xxii INTRODUCTION". 



" The first point to examine is, whetber it be fusible ; and, If so, in what 

 degree. The various grades of fusibility may be conveniently divided into 

 six ; as representatives of which it is convenient to take the following 

 minerals, species wliich are everywhere easy to obtain, and which may 

 therefore be often practised upon : — 



" 1. Antimony- Glance, or sulphide of antimony, which melts at the 

 candle. 



" 2. Natrolite or Mesotype, fine splinters of which may be rounded by the 

 candle-flame. 



" 3. Almandine or Precious Garnet, which fuses in large pieces before the 

 blowpipe. 



"4. Actinolite (Hornblende), fusible only in smaller portions. 



" 5. Orthoclase (Felspar) offers some difficulty ; and 



" 6. Bronzite can only be rounded by the flame Ia the finest splinters. 



" According to this scale, the mineral in question may be referred to 

 either of the above numbers, or placed half-way between any two of them ; 

 as, for instance, Apophyllite, being more easily fused than Natrolite, and 

 yet more refractory than Antimony-Glance, will have its comparative 

 fusibility represented by 1*5. 



" The fragment to be experimented upon is generally held in the 

 platinum forceps, but it is necessary to guard against the melting of the 

 test upon the points, since the platinum, though infusible, is by that means 

 rendered brittle. 



" In other cases the mineral may be supported upon charcoal ; but what- 

 ever be the means of holding it, the phenomena exhibited by the action of 

 the flame must be noted, as — 



" 1st. The manner in which it fuses, whether quietly, or with decrepita- 

 tion, exfoliation, intumescence, or phosphorescence; whether it loses or 

 retains colour and transparency. 



" 2nd. The appearance of the product, whether a glass, an enamel^ or a 

 slag; or, as in the case of ores reduced upon charcoal, a metallic bead or 

 rcgulus. 



"3rd. The separation of volatile substances, and the colour of the 

 deposit on the charcoal, by which we may recognise — 



"a. Lead, giving a greenish yellow deposit. 



*' h. Zinc, having a white crust, which, when heated, becomes yellowish 

 and difficult to volatilize. 



" c. Antimony, a white deposit, easy to volatilize. 



"c^. Bismuth, a crust partly white, partly orange-yellow, without 

 colouring the flame. 



"e. Sulphur, with the well-known odour of sulphuric acid. 



"/. Selenium, in an open glass tube, gives a red deposit of selenium. 



"^. Tellurium, in a similar glass tube, gives a greyish- white crust of 

 oxide. 



" h. Arsenic, gives ofl* a greyish-white vapour, which smells like garlic. 



" i. Quicksilver, in a glass tube, will be precipitated in minute metallic 

 globules. 



" k. Water, from hydrous minerals, deposited by condensation in the 

 same manner. 



