34 Proceedings of Royal Society of Edinburgh. [sess. 
of these bottles containing a known quantity of ferric chloride 
solution, at least sufficient to completely cover the sample of mud. 
Another sample, as nearly similar to the first as possible, is taken 
and stoppered in another bottle for drying. In this way a large 
amount of valuable information might be gained; but it will be 
evident from the nature of the case that the actual figures obtained 
in any one particular case are affected by a considerable possible 
error. 
In the month of June 1881 I carried out a number of laboratory 
experiments bearing on this subject, using the sulphides of different 
metals of the iron group. These bodies were all prepared in the 
same way, namely, by precipitating the sulphates with sulphide of 
ammonium, and washing by decantation in stoppered bottles, always 
filled up quite full. A quantity of hydrated ferric oxide was also 
prepared by precipitating ferric chloride with ammonia and 
washing. All of these precipitates, when thoroughly washed, were 
preserved suspended in distilled water in well-stoppered reagent 
bottles. 
Ferrous Sulphide and Ferric Oxide . — When quite neutral these 
substances do not react on one another, at least at once. But if the 
water has the slightest acid reaction reduction of the sesquioxide 
and production of sulphur take place rapidly. A mixture of Fe 2 0 3 
and FeS in water and quite neutral was corked up and allowed to 
stand for five days, when the sediment was found to be separated 
into two sharply-defined layers — the upper red, consisting of the 
oxide, and the lower black, of the sulphide. When brought 
together, therefore, in presence of nothing but distilled water, there 
is no appreciable resultant action. 
Manganous Sulphide can be preserved perfectly under distilled 
water in well-stoppered bottles filled to the neck. A considerable 
quantity was prepared in the summer of 1881, and, when thoroughly 
washed, it was put away in three separate bottles. The contents of 
only one bottle were used for experimental purposes, and the upper 
part of it got coloured immediately black with oxide of manganese, 
from the oxidation of the flakes of sulphide which adhered to the 
surface of the upper part of the bottle, left dry when some of the 
water and precipitate had been poured out. This took place at the 
time, and was to be expected. The two other bottles, which were 
