vessel. But, what were these crystals? They were pure silex, and had deserted this very acid, which, in all other cases, would have seized on it and dragged it into even aëriform existence. The native fluate of lime is so very generally contaminated with silex, if this expression may be allowed, that it is probable no fluoric acid exists without some of this ingredient; it may indeed owe its origin to this body, so uniformly are they associated. But, that singular influence of fluoric acid upon silex, the corrosion of glass, is what has been chiefly noticed by most authors, for it does not appear that a direct application to the mere silex has yet been attempted, at least, with that precision which might have obtained a satisfactory result. That this acid should prefer the silex to the alkali, and in a case of single elective attraction too, is contrary to every table that has yet been published, and hence, in this example at least, it forms an exception to the general rule. But if, in similar experiments, the acid selects the silex from lime, a substance which is placed at the top of the list, in all arrangements, how much further does this error extend? Though in making experiments with this very curious liquid I have employed various species of glass, principally with a view to improve this method of etching, I have generally preferred plate-glass, on account of its form, convenience, and greater capability to endure the necessary pressure, so as to secure a number of perfect impressions. This glass is always, without exception, composed of lime, silex, alkali, and, occasionally, some other ingredients of less consequence in the present question. It is astonishing, that in all the accounts of the decomposition of glass by fluoric acid, and eyen by other means of still greater energy, by electricity, little notice has been taken of the oxide of lead, and the subsequent disposition of the whole of the ingredients. I make no doubt, that flint-glass has been more frequently employed than any other, but I do not find that silex has ever put on that peculiar character of an earth, an alkali, or a salifiable base, and attached itself to the negative pole. On this subject, I confess, I feel extremely solicitous, as, in the late very Z 4 splendid splendid discoveries, which now, and probably will ever continue to, engross the attention of the scientific world, the decomposition of glass and consequent disposal of all its ingredients, form a question, to me at least, of the ut most interest; since, as far as I can judge of the phenomena, which have already been described, there appear circumstances more likely to confirm, than invalidate, my opinion of the nature of silex. There is a remarkable similitude in the effects of oxygen and silex on the metals, particularly in that process called vitrification, which is, in every meaning of the word, a complete saturation. By means of these, particularly the silex, all the metals, perhaps, with no exception, from being the most opaque bodies in the universe, may be rendered quite pellucid, affording an endless variety of the most charming tints, as useful as they are elegant, since it is chiefly from metals and metallic substances that the most durable and valuable colours are obtained for staining glass and making artificial gems, The best opake colours, such as are most suitable for enamel, water, oil, crayon, and all other descriptions of painting, are derived also from the metals, combined with one or both of these substances; and though alumine and other bodies are occasionally present, they are as often absent. Even the precious stones and the less valuable pebbles, spars, and an infinite list of fossil productions, seem to derive their intrinsic value, beauty and other excellen cies, entirely from the power of silex on the metals. Thus, the dull opacity of lead is as effectually changed by the sand, used in the composition of flint-glass, and the whole compound appears not less diaphanous, than the very same metal is, when, by means of oxygen, it is dissolved in nitric acid, properly diluted with water; such, however, is the infe rence I would draw from these premises. The near connection between potash and silex, is not less manifest than in the other associations which have been already noticed; indeed, seeing with what avidity the base of potash (according to the late discoveries) clings to oxygen, I am furnished with this plea, that its original and necessary quantity had been obtained from silex; for all the potash potash of commerce contains silex, and retains it with some degree of force, not as an adventitious ingredient, but rather as the superabundance of that primitive store, from whence it had derived that portion which is essential to its existence as potash, Now, that the constitution of potash no longer remains in doubt, and that oxygen has been proved to be as essential to the formation of potash as it is to that of sulphuric acid, I see no explanation more congenial and satisfactory than what I have here ventured to suggest, especially when it is proyed that the primitive seat of potash is in rocks and stones, and in the very centre of such bodies, where the atmosphere can have had no influence; for, as far as regards its vegetable and animal existence, all is merely secondary, and, consequently, does