VII. 1 On the Effect of westerly Winds in raising the Level of the winds raise the IN the "Observations on a Current that often prevails to Strong westerly the Westward of Scilly," which I had the honour to lay level of the before the Royal Society many years ago, I slightly men. Channel. tioned, as connected with the same subject, the effect of strong westerly winds in raising the level of the British Channel; and the escape of the superincumbent waters through the Strait of Dover, into the then lower level of the North Sea. The recent loss of the Britannia East India ship, Cap. Loss of the Britain Birch, on the Goodwin Sands, has impressed this fact tannia, more strongly on my mind; as I have no doubt that her loss was occasioned by a current, produced by the running off of the accumulated waters; a violent gale from the westward then prevailing. The circumstances under which she was lost, were generally these: In January last she sailed from her anchorage between Dover and the South Foreland (on her way to Portsmouth), and was soon after assailed by a violent gale between the west and south-west. The thick weather preventing a view of the lights, the pilot was left entirely to the reckoning and the lead; and when it was concluded, that the ship was quite clear of the Goodwin, she struck on the north-eastern extremity of the southernmost of those sands. And this difference between the reckoning (after due allowance being made for the tides) and the actual position, I conclude was owing to the northerly stream of current, which caught owing to a northerly curthe ship when she drifted to the back, or eastern side of the rent from the Goodwin. Strait of Dover. The fact of the high level of the Channel, during strong winds between the W. and SW., cannot be doubted: be Philos. Trans. for 1809, p. 400. cause Effects of SW. winds on the tides in the Channel. Direction of the current from the shape of the shores of the Channel. cause the increased height of the tides in the southern ports, at such times, is obvious to every discerning eye. Indeed, the form of the upper part of the Channel, in particular, is such as to receive and retain, for a time, the principal part of the water forced in; and as a part of this water is continually escaping by the Strait of Dover, it will produce a current; which must greatly disturb the reckonings of such ships as navigate the Strait, when thick weather pre vents the land or the lights of the Forelands, and the North Goodwin, from being seen. I observe in a new publication of Messrs. Lawrie and Whittle, entitled "Sailing Directions &c. for the British "Channel, 1808," that throughout the Channel, it is admitted by the experienced persons whom he quotes, that strong SW. winds" cause the flood tide to run an hour, or more, "longer, than at common times or in other words, that a current overcomes the ebb tide a full hour: not to mention how much it may accelerate the one, and retard the other, during the remainder of the time *. It is evident, that the direction of the current under consideration will be influenced by the form and position of the opposite shores, at the entrance of the Strait; and as these are materially different, so must the direction of the stream be, within the influence of each side, respectively. For instance, on the English side, the current having taken the direction of the shore, between Dungeness and the South Foreland, will set generally to the north-cast, through that side of the Strait. But, on the French side, circum stances must be very different: for the shore of Boulogne, trending almost due north, will give the current a like direc tion, since it cannot turn sharp round the Point of Grisnez, to the north-eastward; but must preserve a great proportion of its northerly course, until it mixes with the waters of the North Sea. And it may be remarked, that the Britannia, when driven to the eastward of the Goodwin, would fall into this very line of current. There * It is also asserted, that in the mouth of the Channel, the extraordinary rise of tide, in stormy weather, is ten feet: that is, at common springs, twenty, and in storms thirty feet. See pages 28, 41, 70, and 133. 5 There is another circumstance to be taken into the account; which is, that the shore of Boulogne, presenting a direct obstacle to the water impelled by the westerly winds, will occsaion a higher level of the sea there than elsewhere; and of course a stronger line] of current towards the Goodwin. sequence of It must, therefore, be inferred, that a ship, passing the Dangerous conStrait of Dover, at the back of the Goodwin Sands, during this. the prevalence of strong W. or SW. winds, will be carried many miles to the northward of her reckoning; and if compelled to depend on it, may be subject to great hazard from the Goodwin. rent. It will be understood, of course, that although the The regular tides subject to stream of current has been considered here (in order to much the same simplify the subject), yet that, in the application of these laws as the cur remarks, the regular tides must also be taken into the account. But from my ignorance of their detail, I can say no more than that I conceive, that the great body of the