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ment of that useful inftrument, the blow-pipe; with which innumerable experiments may be made in chemistry and mineralogy, with very little trouble, and in a very short space of time; to say nothing of the intense degree of heat, which the operator can thus procure from the fame of a candle, in a few seconds.

The Author, after having described the instrument, and the proper management of it, divides an ineral bodies into four classes, viz. Salts, earths, inflammable matters, and metals; and then proceeds to treat methodically of the individuals of each class, and of the effects of the flame, affifted with the proper Aluxes, on each of them.

VII. Traité de l'Elasticité de l'Eau, &c. A Treatise on the Elasticity of Water, and other Fluids, &c. : together with the Description of a Machine constructed to prove the Compreffibility of Fluids, &c. By E. A. G. Zimmermann, &c. Amfterdam. Rey.

In this publication the difficult and celebrated question, concerning the compressibility of water, appears to be satisfactorily decided, in favour of the affirmative; by means of a machine lately invented by a M. Kbich, a German philosopher; and by which the compressibility of water, and some other Auids, is not only proved, but the quantity of the compression seems to be ascertained with accuracy.

The different attempts that have been made to solve this difo ficult question are first related by the Author, in a chronological order, and in a very particular and satisfactory manner; with judicious observations on each. The principal experiments that have been made relative to this subject, which are here described, and occasionally illustrated with plates, are those of -- Lord Bacon, Mr. Boyle, Du Hamel, The Florentine Academicians, Hamberger, Muschenbroeck, Nollet, Hollam, Canton, and Itill more lately, by M. de Herbert, whose apparatus is well imagined, and proves the compreslibility of water and some other fluids : but it is so far imperfect, as the fluids examined in it were exposed only to the pressure of a column of mercury of the height of four feet, By means of that pressure, water was found to be compressed 1-4358th part of its whole bulk, in the temperature of 14 degrees of Reaumur's thermometer.

The last and most simple machine, here very particularly described, is that of M. Abich; whom the Author affifted in the experiments made with it, between the years 1777 and 1779. Some idea of its nature and effects may be formed from the following short account of it:

• See the Philos. Trans. Vol. LII. Part II. Art. 103, or our account of the Article.

M. Abich

· M. Abich first attempted the compression of water in a turket barrel, by means of a piston forced into it, and which was exadly ficted to its cavity; but, by means of the great force employed, the barrel, which was only a line thick, burst. He then procured a stronger cylinder, formed of brass, the sides of which were three quarters of an inch thick. Here he found that the included water sensibly yielded to the compreffing force, which was exerted by a piston, put in motion by means of a screw. On a repetition of the experiment, however, several drops of water appeared on the outside of the cylinder; and it was found that they had been forced through small fiffures which the water had made in the metal.

M. Abich then constructed a cylinder, the fides of which were nearly an inch and a quarter thick; and which was found to refift effectually the immense power employed in compresling the water, or the other fluids, with which it was successively filled. The different degrees of comprellion were produced by means either of a screw, or of a long lever, to which different weights were successively appended ; and the quantity of the compresion was ascertained by the contraction of the water in bulk, as indicated by the delcent of the piston.

As this last mentioned effect however might be suspected to have been, in part at least, produced by the distension of the metal cylinder, which might be supposed to yield to the very great power employed in these experiments; an addition was made to the apparatus, which shewed, in a very satisfactory manner, that no change of dimensions in the cylinder had taken place, in consequence of the great force employed.

It appears from one of these experiments, in which the greatest effects were produced, that 261 cubic inches of water visibly loft by pressure no less than i cubic inch and }; so that the compreffon sustained by the water, in this case, produced a diminution in the bulk of the whole mass, nearly equal to the 1-24th part. From calculations it appears, that well water, subjected to this compressing force, must have had its specific gravity so much increased, as to acquire a density even greater than that of fea water.

After giving a particular account of the experiments made by means of this apparatus with well water, water saturated with sea salt, milk, brandy, &c. the Author proceeds to consider the doubts that may yet remain respecting the results. These prin. cipally relate to the pores or cavities which may exist in the internal surface of the cylinder; the compression or yielding of the leathers belonging to the piston; and the air contained in the water, or other fluids which have been examined. Of these doubts the last seems to be the most worthy of attention : but it appears from the experiments here related, that water, from Rev. Feb. 1783

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the two other principles, is apparent, he observes, from hence,-that the hepatic air cannot be decomposed, except by substances that greedily attract phlogiston. Thus the concentrated nitrous acid exerts this quality, even in water impregnated with hepatic air ; as does nitrous air, though already loaded with phlogiston. Thus, on the separation of the phlogiston, this compound, confisting of three principles, is destroyed; for the other two, fule phur and heat, without phlogiston, do not exhibit any hepatic odour.

But M. Bergman endeavours, to prove the truth of this hypothefis fynthetically; that is, by shewing that these three principles are to be found in the Pseudogalena. He next inquires whether they exist there in a combined state, that is, in the form of hepatic air, in the same manner as fixed air exists in marble ; or whether the hepatic air is then only formed, when the acid is applied. In consequence of the results of certain experiments, he concludes, that it is generated at the time of the experiment. The acid lets loose the latent heat, and the phlogiston, of the ore : these two principles attack the fulphur contained in it; and, combining with it, conftitute a permanently elaftic fluid.

A fingularity respecting a particular species of the P feudogelena (that of Scharfenburg) deserves particular notice. That ore treated alone, with heat, in a close veffel, exhibits the very fame kind of finty sublimate, or fluor crut, as is given by the sparty fluor, or Derbyshire Spar, when treated with oil of vitriol. “The Iparry acid, therefore, says the Author, pre-exifts in this ore, but probably combined with a metallic basis ;' so that it can be expelled from it by fire alone, and, united with an aqueous vapour, can generate the fuor cruft.'

