MECHANICS AND USEFUL ARTS. 49 



the steel, we may state that recent experiments, made by Mr. Clay in testing, 

 at the Liverpool Corporation chain-proving machine, some samples of steel 

 bars manufactured at the Mersey Works, showed that their average tensile 

 strength was 1(30,832 per square inch, while the strength of Russian iron is 

 only 02,044; of English rolled iron, 56,532; Lowmoor, 50,103; American 

 hammered, 53,913 ; of tempered cast steel, 150,000, etc. 



I3IPROYEMEXTS IN STEAM-GAUGES. 



The only steam-gauges known ten years ago, were the mercury-gauge, the 

 air-gauge, and the piston-gauge for locomotives. The first is costly and 

 cumbersome, its length for measuring 150 pounds pressure being 27 feet. The 

 second breaks easily, the divisions are small, and ascertaining the pressure by 

 looking at the instrument is a work that ordinary firemen carefully dispense 

 with. A piston pressed by steam against a spring is unreliable, on account 

 of friction. In June, 1849, Eugene Bourdon took out a patent in France for 

 a spring-gauge, in which the pressure of steam is indicated by a hand on a 

 graduated dial. Inside the case is an elastic metallic vessel, so shaped as to 

 change its form when steam is let in, and it is united by a proper mechanism 

 to the hand which points out the result. The great superiority of this gauge 

 over former ones is obvious. No liquids are used; there are no joints, con- 

 sequently no leakage. The gauge is cheap and compact, and its indications 

 are read at a glance from any part of the engine-room. This instrument 

 earned the highest award at the great London exhibition of 18-31, and in the 

 subsequent year was patented in the United States, and the patent bought 

 by Ashcroft, under whose name it is generally known. The claim read thus : 



" I claim the application of curved or twisted tubes, whose transverse sec- 

 tion differs from a circular form, for the construction of instruments for 

 measuring, indicating, and regulating the pressure and temperature of 

 fluids." 



Since 1852 about twelve patents have been granted for dial-gauges, in 

 which the elastic vessel was different from Bourdon's. Corrugated Disks, 

 made of steel, or diaphrams made of India rubber, are the main feature in 

 most of them. The first substance is destroyed by rusting, especially where 

 sea water is used. India rubber in a still shorter time undergoes internal 

 chemical changes, and requires to be renewed. In a steam-gauge patented by 

 Victor Beaumont in 1854, and recently perfected, the aim has been to embody 

 all the qualities of Bourdon's by using an elastic vessel of brass closed on all 

 sides except that of the boiler, and to avoid the vibrations of the hand or 

 pointer resulting from the momentum of the tube, held by one end, for each 

 jerk of the locomotive to which the gauge is attached. To obtain this 

 result, the elastic vessel is formed of flattened hollow spheres, communicating 

 together; one side of each sphere is turned inside, so that, under the pressure 

 of steam, one part is extended and the other is compressed. The regularly 

 diminishing motion of the extended parts is thus compensated by the regu- 

 larly increasing motion of the compressed portions, and the graduation is 

 perfectly uniform for the range of the gauge. Large surfaces are thus 

 exposed to the action of steam, which acts in consequence with a great deal 

 of power; beside which the effect of momentum is so insignificant, that the 

 gauge may be struck with great force on the table without the pointer 

 vibrating in the least. 



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