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of the general results, and of the confequences deduced from them.

Fixed air, in the first place, reddens fome of the blue vege. table juices, fuch as infufions of litmus, cyanus, or corn flower, and a few others +. It is true, nevertheless, that fome other blue infufions, lefs fenfible tefts of acidity, that of violets in particular, refift its action upon them; because water, when even faturated with this vapour, contains the mephitic acid (as the Letter-writer denominates the acid of fixed air) in too diluted a state to produce a change of colour in them; but its acid quality, he obferves, may be fufficiently evinced by its action even upon thefe; for on previously changing their colour to a green, by the addition of an alcaline falt, the new colour produced by the alcali will be deftroyed, on impregnating the liquor with fixed air. By the fame procefs, the blue colour of the infufion of litmus, though rendered ftrongly alcaline, is changed to a red.

The teftimony of another fenfe is afterwards adduced, to prove the existence of an acid in fixed air. It is fhewn that a ftrong alcaline folution, on being impregnated with this fluid, gradually loses, during the courfe of the impregnation, the acrid and urinous tafte of the alcaline falt. It is at length completely neutralifed; and, on adding more fixed air, it acquires even a fubacid tafte.-From the Letter-writer's experiments it appears that an ounce of fixed air, or vapour of the mephitic acid, will neutralife between three and four grains of mild fixed alcali .

Mr. Bewly proceeds to fhew that the aforefaid acid is, in fact, the very fubftance denominated fixed air; or at leaft that this acid is effential to the conftituence of that fluid, and that it cannot be deprived of it without ceafing to be fixed air, and vanishing from our notice. A folution of a mild fixed alcali in water condenfes, as we have already obferved, a large quantity of fixed air, and is at the fame time completely neutralifed by it. At the fame time, likewife, the fixed air totally disappears, excepting the ufual refiduum; or if too much fixed air has been employed, the overplus retains its acid quality. Hence the Letter-writer concludes that the acid, by which the alcaline falt has been neutralifed, is not an extraneous principle cafually fufpended in an aerial vehicle; but that fixed air is this

+ Some of the Letter-writer's proofs of its acidity were originally given by him in different parts of our Review. See particularly our 44th volume, April 1771, p. 324, &c.

The Letter-writer might more fatisfactorily have determined the quantity of pure or fimple alcaline falt capable of being neutralifed by a given quantity of fixed air, by employing the caustic alcali; which, according to him, is the only true alcaline falt: all the mild alcalis being already neutralifed, in part, by the mephitic acid.

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very acid, in the ftate of a permanent vapour, condenfable, to a limited degree, in water, but capable of being ftill more copiously attracted and condenfed by alcaline falts, and calcined, or pure, calcareous earths. Thefe earths, as he elsewhere fhews, even in a mild or compound ftate, that is combined with a large portion of fixed air, may be diffolved in water, by means of an additional quantity of the mephitic acid.

In Number VI. or the laft of thefe three letters, the Author's philofophical Correfpondent answers certain objections to a material part of his doctrine, contained in his two preceding letters, drawn from fome late publications of Sig. Landriani and Fontana, communicated to him by the Author while this work was at the prefs. It is afferted, particularly by Signor Landriani, that the acid which has been obferved in fixed air is a principle extrinfical or adventitious to it, and which it acquires from the particular acid employed in the ufual procelles for generating it. According to the Italian philofopher, the figns of acidity manifefted in fixed air obtained from chalk, for inftance, by means of the vitriolic, nitrous, vegetable, or other acids, are wholly owing to a part of thefe very acids, refpectively volatilifed and diffolved in the fixed air produced in the particular procefs where they are employed. Paffing over the other proofs which the Letter-writer produces, to fhew that the acid in fixed air is not the attenuated vapour of the particular acid occafionally employed for the expulfion of it from chalk or alcaline falts; we fhall wholly confine ourselves to that drawn from his 20th experiment, which he offers as alone fufficient to decide the queftion, and to prove the natural or inberent acidity of this fluid.

