scribed: indeed, no precise or just idea can be formed without seeing the stone itself.

The dimensions of my specimen are as follows: It is 17 inches broad, 12 high, and seven inches thick at its base: the side which I have got cut and polished presents 15 or 16 of these globules, among which we may remark several that are enchased as it were into each other.

After spending a considerable time on the spot where I found this specimen, I proceeded towards Liamone on the gulf of Valinco.

Having arrived at the village of Olmetto on this gulf, the place pointed out to me as containing the orbicular granite, I proceeded to Taravo. I dug up the makis covering a part of the hillock on which Stazzona is situated, and minutely examined every corner. I sounded the small lake in the neighbourhood: I visited the sea-shore: I also sounded the river, and explored it in various points by means of divers I even followed its course upon the two banks for more than a league and a half: and finding nothing by these means, I formed the resolution of exploring 45 miles of ground beyond Stazzona.

:

I endeavoured to assure myself of the composition of the granites lying upon the heights surrounding the great valley of Taravo: I attacked every rock I saw, and found some specimens the composition of which resembled the granite in question.

After having pursued my researches still further, I entered the bed of the Taravo, and traversed the two banks for more than two leagues at the moment when I was redoubling my efforts to finish my investigation, I was obliged to desist on account of the rain and snow, it being now December.

I collected the various specimens of rocks which I procured at Valinco: and after having made a comparative examination of them with the orbicular granite, I ascertained that in some of these specimens there were hornblend and feldspar, but not in the same order, nor in the same arrangement: nevertheless, I think we may infer from these speci

mens,

mens, that by finishing the object of the visit I paid to the two banks of the torrent, we shall perhaps succeed in discovering the primordial masses of the beautiful orbicular granite of which a small partial mass only has been hitherto dicovered: the angles of it were rounded, and it was found isolated upon the beach of Taravo, half a league from the sea, in the gulf of Valinco.

From the information I procured on this occasion, I think I proved to a certainty that the small mass of this granite, already known, comes from no place except Corsica; for you know that several naturalists have formed various conjectures upon the subject.

In the course of this tedious journey, I had also an opportunity of discovering an ore of iron, the stratum of which is half a league in length.

After having passed the river Oposata, in order to arrive at Calvy, in a plain above the village of Calenzana, to the eastward of Galeria, I found a stratum of iron ore, placed horizontally in a yellow earth, which at times disappears throughout the whole length of the ore, and the mineral of which is presented in three different views. At first it appears under the character of scaly iron, arranged in thin layers, mixed with a yellowish ochrey earth; afterwards it appears as a heavy blackish iron, compact, and almost entirely disengaged from every heterogeneous substance; and under a third aspect, in elongated spheroids from four to five inches in diameter, exfoliating at its surface, and compressed at the two sides: this gives it angles at intervals; and the sandy character and composition of it made me denominate it arenaceous iron: and I procured the necessary specimens for the experiments I intended to try upon it.

Having ascertained from these trials that this ore was very productive, I transmitted to the council of mines several specimens of the above stratum, begging them to publish the result of their assays.

LXVI. On the Identity of Silex and Oxygen. By Mr. HUME, of Long-Acre, London.

SIR,

AMONG

[Continued from p. 280.]

To Mr. Tilloch.

MONG these promiscuous observations, it would be unpardonable to omit iron, which is one of the more constant associates of silex. These two ingredients seem to be almost inseparable companions, especially in every thing of a primeval nature; for, in all original districts, mountains, rocks, and soils, and in every native compound of any consequence and extent, whatever the aspect, situation and contents may be, these two elementary bodies are sure to present themselves, and, I may add, are always united; for, though the silex may be elicited from the mineral in its simple form, the metal, on the contrary, is always oxidized.

