1822.] with only One Axis of Double Refraction. 259 
In the mica with one axis of double refraction which I 
analyzed, the 
Per cent, of oxygen. 
Silica Contains ...- es eeeeceevercees 21°13 
Oxide of iron. .....-- YG). 0, eet oe 
Alumina. .....-ceeeeeeeee WEG SEQUHARGS 
Magnesia....+++- sereeceees 5 éo ait Oe 
Potashiccgyene « Ms bia Nags ie ous BME A Fs: 
Fluoric acid ......-+-- Pitheete UP Eten, Oe 
From which we may conclude, that the oxygen in all the bases 
together amounts to the quantity of oxygen in the silica, that 
the oxygen contained in the bases with three atoms of oxygen 
(peroxide of iron and alumina) together with that of the potash, 
are equal to that of the magnesia. It is, therefore, possible that 
this mica consists of the common mica with two axes of double 
refraction (or of silicates of bases with three atoms of oxygen, 
combined with silicates of potash, like the mica of the former 
three analyses), and of mica composed of silicates of bases with 
two atoms of oxygen, like magnesia, by which combination, the 
interesting effect of this mica upon light is probably produced. 
The kinds of mica with two axes of double refraction differ 
likewise by the effect of acids upon them considerably from those 
with one axis. The former are altogether insoluble in the 
strongest acids, while the latter is acted upon by acids, though 
with difficulty. 
M. Peschier, of Geneva, published a short time ago a pa- 
per in which he asserts, he has found in many different kinds 
of mica a considerable quantity of oxide of titanium. I have 
tried with the blowpipe all the different species of mica which 
he mentions, without having been able to find the least trace of 
that metal in any one of them, though the oxide of titanium ma 
with the greatest ease be discovered by this mstrument. 4 
Peschier hated the mica with nitrate of barytes, dissolved 
the heated mass in muriatic acid, supersaturated the solution 
with carbonate of ammonia, and obtained the oxide of titanium 
from the thus remaining liquid, after having passed it through a 
filter. It is, however, not possible to obtain oxide of titantum 
in this way, which, when dissolved in acids, is completely pre- 
cipitated by carbonate of ammonia. 
Ss. 
