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This last process furnishes an easy test by which a person may at once discover whether quicksilver be pure or not: for if it be impure, the water becomes opaque almost immediately after the agitation commençes; which is by no means the case when pure quicksilver is employed.
The rationale of these processes, at least with respect to the principal circumftances attending them, is pretty evident. They Thew in a clear and singular manner the great power of the air in reducing certain metals into the state of a calx, even in the common temperature of the atmosphere. By their previous difsolution in the mercury, they are in fact brought into a fluid state, or, as it were, into a state of fusion; and by the agitation they are broke into extremely small globules : so that a large quantity of surface, which is every instant changing, is successively exposed to the action of the air included in the vial witb them. Under these circumstances they readily part with their phlogiston to the air, and receive from it, in return, that portion of fixed air, or other principles, to which they, in part, owe their calciform state; and they accordingly acquire, just as happens in calcinations by fire, a weight greater than that of the metal originally employed; as the Author found, on weighing the imperfect calces (for they are far from being pure) produced in this mode of experimenting.
It is much more difficult to give a satisfactory explanation of the effects related in the succeeding set of experiments, made with pure mercury. On its being agitated in pure water, without access of air, in a vial, one-fourth of which was occupied by the quicksilver, and the remaining space filled up with water; the water becomes opaque, by means of innumerable particles of a black matter fufpended in it. Suffering this matter to subfide, and pouring off the clear water, the fame phenomena occur, on agitating the mercury with fresh water.
If the water that had been poured off is again used with the same mercury, the black powder is produced much more readily, or in greater quantity, than when it was employed the first tiine, or than when pure water is used.
The most singular circumstance relating to the black powder, into which mercury is thus converted, by agitating it with water, without the presence of air, is, that on the total evaporation of the water, the powder is, in an instant, converted into running mercury. The turbid water likewise is rendered tranfparent, on heating it: nor can this powder be produced, if hot water is employed in the experiment.
This black mercurial powder differs,' with respect to its state or constitution, in a very effential circumstance, from that above, mentioned, obtained in the agitation of impure mercury. This last required air, and a repeated renovation of air, for its pro
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duction, and for the reducing it to the state of a calx : whereas the former is not only produced without the intervention of air, but on being immediately, or directly, exposed to it, on its being freed from moisture, it instantly assumes its former metallic state. On viewing a little of the moist powder with a microscope, the change is almost instantaneous, when it becomes dry. In this small quantity, the particles of the black powder are instantly converted into white and polished globules,
Further, in the former process, the lead appears evidently to have loft a great part of its phlogiston. On the contrary, in the black mercurial powder, the quicksilver seems to have assumed that form, in consequence of its having acquired phlogiston ; and that, too, in a greater proportion than is necessary to its metallic state : though it is certainly difficult to determine whence it has acquired it.-- That it has, however, got an overcharge of that principle, seems to be fully ascertained by the following experiment:
' I took,' says the Author, “a glass tube, about 18 inches long, and half an inch wide, and pouring into it a quantity of the water and black powder of mercury, turned it every way till it had got a black coating in all places. I then inverted it, and placed it in a cup of water near the fire; but not so near as to convert the water within the tube into steam, and thereby expel too much of the air. In this fituation I perceived, after some time, that the quicksilver was revivified; all the tube to which the heat had reached having now got a white coating, and having the appearance of a looking-glass. I then examined the air in the inside of the tube, and found it to be very
fufficiently phlogisticated. For one measure of it, and one of nitrous air, occupied the space of 1.66 measures, notwithstanding a considerable part of the tube had not been so much heated as to have had all the mercury on it revivified.'--We should observe that it appears, from a preceding experiment, that fimilar proportions of common and nitrous air occupied the space only of 1.27 meafures ; so that the air in the tube must have been considerably phlogisticated, on the black powder's returning ro a metallic state. The Author accordingly is led to confider this powder as mercury super-phlogisticated, or which has acquired' more phlogiston than is necessary to its state of white funning niercury.
