The vast length of pipe which a building of any size requires when it is heated by steam, gives, of course, a large cooling surface, and the steam becomes at first rapidly condensed into water, which, if not removed, prevents the operation of the heating arrangement. To remove this water, and yet prevent the escape of any steam, and to allow all the condensed water to escape as fast as it is condensed away, so that it may not absorb any of the heat which should be employed in elevating the temperature of the building, has long been a desideratum, and has at last been invented by J. W. Hoard, of Providence, R.I. The device is small, being only six inches long by four in diameter, and it cannot freeze. Our illustration is a section of one of these valves, which we will now proceed to describe. A is the cover, which is connected to the end of the heating pipes, and may be any distance from the building. It is attached to the cylinder by bolts, B, an india rubber packing being interposed between them. In the bottom of the case or cylinder, D, is an escape pipe, 0. E is a feathered valve, stepped into a nut, F, and it does not rest on the step, but on the top of the nut. This nut, F, completely closes, by means of an india rubber packing, G, a box, H, which is smaller than the inside of D, so that plenty of water way is obtained between the inside of D and the outside of H, and it is prevented from shaking, and compelled to move steadily up and down D by three projections cast on its outside. This box is hollow, and contains mercury, J, which fills up the narrow tube, H', and presses, in the extended hollow, on the diaphragm of rubber, K; above the mercury is a small quantity of alcohol, I. To the under surface of H is attached by bolts a cylinder, L, which fits loosely around a cap, M, that covers the exit, 0. This cap, M, is supported over 0 by a trident base, N, so shaped that it is firmly secured over the opening, and yet admits of plenty of water way. The operation is as follows :—When the steam is turned on it rushes through, A, (the valve being always open when steam is not in contact with it, so that all water can run out of the pipes when not in use for heating) and coming in contact with H, heats it, and vaporizes tho alcohol. The alcohol vapor being confined, presses on the mercury, and causes it to expand the diaphragm, so that the whole of H is lifted up by the pressure of K upon M, and the feathered valve, E, closes A. It remains closed until water has accumulated, when the alcehol cools down, resumes its liquid state, and the water runs through. The case, D, is chamfered out at a, to increase the water way, and the device works, after once beginning, giving a regular stream of condensed water, and not by jumps, as would be supposed, no steam ever passing through. We have seen certificates from various manufacturing establishments where steam is used for heating and evaporating purposes, and where this trap valve is in use, and all speak in the highest terms of its operation, as it enables them to keep the steam in the pipes at the same pressure as in the boiler, and allows the escape of all the condensed water. It is a simple and useful little contrivance, and recommends itself for general adoption. It was patented May 25, 1858, by the inventor, who has assigned the invention to himself and G. B. Wiggins, 20 Friendship st. Providence, E. I., either of whom may be addressed for further information.