FLATE XI.

St. Michael's Mount from the

Worth?

Etchd by J.Shure, for D Thomsons Annals. Published by RJ'aldrin, Paternoster Row, Oct.

bed. The whole northern base of the mount consists of clay slate. I could not determine either the direction or amount of its dip; but it seemed to lie much more horizontally than the clay slate at Merazion. It does not extend to any height up the mount. The upper part of the mount consists of granite. On the south side this granite continues down to the water's edge, and it continues to constitute the whole of the hill both on the east and west side for about 4ths of its whole extent. Then we come to the clay slate. On the east side, where the granite terminates, numerous veins of it run into the clay slate in different directions. I traced some of them for a length of 125 feet, and then lost them only because they ran under heaps of loose stones, which I was unable to remove. These veins vary in width from an inch or two to about a foot and a half; but their common width is above a foot. Sometimes they contain fragments of clay slate; sometimes they consist of felspar; but most commonly of perfect granite. I consider the descriptions which Mr. Playfair and Mr. Allan have given of them as correct.* No person who will be at the trouble to examine them can doubt that they are real veins, that they run from the granite into the clay slate, and therefore that the granite must have been deposited after the clay slate: but if there be any person not satisfied with the appearance of these veins, he has only to go to the west side of the mount, where he will find two beds of granite in the clay slate, and the position of these beds such as to indicate in the clearest manner that the great body of the granite had been deposited after the clay slate.

*

These facts put it beyond dispute that the granite of St. Michael's Mount is not primitive but transition granite. This is the conclusion that Mr. Allan ought to have drawn from his premises, and the conclusion that he would have drawn if he had given his reasoning powers fair play. He proved that the granite lay over the clay slate, and that it must have been deposited after the clay slate. He proved, likewise, that the clay slate is a transition rock. From all this it follows irresistibly that the granite likewise is a transition rock.

This is not the first time that granite has been observed as a transition rock. Von Buch observed it in a similar position in the neighbourhood of Christiana in Norway. In all probability, when transition rocks, which are so common in this country, come to be examined more carefully than they have hitherto been, granite will be frequently found among them. Why should it not, as well as clay slate, greenstone, and porphyry? (To be continued.)

The clay slate in the neighbourhood of the veins contains so much mica as to have the aspect of mica slate.

ARTICLE III.

On the Nature of Muriatic Acid. By Jacob Berzelius, M.D. F.R.S. Professor of Chemistry at Stockholm.

(Letter from Dr. Berzelius to Dr. A. Marcet.*)

DEAR SIR,

You ask of me an explanation of my ideas respecting muriatic acid, and the reasons that prevent me from adopting the new theory of Sir Humphry Davy respecting this substance. I shall in the first place state the difference between the old theory and that of Sir H. Davy, and then give my reasons for considering the old theory as the most accurate.

According to the old hypothesis, muriatic acid is composed of a combustible radicle still unknown, and of oxygen. Muriatic, like several other acids, cannot be obtained in a separate state. It does not seem capable of existing except in combination with some oxide or other. When combined with water, it constitutes common muriatic acid gas. In this compound the water constitutes a base for the acid, just as I have proved it to do in concentrated sulphuric and nitric acids, in effloresced oxalic acid, &c. The muriatic radicle is capable of combining with different doses of oxygen. I have proved that muriatic acid neutralized by a base contains exactly twice as much oxygen as the base with which it is saturated; that is to say (to employ the expression of Dalton), that the acid is composed of one atom of radicle and two atoms of oxygen. The other compounds formed consist of one atom of radicle combined with three, four, and six atoms of oxygen, constituting oxymuriatic gas (superoxidum muriatosum), euchlorine gas of Davy (superoxidum muriaticum), and hyperoxymuriatic acid (acidum oxymuriaticum). Muriatic is one of the most powerful acids, and possesses in a high degree the property of forming with salifiable oxides, both neutral salts and salts with excess of base.

According to the new hypothesis, oxymuriatic gas, in the present state of our knowledge, must be considered as an elementary body, though its great specific gravity, and the property which it has of crystallizing with water at a low temperature, leads one to conjecture that it is a compound, and even that it contains oxygen. The illustrious author of this hypothesis has given it the name of chlorine. Chlorine has the property of combining with an atom of oxygen; and the oxide thus produced

* Dr. Marcet, having been requested by Dr. Berzelius to publish this letter, in order to promote discussion, has complied with the request.

is called euchlorine. Chlorine combines likewise with an atom of hydrogen. The compound formed is muriatic acid. This acid is analogous to sulphureted hydrogen and tellureted hydrogen, and, like these two acids, it is decomposed by the greatest number of the saline bases, the oxygen of which combines with the hydrogen of the acid, and forms water, at the same time that the metallic radicle of the base unites with the chlorine. Muriatic acid parts with its hydrogen still more easily than the two above-mentioned acids, since it is decomposed by oxides which neither alter sulphureted nor tellureted hydrogen; by potash and soda, for example. On the other hand muriatic acid is neither decomposed by atmospheric air, nor oxygen gas, as happens to the compounds of hydrogen with sulphur and tellurium. What we have hitherto called muriate of potash and muriate of soda, is nothing but a compound of chlorine and the metallic radicles of these oxides. The only bases, which do not decompose muriatic acid, are ammonia, alumina, and in some measure also magnesia. The salts called hyperoxymuriates are combinations of euchlorine with the peroxides of the bases. Chlorine combines with all combustible bodies except carbon, and perhaps also boron, but it combines with the oxide of carbon. Such is an outline of each hypothesis. I shall in the first place examine the circumstances by which the illustrious author of the new hypothesis considered himself as obliged to abandon the old opinion. I shall afterwards state some facts which agree very well with the old hypothesis, but not with the new.

It has not escaped the sagacity of Davy that chlorine may contain oxygen; but having exposed salifiable bases to the action of oxymuriatic gas, he found that the quantity of oxygen evolved was exactly equal to that contained in the oxide employed. Hence he concluded that this oxygen could not be furnished by the oxymuriatic acid gas, but was derived from the oxide; the radicle of which, having a stronger affinity for chlorine than for oxygen, parted with its oxygen and united with the chlorine. Before the establishment of the doctrine of definite proportions in chemistry, the experiments just stated might certainly warrant a new conjecture respecting the nature of oxymuriatic gas; but at present it is established by that doctrine, that the oxymuriatic acid is composed of one atom of radicle and three atoms of oxygen; that it is capable of neutralizing a quantity of any base whatever, the oxygen in which amounts to half the oxygen in the acid; and that, of consequence, the quantity of oxygen disengaged from the oxymuriatic gas decomposed by a saline base is equal to that contained in the base by which it is decomposed. Hydrogen gas unites with oxymuriatic gas, and forms a muriate of water, without any excess either of water or muriatic acid. This experiment, being conformable to the old hypothesis,