1886.] on Properties common to Fluids and Solid Metals. 



405 



TOIVS 



f£ft D INCH 



20, 



Fig. 12. 



first it stretches in a very singular way, without an increase of load, 

 as is shown by the curve, Fig. 11 ; when the limit of elasticity has 

 been passed, the metal continues to stretch with increased load until 

 it gives up resisting and breaks. The limit of elasticity of a solid 

 body marks the moment at which the body begins to " flow " under 

 the influence of the force to which it is submitted. There are many 

 materials which do not stretch when their limit of elasticity is 

 reached : in very hard steel, for instance, the breaking point and the 

 limit of elasticity practically coincide. Further, it must be observed 

 that every minute variation in composition is sufficient to change 

 the property of a body, and to cause what was a viscous body to break 

 close to the limit of elasticity. A most remarkable instance is pre- 

 sented by certain alloys of gold and copper. Standard gold, such as 

 is employed for British gold coin, which contains 9167 parts of gold 

 in 10,000 parts, breaks with a load of 

 18 tons to the square inch. Its limit of 

 elasticity is reached at Ij tons per 

 square inch, but it elongates 34 per cent, 

 before it breaks. If this standard gold 

 has only the o oVo*^ P^^'^ ^^ Iq^l^l added 

 to it, it becomes very brittle, and 

 breaks, as is shown by the diagram, 

 Fig. 12, with a stress of about 5J tons 

 to the square inch, instead of 18 tons 

 borne by the original pure standard 

 gold, and as it does not elongate 

 sensibly it cannot be said to flow at all. 

 A remarkable difference in the property 

 of the alloy, standard gold, is therefore 

 caused by the addition of only the 

 2oVo*^ P^^t ^^ ^^^^' 111 order to 

 understand this it will be necessary to 

 trace the analogy between fluids and 

 solid metals still further, and to 

 ascertain what takes place when metals, 

 in a roughly granular state, are sub- 

 mitted to compression, under conditions 

 in which the escape of the comj)ressed 

 metal is, as far as possible, restrained. 

 I must, therefore, turn to what I believe 



to be the most important work relative to the molecular constitution 

 of metals, which has been done for many years, namely, the researches 

 of Professor Walthere Spring, of the University of Liege, whose 

 labours have since 1878 been devoted to the study of the effect of 

 compression on various bodies.* The particles of a metallic powder 



.7-7 



UfUa 



Vs4 



Percentage of Lead. 



* * Bull, de I'Acad. Koyal de Belgique,' [2] t. xlv. No. 6, 1878. [2] t. xlix. 

 No. 5, 1880. See also subsequent papers in the same publicatiou, iu the ' Bull. 

 Soc. Chhu.' Paris, and in the 'Deutsche Ohemische Gcscllschaft ' (Bilduug von 

 Logirungcn durch Druck), b. xv. p. 595. 



