HH62/1/M-LOTH/25

Transcription

[Page] 24

The pumped water, clear on coming out of the pit,
became opaque in an hour. On standing 48 hours, a
quantity of its iron was deposited, but it still re-
mained somewhat opaque, and distinctly irony. On
standing a week, the water became perfectly clear,
but iron in solution was in considerable quantity.
On standing two weeks, there still remained a large
amount of iron in solution.

The bing water underwent no change on standing,
as was to be expected.

By adding 2 drachms of freshly slaked lime to 1
gallon of the pumped water which had stood for 48
hours, and shaking, a complete precipitation was
effected in less than 10 minutes, leaving a clear water,
free of even the faintest trace of iron. A larger
quantity than 2 drachms was required 24 hours earlier.

The addition of 10 drachms to 1 gallon of the bing
soakage, and shaking, effected as complete purification
and decolourisation in the same time as 2 drachms did
with the other.

A point of great practical importance is this, that
unless lime is added in sufficient quantity to cause
marked alkinity, the precipitate is slow in falling;
but if it be added in sufficient quantity, the water in
a few minutes is rendered absolutely free of iron.

Another point of equal importance is the condition
in which the lime is when added. If freshly burned
limestone can be used, even in a comparatively fine state
of division, a quantity equal to three times the weight
of the freshly slaked lime is required to give as satis-
factory results in the same space of time. The reason
of this is that the presence of too much water pre-
vents the lime assuming that peculiar condition
known as slaked lime, in which the stone falls to an

[Page] 25

almost impalpable powder, exposing an enormous
surface to act quickly in producing alkinity. Care,
therefore, in properly slaking is a desideratum.
Agitating at the moment when added is, of course,
desirable. In working with large quantities of water,
perhaps a good plan might be to add milk of lime,
which is simply properly slaked lime well stirred
with water; or to have recourse to some method of
churning the slaked lime with the irony water at the
moment of its addition. I have specially laid stress
on the words freshly slaked, for slaked lime rapidly
becomes carbonated from exposure to the air.

In suggesting a way of preventing pollution of the
Almond from ironstone water, I would then point out
that for the pumped water, which, from its quantity,
is the only difficult one to cope with, a well-arranged
system of settling tanks, with means of thoroughly
mixing freshly and properly prepared slaked lime
with the water would effectively secure the desired
end. Cleansing of such tanks would require careful
attention, and the removal of the enormous quantity
of sludge, much labour. The bing water can be
collected by well planned drains, and similarly
treated. Its very small quantity offers no difficulty.

I am thus of opinion that by using the means above
indicated this pollution of the Almond by irony
water, and which ranks about first of all its pollutions,
can undoubtedly be wholly prevented, and dealt with
in a thoroughly satisfactory manner.

There still remains the question:- Is this means of
prevention in the meaning of the 'Rivers Pollution
Act' a means that can be considered a practicable
and reasonably available one? I do not know how
ironstone mining pays in this district, but I fear that,