removed, together with most of the sediment which has
formed thereon, as often as necessary. Every few months,
or oftener if required, the sand can be thoroughly washed
and replaced. A layer of finely -granulated polarite and
sand, in equal quantities, may be substituted for the lower
half of the sand layer, and improves the character of the
filtered water in some instances, especially where the water
to be filtered contains much vegetable organic matter, as is
usually the case when taken from ponds. For the polarite,
magnetic carbide, spongy iron, or animal charcoal may be
substituted to suit particular circumstances. Animal char-
coal, from the remarkable power which it possesses of removing
certain colouring matters from water, and of absorbing or
oxidising organic matters generally, of a complex character,
used to be considered one of the best, if not the best, of ail
filtering materials. Water, however, which has been in con-
tact with it forms a favourable medium for the growth of low
forms of life, and bacteria grow within its pores. Prof. P.
Frankiand found that for some days animal charcoal removed
most of the bacteria, but that it gradually lost this power,
and before the end of a month the filtered water contained many
more germs than the unfiltered. It will remove traces of
lead, but this property it does not retain for any lengthened
period. Vegetable charcoal, ground coke, and other forms
of charcoal also are used as filtering media, but they do not
possess the decolorising and oxidising powers of animal char-
coal. They are equally efficacious in removing low forms of
life, and retain this property longer. Ground slag, pumice,
sandstone in slabs, etc., are occasionally employed in filters,
but possess no advantage over good sand. Sponge soon
becomes foul, and only acts as a coarse strainer ; its use is not
recommended.
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254 WATER SUPPLIES
Whatever material be used, it must be remembered that
it can only retain its efficiency for a limited period, and no
filter should be purchased which does not permit of the
filtering media being easily removed for cleansing or re-
newal. The filter should also contain a sufficient amount of
the material to produce something more than a mere straining
action. If not of sufficient depth, it may remove all the
coarser suspended matters, and the water appear bright, yet
the micro-organisms may pass through with the utmost ease.
Earthenware vessels are the best for containing the filtering
medium. Galvanised iron is easily acted upon, and may
contaminate the water with zinc. Wooden casks may be
used if the inside has been previously well charred, and if
the charring be repeated occasionally.
When drinking water is of suspicious quality, and there is
the slightest doubt about the efficiency of the filtration, it
should be well boiled before use, say for ten minutes. This
kills everything save certain very resistant spores; but as
there are good grounds for believing that none of these spores
are disease producing, their presence is of little consequence.
It is better to use the water soon after cooling and before
the spores have had time to develop. Boiling also removes
most of the carbonates of lime and magnesia, rendering the
water softer; as the dissolved gases are also given off, its
taste is flat and insipid. It can easily be again aerated by
pouring through a cullender or sieve from some little height,
when the finely-divided streams of water again take up gases
from the air.
By distillation a pure water may be obtained from the
sea, and from other salt- laden or impure waters. The
saline matters remain behind in the boilers, and the steam,
when condensed, can only contain any traces of volatile im-
purities which may have been present. These volatile sub-
stances have been charged with causing diarrhoea, but it is
much more probable that the illness was due to defective
distillation allowing some of the impure water to gain access
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DOMESTIC PURIFICA TION 255
to the vessel in which the distilled water was being condensed
or collected. By aeration the insipid flavour of distilled
water may be improved.
When tea or coffee is made with boiling water, the astrin-
gent matter in the leaves or berries may tend to produce still
further purification. In many epidemics of typhoid fever,
it has been noticed that persons who drank the infected water
only when made into tea or coffee escaped entirely.
Turbid and polluted waters are sometimes clarified by the
addition of from 2 to 6 grains of alum to each gallon, a very
little lime also being added if precipitation is not sufficiently
rapid. The flocculent precipitate which forms carries down
with it most of the bacteria. Perchloride of iron is sometimes
used instead of alum, and for the same purpose.
Where only foul-smelling, impure water is obtainable, Dr.
Parkes recommended the use of permanganate of potassium,
which is the active ingredient in Condy's Fluid. The solu-
tion of permanganate should be added gradually and with
constant stirring, until a very faint but permanent pink tint
is perceptible. A little alum is then added, and the water
allowed to clear by subsidence. Such waters also are im-
proved in quality by being stored in well -charred casks.
Very foul waters, when kept, often undergo a kind of fermenta-
tion, and become clear, bright, and palatable.
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CHAPTER XV
THE SOFTENING OF HARD WATER
As previously explained, the hardness of water is due to
the presence of compounds of lime and magnesia, chiefly
the former. The temporary hardness is due entirely to the
carbonates of these bases, whilst the permanent hardness is
caused by the sulphates, chlorides, and other salts. The
disadvantages attending the use of hard waters have already
been referred to, the chief being the waste of soap when the
water is used for certain domestic purposes. With very hard
waters this waste is so great that it is much more economical
to soften the whole of a public supply than for each con-
sumer to soften his quota by aid of soda or soap. From
the description of the various processes in use for softening
water, and their cost, the conditions which determine whether
it is advisable to adopt one or other of them will be
manifest.