It is difficult to conceive whence the mercury can have acquired this phlogiston, from mere agitation in the purest water. This difficulty is so great, that, had not the Author shewn that the air was phlogisticated, on the reduction of this powder into mercury, we should have supposed either that a part of the quicktilver had acquired this blackness merely by the extreme fubdivision of some of its particles; or that the powder was a
new and fingular combination of mercury and water, effected by bringing the extremely comminuted particles into which each of them is divided by the agitation, within the sphere of each other's attraction; so as to cause both of them to lose their cha-, racter or form of a fluid, and to constitute, by their combination, a solid and powdery substance. It might be further alleged, that this union is destroyed by the evaporation of the water, in consequence of its superior affinity to air, or by the operation of heat; and that when the watery particles thus quit the mercury, the particles of the latter naturally and instantly unite together, and reassume their metallic state.- But the exa periment above recited will not countenance these speculations. The water, too, is said to acquire a peculiar smell and taste, not easy to be described; and to leave, on evaporation, a particular kind of matter.
One of the Author's conjectures on this subject is, that the mercury acquires this phlogiston from the water.
He does not dissemble, however, the great strength of an objection to this hypothefis, furnished by an observation which we have already recited ;-that a portion of water is so far from having its power exhausted, or even diminiihed, on having been repeatedly employed in this process; that, on the contrary, when it has been previously used in the experiment, it has a much quicker and greater effect, than when it was employed for the first time. The Author accordingly proposes other conjectures, on which, however, we cannot with propriety dwell; unless we had room to recite his many other curious experiments on this subject : as they contain circumstances, the knowledge of which is absolutely necessary to enable the Reader to form a judgment concerning it.
We shall'take an early opportunity of extracting some further interesting particulars from this work.
ART. VII. The Injured Islanders; or, ihe Influence of Art upon the
Flappiness of Nature. 410. Murray. 1779 T.
HE heroic Epistle is supposed to have been invented by
Ovid. It is singular that a species of composition, so beautiful, and, at the same time, so capable of variety, should have been so little cultivated by succeeding writers. Of all his cotemporaries (Sabinus excepted, whose works, unfortunately, are loft) Propertius is the only one, whom we know of, that hath followed his example. His Epistle from Arethufa to Lycotas abounds with many exquisite strokes of passion and tenderness. It is to be lamented that this is the only poem of the kind that he has left us. Among our own countrymen his imitators have been few; and of those few Mr. Pope is the only one who has hitherto been eminently successful. It must be confeffed, indeed, that Drayton, who first revived this fpecies of poetry among us, has left some pieces, that, considering the times in which be wrote, have considerable merit. Drayton was a man of genius, and by no means deficient in judgment; but failing in those powers which the dramatic nature of his subject demanded from him, his England's heroical Episiles want that warmth of colouring so effential to a true representation of the characters be affumes.
In modern times this mode of writing has been adopted, and in fome instances not unsuccessfully, as the vehicle of satire and wit, for which, indeed, it seems not ill adapted. In the present instance, however, it is employed according to the original purpose intended by its inventor. The poem before us is supposed to be written by Queen Oberea to Capt. Wallis. It is founded, as the Author informs us in his preface, on the remembrance of their mutual affection - a sense of her subsequent misfortunes-and a patriotic feeling for the fate of her country. The just and liberal sentiments with which this performance abounds, do great honour to the Author's feelings as a man; and they are expressed in language that will not injure his re. putation as a poet. The subject opens with the following lines :
Remov'd from power, from all its pomp retired,
After explaining whence this indifference to external objects arises, the proceeds,
To thee alone, on Fancy's rapid wing,
Late, as along the verdure-vested lawn
No friend, no fondness to reward my care. The above lines are natural, and adapted to her supposed fie tuation. Nor is her character ill supported in the following passages :
Canst thou forget! can Memory e'er betray
my grief, and friendly to my fears,