or where, from the density of the rock, or its being confined as in the shafts and levels of mines by the numerous points of contact, very great force is required to produce its frac ture. I am inclined to believe that though in these cases both sand and clay must yield to the usual mode of tamping, yet that clay will commonly produce the fracture where sand will fail to do so. About ten years ago an experi ment was made in Cornwall upon a loose rock on the surface, and sand was blown out without any effect having been produced: an equal quantity of gunpowder, confined by a small quantity of tamping, broke the rock; which proved that the resistance was far inferior to that of the common mode. And from many late trials made with clay, in holes moderately deep, in Wheal Friendship copper mine and the tunnel of the Tavistock canal, I have found clay to answer nearly as well as tamping; though certainly in what the workmen call shallow holes, and in very hard rock, neither that nor sand can be depended upon. In quarries and open works where deep holes can and always ought to be had, where the ground is for the most part dry, and the rock is seldom very hard, both will be found eminently useful, and will contribute much to the safety of the work men. Mr. Farey mentions, in his letter in your Magazine, his having seen coal-ashes employed as tamping. The fact is, that most friable substances are proper for this purpose, those being the best that combine with friability a certain degree of tenacity: the miners esteem soft yellow copper ⚫ore, or the common galena, in the highest degree, and next perhaps is broken tile ; but what is commonly used is the soft schistus rock which is attendant on most metallie veins. These substances are beaten into the hole upon the charge of gunpowder, while a small taper iron rod called the nail, kept in during the process, forms, on being withdrawn, the vent for the rush filled with gunpowder, which constitutes the fuse. It is by the occasional attrition of this iron nail against siliceous particles, either in the act of ramming of striking it out, that dreadful accidents sometimes occur. The use of copper nails would prevent this; but though often tried, the miners, from their being not quite so convenient, will not continue the use of them. The plan of adding to the resistance of tamping by loading the aperture of the hole, as proposed by M. Gillet Laumont, is in continual use among the Cornish miners, but in a more simple and effectual way than he suggests; and it is certain that some rock could not be blasted without this assistance. M. Pictet, it is said in the same article of the Philosophical Journal for July, has conceived that a more effective explosion for the purposes of mining might be obtained by leaving a partial vacuity, or by the 'chamber not being completely filled by the gunpowder. Now this idea is directly in opposition to the received opinion of persons conversant with these operations; but not having made any accurate experiments on the subject, I shall only state a case that appears to be in point. We are frequently obliged in very wet ground to use gunpowder in cartridges of thin tinned plate; and as these cannot be made to fill up the diameter of the chamber completely, we obtain, what he conceives is desirable, a less concentrated explosion; but so far is it from being beneficial, that every miner will use every other means before he employs gunpowder in this way, because it is universally found to require a much greater quantity for a given effect, and much more, I conceive, than can be attributed to the small degree of resistance offered by the material of which the cartridge is formed. The most promising scheme for facilitating the operation of blasting rock that I have heard of, has been suggested. very lately to me by a friend whose mechanical skill and ingenuity are well known, and who has lately applied with surprising dexterity that powerful agent gunpowder at great depths under water. A sort of powder is made of double or treble the strength of common cannon powder, and if this be applied to the uses of mining, he thinks that holes of half the usual capacity might contain sufficient charges in equal lengths, If so, it is certain that such holes, being considerably less in diameter more ease and rapidity; and those only who know the labour and tediousness of the operation, besides the great expense of tools in hard siliceous rocks, can justly appreciate the value of such an improvement. I have not yet been furnished with the means of making any trial of this plan, but I hope before long to have it in my power. I have troubled you at some length on this subject; but as it is one with which is connected the safety of several thousand men in this kingdom alone, and when it is considered, as I have heard from good authority, that the annual expense of gunpowder for the mines in Cornwall and Devon amounts to more than 30,000l., it becomes an object worthy discussion, if means therefrom should arise of lessening the risk to the workmen or of cost to the mines, particularly in the present distressing state to which they are reduced from the very low price at which the metals are now sold. I am, sir, your most obedient servant, JOHN TAYLOR, Engineer, Holwell House, Devon, Dec. 1, 1807. XXIII. Extract of a Memoir upon