1890-91.] Mr Irvine and Dr Gibson on Manganese Deposits. 57 
carbonate, which has become crystalline, remains in contact with 
aerated water, at an ordinary temperature, without any peroxide. If 
the precipitated carbonate remains in contact with aerated water 
for ten years about one-third is decomposed, and the product has 
the composition MnO,Mn0 2 . Two specimens, containing respec- 
tively eighty and seventy per cent, of manganese carbonate, were 
exposed to air in the dry state for eight years. In the first case 
thirty-three per cent., and in the second fourteen per cent., of 
manganese carbonate remained — the rest being converted into “ the 
oxide MnO,Mn0 2 .” Other observers have found that under certain 
conditions, and notably in presence of carbonate of lime, peroxida- 
tion takes place, although very slowly. This is in accordance with 
our own experience. Some eighteen months ago, in connection 
with Irvine and Anderson’s investigation on the action of metallic 
salts on carbonate of lime,* some pieces of coral and chalk were 
placed in a weak solution of chloride of manganese in sea-water. 
Interchange has taken place, and fully fifty per cent, of the 
calcium has been replaced by the manganese. The outer portion 
of the coral is blackened, owing to the peroxidation of the carbonate, 
and the bottle in which the coral was placed has become covered 
with a film of peroxide of manganese. There is also a distinct 
precipitation of peroxide in the liquid. 
C. — Behaviour of Sulphide of Manganese. 
Precipitated sulphide of manganese in a moist condition is well 
known to be very unstable in presence of oxygen or air, and rapidly 
becomes brown owing to peroxidation. It also behaves like an 
alkaline sulphide towards certain metallic salts, and even gives up 
its sulphur to ferric hydrate, as was found by Buchanan (see his 
paper read before this Society, December 1890). In the presence, 
however, of carbonic acid sulphide of manganese is quickly and 
completely decomposed — sulphuretted hydrogen being given off and 
carbonate of manganese formed. This decomposition of sulphide of 
manganese takes place even when the carbonic acid is loosely 
combined, as in solution of bicarbonate of lime or manganese. 
Further, in the presence of carbonate of lime and oxygenated sea- 
* Proc. Boy. Soc. Edin. , vol. xvi., p. 319. 
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