512 Professor W. Chandler Roberts- Austen [March 15, 



are in a fair way to answer the question why -fo P er cent, of zirconium 

 doubles the strength of gold, while T 2 ^ per cent, of thallium, another 

 rare metal, halves the strength. In the case of the zirconium the 

 subordinate point is very high up, while in the case of the thallium 

 it is very low down. So far as my experiments have as yet been 

 carried, this seems to be a fact which underlies the whole question of 

 the strength of metals and alloys. If the subordinate point is low, 

 the metal will be weak ; if it is high in relation to the main setting 

 point, then the metal will be strong, and the conclusion of the whole 

 matter is this : The rarer metals which demand for their isolation 

 from their oxides either the use of aluminium or the electric arc, 

 never, so far as I can ascertain, produce low freezing points when 

 they are added in small quantities to those metals which are used for 

 constructive purposes. The difficultly fusible rarer metals are never 

 the cause of weakness, but always confer some property which is 

 precious in industrial use. How these rarer metals act, why the 

 small quantities of the added rare metals permeate the molecules, or, 

 it may be the atoms, and strengthen the metallic mass, we do not know ; 

 we are only gradually accumulating evidence which is afforded by this 

 very delicate physiological method of investigation. 



As regards the actual temperatures represented by points on such 

 curves, it will be remembered that the indications afforded by the 

 recording pyrometer are only relative, and that gold is one of the 

 most suitable metals for enabling a high, fixed point to be determined. 

 There is much trustworthy evidence in favour of the adoption of 

 1045° as the melting point hitherto accepted for gold. The results of 

 recent work indicate, however, that this is too low, and it may prove 

 to be as high as 1061*7, which is the melting point given by Heycock 

 and Neville * in the latest of their admirable series of investigations 

 to which reference was made in my Friday Evening lecture of 1892. 



It may be well to point to a few instances in which the industrial 

 use of such of the rarer metals, as have been available in sufficient 

 quantity, is made evident. Modern developments in armour plate and 

 projectiles will occur to many of us at once. This diagram (Fig. 7) 

 affords a rapid view of the progress which has been made ; and in col- 

 lecting the materials for it from various sources, I have been aided 

 by Mr. Jenkins. The effect of projectiles of approximately the same 

 weight, when fired with the same velocity against 6-inch plates, 

 enables comparative results to be studied, and illustrates the fact that 

 the rivalry between artillerists who design guns, and metallurgists 

 who attempt to produce both impenetrable armour-plates and irre- 

 sistible projectiles, forms one of the most interesting pages in our 

 national history. When metallic armour was first applied to the 

 sides of war vessels, it was of wrought iron, and proved to be of very 

 great service by absolutely preventing the passage of ordinary cast- 

 iron shot into the interior of the vessel, as was demonstrated through 



* Trans. Chem. Soc, vol. lxvii. 1895, p. 160. 



