ing. I may add to this, that the practice of building up water-pipes in the centre of a wall, with the view of preserving them from bursting, is dangerous in the extreme. The ill effects of the frost on the pipes is often imperceptible at the time. The expansion sustained by the pipe may not be sufficiently great to burst it; but in that case it produces a regular enlargement of the pipe, which part necessarily becomes the weakest; and it accordingly yields sooner or later to the mere pressure of the water. Cases of burst pipes in summer have thus not unfrequently to be attributed to the frost of the previous winter. The only really practicable and unfailing means of preserving water-pipes from bursting with frost, is to adopt the simple precaution of keeping them empty. This has been well ascertained to be the only security in every country where precautions are adopted. The best of those in use at present, consists in attaching a stop-cock to the lowest part of the pipes, and another immediately above it. By the one, the water is shut off when a low temperature approaches, and by the other, the pipes are emptied of the water they contain. To render these precautions of any avail however, the utmost watchfulness is necessary, and even where the cocks exist, they are rarely used in time. Besides, a severe frost will frequently occur in course of a single night, and in that case the opportunity of shutting offthe water is lost. The same objection applies to the mode of heating by fires, of circulating the water, and to all other precautions of a similar kind. Reasoning on this, I have conceived the possibility of employing some self-acting apparatus, which, on the approach of a low degree of temperature, would of itself shut off the water and empty the pipes; or, in other words, of having a machine so constructed and regulated, that it would shut a cock before the freezing-point of water, and open it again, when the temperature assumed its normal state. I first thought of applying a machine on the principle of the thermometer. If, in place of the small bulbous glass of an ordinary thermometer, I took a vessel of much larger dimensions, and in place of being sealed at the top, it was closed by means of a small sliding piston on the surface of the mercury;-if it were possible to adjust this, so as to elevate the piston at a temperature of 60°, it is evident that a decrease of the temperature to the freezing-point would produce a diminution of bulk in the mercury, and a corresponding descent of the piston. A stop-cock on the supply-pipe, attached to the piston-rod, might thus be made to stand open at all ordinary temperatures, and to shut precisely at the freezing point. Such an apparatus, however, would be subject to a few serious and insurmountable objections. In the first place, it would require some intricate mechanical arrangement, to prevent it diminishing the supply of water at low temperatures, although still above the freezingpoint. In the next place, its whole available power in shutting the cock would necessarily be small, since it could only be derived from the atmospherical pressure on the surface of a very small piston; and, lastly, it would, according to the determination of Dulong and Pétit, require about 400 cubic inches of mercury to produce one single cubic inch of vacuum in its depression between those two degrees of temperature. In short, it would not answer the purpose. The next idea was kindly suggested to me by Sir David Brewster. It was to employ the expansion of metallic rods, on the principle of the pyrometer, to effect the same purpose; and something analogous to the original pyrometer of Muschenbrock would probably be the best adaptation. A bar of zinc, or any other expansive metal, of convenient length, may have its expansion or contraction increased to any extent, by a series of compound levers; and this might be applied as the motive power in a manner precisely similar to that described. But the mechanical difficulty of regulating the action of the pyrometer between two specific degrees of temperature again interposes; otherwise, I have no doubt but that a properly-constructed apparatus of this kind might be the most unfailing means of action I could adopt. It has these advantages over the mercury, that its power is irresistibly great, its cost would be trifling, and it would be of much easier application. Finding these instruments to be practically inapplicable, I was driven to think of something more resembling the sudden expansion of water when freezing. It is obvious that this remarkable property of water is unlike the regular expansion of metals. What was necessary, I then thought, must be some liquid that will solidify a degree or two higher than water, and of its expansion being applied to shut off the water. Glacial acetic acid assumes the state of a solid at a temperature so high as 45°, and sulphuric acid of the density of 1.78 does the same at 46° Fahr. I was proceeding to experiment upon these, or similar bodies, when it occurred to me that of all the applications of this kind the best might be found to exist in the expansive force of water itself when freezing. Water, according to the experiments of Boyle and Dalton, increases in bulk about one-ninth in its transition from the fluid to the solid state. This expansion occurs with an irresistible degree of force. The Florentine academicians burst a hollow brass vessel with a cavity of only 1 inch in diameter, by freezing the water it contained. The force produced was equal to 27,000 lb. Major Williams, in his experiments at Quebec, in 1784-5, besides bursting bombshells, projected an iron plug, 2 lb. in weight, from one of the shells, to a distance of 415 feet by the expansive force of the water it contained when freezing. These facts afford sufficient grounds for establishing the most important points of the desired motive power; those, namely, of the amount of expansion the water sustains, and the prodigious force with which that is accompanied. I calculated, that I would require in a vessel, such as I have described, 27 cubic inches of water, which would produce 3 inches of expansion, to act effectively on a stop-cock. I therefore procured a globular glass vessel of these dimensions, accurately fitted with a cylinder and piston, and filled it with water. On exposing it to freeze, however, the water expanded equally on all sides of the vessel and burst it, instead of elevating the piston. A thin sheet brass vessel I employed for the same purpose succeeded no better. But, after a number of similar experiments, on vessels of different