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250 



MINERALOGY. 



[Sect VIII. 



Oxide of copper in very small quantity giTes a green tint, -which 

 grows blue in 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 finXj 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 



dstened soda in 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 

 eombhied with silver or copper, the latter maybe separated by adding 

 metallic lead or boracic acid, according to circumstances, and main- 

 taining a continued oxidizing flame, till the whole of the lead has 

 passed into the state of litharge.* 



We will now suppose the voyager landing upon some 

 coastj and desirous, among other things, either of adding 

 to our knowledge of minerals or their localities, or of dis- 



covering ores of the useful metals or coaL With respect to 



many minerals and the ores of the metals, it fortunately 

 so happens that precisely the same places may be searched, 

 and these are cracks and fissures, or those dislocations of 

 rocks known as faults, either partially or wholly filled 

 with mineral matter. Should he see before him such veins 



as a and b traversing the rocks of a cliff, he should not 



neglect to land there. If any hollow spaces present them- 



let him there search for the crystalline minerals. 



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* By means of more complete apparatus and extended operations, the 

 mosrexact assays may be undertaken with the blowpipe; and those who 

 desire a farther insight into the subject may consult Plattner's 'Art of 

 Assaying by the Blowpipe ;' Berzelius 'Oa the Blowpipe;' and the above- 

 mentioned work by Von Kobeil of Miinich,— all of which are translated 

 int English. 





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