434 REPORT — 1891. 



the physical properties of the materials, such as the tenacity, 

 ductility, elasticity, and their rate of expansion by heat, 

 their power to resist compressive, torsional, and shearing 

 stresses, &c. 



The science of construction is partly an exact science and 

 partly an inexact science. It is exact in so far as it consists 

 in the determination of the stresses in structures, but it is 

 inexact with regard to materials, although, by means of the 

 modern appliances for testing materials, it is possible to arrive 

 at results the accuracy of which, as far as the requirements of 

 the architect and engineer are concerned, leave little to be 

 desired. 



Testing Appliances. 



The most important testing-machines used in the labora- 

 tories in England and Europe are based on the constructive 

 principle first adopted by Mr. David Kirkaldy, M.Inst.C.E., 

 — that, namely, of applying the load by water-pressure, and 

 measuring it by dead-weight. In some of the larger testing- 

 machines used in America, and generallj^ in smaller machines, 

 spur-gearing and screws are used to apply the load. It should, 

 however, be mentioned that a large and accurate testing- 

 machine was designed by Mr. A. H. Emery for the Water- 

 town Arsenal, in which the power is applied by means of an 

 hydraulic press supplied by a set of pumps driven by a steam- 

 engine through an accumulator. The stresses are measured 

 by scale-beams, to which they are transmitted through a set 

 of diaphragms and cells containing a mixture of alcohol and 

 glycerine, and which operate as a frictionless reducing 

 mechanism. The machine, once standardised, is said to be 

 almost absolutely accurate. Its capability of recording accu- 

 rately large and small stresses was shown when it was first 

 used for breaking a bar of iron 5in. in diameter, and afterwards 

 a single horse-hair. It has been since used for a variety 

 of most valuable tests, which are recorded in the reports 

 published each year by the United States Government. 



The machine used at the University of Sydney, and also at 

 the University of Melbourne, consists of a force-pump and 

 hydraulic press for applying the load, and two levers for 

 measuring it. It is proposed to add an accumulator to 

 the Sydney machine. There is a knee-lever, 5:1; and a 

 steelyard, 20:1; the total leverage being 100:1. The poise- 

 weight may be varied from 501b. to 1,0001b. ; so that the 

 maximum load that can be applied is 100,0001b. There are 

 also appliances for testing in tension, compression, cross- 

 breaking, and torsion up to this load. 



In using the machine to test a piece of iron or steel in 

 tension, it must be prepared to one of the forms shown on 

 Plate XL ; it is then fixed in the machine, and the load ap- 



