to object to the

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