~ 
258 M. Rose on Mica [Ocr. 
tate by ammonia, and that which had been filtered from the 
succinate of iron were concentrated together by evaporation, 
mixed with carbonate of potash in sufficient quantity so as to 
decompose all the salts of ammonia, and evaporated to dryness. 
The dry mass was dissolved in water, boiled, and the magnesia 
thus obtained separated by a filter. When, after having been 
heated to redness, it was redissolved in muriatic acid, some 
silica remained undissolved, which is almost always the case 
in the analysis of minerals containing silica. The manganese 
which the magnesia contained was so extremely small that it 
could not be separated. 
The reason why the silica obtained by this method had agglu- 
tinated could only be that fluoric acid existed in the mica.) The 
insoluble triple compound of silica, fluoric acid, and, potash, 
must have remained with the pure silica, and muriatic acid could 
not completely decompose it. By heating it, it lost its fluoric 
acid, and the potash combining with the silica made it aggluti- 
nate. To find the fluoric acid, the analysis was repeated a third 
time, which I did in the same manner as Berzelius made use of 
in analyzing the topaz. 
This mica remaining unchanged both in external appearance 
and in weight, when exposed to a heat in which other varieties 
of mica that I had analyzed, had lost water and fluoric acid, I 
was surprised to find fluoric acid likewise in this kind. Ina 
paper published two years ago, 1 ascertained to be a property of 
mica which contains much fluoric acid, that it does not lose its 
metallic lustre and become dull, even in a very strong heat, 
whereas those which contain small traces of fluoric acid change, 
according to my former statement, their colour by ignition, but 
they keep their metallic lustre. This mica, however, contains 
more fluoric acid than mica from Utoe, which loses its lustre 
easily in a moderate heat; while the same heat has no effect 
upon this mica. It is, therefore, no certain proof of the presence 
of a greater quantity of fluoric acid, that certain kinds of mica 
become dull in a moderate temperature. It seems as if fluoric 
acid escapes more easily from mica containing water, by which 
its appearance becomes dull. When the heat is increased, mica 
with one axis of double refraction also loses its lustre, and about 
two per cent of its weight. In respect to the chemical composi- 
tion, this mica differs materially from those three kinds which I 
formerly analyzed, and for which I gave a formula that answered 
for all three kinds which likewise agree in their action on light. 
But whether the potash really is in the form of trisilicate con- 
tained in the mineral I am scarcely able to determine, the quan- 
tity of potash being difficult to ascertain exactly, and this sub- 
stance containing not much oxygen. This, however, is certain, 
that oxide of iron and alumina are present, in the form of sili- 
cates, in the mica with two axes of double refraction. 
