PROFESSOR W. C 1 . ROBERTS-AUSTEN ON MECHANICAL PROPERTIES 



metal. When the metals are ranged in order of atomic volumes, potassium, which 

 renders gold very brittle, assumes the position to which its very high atomic volume 

 of 45 entitles it. Aluminium, indium, and lithium occupy somewhat abnormal positions 

 on the diagram, for they possess high atomic volumes and yet they appear to increase 

 the tenacity of gold, although they reduce its capability of being elongated. 



The influence of cadmium in increasing the extensibility is very remarkable. 

 Arsenic, again, has a higher atomic volume than gold, and should therefore render 

 gold somewhat fragile. Several experiments were made with it, and the bars proved 

 to be very fragile, but the results are not embodied in the table, as the bars did not 

 appear to be uniform in composition. The influence of zirconium is also noteworthy. 

 A fine specimen of crystalline zirconium was obtained from Messrs. HOPKIX and 

 WILLIAMS, but the metal appears to unite itself with gold with great difficulty. 

 When wrapped in the foil and added to gold, purposely kept considerably above its 

 melting-point, the foil melted and released the zirconium, most of which fell, through 

 the molten metal, to the bottom of the crucible, and remained there when the gold 

 was poured out. After several attempts, an amount of material, which subsequently 

 proved, on assay, to be about 0'2 per cent., was alloyed with the gold, and a perfectly 

 sound bar obtained, which appeared to have extraordinary strength, for it broke with 

 a load of 12 tons per square inch, pure gold breaking at 7 tons. Its fracture was 

 remarkably close-grained, and it elongated 12 per cent, before breaking. If 

 subsequent experiments should confirm this high tenacity, the result would be 

 opposed to the view set forth in this paper, as zirconium has a high atomic volume, 

 and should diminish the tenacity of gold. 



It may be added that it was useless to employ anything but chemically pure gold, 

 and the supply available only amounted to 40 ounces. As the preparation of gold of 

 high purity occupies a considerable amount of time, it was considered best to publish 

 the results already obtained. The effects of 0'2 per cent, of nickel, cobalt, iron, and 

 platinum, which occupy very low positions on MEYER'S curve, have severally been tried 

 with standard gold, and do not appear to reduce either its tenacity or extensibility, and 

 there is no reason to assume that they will behave differently in the case of pure gold. 



Allusion has already been made to the close connection which exists between the 

 tenacity of metals and their melting-points, and CARNELLEY has pointed out that 

 the melting-points are inversely as the atomic volumes, " the only important excep- 

 tions to the rule being arsenic, selenium, tin, antimony, tellurium, thallium, lead, and 

 bismuth." It can hardly be a matter of chance that, as my experiments prove, all 

 these elements (with the exception of selenium, about the effect of which I am at 

 present uncertain) diminish the coherence of gold, and there are but few others that 

 do so a fact which is alone sufficient to point to there being some connection between 

 the action of minute quantities of impurities and the Periodic Law. 



It would be difficult to suggest any explanation as to the mode of action of the 

 various elements until the influence of each element in small but varying qunntities, 