tide from the Channel must be subject to much the same laws, as the current itself. The opposite tide will donbtless occasion various inflexions of the current, as it blends itself with it; or may absolutely snspend it: and the subject can never be perfectly understood, without a particular attention to the velocity and direction of the tides in moderate weather, to serve as a ground-work*. I am, with great respect, Dear Sir, Your faithful humble Servant, J. RENNELL. VIII. On dead Lime, by MR. BUCHOLZ t. IT has long ago been said, that under certain circumstances which are not yet well ascertained, and particularly after * Meffrs. Lawrie and Whittle's publication allows the tides in this quarter a velocity of one mile and a half per hour at the springs; half a mile at the neaps. The Britannia's accident happened at dead neaps. ↑ Journal des Mines, vol. xxii, p. 234. a violent neither heat nor slack. Lime that will a violent and long continued fire, limestone may be converted into a kind of lime that does not heat with water, and does not slack; and this has been called dead lime. This state of lime does not appear to be recognized by all chemists, since it is not mentioned in elementary treatises on chemistry: some however think, that clay combined with lime may give it the property of hardening by great heat, and thus cause it to lose those of heating and slacking with water, giving rise to dead lime. Perhaps I may remove the uncertainties, and reconcile the different opinions, to which this substance has given rise. May be owing to alumine, silex, too hasty and strong a fire, or fire too long continued. Dead Lime from oyster. shells. Four cases may be supposed, to each of which lime may pass to this state. 1. When it contains a great deal of clay, and is heated so strongly as to become very hard. In this state it will not effervesce with acids, because all the carbonic acid is expelled. 2. If it contain silex, and be heated strongly after the complete expulsion of the carbonic acid, it will not effervesce with acids. 3. In the third case, lime being heated at once very violently, forms a mass perfectly similar to dead lime. It passes into a semifluid state, the possibility of which I have shown in the Berlin Journal, and it requires to be heated gradually, to expel the carbonic acid of large pieces in particular. When the kiln is emptied, there will remain pieces halffused, that will neither heat nor slack with water, but effervesce with acids: these are carbonate of lime, fused or hardened by the fire. 4. Lastly on calcining carbonate of lime in a fire continued long after the expulsion of the carbonic acid, a true dead lime is formed, which neither heats with water, nor effervesces with acids. All the circumstances of its formation are not yet well known. I saw some years ago this kind of lime formed by the calcination of chalk and of oyster-shells; but not being satisfied, that they contained neither silex uor alumine, I ascribed to these earths the peculiar properties of the lime obtained. Lately the same phenomena occurred to me, and as I was very certain, that the oyster-shells employed contained no earth but lime, no phosphate of lime, and no salt soluble in water, water, I can affirm, that the properties of the lime obtained were altogether independent on the presence of these circumstances: yet I obtained from the same shells, by a somewhat more gentle heat, common caustic lime easily slacked. The dead lime obtained heated very strongly with muriatic Its properties. acid diluted with a small quantity of water, without emit ting the smallest bubble of carbonic acid. Pieces of it remained in water for twenty-four hours without falling to powder; and notwithstanding this common lime-watcr was formed, which is very remarkable. When the calcined oyster-shells were thrown into a boiling lixivium of carbonate of soda, the soda was completely decomposed, and a very fine pap was formed. If this account be not sufficient to throw much light on the subject in question, it will serve at least to guide the reflections of men of science, and show how different opinions on the existence of dead lime may be reconciled. IX. On the Muriates of Barytes and of Silver; by BERTHIER, IN a paper on the sulphate of barytes &c. + I took it for Proportion of ver mistaken. granted, that muriate of silver contained 20 per cent of muriate of silmuriatic acid, and hence I deduced the composition of the muriate of barytes, which I afterward employed in my inquiries concerning the sulphates. Recent experiments having taught me, that this supposition was not strictly accurate, I endeavoured to ascertain with more precision the proportions of the muriates of barytes and silver. I put 10 gr. [154 grains] of barytes recently obtained Muriate of ba from the calcined nitrate into a glass stoppled phial filled ytes formed. with water. 0.4 of a gr. of carbonate of barytes remained undissolved. The solution was supersaturated with some muriatic acid, and evaporated to dryness. The residuum, calcined in a platina crucible, weighed 12.75 gr. It contained 3.15 gr. of muriatic acid, since I had employed * Journal des Mines, vol. xxii, p. 323. + See Journal, vol. xxiii, p. 280. |
