An Improved Method of Purifying Water.
Year: 1899

page_text: COMPLETE SPECIFICATION.
An Improved Method of Purifying Water.
I, DR. JOHANN OTTO KRÖHNKE, of 54, Kaiser Wilhelmstrasse, Hamburg, Ger-
many, Chemist, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement:-
-
It is well known that on adding suitable chemicals to dirty water the latter
is clarified mechanically, the flocculent precipitates generated by the chemicals
bringing down with them matter suspended in the water and in part also matter
dissolved therein. In practice, iron salts and quick-lime, alumina and quick-
lime, magnesium sulphate and quicklime, are principally used. These methods
have not up to now been available for producing water well suited for human
consumption and free from foreign bodies, since even a small excess of lime,
which can never be avoided in continuous working, makes the water alkaline and
gives it a disagreeable taste. Furthermore, experience has shewn that the
application of lime in the proper proportions can be carried out only with difficulty
and that for complete chemical reaction the lime must be entirely slaked; but
the complete slaking of the lime requires a long time.
All these inconveniences are avoided by substituting levigated chalk for the
lime.
Chalk has several advantages over lime. It is first of all very easily levigated
and hence it can be well and easily applied in the proper proportions. It forms
with suitable precipitating and clarifying media, as iron oxide salts, alumina
salts, magnesium salts, well pronounced flakes; by means of which waters rendered
turbid by the presence of very minute suspended matter (mostly of the argillaceous
variety) which no filter can retain, are clarified in a short space of time, after which
they can be filtered. It has further been found that by the combination of the
aforesaid precipitating media with chalk, the water is deprived of colour, whether
the colouring be occasioned by organic substances or by iron dissolved in the
water. Chalk is, moreover, far less soluble than lime. Thus in neutral water
1 part of chalk dissolves in 16,000 parts of water, whilst quite one
part of lime dissolves in 750 parts of water. An excess of chalk, which by
reason of the slight solubility of chalk can only be trifling, would, in contra-
distinction to an excess of lime, do no harm; for chalk is not dangerous and has
a neutral reaction. Finally, the reaction of iron oxide salts and alumina salts
with chalk liberates some carbonic acid, whereby the palatability of the water
is increased. On the last two grounds the improved method is especially suitable
for the preparation of water for human consumption.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
An improved method of clarifying, decoloring, and removing iron from water,
especially for the purpose of human consumption, according to which, to the water

page_text: to be purified, there are added suitable known chemicals, as iron oxide salts,
alumina salts, or magnesium salts, in conjunction with chalk, in consequence of
which flakes are formed owing to the chemical reaction of the said chemicals with
the chalk.
Dated this 26th day of Sentember 1800
:
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.