540 General Notes. { May, 
vite as the summit of the biotite crystal is approached. The inner 
black crystal contains a small hole filled by white muscovite, and 
this hole enlarges with successive plates until finally the biotite 
has completely disappeared, as though eaten away by the 
muscovite, 
The author confirms the observations of Reusch and Rose on 
the parallelism of the crystallographic planes of the micas, as 
proved by their “strike-figures.” The biotite is often altered into 
an exfoliating hydro-diotite, just as muscovite changes into mar- 
garodite (kydro-muscovite). 
The superficial markings of reticulated magnetite are also dis- 
cussed, and shown to be always parallel in direction with the lines 
of the artificial “ strike-figures.” Their direction is, therefore, not 
due to any twinning crystallization of the dendrites themselves, 
but to the governing influence of the crystallographic lines of the 
muscovite, 
DoPPrLERITE.—W. Demel has analyzed a homogeneous speci- 
men of dopplerite from Aussee, and after drying at 100°-120°, 
finds 56.42-56.51 per cent. of carbon, and 5.34-5.20 hydrogen, 
leading to the formula, C,,H,,O,. The ash contained a large pet 
centage of calcium, the greater parts of which had probably been 
combined with the organic matter. Experiments were made to 
show that dopplerite could combine with calcium, and the conclu- 
sion is reached that this mineral may be regarded as the calcium 
salt of one or several acids belonging to the humus group. 
“ MOTHER oF Perre.”— The very interesting discovery, a 
nounced a few years since, that saltpetre (nitre) is formed in mar 
by the action of a living ferment, just as alcohol is formed by pe 
growth of the yeast fungus, introduces new conceptions of | 
origin of the nitrates, and shows that the process of nite : 
like that of acetification, is a true growth. As shown by F. i 
Storer, in a recent number of Science, the practical application © 
this fact was made use of as long ago as 1686, when Sewall speaks 
h has beet 
shown by Schlésing and Miintz to consist of very oe joined ; 
