be made of it on board fome of his majesty's fhips. To make this procefs more generally known, and that more frequent trials may be made by water thus medicated, at land as well as at fea, I have been induced to make the present publication.

Sir John Pringle first observed, that putrefaction was checked by fermentation, and Dr. Macbride discovered that this effect was produced by the fixed air which is generated in that process, and upon that principle recommended the use of wart, as fupplying a quantity of this fixed air, by fermentation in the ftomach, in the fame manner as it is done by fresh vegetables, for which he, therefore, thought that it would be a substitute, and experience has confirmed his conjecture, Dr. Black found that lime-ftone, and all calcareous fubftances, contain fixed air, that the prefence of it makes them what is called mild, and that the deprivation of it renders them cauftic; Dr. Brownrigg farther difcovered that Pyrmont, and other mineral waters, which have the fame acidulous tafte, contain a confi derable proportion of this very kind of air, and that upon this their peculiar spirit and vir tues depend; and I think myfelf fortunate in having hit upon a very eafy method of communicating this air to any kind of water, or, in

deed,

deed, to almost any fluid fubstance. In fhort, by this method this great antifeptic principle may be administered in a variety of agreeable vehicles.

If this discovery (though it doth not deserve that name) be of any use to my countrymen, and to mankind at large, I fhall have my reward. For this purpose I have made the communication as early as I conveniently could, fince the latest improvements that I have made in the procefs; and I cannot help expreffing my wishes, that all perfons, who discover any thing that promifes to be generally useful, would adopt the fame method.

SECT. 2. The Directions.

If water be only in contact with fixed air, it will begin to imbibe it, but the mixture is greatly accelerated by agitation, which is continually bringing fresh particles of air and water into contact. All that is neceffary, therefore, to make this process expeditious and effectual, is first to procure a fufficient quantity of this fixed air, and then to contrive a method by which the air and water may be strongly agitated in the fame veffel, without any danger of admitting the common air to them; and this

is easily done by firft filling any veffel with water, and introducing the fixed air to it, while it ftands inverted in another veffel of water. That every part of the process may be as intelligible as poffible, even to thofe who have no previous knowledge of the fubject, I fhall defcribe it very minutely, fubjoining feveral remarks and obfervations relating to varieties in the process, and other things of a mifcella

neous nature.

The Preparation.

Take a glafs veffel, a, pl. 2. fig. 1. with a pret ty narrow neck, but fo formed, that it will stand upright with its mouth downwards, and having filled it with water, lay a flip of clean paper, or thin pafteboard, upon it. Then, if they be preffed clofe together, the veffel' may be turned upfide down, without danger of ad mitting cominon air into it; and when it is thus inverted, it must be placed in another veffel, in the form of a bowl or bafon, b, with a little water in it, fo much as to permit the flip of paper or påfteboard to be withdrawn, and the end of the pipe c to be introduced.

This pipe must be flexible, and air-tight, for which purpose it is, I believe, best made

of

of leather, fewed with a waxed thread, in the manner ufed by fhoe-makers. Into each end of this pipe a piece of a quill fhould be thruft, to keep them open, while one of them is introduced into the veffel of water, and the other into the bladder d, the oppofite end of which is tied round a cork, which must be perforated, the whole being kept open by a quill; and the cork must fit a phial e, two thirds of which Thould be filled with chalk juft, covered with

water.

I have fince, however, found it most convenient to use a glass tube, and to preserve the advantage which I had, of agitating the veffel I have two bladders, communicating by a perforated cork, to which they are both tied. For one bladder would hardly give room enough for that purpose.

The Process.

Things being thus prepared, and the phial containing the chalk and water being detached from the bladder, and the pipe alfo from the veffel of water, pour a little oil of vitriol upon the chalk and water; and having carefully preffed all the common air out of the bladder, put the cork into the bottle presently after the effer

I

effervefcence has begun. Alfo prefs the bladder once more after a little of the newly generated air has got into it, in order the more effectually to clear it of all the remains of the common air; and then introduce the end of the pipe into the mouth of the veffel of water as in the drawing, and begin to agitate the chalk and water brifkly. This will presently produce a confiderable quantity of fixed air, which will diftend the bladder; and this being preffed, the air will force its way through the pipe, and afcend into the veffel of water, the water at the fame time defcending, and coming into the bafon.

When about one half of the water is forced out, let the operator lay his hand upon the uppermost part of the veffel, and fhake it as brifkly as he can, not to throw the water out of the bafon; and in a few minutes the water will absorb the air; and taking its place, will nearly fill the veffel as at the first. Then shake the phial containing the chalk and water again, and force more air into the vessel, till, upon the whole, about an equal bulk of air has been thrown into it. Alfo fhake the water as before, till no more of the air can be imbibed. As foon as this is perceived to be the cafe, the water is ready for use; and if it be not used immediately, fhould be put into a bottle as

foon