shapes, which I need not detail, I ultimately found that a true and accurately bored cylinder was the only vessel in which water could be frozen under pressure. This it was of great importance to ascertain; for had it occurred that ice expanded uniformly in a lateral direction it is plain that no vessel of moderate strength could have resisted the pressure. From these experiments I found that in a simple tube of any convenient dimension, fitted with a piston, it would be, without bursting, elevated by the freezing of the water it contained, and with a force far beyond what was absolutely necessary. This could be applied to shut a cock, or operate in any other manner found to be most appropriate. Such is the principle of the apparatus represented. The only apparent objection that presented itself next, was, that the water contained in the pipes being subjected to the same degree of cold as that portion confined in the small tube, would freeze as soon, or at all events so nearly at the same time that there would not be space intervening of sufficient duration to allow of the water being shut off. This objection, however, is easily disposed of by the application of a tube possessed of superior powers of conducting heat to that of the lead pipes. Copper at once suggests itself as the most appropriate, and for two reasons: 1st, Copper is to lead, as a conductor of heat, as 18 to 89, or, as nearly as possible, 5 to 1; and, 2d, Its tenacity or cohesive power is exactly ten times that of lead. These, it will be seen, are valuable properties for the purpose, since it not only guarantees a quicker conduction of heat, or, in other words, a quicker freezing of the water it contained, but a power of resisting ten times the pressure. But there is no occasion to employ a copper tube of the same dimensions as the lead pipe. One of half, or even a fourth of the size, I have found to answer quite as well. This, again, gives a still greater advantage, since the conduction of heat holds a direct ratio to the mass of the body. In short, it is very apparent that a properly-constructed copper tube, containing a small portion of water, will be the first to freeze, and so shut off the water. The practical application deducible from these principles, consists of a very simple apparatus. A copper tube of any convenient dimensions fitted with a piston filled with water, and firmly attached to the lead pipe, would, from its superior conducting power, be the first to freeze, and by the vertical expansion of the ice to elevate a piston and shut a stop-cock, while the water in the lead pipes was still fluid. On similar principles it would be the first to become VOL. LII. NO. CIV.-APRIL 1852. 242 Apparatus for preventing Pipes Bursting during Frost. liquid on a return of temperature. But in that case it is not so certain that the piston would descend to its original position and open the cock. Indeed, unless the combined friction of the piston and cock was very small it would not. Besides, it being a primary object of the plan to empty the pipes at the moment of shutting off the water, it would be necessary in that case to employ two cocks- -one for each purpose. To obviate this I have, therefore, thought it preferable to employ a double-action valve of the description indicated in the diagram, both as regards the relative simplicity of action in a valve to that of a stop-cock, and, what is of greater importance, with the view of effecting, at the same time, the shutting off of the water and the emptying of the pipes. Explanation of the Plate (III.)-Fig. 1 is a section; fig. 2, an elevation of the apparatus about one-fourth of full size. A represents the junction of the ingress supply-pipe, which performs a curve into the top of the double-action valve B. C is the supply-pipe continued on its ascent to the cistern. D is the waste-pipe through which the pipes are emptied. E is the small copper tube containing a measured quantity of water; it is supported by a small bracket attached to the pipes. F is the piston accurately fitting into the copper tube, and acting in direct conjunction with the valve in B. O is an airvessel. Now, if frost act on the small copper tube, the water it contains is the first to freeze, expand, and elevate the piston, which in its turn pushes up the valve from its present seat, and shuts it with great force against the projected extremity of the ingress supply-pipe. A passage is thus opened between the ascending supplypipe C and the waste-pipe D, through which the whole water in the pipes immediately escapes. By this means the water is shut off, and the pipes emptied at the same time. By observing that the valve shuts against the pressure of the water, it is evident that so soon as the water again becomes fluid, it must exert that whole pressure on the valve before it can escape, and it thus constitutes the external pressure, if any were required, to depress the piston when the temperature returns to its normal state. This construction of valve overcomes the only remaining difficulty to the effective working of the apparatus. It should be attached to the supply-pipe at the very lowest part of it. The place where the pipe enters the house-often that of the cellar, area, or other low, exposed situation-is the best. The water-pipes should possess a downward inclination to this point-as, indeed, is generally the case -for the purpose of being completely emptied. Mr Charles Baldwin, civil engineer, of Boston, United States, to whom I am indebted for much valuable information on this subject, suggests that an instrument of this kind might with advantage be employed to indicate the sudden approach of frost. Other applications of a similar nature may very likely be made. Meantime, I rest content with pointing out the existence of a principle which is October,. 29.584 29.4 ⚫304 3.48 3.85 54. 50.6 64. 48.2 54.3 54.1 47.2 2.66 16 W.; wsw. 49.8 2.64 14 W.; NW. 56.8 56.8 49.8 4.15 19 ENE.; Sw. 53.352.9 ... .75 7 WNW. 49.6 50.1 43.9 2.89 19 E.; W.; SW. 38.8 36.7 42.2 34.9 38.1 38.4 33.5 43.4 41.6 45.6 38.5 42. 42.7 39.6 1.43 12 SW.; SE. 1.10 12 W.; SW.; SE. Means at 29-742 29.581 284 3.26 47.8 44.7 53.9 42.5 47.1 47.4 41.131.24 180 W.; SW.; SE. racteristics of another. counteract the destructive consequences which are the ordinary chacation of the expansive force of one body of water, while freezing, to ledged, and which may be described, in a word, as the simple applicalculated to supply a desideratum long and universally acknow Climate and Mortality of Glasgow, 1851. By Robert Dundas THOMSON, F.R.S.E., Lecturer on Chemistry in the University of Glasgow. |