form of a letter, the following observations respecting the folvent power of fixed air on the urinary calculus. Among other people to whom this letter has been circulated, a copy has been fent to the editor of the Medical Commentaries, who flatters himself that the reprinting of it in this publication will not be unacceptable to his readers.

A review of the discovery of the folvent powers of fixed air on the urinary calculus; of the ap lication of this remedy to other disorders of the kidneys and bladder; and of the fuccefs which has attended the use of it.

A late amiable and learned philofopher, (the Rev. Dr Hales), whofe experimental inquiries were generally directed to the good of his fellowcreatures, first obferved the lithontriptic powers of certain fermenting mixtures: But he acknowledges the impracticability of injecting fuch mixtures into the bladder with fufficient frequency for the purpose of folution; and he recites his experiments chiefly with a view to engage others in the fame laudable and important purfuit. The fubject, however, funk into oblivion; and no farther attempts of this kind were made, till the notice of the public was again excited towards the pro

perties

perties and uses of factitious air, by the writings of various learned and ingenious men. At this time, 1774, Dr Saunders, a phyfician in London, eminent for his knowledge of chemistry, applied himself to profecute the experiments which Dr Hales had begun ; and he found, that the folvent power, ascribed to the fermenting mixtures, refided only in the fixed air feparated during the act of effervefcence. Dr Percival heard an imperfect account of this discovery. His curiofity was excited: The acquifition of a remedy for the ftone was highly interesting to humanity; and he engaged with ardour in the pursuit of it, though ignorant of the manner in which Dr Saunders had conducted his trials. He recollec ted that Dr Black and Mr Cavendish had proved the folubility of various earthy bodies in water, either by abstracting from, or fuper-adding to the fixed air which they contain: And, as the human calculus is diffolved in the former way by lime water and the cauftic alkali, it appeared highly probable that the like effect would be produced, in the fame fubftance, by the latter mode of operation. Analogy feemed favourable to the hypothesis; and his experiments have, in the fullest manner, confirmed it.

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In the year 1776, a very ingenious phyfician at Bath (Dr Falconer) engaged in the fame inquiry; and the refults of his trials coincide with those related by Dr Percival. Perhaps it may be doubted whether fixed air can be conveyed, by the urinary courfe of circulation, to the kidneys and bladder. In an elastic state, it certainly cannot; but diffolved in water it may pafs through the vascular fyftem, without creating the least disturbance or diforder; and, by its diuretic qualities, will be powerfully determined to the urinary organs. Dr Percival has given a decifive proof of the truth of this obfervation. For a young gentleman, Mr Thomas Smith, at his defire, drank large quantities of mephitic water daily, during the fpace of a fortnight. And, whilft he continued this courfe, his urine was ftrongly impregnated with fixed air, as appeared not only from the precipitation which it produced in lime water *, but alfo from the bubbles which it copiously emitted, when placed under the receiver of an air pump, and from the folution of feveral urinary stones which were immersed in it. • The

*The precipitation of lime from lime water, by urine, is mentioned by the late Dr Whytt, and confirmed by Dr Macbride.

The following paragraphs are extracted from Dr Priestley's fecond volume of experiments and obfervations on air.

It might be queftioned, whether the fixed air, contained in our aliment, can be conveyed, by the courfe of circulation, into the blood, and by that means impregnate the urine. 1 haye found, however, that it may do it; having more than once expelled, from a quantity of fresh made urine, by means of heat, about one fifth of its bulk of pure fixed air, as ' appeared by its precipitating lime in lime water, and being almoft wholly abforbed by water; and yet a very good air-pump did not difcover that it contained any air at all.

It must be obferved, however, that it required feveral hours to expel this air by heat; and, ' after the process, there was a confiderable whitifh fediment at the bottom of the veffel. This was probably fome calcareous matter, with which the fixed air had been united; and by this fixed air, the calcareous matter, which would otherwife have formed a ftone or gravel, may have been held in folution. And, therefore, drinking water, impregnated with fixed air, may, by impregnating the urine, enable it to diffolve calcareous matters better than it Ggg 2 • would

• would otherwife have done; and may, therefore, be a means of preventing or diffolving the • stone in the bladder, agreeable to the proposal ❝ of my friend Dr Percival.”

Thus has the discovery been established of a new lithontriptic medicine, that is at once grateful to the palate, ftrengthening to the stomach, and falutary to the whole fyftem. Lime water often nauseates the patient, destroys his appetite, and creates the heart-burn. And the soap-ley is fo cauftic and acrimonious, that it can be taken only in the smallest quantity; frequently produces bloody urine, and aggravates the tortures it is intended to relieve. Both thefe remedies, alfo, require a very strict regimen of diet; and their qualities are liable to be changed either by acidity, or the fermentation of our food in the first paffages. But the mephitic water may be drunk in the largest quantity, without fatiety or inconvenience: It requires no reftrictions in diet, and its medicinal virtues will be undiminished in the ftomach or bowels.

As the vapour of chalk and oil of vitriol have been found fo efficacious in correcting the fanies, and abating the pain of foul ulcers, when externally applied, we may reasonably presume that the

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