320 Proceedings of Eoyal Society of Edinburgh. [sess. 
spar dissolving to about double the extent. A very important 
factor to be taken into consideration in conducting these experi- 
ments is the time of exposure. When the same sea water stands 
over carbonate of lime for a lengthened period a curious and 
interesting reaction sets in, and the carbonate of lime it has dissolved 
appears gradually to diminish in quantity and be thrown out of 
solution again. This was observed by Professor Dittmar, who, in 
his paper on the composition of sea water (“Challenger” Eeport), says 
— “It seems that under certain abnormal conditions sea water 
dissolves lime largely in addition to what it contains normally, and 
subsequently will redeposit even more than the surplus lime in 
crystals of carbonate.” This result was also found by my predecessor, 
Mr A. Drysdale. 
Of course such a condition as this last may not occur in nature, 
as Dr Murray states, where the sea water is in continual circulation 
by tides, currents, &c., but it will help to explain the gradual 
petrifaction of the porous masses of dead coral reef, which being 
constantly supplied with salt water saturated with amorphous car- 
bonate of lime on standing, depositing, will gradually fill up the 
interstices, and produce the massive condition all old coral formations 
exhibit. This would take place in comparatively shallow waters 
and while in contact with carbonate of lime, but in deeper waters, 
and under greater pressure, any carbonic acid present might be 
called into play, as shown by Mr Eeid in his paper to the Society 
in February 1888. 
As is well known, carbonic acid water has a powerful solvent 
action on calcspar ; the more finely . divided it is the greater the 
solubility. One litre of water, saturated at ordinary temperature 
and pressure, dissolved in twenty-four hours, of the massive 0*0815 
grammes, and of the powder 0*472 grammes per litre, or nearly 
six times as much (see Table). 
In order, if possible, to throw some light upon the condition in 
which the carbonate is present in sea water, a series of experiments 
was undertaken on the solubility of carbonate of lime in solutions 
of the different salts said to enter into the constitution of sea water. 
A hard variety of coral skeleton ( Oculina coronalis) was finely 
powdered, and the solutions allowed to act upon portions of it 
separately for four days. 