So universally is this metal dispersed through the works of nature, that very few instances occur in which it is totally absent; its ubiquity is truly proverbial, and is exceeded by nothing, if we except silex or oxygen; indeed it pervades almost every solid substance, and even animal and vegetable bodies are seldom exempt from its influence, but often exhibit iron evidently as a constituent in their system. Hence, the history of iron becomes a most interesting subject to the physiologist, and, if we add its wonderful property of magnetism, it seems to be one of the most fertile for the ima gination of every philosopher. As this metal is never discovered in the pure state, but is more frequently conjoined with oxygen than any other body; and as this process seems to have been effected in the immediate vicinity of silex, I see no particular or unreasonable objection, if, in all such instances, we assign the genuine cause of the oxidizement of iron, solely to this prototype of oxygen. I feel less difficulty in admitting this conclusion, when it is considered, that the more cogent examples are deducible from originally formed matter, from the real primordial rock, eoeval with the globe itself, and made tangible, probably,

soon

soon after, or even at that very period when, the "Earth was without form and void."

The intimacy between silex and iron, and the consecutive oxidizement of the latter, need not be further urged; it oc curs in such numberless cases, that whoeyer is at all conversant in mineralogy, and will take the trouble to search with candour, can be at no loss for evidence, sufficient to establish this singular concomitance. Thus, let us take, as an instance, that substance, familiarly known by the name of emery. Here, the iron is truly united to the silex in a very close manner, and not as a mere mixture, for the metal is oxidized and imbedded in this surplus of oxygen. "This," says M. Haüy, speaking of emery, "is a true combination of quartz and iron, in which the two substances contract a stronger adherence than a mere interposition of their molecules."

Though iron is considered as a pure metal and a simple substance, that is, when divested, by the usual methods, of the common impurities, to which it has a habitual affinity, particularly of these, viz. carbon, phosphorus, and silex ; still, there is strong reason to believe that it has never been totally exempt from one or other of these substances. Indeed, it appears that some of these very impurities are required to render the metal more perfect, to add to its splendour, ductility, and other properties, which the arts demand. Thus, to make good steel there must be an addition of carbon as well as silex; and, if brilliancy, hardness, and a susceptibility of higher polish are to be considered as improvements, the carbon and the silex, in this case, seem to render the metal still more metallic, if such a term may be allowed.

In an analysis of four different specimens of steel, by M. Vauquelin, the result was this, taking it on an average to avoid fractions: that one hundred thousand parts of these samples of metal consist of 9817 of iron, 723 of carbon, 870 of phosphorus, and rather more than 288 of silex. That it is very difficult to deprive iron of all foreign matters, may be readily conjectured from this philosopher's labours, and the following observation confirms this truth, that iron is never pure. "The analysis of the varieties of steel," says this very accurate chemist, is one of those parts of the

Za

science

science the least advanced and the most difficult, especially when our object of research is the exact estimation of the principles which they contain :-it is thus, for example, that, in dissolving steel in dilute sulphuric acid, the hydrogen which is evolved, dissolves and carries off a part of the carbon, the quantity of which varies according to a multitude of circumstances."

From this and other authorities, and from a prejudice, which, I acknowledge, I have long been disposed to cherish, it may be inferred, that whatever emits smell cannot be considered as a simple body, and hence, the purity of hydrogen as an element must be doubted; that species, however, which we obtain from the decomposition of water by the metals, is certainly very objectionable, if there be any truth in this observation; for the gas is never free from a very perceptible odour, whether it has been procured by means of zinc or iron.

It is certainly not always prudent to generalize too freely upon these subjects, yet it is difficult on some occasions to avoid it entirely. The hydrogen gas, alluded to by M. Vauquelin, in these analyses, was undoubtedly impure, as it contained a certain portion of carbon from the metal, though not the whole; for, finding this mode of operating inconclusive, he at last had recourse to the sulphurous acid, with which he apparently succeeded in separating the whole.

Fluoric acid, from its peculiar effects upon the siliceous compounds, deserves a particular notice in the present inquiry, especially as its whole history remains still clouded with inconsistency and ambiguity; for, either the tables of affinity respecting its habitudes are erroneous, or the acid itself must be considered as a monstrous anomaly in the doctrine of chemical attractions. These tables begin with lime, and go on progressively with some of the earths and alkalies to silex, the very last in the enumeration, with which, by the way, it has never yet been united so as to produce a true salt, From Bergman's experiment, we learn, that he dissolved silex in fluoric acid, and that after the solution had remained undisturbed for two years, a number of crystals had formed at the bottom of the liquor in the vessel.