Water may be softened — (a) by boiling; (6) by distillation;
and (c) by the addition of lime, with or without carbonate of
soda, soda ash, or other chemicals.
(a) By boiling, the carbonic acid gas is driven off, and
the carbonates of lime and magnesia which had been held
in solution by this gas are deposited. The process is trouble-
some and expensive. The Rivers Pollution Commissioners
calculated that the fuel (coal) necessary to be used to soften
1000 gallons of water by boiling for half-an-hour would cost
about 7s. 6d. The same quantity of Thames water softened
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THE SOFTENING OF HARD WATER 257
by soap would cost 9s., so that boiling is not much less
expensive than softening by soap. ♦
(b) Distillation naturally is much more expensive than
simple boiling, and would never be resorted to simply for
softening a water. Boiling merely removes the temporary
hardness ; distillation separates all the saline ingredients, so
that distilled water is the softest of all waters.
(c) By the addition of lime. Lime has a great affinity
for carbonic acid, combining therewith and forming carbonate
of lime or chalk. When lime, therefore, is added to a natural
water, the carbonic acid is absorbed, and the chalk previously
held in solution thereby is precipitated, together with any
carbonate of magnesia which may have been present. The
sulphates and chlorides are unaffected, so that the permanent
hardness is not reduced. Care has to be taken that an
excess of lime be not added, since it is somewhat soluble in
water, and any excess present will again increase the hard-
ness. As 1 cwt. of lime, costing Is., will soften as much
water as 2 cwts. of 60 per cent soda ash, costing 14s., or 1
ton of soap, costing over £30, there can be no question as
to the economy of using lime. Dr. Clark was the original
patentee of the lime process, and it is the one almost uni-
versally adopted. Since the lapse of his patent many
modifications have been devised for the purpose of dosing
the water automatically with the proper quantity of lime,
and for facilitating the removal of the carbonates precipi-
tated. Atkins', Gittens', the Porter-Clark, the Stanhope,
the Howatson, and Archbutt and Deeley's processes, are
those best known, but some of these are more especially
designed for softening water for manufacturing purposes and
for use in steam boilers, than for water for domestic use.
In Clark's original process lime water was added to the
water to be treated, and the mixture was allowed to clear
by subsidence in large tanks or reservoirs. To ensure com-
plete clarification required at least 24 hours. Large tanks
were necessary, and these had frequently to be cleansed.
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258 WATER SUPPLIES
Modem inventors have devised means for dispensing with
the large* settling tanks, and for ensuring much more rapid
and complete removal of the precipitated carbonates. In
Atkins' process lime is mixed with water in a cylinder called
the "lime cylinder," and the solution so formed passes
through special regulating valves into a " mixer," in which
it is mixed with the water to be treated in the proper pro-
portion. The mixture then flows into a " softening cistern,"
in which a portion of the precipitated matter is deposited,
and the partially clarified effluent is next conducted into
patent machine filters, which " are constructed with a series
of hollow metal discs, covered with cloth, so arranged as to
give the largest possible amount of surface in the smallest
space." Sets of revolving brushes are attached in such a
manner as to play over the whole surface of the discs when
set in motion, and by means of pulleys outside the tanks,
worked if necessary by steam, the brushes are made to
revolve, and the filters are rapidly cleansed. At Henley
(population 5000) such an apparatus, with three filters, has
been in use since 1882, and, according to Professor Attfield's
analysis, the water is reduced by the treatment from 19*5°
to 4*2° of hardness. At Southampton (population 65,000)
about 2,000,000 gallons of water per day are softened, and
the plant is said to be the largest in the world. It includes
twelve filters, a softening tank 76 feet x 45 feet x 5 \ feet,
two "lime" cylinders, mixer, and lime-slacking mill, all
comprised in one building measuring about 134 feet by 48
feet. Without enlarging the building additional plant can
be added, so as to increase the supply of softened water to
3,000,000 gallons per day. 1 At Lambeth Workhouse, with
1500 inmates, there is an installation for softening 300,000
1 Much dissatisfaction has arisen lately at Southampton in consequence
of the water, after being softened, .depositing calcareous matter in the
mains, and not always being delivered free from turbidity. Whilst, ou
the one side, this is declared to be the fault of the process employed,
the patentees assert that is entirely due to the careless way in which the
system is worked.
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THE SOFTENING OF HARD WATER 259
gallons of water per day. The plant occupies a space of
22 feet by 16 feet, and the only attention required is said
to be the labour of one man for an hour a day. The cost
of the plant was about £2000, and the total expense of
treating the water supply is said not to exceed £50 per
year, or, including interest on capital, about £d. per 1000
gallons. The saving in soap, soda, fuel for boilers, repairs
to boilers, tea, etc., is believed to amount to over £1000 per
year. The Atkins Company, recognising the validity of
the objections to this system where comparatively small
quantities of water are required, have recently introduced a
plant dispensing with the costly machinery, and reducing
the expense and trouble of cleaning and renewing the filters.
