OF ARTS AND SCIENCES : MARCH 28, 1865. 487 



the precipitate somewhat globular. Arsenious acid does not seem 

 materially to affect the character of the precipitate ; nor do the sesqui- 

 oxides of iron and chromium, and the red oxide of manganese. With 

 equal parts of the oxides of nickel and copper, the color of the pre- 

 cipitate indicates the presence of both metals, in some parts the cupre- 

 ous, and in others the uickelic hue prevailing. Where the oxide of 

 copper is very considerably in excess of the nickel, the precipitate 

 has still a decidedly grayish cast; but when the latter oxide is in 

 excess, the presence of copper is scarcely perceptible, aside from the 

 blue color it imparts to the glass. 



With microcosmic salt, the reactions are similar to those described 

 with borax ; but not so easily obtained, owing, perhaps, to the greater 

 fluidity of glasses made with that flux.* 



Cobalt. — With borax, oxide of cobalt, in the reducing flame, gives 

 a gray metallic precipitate, not distinguishable from that of nickel. 

 Arsenious acid causes a larger precipitate, but does not affect its ap- 

 pearance. Sesquioxide of iron seems to promote the precipitation of 

 the cobalt. With an equal amount of oxide of copper, the precipitate 

 is cupreous, inclining to gray, the latter shade being best recognized 

 by comparison with a pure copper precipitate. 



Manganese. — In a borax bead, highly colored by oxide of manga- 

 nese, but still translucent, a scanty dark-colored precipitate is obtained 

 in the reducing flame ; but this precipitate is not metallic, and seems 

 to be within the glass rather than on its surface. Lime seems to 

 hasten this reaction; and after adding this substance I have noticed 

 a crystalline precipitate form upon flaming. The crystals were trans- 

 parent prisms, quite large, and apparently modified. 



With microcosmic salt, in the reducing flame, there is a crystalline 

 precipitate, composed of spiculae, bearing some resemblance to those 

 of lime, only rather larger and more conspicuous than any I have ob- 

 served with that earth. 



Iron. — Sesquioxide of iron, fused with borax, in the outer flame, 

 to a dark, brownish-yellow bead, and then treated with the reducing 

 flame, affords an amorphous precipitate, in streaks and reticulated 



* In treating pyritic minerals, they should be carefully roasted before fusion with 

 borax, otherwise a precipitate of sulphide of iron may occur, which somewhat re- 

 semliles the metallic precipitates of Nickel and Cobalt, and might be mistaken for 

 one of those metals, thereby misleading the operator as to the constitution of the 

 substance under examination. 



