INTRODUCTION. xxiii 



" 4th. The colour of the flame when the tip of the blue part is neatly 

 directed upon the mineral ; whence may be distinguished — 



" a. Red tint, given by several minerals containing strontia and (?) 

 lithium. 



" h. Green, produced by some phosphates and borates, sulphate of baryta, 

 some copper ores and tellurium ores. 



"c. Blue, given by chloride of copper, chloride of lead, Sco,. 



"5th. The development of magnetic properties after treatment in the 

 reducing-flame, as in ores of iron, nickel, and cobalt, 



" So far the assay has been considered by itself, but it is frequently 

 necessary to mix it with fluxes, either to render it fusible or to produce a 

 glassy compound of a characteristic colour. 



" Thus if borax or microcosmic salt be fused into a glass at the end of 

 a platinum wire bent into an eye, and a little powder of the unknown 

 mineral be added to it, we shall obtain by the use of the oxidizing flame the 

 following results : — 



" Manganese, in all its compounds, gives a beautiful violet or amethyst 

 colour. 

 ^ " Cobalt causes a sapphire-blue colour ; chromium an emerald-green- 



" Oxide of iron produces a yellowish-red glass, which becomes paler as it 

 cools, and at length grows yellow or disappears. 



" Oxide of cerium gives a red or dark-yellow colour, which also grows 

 paler as it cools. 



" Oxide of nickel renders the glass a brown or violet tint, which after 

 cooling becomes reddish-brown. 



" Oxide of copper in very small quantity gives a green tint, which grows 

 blue on cooling. 



" Oxide of uranium renders the glass bright yellow, which in cooling 

 takes a greenish tint. 



" Oxide of antimony gives a pale yellow colour, which soon disappears. 



" When soda is used as a flux it is generally upon charcoal, and by this 

 aid the metals may be obtained from most of their combinations in a pure 

 state. For this purpose the powdered ore is either mixed with the 

 moistened soda into a paste, or is enveloped in a piece of thin paper which 

 has been dipped in a solution of soda. After fusion, that portion of the 

 charcoal which has absorbed any of the fluid substance is to be cut off and 

 ground down with it in the mortar, when the metal, if malleable, will at once 

 be recognised. If several metals are combined, of which one is more easily 

 oxidized than another, as, for instance, lead when combined with silver and 

 copper, the latter may be separated by adding metallic lead or boracic acid, 

 according to circumstances, and maintaining a continued oxidizing flame, 

 till the whole of the lead has passed into the state of litharge. By means 

 of more complete apparatus and extended operations, the most exact 

 assays may be undertaken with the blowpipe ; and those who desire a 

 further insight into the subject may consult Plattner's 'Art of Assaying 

 by the Blowpipe ; ' Berzelius ' On the Blowpipe ; ' and the before- 

 mentioned work by Yon Kobell of Miinich, — all of which are translated 

 into English." 



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