137
MANGANIFEROUS NODULES IN THE
BOULDER-CLAY OF ESSEX.
By [MISS] MAY THRESH.
[Read December 14th, 1901.]
Some time ago it was remarked that in certain soils in Essex
there occurred small nodules which in appearance bore so close a
resemblance to seeds that they were almost indistinguishable in
situ. It was observed that these nodules were only found in soil
overlying the Essex boulder clay. They are brown in colour,
often almost a perfect sphere in shape, and very hard. In size
they vary considerably, the largest being about five millimeters
in diameter and the smallest exceedingly minute.
A sample of the soil containing these nodules was taken ;
they were carefully sorted out and weighed, and it was found
that they formed about .1 per cent, of the total weight of soil
examined. The nodules were then submitted to a qualitative
analysis and were found to contain iron in considerable quanti-
ties. It was noticed on the addition of hydrochloric acid that
chlorine was given off, proving the unexpected presence of the
peroxide of manganese. On separating the insoluble part from
the soluble filtrate it was seen that the former consisted of a
sandy whitish residue of silica.
The presence of manganese dioxide rendering the nodules
of greater interest, a quantitative analysis was made. The sub-
stance was first powdered and a weighed portion was heated to
200° C. in order to drive off any water present and determine the
percentage of moisture. The dried substance was then digested
with strong hydrochloric acid and the metallic compounds were
thus separated from the insoluble silica, which was dried and
weighed. The soluble portion containing the chlorides of the
metals was next neutralised with ammonium carbonate and the
iron was precipitated by means of ammonium acetate, washed,
dried, and weighed as ferric oxide.
The manganese left in the filtrate was precipitated by means
of ammonia and a saturated solution of bromine water, dried,
and weighed as manganese tetroxide. The calcium left in the
filtrate was precipitated by ammonium oxalate, dried and
weighed as lime.