On fubjecting a fmall quantity of pure magnefia to a moderate red heat, in a vial fitted with a bent tube, he expelled from it, by the fole action of the fire upon it, a confiderable quantity of fixed air; which, by every teft to which it was expofed, appeared to be as pure, and as acid, as that which is obtained, from the fame or other fubftances, by employing any of the acid fpirits in the ufual manner, It reddened the blue vegetable infufions, made excellent Pyrmont water, and neu tralifed folutions of alcaline falts, as readily and effectually, as the fixed air procured from mild alcalis, calcareous earths, or magnefia by oil of vitriol. Tracing the fixed air, thus obtained, from its origin, he fhews that the magnefia acquires the whole of that acid principle from the mild alcali employed in precipitating the magnefia from the solution of Epsom falt. For, making a rough effimate of the large quantity of mephitic acid obtained in this experiment, he fhews that the acid quality of the fixed air cannot be derived from the vitriolic acid in the Epfom falt; the whole of which, in the procefs for procuring magnefia

magnesia, leaves the earth, on the addition of the alcali, and evidently unites with the alcali in the form of vitriolated tartar; having previously expelled the mephitic acid from it, which inftantly combines with the magnefia:-fo that the experiment, according to him, is as fatisfactory as if he had driven the fixed air, by means of the fire, directly from the alcaline falt itself, As it cannot however be thus expelled, a substance is employed to which it had been previously transferred, and from which it may be easily driven, by the fole application of a very moderate

red heat.

Towards the end of this third letter Mr. Bewly recommends to the notice and trial of the faculty the method indicated in thefe papers, of impregnating water, through the medium of alcaline falts, with much larger quantities of fixed air, or the mephitic acid, than fimple water is capable of receiving; as well as the new set of neutral falts which may be obtained by faturating aqueous folutions of fixed or volatile alcalis with this acid. By this means, undoubtedly, very large quantities of fixed air may be introduced into the fyftem, where it may reafonably be expected to produce the most falutary effects; particularly in difeafes of a putrid tendency; whether the neutral mephitic falt be capable of being wholly, or in part, decompounded, or not, in the ftomach and prime via:-a point which the Letter-writer had not yet had an opportunity to afcertain.

In Number II. of this Appendix Dr. Percival, in a letter to the Author, gives an account of an interefting discovery relative to the power which water acquires, on being impregnated with fixed air, of diffolving ftones or calculous concretions in the urinary and gall bladders. The lithontriptic quality communicated to water by calcareous earths and alcaline falts, deprived of their fixed air, is well known. From the experi ments here related it appears that, by a contrary procedure, or by impregnating water with fixed air, the water likewife acquires the property of diffolving the human calculus. A cafe is mentioned alfo from which it follows that the impregnated, or mephitic, water preferves this quality even in its paffage through the body; fo as to communicate it to the urine of thofe who drink it, which is thereby rendered a powerful folvent of calculi that are immerfed in it. Dr. Saunders has made experi ments of a fimilar kind, the refults of which are faid to be perfectly conformable to thofe of Dr. Percival. These experiments promife to furnish us with a new lithontriptic medicine, perhaps more efficacious, and undoubtedly more fafe and grateful than the cauftic alcali; the ufe of which, at leaft in certain habits, may be productive of very difagreeable confequences.

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In Number III. Dr. Dobson of Liverpool relates four cafes, felected from feveral others, which he proposes hereafter to publifh, of patients affected with putrid diforders; the cure of which appears evidently to have been produced by the adminiftration of fixed air. In all of them, this antiseptic fluid was introduced into the body by frequent and regular exhibitions of a fcruple of alcaline falt, diffolved in a fmall quantity of wa ter, and fwallowed during the effervescence excited on the addition of half an ounce of juice of lemons. In the fourth cafe Dr. Dobson relates the happy effects produced by fixed air thus administered, in the fecond fever of the fmall-pox, attended with fymptoms of the moft alarming nature.

