15 
of the tubes, but in the substance of the coral, forming the sides of the 
tubes. 
It appears, from the experiments of Mr. Hatchett, that the colouring 
matter of the organ-pipe coral is similar to that of the red coral, 
( gorgonia nohilis,) being some unknown modification of animal matter. 
The red colour of both these substances having been gradually destroyed, 
during the action of the diluted nitric acid, as the solution of the 
calcareous substance advanced ; and could not afterwards by any means 
be restored : nor could any colouring principle whatever be detected by 
the re-agents usually employed.* 
We also learn, from the Count de Marsilli, that by digesting red 
coral, with and without its membranaceous tunic, in milk, over a slow 
fire, the colouring matter was dissolved by the milk, which became 
thereby of a pink colour ; whilst the coral became first of a saffron, then 
of an ash colour, and at last of a livid white. The same effects resulted 
from its digestion in heated wax. A similar deprivation of colour is also 
found to take place in those pieces of coral, which, having been broken, 
have fallen into, and have remained for some time in the mud at the 
bottom of the sea.-^- 
As the colouring matter of these corals is capable of being thus 
I’emoved by digestion, it is not to be wondered at, that, in general, in 
the fossil specimens, which must, in most instances, have been exposed 
to long continued maceration in water, little or none of the original 
colour remains. 
From the weight and other physical characters, as well as from 
exposure to chemical agents, I found that every fossil of this species 
in my collection, not imbedded in stone, contained too much silicious 
matter, to admit, by the agency of an acid, the examination into the 
change which had taken place in the original constituent parts of the 
coral. 
* Philosophical Transactions, for 1800. 
f Histoire Physique de la Mer, par Louis Ferdinand Compte de Marsilli. 
