The vessel A will thus be detached, and agitation may be easily applied; after which, again screw it into its former place, and, on opening the two cocks, the mercury will rise in the vessel A. Supply the descent in B by fresh mercury, and proceed as before, repeating alternately the pressure and agitation, as long as any further absorption takes place.

A further amendment of the apparatus, would consist in the substitution of cocks of some other metal than brass, which, however perfect at first, are always injured by the repeated action of the mercury. If cocks of glass could be ground sufficiently tight, metal caps with screws might be cemented to them.

For observing the increased absorption of less condensible gases, I found it necessary to substitute a vessel of larger size than A, and of the capacity of at least 50 cubical inches. It is represented by the dotted lines in Fig. 1, and was furnished with a cock and screw at c. As it would have been troublesome to have filled so large a vessel entirely with quicksilver, it was filled with boiled water, with the exception of a quantity of quicksilver rather exceeding the bulk of the gas employed. The gas was admitted, as usual, from a transfer bottle, the mercury which it replaced escaping through the cock b. The increased pressure was next applied; and the experiment conducted as before, except that the agitation was much longer continued.

The results of a series of at least fifty experiments, on carbonic acid, sulphuretted hydrogen gas, nitrous oxide, oxygenous and azotic gases, with the above apparatus, establish the following general law: that, under equal circumstances of temperature, water takes up, in all cases, the same volume of condensed gas as of gas under ordinary pressure. But, as the spaces occupied

by every gas are inversely as the compressing force, it follows, that water takes up, of gas condensed by one, two, or more additional atmospheres, a quantity which, ordinarily compressed, would be equal to twice, thrice, &c. the volume absorbed under the common pressure of the atmosphere. By frequent repetition of the experiments, I obtained results differing a little from the general principle above stated; but, for all practical purposes, I apprehend, the law has been announced with sufficient accuracy.

In place of the cock a, I cemented, in one experiment, a very sensible thermometer. The vessel was next filled with mercury through the cock b; and the tube B being also filled, the cock b was shut, and a bottle of carbonic acid gas screwed on. The cock b being then opened, the mercury descended, and a measured quantity of carbonic acid arose into the vessel A. In the same way, a measured quantity of water was introduced. When the density of the air was suddenly doubled by a column of quicksilver, the mercury in the thermometer, whose bulb was still surrounded by the condensed gas, rose about 11⁄2 degree. On agitating the vessel, till the water encompassed the bulb of the thermometer, an elevation of barely a degree ensued in the temperature of the water. This ascent would probably have been greater, if the evolved heat had not been carried off by the mercury on which the water floated.

Manchester,

Dec. 8th, 1802.

That the facts did not, with invariable accuracy, correspond to the law, was perhaps, in part, owing to the addition of only 28 inches of pressure; when, in strictness, 29 should have been used, or twice the elevation of the mercury in the barometer, during each experiment.

IV. Experiments and Observations on the various Alloys, on the specific Gravity, and on the comparative Wear of Gold. Being the Substance of a Report made to the Right Honourable the Lords of the Committee of Privy Council, appointed to take into Consideration the State of the Coins of this Kingdom, and the present Establishment and Constitution of his Majesty's Mint. By Charles Hatchett, Esq. F. R. S.

Read January 13, 1803.

LIST of the COMMITTEE appointed on the 10th of February, 1798, to take into Consideration the State of the Coins of this Kingdom.

EARL OF LIVERPOOL, PRESIDENT.

THE LORD HIGH CHANCELLOR OF GREAT BRITAIN.

THE LORD PRESIDENT OF THE COUNCIL.

THE LORD PRIVY SEAL.

HIS MAJESTY'S PRINCIPAL SECRETARIES of State.

THE MASTER GENERAL OF THE ORDNANCE.

THE FIRST LORD COMMISSIONER OF THE ADMIRALTY.

THE FIRST LORD COMMISSIONER OF HIS MAJESTY'S TREASURY,

AND CHANCELLOR OF THE EXCHEQUER.

HIS MAJESTY'S SECRETARY AT WAR.

HIS GRACE THE DUKE OF MONTROSE.

THE LORD CHIEF Justice of HIS MAJESTY'S COURT OF KING'S BENCH.