1888-89.] Mr Anderson on Solubility of Carbonate of Lime. 321 
As in the case of Iceland spar, the solubility was greater in 
distilled water than in sea water (some experiments conducted by 
Professor Thoulet, Nancy, confirming this result in the case of 
crystalline varieties of carbonate of lime). 
As shown in the Table, the magnesium salts dissolved the largest 
quantity of carbonate of lime, the solution of sodium chloride 
coming next, the calcium sulphate solution dissolving the least. 
Calcium sulphate appears rather to retard the solubility. It was 
to be expected that the magnesium salts would dissolve a compara- 
tively large amount of the carbonate and the sulphate of lime very 
little, for such is their action towards the amorphous, or non- 
crystalline, form of carbonate of lime. A solution of calcium 
sulphate dissolves very little amorphous carbonate, but a solution 
of magnesium chloride, holding the same amount as is present in 
normal sea water, takes up a large quantity of it, forming a clear 
solution, which on standing throws out the greater part of the 
carbonate of lime in a crystalline form. If a stronger solution of 
magnesium chloride be used, rhombohedral crystals of carbonate of 
lime are obtained large enough for their form to be seen distinctly 
with the eye. 
This experiment is indirectly important, as if there is an inter- 
change between the sodium chloride and the carbonate of lime 
entering the ocean, as is held by Tornoe, we might reason by 
analogy that since magnesium chloride dissolves more carbonate of 
lime than sodium chloride (although there is seven times the 
amount of the second than of the first in sea water), an inter- 
action between these salts would also take place, as — 
MgCl 2 + CaC0 3 = MgC0 3 + CaCl 2 . 
But such is not the case. Magnesium carbonate is not thrown 
down along with the calcium carbonate, as would be expected if 
such a reaction took place. It seems to be nothing more than a 
question of solubility. 
Sea water acts in very much the same manner as a solution of 
magnesium chloride, as amorphous carbonate of lime is soluble to the 
extent of 0*6 grammes per litre, which may be taken as the greatest 
amount of carbonate of lime in its most soluble form that sea water 
can dissolve without the help of free carbonic acid, in this case acting 
vol. xvi. 30/8/89 X 