DISSERTATION XXIII. On Metallic Precipitates. That man must have been greatly astonished, as the Author in part observes, who first saw lo ponderous and opaque a body as a metal, gradually, and at length totally, disappear in a fluid;

the liquor which contained it still appearing perfectly limpid and homogenous. Nor would his furprise be less, when, merely on the affufion of another transparent liquor, he perceived the metal suddenly to re-appear in its former ponderous and opaque itate, and soon fall down to the bottom of the vessel, in the form of what is called a precipitate. These two operations, solution and precipitation, are the two most important in the whole practice oi chemistry; and are most satisfactorily, though compendiously, treated in this differtation. We must content ourselves with only extradling a particular or two from it.

No metal,' the Author says, 'can be diff»lved by an acid, wbile it retains the whole of that quantity of phlogiston, which is essential to its metallic fate? Tnat puit of its infiammable principle, which is the obitacle to this process, muft therefore neceffarily be re

mured, moved, before any solution can take place. The different acids, by their strong attraction of this principle, produce the solution of the various metals, in proportion to the strength with which they respectively attract it, and, we may add, to the Atrength with which each metal retains it.

Among the acids, the nitrous attracts phlogiston the most powerfully; and can even rob the vitriolic acid of it. If any one doubts this, says the Author, let him expose sulphur to the action of the concentrated nitrous acid, in a gentle boiling heat, and he will find the fulphur at length robbed of all its phlogiston, and the vitriolic acid left naked.

The marine acid, as we have already observed, contains phlogifton as a proximate principle; but when it has been robbed of it, or dephlogisticated (by manganese or otherwise), it readily attacks every one of the metals, in consequence of the avidity with which it is disposed to recover its phlogiston. Gold and platina, which retain their phlogifton fo ftronly, and on which it could not before act, yield readily to its power, in its dephlo. gifticated state.

In this Differtation, M. Bergman boldly attempts to loose that most intricate Gordian knot--the genesis of all the aeriform fluids. But those who do not fully adope the peculiar theory of M. Scheele, on air and fire, will think perhaps that, in this attempt, he has, at least occasionally, practised the ancient man. æuvre of Alexander. This part of the essay, however, highly merits an attentive perusal. Dissertation XXIV. On the Esaying of Metallic Ores, in the

Humid Way. The many difficulties and disadvantages attending the essaying of metallic ores in the dry way, or by fire, have induced the Author to form a regular system, comprehending the various methods by which the same object may be still more easily and accurately obtained, in the humid way, or by solution, precipitation, &c. He proceeds regularly through the ores of all the metals and semi-metals, in a compendious but inftru&tive manner. • We shall only extract from this dissertation a piece of curious information respecting one of the ores of lead (plumbum calciforme) which has been discovered by M. Gahn to contain the acid of phosphorus. When the lead has been precipitated, from a folution of the ore in nitrous acid, by means of the vicriolic acid, the remaining liquor, on evaporation, leaves a true acid of phosphorus behind it. DISSERTATION XXV. and Last. On the Blowpipe, and its Use

in the Examination of Bodies, particularly Mineral Substances.

This dissertation, which is accompanied with a plate, contains a regular series of instructions with respect to the manage

ment of that useful inftrument, the blow-pipe; with which innumerable experiments may be made in chemistry and mineralogy, with very little trouble, and in a very short space of time; to say nothing of the intense degree of heat, which the operator can thus procure from the fame of a candle, in a few seconds.

The Author, after having described the inftrument, and the proper management of it, divides nineral bodies into four classes, viz. Salts, earths, inflammable matters, and metals ; and then proceeds to treat methodically of the individuals of each class, and of the effects of the fame, affifted with the proper fluxes, on each of them.

VII. Traité de l'Elasticité de l'Eau, &c. A Treatise on the Elasticity of Water, and other Fluids, &c. : together with the Description of a Machine constructed to prove the Compreffibi. lity of Fluids, &c. By E. A. G. Zimmermann, &c. Amfterdam. Rey.

In this publication the difficult and celebrated queftion, concerning the compressibility of water, appears to be satisfactorily decided, in favour of the affirmative; by means of a machine lately invented by a M. Abich, a German philosopher ; and by which the compreffibility of water, and some other Auids, is not only proved, but the quantity of the compression seems to be ascertained with accuracy.

The different attempts that have been made to solve this difficult question are first related by the Author, in a chronological order, and in a very particular and satisfactory manner; with judicious observations on each. The principal experiments that have been made relative to this subject, which are here described, and occasionally illustrated with plates, are those of -- Lord Bacon, Mr. Boyle, Du Hamel, The Florentine Academicians, Hamberger, Muschenbroeck, Nollet, Hollam, Canton, and still more lately, by M. de Herbert, whose apparatus is well imagined, and proves the compreffibility of water and some other fluids : but it is so far imperfect, as the fluids examined in it were exposed only to the pressure of a column of mercury of the height of four feet, By means of that pressure, water was found to be compressed 1-4358th part of its whole bulk, in the temperature of 14 degrees of Reaumur's thermometer.

The last and most fimple machine, here very particularly described, is that of M. Abich; whom the Author afifted in the 'experiments made with it, between the years 1777 and 1779. Some idea of its nature and effects may be formed from the following short account of it:

• See the Philos. Trans. Vol. LII. Part II. Art. 103, or our account of the Article.

M. Abich

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