decrease; that about two thousand square leagues had disappeared, and that land was again visible. We learn too, from Copenhagen, that intelligence was there received, in August last, that the ice which from time immemorial had interrupted the communication with East Greenland, had vanished. It is further probable that the process of thawing is going on to a yet greater extent further north, for the ice islands met with in the Atlantic are almost entirely conveyed thither by the southern current which constantly runs in Davis's Streight, and they were last year much more numerous than usual-many, and large ones, were even seen in 42° south latitude in the summer and autumn of 1816, and we think it by no means improbable that the extreme chillness of that season may in great measure be referred to these visitors from the north; for the southwest winds could not but have been chilled by passing over these frozen masses. We think there is one other remark worth recording, though we would not be understood to lay any stress upon its reference to, or connexion with, the more propitious state of weather that we now look for it is, that at the very time we heard of the thawing of the northern ice, and a consequent probability of the return of those regions to their former state, the westward variation of the magnetic needle began to decline, and it has already retrograded some degrees towards due north.

ART. XII. On the Fluo-Silicic and Chloric Acids. In a Letter to the Editor from JAMES LOWE WHEELER, Esq.

DEAR SIR,

WHILE perusing the account of the Fluo-silicic acid, which

is contained in the second volume of the last edition of Dr. Thomson's System of Chymistry, I observed, that this acid was said to be capable of decomposing the sulphate, nitrate, muriate, and consequently all the salts of potash.

These remarkable properties, which were ascribed to the fluo-silicic acid, led me to put them to the test of experiment,

when I had the pleasure of finding the statement perfectly correct.

It thus appeared that the fluo-silicic acid is a very useful precipitant of potash, when, either in a free or combined state; and, since it was shown to be capable, in the moist way, of taking potash even from sulphuric acid, a fortiori, it would also decompose the chlorate of potash, and thus afford a ready means of separating the acid of that salt, the process for obtaining which was before both tedious and expensive.

My next object was, of course, to obtain the fluo-silicic acid in quantities: the requisite mixture of powdered fluate of lime, fine sand, and sulphuric acid was therefore put into a flask, and by means of a glass tube, twice bent at right angles, the fluo-silicic acid gas was passed into distilled water.

But in this mode of operating, the orifice of the tube was quickly choaked by an abundant deposition of silica, and the gas soon ceased to pass through the water.

As this method of proceeding was not attended with success, in all subsequent operations, instead of immersing the tube, conveying. the acid gas, into the water, I merely brought it within half an inch of the surface of the liquid; when the gas, from its great weight, fell down upon the water and was absorbed in large quantities; while its excess of silica was precipitated in abundance.

Having thus obtained a strong solution of fluo-silicic acid in water, it was then my object to procure it of a definite strength, and to ascertain its equivalent by saturating with it a given quantity of the carbonate of potash, obtained by heating the bi-carbonate of that alkali in a platinum crucible; but these previous steps were unnecessary, as I afterwards found, that by means of a solution of fluo-silicic acid of unknown strength, the chloric acid could be detached from its combination with potash, and obtained pure by the following process. Mix a warm solution of the chlorate of potash, with one of fluo-silicic acid; heat the mixture moderately for a few minutes, and, to ensure the perfect decomposition of the salt, add a slight excess of the acid, which may be ascertained by its property of being wholly deprived of its silica, by an

aqueous solution of ammonia. By this means the chlorate of potash will be entirely decomposed; the mixture will become slightly turbid, and fluo-silicate of potash will be precipitated abundantly in the form of a gelatinous mass. The superna

tant liquid will then contain nothing but chloric acid, contaminated with a small quantity of fluo-silicic acid; it is to be filtered, and the whole of the chloric and fluo-silicic acids are then to be neutralized by carbonate of barytes, and the chlorate of that earth, after having been obtained in crystals by filtering and evaporating, the solution is to be redissolved in a small quantity of water, and decomposed by the cautious addition of sulphuric acid, in the manner originally recommended by M. Gay Lussac. It is unnecessary to expatiate on the importance of chloric acid; the fluo-silicic will perhaps also become an useful instrument of analysis.

Yours, &c.

JAMES LOWE WHEELER.

St. Bartholomew's Hospital, 11th December.

ART. XIII.

Table exhibiting the average Quantity of Spirit in different Kinds of Wine. By W. T. BRANDE, Esq. Sec. R. S. &c.

SINCE the publication of the researches upon the state of

spirit in fermented liquors, contained in the Philosophical Transactions for the years 1811 and 1813, I have through the kindness of different friends had ample opportunities of extending my experiments, and to my former list of wines, already copious, a few additions have been made, of which I have from time to time given notice, and which are put down in the following table. It does not seem necessary in this place to allude to the experimental details, nor to notice the precautions required in conducting the distillations, as these are fully given in the Papers above noticed: I have therefore omitted the column which will be found in the Philosophical Transactions (1811, page 345.) showing the specific gravity of the distilled liquor, upon which the calculations are founded.

ART. XIV. Experiments to determine the Constitution of liquid Nitric Acid, and the Law of Progression followed in its Densities, at successive Terms of Dilution. By ANDREW URE, M.D., Professor of the Glasgow Institution.

THOUGH nitric acid has been employed for nearly 800 years in the most important chymical operations, and though its general composition was clearly demonstrated by the Hon. Mr. Cavendish, in the very dawn of pneumatic chymistry, yet the exact proportion of its two constituents, azote and oxygen, is a problem which seems hitherto to have baffled the best directed efforts of modern science. M. Gay Lussac states, as its