RECENT PROGRESS IN THE STUDY OF ALLOYS. 79 



melting, 1 and of Le Chatelier's interesting experiments on 

 the connection between the temperature and the resistance 

 of certain alloys.' 2 



Matthiessen's theory that certain metals when added, 

 even in very small quantity, to another metal bring the 

 latter into an allotropic state, has been often quoted, but 

 cannot be regarded as having borne fruit up to the present 

 time. On the other hand, his distinction between alloys — 

 which are: (1) a homogeneous solution of one metal in 

 another ; (2) a homogeneous solution of a definite chemical 

 compound of the two metals in the one which is present in 

 excess ; (3) a mechanical mixture of two different liquids, 

 each containing both metals, but in different proportions 

 — has been a most useful one. 



As an example of class (3) he gives the case of a 

 mixture of equal parts of water and ether. This, if well 

 shaken, would for a short time appear fairly homogeneous, 

 although it really consisted of drops of water containing 

 some ether mingled, but not mixing, with drops of ether 

 containing some water ; such a mixture would on standing 

 separate into two layers. 



It is probable that many alloys are of this class, although 

 the separation into two layers is a slow one which is very 

 far from being complete when the alloy is solidified by rapid 

 cooling. It seems improbable that any alloy of this class 

 can be thoroughly satisfactory for mechanical purposes, or 

 can be sufficiently homogeneous to make its properties 

 worth studying. For such an alloy when solid would be a 

 sort of conglomerate or concrete, and although such a tex- 

 ture might not be inconsistent with mechanical strength if 

 a sufficient uniformity of grain could be ensured, yet it 

 would be difficult to prevent parts of the mass differing in 

 character. Moreover, differences in the coefficients of ex- 

 pansion of the two materials would be a cause of weakness. 

 Professor Roberts Austen says that alloys of iron and 

 aluminium containing from 40 to 60 per cent, of aluminium 

 disintegrate spontaneously into clean metallic grains when 



1 Annalen, N.F., bd. 34, p. 576, 1888. 



2 Zeitschrift fier Physikalische Chemie, bd. viii., p. 183, 1891. 



