1890 - 91 .] Mr Irvine and Mr Anderson on Action of Salts. 53 
the salts of nickel and cobalt. On the other hand, with salts of 
copper and manganese, the action was sufficiently rapid so as to 
make a material difference, within a few weeks, in the composition 
of the coral exposed to their action. 
In most cases there is a direct interchange between the lime (of 
the carbonate of lime) and the oxide of the metal which takes its 
place. Thus we have : — 
1. With a copper salt, in seven months, 26*4 per cent, of carbonate 
of copper taking the place of an equivalent amount of car- 
bonate of lime. 
2. "With chloride of manganese, in twelve months, 58*4 per cent. 
of carbonate of manganese. 
3. With salts of iron practically the whole coral is altered — first, 
into carbonate, and ultimately, on exposure to air, into 
sesquioxide of iron. 
4. With salts of zinc, 26 ‘8 per cent, of carbonate of zinc had 
formed in six months. 
5. With phosphate of ammonia the transference was between the 
carbonic acid of the coral and the ammonia of the salt. The 
lime having combined with the phosphoric acid to an extent 
equal to 60 per cent, of phosphate of lime. 
Without doubt, phosphate of lime deposits, especially those 
found on old coral islands, have had their origin in this manner, 
the phosphoric acid being derived from the excreta of wild fowl, 
deposited upon dead coral or carbonate of lime, the amount of 
pseudomorphic change being in accordance with the quantity of 
guano deposited. Of course, transference between carbonate of 
lime and alkaline phosphates can only take place in the presence of 
water, so that we have no such, pseudomorphs where the climate 
is rainless ; there the guano remains as deposited, whilst these 
deposits in rainy zones always assume the form of insoluble phos- 
phate of lime. 
Carbonate of lime, with silver and mercury salts, seems to throw 
down oxides, not carbonates. But the compounds with nickel and 
cobalt we have, as yet, been unable to determine. 
With a true pseudomorph, the structural form of the carbonate 
of lime, be it in the shape of coral , shells , or calcite , remains 