the Muriatic Ether, as read at the French Institute, 17th of February, 1807. By M. THENARD *, AFTER having examined why the muriatic ether has hi herto remained almost unknown among chemists, although Frequently the object of chemical experiments, the author gives the method of obtaining it. For this purpose, as the bove ether is habitually in the state of gas, the following pparatus must be employed: We put in a retort barely capable of containing the mixure, an equal part in volume of highly concentrated muriatic cid and alcohol at 36°; we shake them well, in order to ring all their molecules in contact. This being done, we hrow into the retort seven or eight grains of sand, in order avoid the boiling up, which, without this precaution, * Ann. de Clinic, tom. Ixi. p. 290. might might take place in the course of the operation; we then place if in the naked fire upon a common furnace, by means of a grating of iron wire, and adopt Welter's tube to it, which enters into a flask with three necks, double in capacity to the retort employed, and half filled with water at the temperature of 20 or 25o*, so that the tube penetrates a considerable way into the water: afterwards we introduce into the second neck a straight tube of safety; and into the third we introduce a crooked one, which is fixed into an earthen vessel under flasks full of water, at the same degree of heat as the former, and supported by a knob screwed into the middle of it. When the apparatus is thus arranged, the retort must be gradually heated; and in about 20 or 25 minutes we see bubbles arise from the lower part of the liquid, and particularly from the surface of the grains of sand. These bubbles soon increase, and abundance of etherized gas is obtained; acid, alcohol, and water, pass over at the same, time, but they remain in the first flask. From 500 grammes of air and an equal volume of alcohol, we may obtain twenty litres and upwards of etherized gas perfectly pure, But we shall extract much more from it, if, when the extrication of the gas begins to slacken, we add a fresh quantity to the residue, namely, the strongly acid liquor which remains in the retort, and the volume of which is then nearly equivalent to two fifths of the liquor from which it comes, M. Thenard even thinks, that if, by means of a straight tube going to the bottom of the retort and of a proper length, we could pour from time to time warm alcohol into the latter, the etherized gas would be formed in still greater abundance; for we should conceive that there is every moment more alcohol volatilized than muriatic acid, and that we should thus reestablish between these two bodies the primitive proportions, which are more proper than any other for the success of the operation. In all cases the management of the fire is of the greatest importance: if it be too weak, no etherized gas produced; if too strong, but very little is produced. Besides, we do not etherize the alcohol sensibly by charging it with muriatic acid gas, nor do we obtain ether more sen* The centigrade thermometer is the one intended.-EDIT. is sibly by bringing together the acid and the alcohol in vapours into a tube about the temperature of about 80°. It is therefore by preserving a just medium in the application of the fire that we succeed completely. All this proceeds from too small or too great an elasticity in the alcohol, and the muriatic acid prevents their reaction upon each other. One precaution we must also take, is to use the same water for collecting the gas, and to employ the least quantity possible, because it dissolves it in a remarkable degree. This gas is absolutely colourless; the smell of it is strongly etherized, and the taste sensibly saccharine. It has no kind of action either upon turnsole tincture, syrup of violets, or lime-water. Its specific gravity compared to that of air is 2.219 to 18° of the centigrade thermometer, and at 0m 75 of pressure at the same temperature, and at the same pressure water dissolves its own volume of it. At this same degree of pressure also, but at + 11° of temperature, the etherized gas becomes liquid. We may procure a great quantity of it in this state, by using an apparatus similar to that we have just described; simply, in place of fixing the last tube under a flask full of water, we must plunge it to the bottom of a long, straight, well dried probe, and surrounded with ice, which we must renew in proportion as it melts. It is in this probe that the etherized gas alone arrives and is entirely liquefied; for, when once the vessels contain no more air, we may without the least danger suppress its communication with the atmosphere. When thus liquefied, this ether is of a remarkable limpidity, as in the state of gas it is without colour and without action upon turnsole tincture and syrup of violets; as well as the etherized gas, it is very soluble in alcohol, from which we may in a great measure separate it by water; like this gas, it has also a very decided smell, and a very distinct taste, which has something analogous to that of sugar, and which is particularly remarkable in water which is saturated with it, which may perhaps be employed successfully in medicine. When poured upon the hand, it suddenly evaporates and produces a considerable cold, leaving a small whitish residue, At+5° of temperature (centigrade G4 |