1888.] on some curious Projjerties of 3Ietals and Alloys. 369 



given a case of an alloy in which a simple elevation of temperature 

 induces allotroj^ic change in the constituent metals. It is prepared 

 as follows : ninetj-five parts of zinc are alloyed by fusion with five 

 parts of rhodium, and the alloy is treated with hydrochloric acid, 

 which dissolves away the bulk of the zinc, leaving a rich rhodium- 

 zinc alloy, containing about 80 per cent, of rhodium. When this 

 alloy is heated in vacuo to a temperature of 400° C, a slight 

 exjDlosion takes place, but no gas is evolved, and the alloy is then 

 insoluble in aqua regia, which dissolved it readily before the elevation 

 of temperature caused it to change its state. We are thus presented 

 (as the experiment shown to the audience proved) with another 

 undoubted case of isomerism in alloys, the unstable, soluble modifi- 

 cation of the alloy being capable of passing into the insoluble form 

 by a comj)aratively slight elevation of temperature. 



The industrial importance of the passage of metals and alloys 

 into allotropic states, and the possibility of changing the mechanical 

 properties of metals by apparently slight influences, was fully dealt 

 with, and the lecture concluded with a detailed description of Pro- 

 fessor Austen's own experiments w^hich have since been printed in 

 the ' Philosoj)hical Transactions ' of the Royal Society, the results 

 showing that very small amounts of metallic impurities exert an 

 extraordinary effect on the tenacity and extensibility of gold, and 

 that small as the amounts of these impurities are,. their influence is 

 rigidly controlled by the Periodic Lawof Newlands and Mendeleef, 

 the deleterious action of a metallic impurity being in direct relation 

 to its atomic volume. The audience was asked " to remember that 

 the knowledge of the kind of facts which had been considered comes 

 to us from very early times, for the influence produced on metals by 

 small quantities of added matter had a remarkable efi'ect on the 

 development of chemistry, mainly by sustaining the belief of the 

 early chemists in the possibility of ennobling a base metal so as to 

 transmute it into gold. This was the object to which they devoted 

 life and health, and laboured with fast and vigil. We inherit the 

 results of their labours, and their prayers have been answered in a 

 way they little anticipated, for, from an industrial point of view, if not 

 from a scientific one, metals are " transmuted " by traces of impurity. 

 Possibly we are nearing an explanation of the causes which are at 

 work, but the fact remains that iron may be changed from a plastic 

 material, which in ornament can be fashioned into the most dainty 

 lines of flow, into one of great endurance, to which, for the present at 

 least, the defence of the country may be trusted, apparently because 

 armour-plates and missiles owe their respective qualities to the fact 

 that carbon, manganese, and chromium have small atomic volumes." 



