SECTION XV. Of the Impregnation of WATER with FIXED AIR. PART I. The Hiftory of the Discovery. It often amufes me when I review the history of experimental philofophy, to obferve how very nearly one difcovery is connected with another, and yet that, for a long time, no perfon fhall have perceived that connection, so as to have been actually led from the one to the other; and efpecially that he who made the first discovery should stop short in his progress, and not advance a fingle step farther, to make the other, which was perhaps of infinitely more confequence. And yet the cafe may be fuch, that it fhall be fo far from requiring more genius, or ingenuity, to advance that other step, that it is rather a matter of wonder, how it was poffible for the most common capacity to ftop fhort of it. We alfo frequently find that they who make the most important philofophical discoveries overlook the most obvious ufes, of them. Several ftriking examples of S 4 this this kind will be found in my Hiftory of electricity, and alfo in the History of difcoveries relating to vifion, light, and colours. In fuch cases as these it behoves an hiftorian to be much upon his guard, left he fhould haflily conclude that to have been fact which he only imagines must have been fo, but for which no direct evidence can be produced. As this is a cafe of fome curiofity refpecting the human mind, I fhall give an instance of it; and I am able to produce a very remarkable one relating to the fubject of this fection. When it was difcovered that the acidulous tafte and peculiar virtues of Pyrmont water, and other mineral waters of a fimilar nature, were owing to the fixed air which they contained; when this air had been actually expelled from the water, and it was found that the fame water, and even other water, would reimbibe the fame air; we are apt to conclude, that the perfon who made thefe discoveries, and especially the laft of them (who alfo muft have known that fixed air is a thing very eaty to be procured) muft have immediately gone. to work to reduce this theory into practice, by actually impregnating common water with fixed air, in order to give it the peculiar virtues of thofe medicinal mineral waters which are are fo highly, and fo justly valued, and which are procured at fo great an expence, especially in this country. Accordingly, Dr. Nooth has advanced, Phil. Tranf. vol. 65, p. 59, that "the poffibility of impregnating water with "fixed air was no fooner afcertained by expe"riment, than various methods were con"trived to effect the impregnation;" and I doubt not this ingenious philofopher impofed upon himself in the manner described above. This, however, is fo far from being the cafe, that I do not believe it is poffible to produce the least evidence that any person had the thing in view before the publication of my prophlet upon that fubject, in the year 1772. Indeed, had this thing been fo much as an object of attention to philofophers, it is impoffible but that fome of them must have hit upon a method that would have fufficiently fucceeded. Nay, the thing is fo very easy, and the end attainable in fo many ways, that there must have been, in a very short time, a great variety of methods to impregnate water with fixed air, as there are now; and we fhould certainly have heard of artificial mineral waters being made according to them. It is impoffible not to conclude fo, when we consider the time that has elapfed fince the publication of all the discoveries that led to it. Dr. Dr. Brownrigg's paper, giving an account of his discovery of fixed air in the Spa water, was read at the Royal Society June the 13th 1765, and was published in 1766. This excellent philofopher compleatly decompofed that mineral water, but he gives no hint of his having fo much as attempted to recompose it, or of making a fimilar water, by impregnating common water with the fame volatile principle. It is fufficiently evident that he had not thought of this, though we may wonder that he fhould not have done it, because he has not mentioned it as an object of purfuit. In the year following, Mr. Cavendish's valuable papers on the fubject of factitious air were published. He firft afcertained how much fixed air a given quantity of water could be made to imbibe; yet it does not appear that he ever thought of tafting the water, much less that he thought of making any practical use of his discovery. If any negative argument can be decifive, it is that in 1772, the very year in which my pamphlet came out, Dr. Falconer published his excellent and elaborate treatife on the Bath waters, in which he treats very largely of mineral waters in general, and all their poffible impreg impregnations; and yet, though he treats of fixed air as one ingredient in many of them, fee p. 185, he drops no hint about compofing fuch water, by imparting fixed air to comAlfo on the 12th of September mon water. in the fame year, Dr. Rutherford published his ingenious Differtation on Fixed Air, in which he fpeaks of the presence of it in Pyrmont water, P. 3, but without giving the leaft hint of his being acquainted with any method of imitating them. And yet Dr. Nooth fays, in fact, that from the year 1766, at the latest, various methods were contrived to effect the impregnation, though he allows that I was the only person who "published any defcription of an apparatus calculated entirely for this pur"pose." According to this account of the matter there were, in the interval between 1766 and 1772, a space of fix years, a variety of methods for impregnating water with fixed air, fome of them prior to, and perhaps much better than mine (though he gives no hint of his own having been invented in that period, but speaks of it as fuggefted by the confideration of the imperfection of mine) but that I happened to get the ftart in the publication. Dr. Falconer, however, though the friend of Dr. Nooth (fee his Treatife on Bath Water, |