Books with author John Scott Russell

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1841 edition. Excerpt: ...and the spring. S T, fig. 55, is what is commonly called a Salter's spring balance, the box #y containing a spiral spring, which is compressed in the box when the end S is drawn away from, or raised above the point S. The finger-screw S adjusts the degree of tension on the end of the lever. The two last species of safety-valve are used in locomotive steam-engines. Fig. 56. Fig. 57. A totally different method of indicating the pressure of steam in a boiler, is by means of what is called a mercurial gauge, communicating with the boiler. Mercury is poured into a bent tube, one end of which springs from the boiler, and the other end is exposed to the air, so that the steam by its pressure raises the mercury in the straight limb of the tube to a height above the level proportioned to that pressure. In the figure, a c d e is the bent tube, communicating with the boiler at a, and open at the end e, the steam presses on the end c of the mercury, and raises the other extremity of the fluid to the height C. From calculating the weight of mercury, it is reckoned that, for every pound of pressure of the steam in the boiler, there is an inch of mercury raised in the tube; so that, if the space d C be nine inches, a pressure of nine lbs. on the square inch in the boiler is indicated. Sometimes also a small float of iron is placed on the mercury, which, carrying a slender rod with an index, points the elevation of the mercury on a scale above the gauge. It is evident that this instrument also acts as a safety-valve, inasmuch as the steam, when too strong, must force the mercury entirely over the top of the tube, and make its escape. A double pipe, on a larger scale, with water in it instead of mercury, would answer the same purpose equally well; only the water...