OF ARTS AND SCIENCES : MARCH 28, 1865. 489 



(see Plate, Fig. 5) ; and, when viewed by reflected light, it exhibits 

 a frosty lustre. Mixed with an equal quantity of sesquioxide of iron, 

 the tungstic acid reaction is easily obtained, and quite apparent, in a 

 translucent glass ; but where the bead is opaque from excess of iron, 

 a slight gi'ayish precipitate only is distinguishable. Silicic acid seems 

 to promote the formation of this precipitate, even when added in large 

 quantities. Equal parts of tungstic acid and oxide of copper give a 

 cupreous precipitate, but decidedly grayish. 



With microcosmic salt, the reactions are much the same as with 

 borax ; except that in a transparent bead containing a mixture of 

 sesquioxide of iron and tungstic acid I have noticed, besides the arbo- 

 rescent variety, crystals of a hexagonal stellate form, one of the axes 

 being, however, at least one half longer than the others, thus giving 

 to the crystals a distorted aspect. 



Titanic Acid. — In borax, treated with the reducing flame, titanic 

 acid affords an amorphous, blue precipitate, usually as a band stretch- 

 ing across the surface of the bead. Mixed with equal parts of tungstic 

 acid, in the reducing flame, the reaction of the last-named acid is very 

 apparent, while that of titanic acid might easily be confounded with the 

 blue boi'der mentioned as frequently accompanying the tungstic acid 

 precipitate ; though I am inclined to think that the presence of the 

 titanic acid renders the blue color deeper and more distinct. An excess 

 of titanic acid gives a blue band, too well defined to be easily mistaken 

 for any similar appearance of tungstic acid ; yet the reaction of the 

 latter is quite apparent, even when the former is three or four times in 

 excess. Mixed with sesquioxide of iron, avoiding an excess of iron, 

 however, the blue titanic acid precipitate is easily obtained and recog- 

 nized, the glass being still translucent. When the quantity of sesqui- 

 oxide employed was six or seven times that of the acid, I obtained a 

 very dark iron-gray precipitate, on the surface of an o[)aque bead. 

 Equal parts of titanic acid and oxide of copper yield a slightly gray 

 copper precipitate. 



With microcosmic salt, in the reducing flame, titanic acid gives a 

 transparent, colorless crystalline pi-ecipitate. 



Molyhdic Acid. — With borax, in the reducing flame, molybdic acid 

 yields quite easily a lustrous, iridescent metallic precipitate, in color 

 from silver-gray to black, and bordered, on the side remote from the 

 flame, by a brown band. In the portion of the glass not obscured by 

 this precipitate I have noticed transparent hexagonal and rhomuoidal 



