210 SCIENCE PROGRESS. 



able precision the fusibility of a mineral on the Wedgewood 

 scale ; while, by a further refinement, the mutual reactions 

 of two minerals before the blow-pipe were utilised in the 

 identification of the minute fragments investigated. 



These various methods clearly demanded considerable 

 skill and patience, and this is doubtless one reason why the 

 new field opened out by Cordier's memoir remained so long 

 almost uncultivated. None the less must he be regarded 

 as the pioneer in this line of research, and indeed some of 

 the devices now in vogue among petrologists are no more 

 than adaptations and improvements of those noticed above. 

 The use of the blow-pipe in chemical and mineralogical 

 investigations has, of course, been greatly developed, partly 

 with the aid of special fluxes or solvents. Another kind of 

 flame-test, closely following" Cordier's lines, is the method 

 elaborated by Szabo (1876) for discriminating the various 

 felspars in small fragments. Here the criterion of relative 

 fusibility is used in conjunction with Bunsen's flame-colora- 

 tion tests. Szabo's method has been employed with advantage 

 by several petrologists, and various devices have been utilised 

 by Cole (1) and others to simplify the practice of it. 



As a method of precision for identifying minerals by 

 observation of their melting-points and their behaviour at 

 high temperatures must be mentioned Joly's " meldometer " 

 (2). In this the finely ground material is examined under 

 a low power of the microscope upon a narrow platinum 

 ribbon, which can be raised to any desired temperature by 

 the passage of a regulated electric current. The observa- 

 tions may be comparative, or the actual temperature may 

 be ascertained with considerable accuracy by means of a 

 device for measuring the expansion of the platinum ribbon. 

 It is evident that this instrument is capable of numerous 

 important applications. 



Coming to methods of mechanical analysis, we may 

 note first that for Cordier's bar-magnet Fouque (1876) and 

 other experimenters have substituted a powerful electro- 

 magnet, which attracts in varying degree all the iron-bearing 

 minerals. Dolter, in particular, has shown (1882) how, by 

 gradually increasing the strength of the current, the several 



