OF ARTS AND SCIENCES: MARCH 28, 1865. 493 



is liable to be confounded with that given by titanic acid when treated 

 with the intermittent flame, unless submitted to microscopic examina- 

 tion, when it is easily distinguished, the titanic acid precipitate being 

 amorphous matter, sometimes presenting a reticulated structure, but 

 never, to the extent of my observation, either in numex'ous distinct 

 points or spheroidal. 



When a small proportion of tungstic acid is present, both it and nio- 

 bic can easily be distinguished, though in this case the reducing flame 

 sometimes produces an amorphous precipitate not unlike that of titanic 

 acid, but subsequent treatment with the intermittent flame will bring 

 out the characteristic spheroids of niobic acid. 



Mixed with titanic acid, niobic acid being in excess, the precipitate 

 shows traces of the presence of the former acid ; but the reaction is 

 not nearly so definite or delicate as that just described with tungstic 

 acid. 



Manganese seems to facilitate the precipitation of niobic acid. 



Columbite, from Middletown, Connecticut, gives the niobic acid pre- 

 cipitate, though the presence of iron detracts from its iridescence as 

 viewed by transmitted light. 



With microcosmic salt, there is a slight amorphous, brownish-yellow 

 precipitate. 



Selenium. — Fused with borax in the outer flame, the selenium glass, 

 when very slightly touched with the reducing flame, gives minute, 

 transparent, spindle-shaped crystals, forming apparently a crust on the 

 surface of the bead. These crystals closely resemble those of selenious 

 acid formed when selenium is heated in the closed tube. 



With microcosmic salt I have obtained no reaction, the glass being 

 exceedingly fusible. 



Tellurium. — Its reaction is like that of selenium, except that with 

 microcosmic salt I have observed crystals similar to those obtained with 

 borax. 



Protoxide of Cerium. — With borax, both in the reducing and inter- 

 mittent flames, I have noticed a granular, crystalline precipitate. The 

 crystals are very minute, and with the microscopic facilities at my dis- 

 posal, I have not been able to determine their form, though of their 

 crystalline character I think there can be no doubt, except in cases 

 where the reheating process has been too much prolonged, when they 

 appear to lose their angular structure, and sometimes fuse together to a 

 mass not unlike the precipitate of titanic acid in the reducing flame. 

 VOL. VI. 65 



