58 Proceedings of Royal Society of Edinburgh. [sess. 
water, sulphide of manganese is not peroxidised, carbonate of 
manganese and sulphate of lime being formed. This is shown by 
the following experiment : — Equivalent proportions of sulphide of 
manganese and precipitated carbonate of lime were added to sea- 
water, and a current of air was passed through the mixture for 
twelve hours. The mixture did not become brown, and when 
examined it was found that the whole of the manganese had 
been converted into carbonate, and the lime into sulphate. A 
similar quantity of sulphide of manganese to that used in the above 
experiment was mixed with distilled water and exposed to the 
action of a current of air for a like period. It became brown, and 
instead of giving off sulphuretted hydrogen on addition of hydro- 
chloric acid, chlorine was evolved, so that the decomposition of the 
sulphide by oxidation was in this case evidently complete. 
We find, further, that when sulphide of manganese is added to 
sea-water, in quantity not more than sufficient to form carbonate of 
manganese with all the carbonic acid present in the sea-water, the 
sulphide is completely decomposed, sulphuretted hydrogen liberated, 
and the manganese dissolved. 
These facts appeared to us to be incompatible with the theory of 
the formation of manganese deposits propounded by Buchanan, 
which hitherto had appeared to us to offer a very plausible and 
probable explanation of many of the points connected with these 
curious formations. 
In this change of view we were confirmed by the following 
experiment : — 
A mixture of ferrous and manganous carbonates was added to 
sea-water along with a quantity of decomposing mussel flesh, and 
the whole mass allowed to decompose, air being excluded. After 
four or five days the contents of the vessel became black, and 
sulphuretted hydrogen was freely evolved. Air was then blown for 
twelve hours through a portion of the mixture, which was then 
filtered and carefully washed. The residue left in the filter was 
then examined for manganese, which was found to be entirely 
absent. Another portion of the decomposing mixture was examined 
for sulphide of iron. The whole of the iron which had been added 
as carbonate was found in the form of sulphide. 
