330 Analysis of Scientific Books. 



orange-coloured ring is not only conspicuous upon the platina, 

 but by exposing it to the point of the blue flame, the metal is 

 revived, and afterwards deposited upon the platina, during its 

 combustion, in the form of a protoxide, exactly like polished 

 bronze or copper *." 



The method of distinguishing bismuth from antimony and 

 tellurium is very satisfactory, as well as the following for de- 

 tecting very minute portions of tin and copper. " With soda, 

 on the platina wire, oxide of tin combines with effervescence, 

 forming an infusible turgid mass, insoluble in an additional 

 quantity of soda. On charcoal it is readily reduced into a 

 globule of metallic tin. Some native oxides of tin, especially 

 such as contain columbium, are not easily reduced with soda, 

 so that, on a first experiment, one might doubt its presence; 

 but if we add a small quantity of borax, the reduction is im- 

 mediately accomplished. 



" Tin often occurs in nature as an accidental, and relatively, 

 very small constituent part of the ores of columbium, titanium, 

 and uranium, and perhaps of some others, where its presence 

 would be little suspected in experiments made in the moist 

 way; but when treated with soda in the reducing flame, parti- 

 cularly after separating the iron, metallic tin is always detected, 

 even though it enter in no larger proportion than 1 -200th part 

 of the weight of the ore. If the proportion of iron be incon- 

 siderable, its reduction may be prevented to a certain point, by 

 adding borax to the soda." 



Oxide of copper, " with salt of phosphorus, fuses and ex- 

 hibits the same shades as with borax. If the proportion of 

 copper be inconsiderable, the glass sometimes becomes trans- 

 parent and ruby red, after exposure to the reducing flame, 

 nearly at the moment of congelation. Commonly the glass 

 becomes red and opaque like enamel. If the quantity of cop- 

 per be so small that the character of the protoxide cannot be 

 developed by the reducing flame, we add a little tin to the 

 assay, (whether the flux be salt of phosphorus or borax,) and 

 immediately continue the blast. The before colourless glass 

 now becomes red and opaque on cooling. If the blast be kept 

 up too long, the copper precipitates in the metallic state, par- 

 ticularly with salt of phosphorus, and the colour is destroyed. 



" With soda on the platina wire, oxide of copper fuses into 

 a fine green glass, which loses its colour and transparency on 

 cooling. On charcoal the mass is absorbed and the oxide 

 reduced. There is probably no other possible method of dis- 

 covering such minute proportions of copper as may be detected 

 by the blow-pipe, in all cases where it is not combined with 

 other reducible metals, liable to disguise its properties. In the 



* If we not mistake, the invention of this process should be ascribed to 

 Dr. VVolIaston. 



