1891.] Properties of Metals in relation to the Periodic Law. 347 



IV. " On Certain Properties of Metals considered in Relation to 

 the Periodic Law." By W. C. ROBERT s-AusTEN, C.B., 

 F.R.S. Received March 12, 1891. 



In a previous paper published in the ' Philosophical Transactions ' 

 (1888, A, pp. 339349), the effect of about 0'2 per cent, of im- 

 purities on the mechanical properties of gold was examined, the 

 results of the experiments showing that metals which diminish its 

 tenacity and extensibility have high atomic volumes, while those 

 which increase these properties have either the same atomic volume 

 as gold or a lower one. The behaviour of aluminium and of lithium 

 appeared to be somewhat exceptional. Gold contaminated with 0'2 

 per cent, of aluminium should, if the theory set forth in the paper 

 be correct, have a tensile strength of about 7 tons per square inch ; 

 but it was found to be capable of sustaining a load of nearly 9 tons 

 per square inch without breaking. It became necessary, therefore, 

 to ascertain whether the cooling of a mass of gold containing alu- 

 minium presents any peculiarities, more especially as Osmond's* 

 recent work leads to the conclusion that a pure metal can exist in 

 two distinct molecular forms, and that the passage of the ordinary 

 modification of a metal to the allotropic one may either be hastened 

 or retarded by the presence of impurity. 



In order to continue the investigation, a trustworthy pyrometer 

 LS needed, and this has fortunately been provided by the thermo- 

 lectric -junction of platinum, and platinum with 10 per cent, of 

 lodium, the use of which was suggested by M. Le Chatelier.f It 

 pears to be superior to any other of the thermo- junctions which 

 ive previously been used, and some experiments made in 1889 

 tisfied me that the appliance is an extremely delicate and useful 

 ie for temperatures between 500 and 1100 C. In a recent 

 ;port to the Institution of Mechanical Engineers, in which details 

 the method of calibration are embodied, I have described a suitable 

 tngement for obtaining, by the aid of photography, autographic 

 irves which represent the cooling or heating of masses of metal. 

 It consists in enclosing a galvanometer of the Deprez and 

 L'Arsonval type in a large camera ; a fixed mirror, F, being placed 

 ilow the movable mirror, M, of the galvanometer, so that the light 

 >m the lime cylinder, L, reflected in the mirror H, passes to both 

 drrors, F and M, and is reflected in the direction of a fine hori- 



* 'Comptes Eendus,' vol. 110, 1890, p. 346. ' Journ. Iron and Steel Inst.,' 

 L890, Part 7, p. 38. 



t ' Bull. Soc. Chim., Paris,' vol. 47, 1887. p. 2. ' Journal de Phjsique,' vol. 6, 

 '17, p. 23. 



