36 
Proceedings of Royal Society of Edinburgh [sess. 
kernels of some manganese nodules was very striking. It is not 
improbable that the first action of the MnS on the Fe 2 0 3 may be 
accompanied by the formation of mixed oxides of iron and man- 
ganese ; but there is much to be done in this direction in the strictly 
quantitative investigation of the interaction of the insoluble, but 
not inert, compounds of this as well as of other groups of metals. 
Ferric Sulphate and Manganous Sulphide . — Experiments were 
now made, using the iron as a ferric salt in solution, and for this 
purpose ferric sulphate was used. It was made as nearly neutral as 
possible by addition of ammonia. The MnS was, as before, sus- 
pended in distilled water. 
On adding ferric sulphate to excess of MnS, the formation of FeS 
is immediate. 
On adding a large excess of Fe 2 (S0 4 ) 3 the FeS is decomposed, 
there is formation of basic salt, and on dissolving it with H 2 S0 4 the 
solution contains large quantities of ferrous sulphate. 
On experimenting with solution of ferrous sulphate it was found 
that excess of MnS precipitates the iron completely as FeS, acting 
exactly like an alkaline sulphide. 
The rationale, therefore, of the above reaction is very simple. 
Thus 
Fe 2 (S0 4 ) 3 + MnS = 2FeS0 4 + MnS0 4 + S 
and 
2FeS0 4 + 2MnS = 2FeS 
+ 2MnSO, 
adding (1) and (2) we have 
Fe 2 (S0 4 ) 3 + 3MnS = 2FeS + 3MnS0 4 + S 
and 2Fe 2 (S0 4 ) 3 + 2FeS =6FeS0 4 + 2S . . . 
and (3) + (4) = 3Fe 2 (S0 4 ) 3 + 3MnS = 6FeS0 4 + 3MnS0 4 + 3S 
A3 
(1) 
( 2 ) 
(3) 
( 4 ) 
(5) 
or jks= Fe 2 (S0 4 ) 3 + MnS = 2FeS0 4 + MnS0 4 + S . (6) 
\ 6 ) 
which is identical with (1), and by adding more MnS we get the 
conditions of equation (2), and so on, repeating the cycle. 
Hence, if we add MnS to excess of Fe 2 (S0 4 ) 3 , we should get 
reduction of the ferric salt without formation of FeS. On adding 
excess of MnS, we get formation of FeS, and then on adding 
excess of Fe 2 (SO) 4 we get back to the same state of things as at 
first. 
The reaction of equation (1) can be obtained by very cautiously 
adding small quantities of suspended MnS to a very large excess of 
