44 On the Blow-pipe. [Jan. 



brownish, and hyacinth-brown, with a slight tinge of green. In 

 the interior flame the colour passes from yellow-green, through 

 yellow-brown and brown-red, to black ; and if the proportion of 

 acid be large, it acquires a metallic lustre, like the sulphuret, 

 which sometimes remains after the glass has cooled. Molybdic 

 acid is but little dissolved by borax. In the exterior flame the 

 glass acquires a grey-yellow colour. In the interior flame a 

 quantity of black particles is precipitated from the clear glass, 

 and leaves it almost colourless when the quantity of molybdenum 

 is small, and blackish when the proportion is larger. If to a 

 glass formed of this acid and microcosruic salt a little borax be 

 added, and the mixture fused in the exterior flame, the colour 

 becomes instantly reddish-brown ; in the interior flame the black 

 particles are also separated, but in smaller quantity. By long 

 continued heat the colour of the glass is diminished, and it 

 appears yellower by the light of a lamp than by day-light. This 

 acid is not reduced by soda in the interior flame. 



Tnngstic Acid becomes upon the charcoal at first brownish- 

 yellow, is then reduced to a brown oxide, and lastly becomes 

 black without melting or smoking. With microcosmic salt it 

 forms in the interior flame a pure blue glass, without any violet 

 tinge ; in the exterior flame this colour disappears, and reappears 

 again in the interior. With borax, in the internal flame, and in 

 small proportion, it forms a colourless glass, which, by increasing 

 the proportion of the acid, becomes dirty-grey, and then 

 reddish. By long exposure to the external flame it becomes 

 transparent, but as it cools it becomes muddy, whitish, and 

 changeable into red when seen by day-light. It is not reduced. 



Oxide of Tantalum undergoes no change by itself, but is 

 readily fused with microcosmic salt and with borax, into a clear 

 colourless glass, from which the oxide may be precipitated by 

 heating and cooling it alternately. The glass then becomes 

 opaque, and the oxide is not reduced. 



Oxide of Titanium becomes yellowish when ignited in a spoon, 

 and upon charcoal dark brown. With microcosmic salt it gives 

 in the interior flame a fine violet-coloured glass with more of 

 blue than that from manganese. In the exterior flame this 

 colour disappears. With borax it gives a dirty hyacinth colour. 

 Its combinations with soda have not been examined. 



Oxide of Cerium becomes red-brown when ignited. When the 

 proportion is small it forms with the fluxes a clear colourless 

 glass, which by increasing the proportion of oxide becomes 

 yellowish-green while hot. With microcosmic salt, if heated a 

 long time in the internal flame, it gives a clear colourless glass. 

 With borax, under similar circumstances, it gives a faint 

 yellow-green glass while warm, but is colourless when cold. 

 Exposed again for some time to the external flame, it becomes 

 reddish-yellow, which colour it partly retains when cold. If two 



