36 REPORT—1849. 
On the Black Colouring Matter of the Lungs. By Dr. De Vaus. 
This was a statement ofan examination of a peculiar black substance which is often 
found in the lungs of aged persons. It could not be detected in the lungs of in- 
fants; and its nature does not appear to have been yet determined, or the causes 
which produce it ascertained. 
On Artificial Gems. By M. Exeimen, 
This was a note accompanying some specimens of artificial gems prepared by M. 
Ebelmen under the influences of heat and pressure, as described in his communica- 
tions to the Academy of Sciences of Paris. 
Dr. Percy read a communication from M. Ebelmen, informing the Section that 
in addition to the specimens of crystallized gems recently furnished, he had now ob- 
tained artificially oxide of titanium, niobic acid and tantalic acid by some modifica- 
tions of his process. 

On the Formation of Dolomite. By Professor FornchuaMMER. 
Prof. Forchhammer communicated some observations upon dolomites. He stated 
that the white chalk of Denmark is covered by a bed only a few feet thick, contain- 
ing corals of the genera Caryophyllia and Oculina, and a number of fossils different 
from those of the white chalk; that this bed, which may be seen over a great part 
of Denmark always in the same position, the same fossiliferous character, and the 
same thickness, is enlarged in the hill of Fax6e toa thickness which cannot be much 
less than 150 feet. Here the Faxde limestone is covered by a bed of dolomite, which 
again is covered by a thick bed of limestone, consisting almost entirely of fragments 
of Bryozoa, and belonging likewise to the chalk formation. The limestone of Faxde 
contains about 1 per cent. of carbonate of magnesia, arising froin the shells and corals, 
which always contain it in a small quantity, but which in some instances, as in the 
Isis and some Serpule, amounts to 6 or 7 per cent. The bryozoan limestone which 
covers the dolomite contains not more than 1 per cent. of carbonate of magnesia, 
while the dolomite contains 16 or 17 per cent. 
The dolomite occurs generally in round globular masses, very similar to those of 
Humbledon Hill, and are evidently, like most of the globular masses of limestone, 
such as confetti di Tivoli and the peastone from Carlsbad, the produce of springs; an 
opinion which is still more confirmed by a number of large vertical tube-like cavities, 
which pass through the compact limestone, and are completely similar to those de- 
scribed by several English geologists as passing through the chalk, which have been 
recognized as the natural pipes of springs. Thus the I'axde dolomite is the produce 
of springs; but then these springs have deposited stalagmitic limestone wherever 
they have passed through the crevices of the limestone rock, which, as a more or less 
thick coating, covers all the fossils. Now this produce of the springs contains only a 
very small quantity of magnesia, but, besides lime, a great quantity of oxide of iron. 
It appears thus that if no other reaction takes place than the escape of carbonic acid, 
the springs do not deposit carbonate of magnesia, but that the dolomite is formed 
where the carbonic acid springs come in contact with sea water. , 
The author has made a great number of experiments on the decomposition which 
takes place when water containing carbonates dissolved by carbonic acid acts upon 
sea water, and found that always a more or less great quantity of carbonate of mag- 
nesia was precipitated with the carbonate of lime. When using water containing 
only carbonate of lime, the quantity of carbonate of magnesia thrown down at a boil- 
ing heat amounted to 122 per cent., the rest being carbonate of lime. The results 
of this decomposition vary however very much, and according to conditions not yet 
well known. So much however may be stated, that the quantity of carbonate of 
magnesia precipitated increases with the increasing temperature, Water which, be- 
sides carbonate of lime, contains carbonate of soda, throws down a much larger quan- 
tity of carbonate of magnesia, amounting in one experiment to 27°93 per cent. of the 
precipitate. 