Number IV. contains a fingular medical cafe related by Dr. John Warren, in which, after taking notice of the great fuccefs which has attended his adminiftration of fixed air in putrid diseases, he gives a particular account of the recovery of a pa tient finking under an almoft univerfal putridity of the humours; who was foon relieved, and afterwards perfectly cured, at a time when every breath he drew feemed to be his laft,' by the injection of near two quarts of fixed air every three or four hours, accompanied with the exhibition of fome bolufes of the bark, when his ftomach could bear them. We fhould obferve however that the bark, in the fame form, and in the quantity of two fcruples for a dofe, together with 30 drops of elixir of vitriol, had before been daily administered, every two hours, without effect. The putrid fymptoms increased under this course; but vifibly began to abate within eighteen hours after the commencement of the exhibition of glyfters of fixed air.

The laft article that remains to be noticed in this Appendix, is a letter from Mr. Magellan to the Author; in which the Writer relates fome experiments which confirm Dr. Prieftley's doctrine concerning the nature of atmospherical air, as explained in our preceding Article. Among other particulars, it appears from these experiments that, after all the dephlogifticated or pure air has been expelled by fire from a mixture of spirit of nitre with red lead, chalk, or other dephlogisticated earths, the remaining mafs, put into tincture of turnefole, exhibits no fign of acidity, or marks of the prefence of the nitrous acid; the blue colour of the tincture remaining perfectly unchanged. The nitrous acid therefore, Mr. Magellan obferves, muft of course have been all expelled from the mafs, together with a part of the earth, under the modification or form of the pureft refpirable air. We fcarce need to add that, on repeatedly adding fresh nitrous acid to the fame refiduum, á fresh production of air, or converfion of the acid and earth into air, takes place till all the earthy matter is exhausted and dif

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appears; nor would the residua, if examined in the fame manner each time, after each expulfion of the air, exhibit any figns of their retaining any fenfible portion of the nitrous acid.

Though we have extended our account of this work to two Articles, we have been obliged to pafs over numerous particulars, of a very interesting nature, without notice. Experimental philofophy has, perhaps, never been enriched, in fo fhort a space of time, and by a fingle individual, with fo great a number of new and important facts, as are contained in the present publication and that which preceded it. The bounds of natural knowledge will, we hope, continue to be enlarged by the genius and investigating fpirit of the Author; as well as by the la bours of the many other philofophical inquirers throughout Europe, who have been incited by his discoveries to direct their attention to this part of fcience, and to prosecute the exten❤ fion of it, by fpeculating and experimenting on the numerous and important data with which he has furnished them.

ART. II. A Treatise on the Nervous Sciatica, or Nervous Hip Gout. By Dominicus Cotunnius, Phil. and M. D. 8vo. 3s. Wilkie.

1775

THE original of this treatife, of which Baron Van Swieten

makes honourable mention, particularly in the laft volume of his Commentaries on Boerhaave's Aphorifms, was publifhed feveral years ago, we believe at Naples, from whence the Author dates his dedication of it to the Governors of the Hospital of Incurables in that city, of which he was phyfician. The method propofed in it, for the cure of a moft obftinate and painful diforder, is founded on phyfiological observations, principally deduced from an anatomical confideration of the parts immediately affected by the difeafe; and the juftice of the Author's hypothefis feems to be fully ascertained by the fuccefs attending the method of cure founded upon it. A fhort account of the Author's rationale of the disease, and of the fimple method of cure established upon it, will not be unacceptable to many of our Readers.

The Author divides the nervous fciatica into two fpecies, under the denominations of the anterior and pofterior nervous fciatica. Treating of the latter particularly, and attending to its peculiar symptoms, he endeavours to fhew that its feat is in the ischiadic nerve; and its cause, an acrid matter, which pervading the vagine of this nerve and its branches, and even the nervous flamina themselves, greatly irritates those very fenfible parts of the human frame, and produces a moft excruciating and lasting pain.

That an affection of the ifchiadic nerve is the true cause of this disease, I am,' fays the Author, very well fatisfied,

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