78 SCIENCE PROGRESS. 



Moreover, compounds of two metals retain a metallic 

 appearance, and electrolysis, which has thrown so much 

 light on the other parts of chemistry, here fails us com- 

 pletely ; for an alloy, whether it be a compound or a 

 mixture, appears to conduct without separation into its 

 component metals. 1 The fact that all metals and their 

 alloys are opaque, and that on account of the high tem- 

 perature at which they melt vessels of clay or other opaque 

 substance must in general be used to contain them, enor- 

 mously increases the difficulty of experiment. We cannot 

 note by eye the stage at which a liquid ceases to be homo- 

 geneous, or study the appearance of the bodies which 

 crystallise out one after another from solution. 



Hence the problem of the nature of alloys, although 

 it is in part a chemical one, has hitherto been most suc- 

 cessfully attacked by physical methods. We shall there- 

 fore begin by briefly reminding our readers of Matthiessen's 

 work, and then go on to the results arrived at by the late 

 Professor Alder Wright, Professor Roberts Austen, and 

 by Heycock and Neville. The main outcome of this 

 work can be summed up in the statement — that mixtures 

 of liquid metals obey those general laws of solution which 

 have been so brilliantly developed in the last ten years. 



We shall then consider the more purely chemical at- 

 tempts that have been made to isolate alloys of definite 

 formula, work principally due to Deville and Debray, 

 Schiitzenberger, Osmond and Werth, Guillemain, Levy, 

 Joanniss, Charpy, and Le Chatelier. 



Matthiessen's remarkable experiments on the electrical 

 conductivity of solid alloys drawn into wire 2 must ulti- 

 mately find a simple explanation ; but partly, perhaps, 

 because solid alloys are more complex than liquid ones, no 

 satisfactory explanation has yet been given, and therefore 

 these experiments will not be described in the present paper. 

 The same must for the present be said of Weber's work 

 on the changes in the electrical resistance of alloys during 



1 Obach, Pogg. Annalen. Ergdnzungs, bd. vii., p. 280, 1876; and 

 Elsasser, ibid., N.F., bd. viii., p. 455, 1879. 

 2 B.A. Report and Phil. Trans. 



