232 
PROFESSOR FORCHHAMMER ON THE COMPOSITION 
which, seems to prove that the under-current from Elsinore, at least at that season, 
reached Copenhagen. The difference between the water from the bottom of the har- 
bour and the tunnel might either be occasioned by the slowness with which the water 
filters through the limestone of 30 feet thickness, so that it was water from another 
period which at last reaches the tunnel, or it may be explained by the way in which the 
samples from the bottom were taken, by sending an open bottle reversed down to the 
bottom, where it was turned and allowed to stand some time, to let the heavier water 
from the bottom dislodge the lighter water which had entered the bottle. The mean 
relative quantity of lime and magnesia was — 
For the surface . . 1 lime to 4-062 magnesia. 
For the bottom . . 1 lime to 4-153 magnesia. 
For the tunnel . . 1 lime to 3-485 magnesia. 
The proportion between lime and magnesia is therefore pretty much the same in the 
water from the surface and the bottom of the harbour, but in the water from the 
tunnel the relative proportion of the lime is increased. This may depend either upon 
a diminution of the magnesia, or upon an increase of the lime, or upon a combination 
of both effects ; but if these changes took place only according to equivalents, it would 
prove that there had been formed dolomitic combination by the filtration of the mag- 
nesia salts of sea-water through the carbonate of lime in the limestone. To ascertain 
this point, I have compared the lime and magnesia with a third substance in sea-water, 
for which I chose chlorine. This mean proportion was — 
For the surface . . 100 chlorine : 2-82 lime : 11-07 magnesia. 
For the bottom . . 100 chlorine : 2-62 lime : 10-96 magnesia. 
For the tunnel . . 100 chlorine : 3-11 lime : 11-08 magnesia. 
It follows from these comparisons that the absolute quantity of lime had increased 
in the water of the tunnel, but that the absolute quantity of the magnesia in the same 
filtered water had not decreased, but was as nearly the same as an analysis could show. 
Thus the increase of the lime depended upon the solution of some carbonate of lime 
from the limestone. It was further found that water from the tunnel, when evaporated 
to dryness and dissolved, left more carbonate of lime than surface-water. The cause of 
this solution of the carbonate of lime was evidently to be sought in a bed of black mud 
which covers the bottom of the harbour, and is slowly converted into carbonic acid by 
the atmospheric oxygen absorbed by the sea-water. The sea-water impregnated with 
carbonic acid had dissolved some of the limestone through which it filtered. 
Here might also be the place to mention and explain a rather curious phenomenon 
which is observed all along our coasts of the 'Sound and the Baltic, at least as far as 
Kiel. When the ice in spring begins to thaw, it disappears quite suddenly, and all the 
fishermen along the shore assure you. unanimously that it sinks. I have examined a 
great number of these men, and have .not found a single one who did not confirm the 
sudden disappearance of the ice in spring,, and who did not consider it to be quite 
