94 THE EMERY MACHINE. 



this machine are its absolute freedom from friction, the 

 ease and speed Avith which it can be manipulated, and the 

 fact that it works with equal accuracy when testing either 

 large or small specimens. The machine consists of three 

 essential parts, namely, the straining-head, the weighing- 

 head, and the lever-weighing apparatus. The specimen, 

 which is held horizontally, is gripped at one of its ends by 

 Avedges held in a cross-head, which is attached to the rod 

 of a hydraulic piston. This Avorks in a cylinder carried by 

 the straining-head. The other end of the specimen is held 

 in a cross-head, Avhich is connected to the movable plate of 

 the Aveighing-head. When a load is applied to the specimen 

 by the Avater pressure on the hydraulic piston, the above- 

 mentioned moA T able plate is pulled against a fixed plate, or 

 rigid support. BetAveen these tAA'o plates is Avhat is 

 essentially a thin metal diaphragm or sac Avhich is holloAv, 

 and about in. thick. This diaphragm, Avhose area is large, 

 and supports the Avhole load on the specimen, is tilled Avith 

 a mixture of alcohol and glycerine. The load on the 

 specimen induces a certain pressure in the liquid, Avhich 

 is transmitted along a pipe to a similar, but smaller, 

 diaphragm, Avhich is made to act upon the small arm of a 

 system of compound levers. In one of these machines the 

 total leverage of the lever system is 16,000 to 1, and the 

 ratio of the areas of the tAvo diaphragms is 20 to 1 ; so that 

 a Aveight placed on the end of the last Aveighing lever 

 induces a load on the specimen 320,000 times as great as 

 itself. It Avill be seen from this that to have a load of 

 100 tons on the specimen, it will only be necessary, oAving 

 enormous leverage obtained, to place a load of something 

 like 10 oz. at the end of the last lever. The " Emery " 

 machine is thus a compound-lever machine Avith three 

 mechanical levers and one hydraulic lever. It is said to 

 possess great sensitiveness, and its readings are said to be 

 accurate beyond the requirements of ordinary work. 



COMPARISON OF VARIOUS TYPES. 



49. It is not possible, for several reasons, to say definitely 

 that one testing machine, or one type of testing machine, is 

 better than another. Testing machines are used for a variety 

 of purposes. There are machines in use in many of the iron 

 ana steel Avorks throughout the country ; these are chiefly 

 used for carrying out a succession of comparatively crude 

 tests on specimens which do not vary to any great extent 



