OF METALS CONSIDERED IN RELATION TO THE PERIODIC LAW. Ml 



employed had been well established by careful comparison with gold purified by 

 myself in 1873* for use as Trial-plates in connection with the coinage of this country ,t 

 the purity of which has been recognised by no less an authority than M. STAS. The 

 amount of foreign matter added to the gold could therefore be readily ascertained 

 with minute accuracy by the ordinary method of assay, except in the case of metals 

 of the platinum group. It should be observed, however, that the method of assay, 

 which consists in eliminating impurities and in comparing the weight of the purified 

 gold with that of the portion of metal taken for assay, does not enable the assayer to 

 distinguish whether an impurity is metallic or a metallic oxide. However carefully 

 the experiments were conducted, it was at times found impossible to prevent the small 

 amount of added metal from being oxidised to a certain extent during the casting of 

 the bars. The error thus occasioned is believed to be but small, and was proved not 

 to be serious in the case of those metals whose oxides can be reduced by hydrogen, 

 by laminating or breaking in fragments the portion of metal to be submitted to 

 Bay and heating it to bright redness in a stream of pure and dry hydrogen. 



The testing-machine used in the following experiments belongs to the Metallurgical 

 Laboratory of the Royal School of Mines, and is of the form devised by Professor 

 GOLLNEB, and used by himself at Prague, and by Professor BOCK at Leoben. It is a 

 double lever vertical machine, adapted only for testing short pieces of metal, and 

 working up to a stress of 20 tons.J The pieces of metal tested were not provided, as 

 they should have been, with enlarged ends, but they nevertheless seldom broke within 

 the jaws of the machine, and when they did the result was rejected. 



The purest gold attainable has a tenacity of 7*00 tons per square inch, and an 

 elongation of 30 '8 per cent. Professor KENNEDY found that a less pure sample, 

 which contained 999'87 parts of fine gold in 1000, broke with a load of 6'29 tons per 

 square inch, and elongated 18 '5 per cent, before breaking. 



In selecting tenacity as the property to be tested with a view to ascertain the effect 

 of the added matter, the following considerations presented themselves : 



Professor SPRING has built up alloys by compressing the powders of the constituent 

 metals ; and, by pointing to the evidence of molecular mobility in solid alloys, he has 

 done much to show the close connection which exists between cohesion and chemical 

 affinity. KAOUL PICTET has concluded that there is an intimate relation between the 

 melting-points of metals and the lengths of their molecular oscillations, the length of 

 the oscillations diminishing as the melting-point increases, and, as CABNELLEY has 

 pointed out, " we should expect that those metals which have the highest melting- 

 points would also be the most tenacious." It is known that the melting-points of 

 metals are altered by the presence of small quantities of foreign matter; their 



* Chem. Soc. Jonra.,' vol. 27, 1874, p. 197. 

 t Cantor Lectures, ' Soc. Arts Journ.,' vol. 32, 1884. 



J This machine is described by Professor KENNEDY, F.R.S., ' Instit. Civil Engineers Proc.,' vol. 88 

 1886-87, part 2. 