not apply so forcibly in this theory, though, even here also, we need be at no loss for proofs. The power which silex exercises over potash, soda, and a variety of other substances which enter into the composition of glass, is a notorious instance of its neutralizing efficacy; for no acid more completely obtunds the acrimony of alkaline bodies and disarms them of their corrosive character, The effervescence, which results when silex and the alkali enter into fusion, and form this insipid compound, is not observable till the materials are on the point of perfect combination; hence, as something is apparently evolved, neither oxygen nor any other aëriform fluid can he supposed to enter; so that the acidity, if the term may be applied, to coerce the alkaline matter, is alone due to the sand which is usually employed in the making of this beautiful and useful compound. Indeed, vitrification, in all instances, seems to be accomplished by silex or by oxygen; and the glass of lead, of antimony, of phosphorus, borax, or of any other body, is due to one, as much as the glass in common use, is to the other of these oxygenating agents. In many very trite and familiar experiments, upon bodies containing either silex, an acid, or oxygen in some condition or other, the phenomena which succeed may be traced to the same cause. Thus, scintillation of hard bodies on collision against each other, as flint against seel; that of two siliceous stones, which emit not only light but the pe culiar quartzy or rather sulphurous smell, already noticed; the effects produced by various species of phosphori; friction of two pieces of borax; the electric nature of glass; that of amber, tourmaline, and of resinous bodies; the light evolved by friction and collision of bonnet-cane and other vegetables which contain silex; and, in short, all other analogous examples may be adduced as additional illustrations on this subject. If I were to select a case, in which silex seems to be deposited as it were, and deprived of the caloric which had suspended it in the state of gaseous oxygen, it would be that of a natural hot-spring, such as the Bath-waters, which are confessedly impregnated with sand or silex, not merely in suspension as an accidental material, but perfectly dissolved so as to be imperceptible to our sight. Besides these waters, all other hot springs contain silex in solution; that of Carlsbad; the Geyser, and Rykum, in Iceland; and many others, which, it is said, issue, for the most part, from granitic and other siliceous rocks. If these waters were cold the argument might fail, but while the temperature of the ambient medium can be taken into the account, I should not be willing to retract this opinion, as far as it concerns the nature of all hot-springs. It is stated from good authority, that in the kingdom of Portugal alone, there are upwards of 200 of these springs, the greater number of which, and the hottest, originate where silex is most abundant. The presence of nitrogen in the Bath-waters, and, probably, in all other hot-springs, is a curious occurrence, and furnishes a proper theme for speculation. Whether it be the remainder of decomposed atmospheric air, which has been bereft of its oxygen, and that this is disposed of in the water, in the way I have supposed, is a question I shall not urge. The late Doctor Black analysed the hotsprings of Iceland, but the analysis, I believe, was not performed upon the spot, and, consequently, no notice could be taken of nitrogen gas. In the gallon of Geyser water, he found upwards of 31 grains of silex; and in the other, that of the Rykum spring, the proportion was 22 grains of the same ingredient in the English gallon. The The effect of silex in various cases is the same as an acid, and in some situations, where an acid or acid properties really exist, no other cause is present. All acids we know are not sour, some on the contrary, are insipid, and, therefore, it would be too much to expect silex to possess this property. It is, however, a strong support to this question to see my idea of its general acid quality corroborated by others, for it has lately been observed, (Journal des Mines, tome xx. p. 245.) that "in the analysis of ores, silex acts very sensilly as an acid." [To be continued.] LXVII. Report of Surgical Cases in the City and Finsbury Dispensaries, for November 1807; containing a Dissection of a Case of Hydrocephalus internus. By JOHN TAUNTON, Esq. In the month of November there were admitted on the books of the City and Finsbury Dispensaries 257 surgical patients. Since which time there have been admitted 1007. Some time since I was requested to examine by dissection, the head of J. W. ætat. about 9 years. It was remarked at the birth of this child, by a very intelligent surgeon, that the head was large, and that it was probable there was water contained in the brain. The child grew, and enjoyed good health till the 17th month after birth; but the head continued large. He was then seized with the hooping-cough, which was very violent, and he lost his sight for some time. It was now pronounced decidedly, to be a case of hydrocephalus internus. On his recovering from the hooping-cough he règained his sight and strength, so as to enable him to walk with the hand of his nurse, or in a go-cart: his appetite was good, and |