The apparatus (Fig. 17) consists of three parts, viz. a "lime
cylinder," B; a mixer, A; and a " softening cistern," D, holding
two hours' supply. The mixture of lime and hard water is
delivered at the bottom of the cistern, and the softened and
clarified water flows over the top into troughs, which convey
it into the storage cistern. The action is continuous.
Mr. W. G. Atkins has also recently introduced a new form
of filter, which is stated to be " capable of dealing with un-
limited quantities of suspended matters, and in which the filter-
ing medium is constantly being cleaned, sterilised and aerated."
The Porter-Clark Company claim that their system is
the most economical, since the apparatus is of a very simple
character, requires very little labour and attention, and
works under pressure, so that the softened and filtered water
can be delivered into high-pressure cisterns without pumping.
It consists of two vertical cylinders and a filter press. In
the first cylinder there is a continuous preparation of lime
water. In the second the hard water and proper proportion
of lime water are mixed, and in the press, which is made up
of a series of plates, with cloths interposed, the precipitate
formed is filtered out. Where large quantities of water are
being treated, some motive power is required to keep the
contents of both cylinders in a state of agitation. The
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THE SOFTENING OF HARD WATER 261
approximate price of a plant softening, automatically, 1000
gallons an hour, is £200 ; for softening 2000 gallons, £280.
The London and North- Western Railway Company use this
system at various depots. At Liverpool, Camden, Willesden,
and Kugby, about 1,000,000 gallons, in all, are softened
daily for use in their locomotives. Modified forms of this
apparatus are made for special purposes. One form, which
dispenses with motive power, save that of a man for a few
minutes daily, will soften from 500 to 2000 gallons of water
per hour, and by the use of various other reagents besides lime,
such as caustic soda and carbonate of soda, the permanent as
well as the temporary hardness can be reduced where necessary.
The Porter-Clark process has been adopted in a large number
of public institutions, manufactories, mansions, etc.
The " Stanhope " water softener (Fig. 18) occupies but little
space, possesses no movable parts, and no filtering apparatus,
the water being clarified by subsidence in special tanks con-
taining numerous sloping shelves, upon which the carbonates
are deposited. It aims at reducing both the permanent and
temporary hardness, lime and soda being the chemicals used
for this purpose. The only attendance required is that of a
man to mix the lime-water and soda every few hours, and to
open the mud cocks occasionally to let out the accumulated
precipitate. The cost of softening by this process is stated
by the makers to average Id. per 1000 gallons, though this
will depend upon the character of the water treated. It
appears to be a favourite with manufacturers, especially wool-
washers and bleachers, and with large users of steam power
for boiler purposes. Quite recently the Stanhope water
softeners and purifiers have been considerably improved. For
the sloping shelves in the clarifying tower a series of perforated
funnel-shaped cones (Fig. 19) have been substituted. These
cause the water to traverse the tower more slowly, and more
perfect sedimentation results; A continuous mechanical lime
mixer has also been added. For potable purposes some system
of filtration is necessary to secure absolute clearness. The
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Fio. 18.— The "Stanhope ' Water Softener,
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Til E SOFTKNtNa OF ttAK» WATJiK 263
makers recommend filter prossos, sineo thu work left for tho
cloths to do is altuoHt hi/, and they may bo used for a length
of time without requiring cleaning. Tho natural head of
water from tho clarifying tower supplies all the procure
necessary. Thin simple mode of filtration may he sufficient
for certain very pure waters, hut for contaminated waters
sand filtration would he far preferable.
The " llowatson " softener is somewhat similar in principle
to tho above. Tho lower portion of tho apparatus consists of
a tank divided into two. compartments, each having a hopper
bottom. Into one tho water and chemicals are introduced,
and after chemical action has taken place tho mixture passes
at tho bottom into tho other, which acts as a "subsidence
filter." Tho limo and other chemicals are contained in two
smaller tanks placed above tho larger, and which are used
alternately. Uy means of floats, cocks, and nozzles, tho
proportions of tho chemical solution and of the hard water to
bo softened can be regulated. No agitator is required, and
tho deposited carbonates aro removed by occasionally turning
tho sludge taps at the bottom of tho hoppers.
At Stroud Waterworks the water is softened and clarified
by a very simple modification of (Mark's original process, all
filtering machines being abandoned, lly aid of a small water
wheel, driven by tho water to be treated, two pumps aro
worked, one raising limo water and tho other the hard water.
By altering tho length of tho stroke the proportion of tho two
can bo adjusted, and as tho rapidity with which tho wheel
rotates depends upon the pressure of tho water in tho mains,
tho relative quantities of limo water and hard water pumped
remain constant. Tho treated water is clarified by subsidence
in largo settling tanks. Tho machine above referred to is tho
patent of (J. K. Uittons, Limited, and will soften 1,000,000
gallons of water per day. 1
Messrs. Arehbutt and Deeloy have recently devised an
apparatus which they regard as having many advantages
1 Tho amount actually noftunutl in 300,000 gallon* pur day.
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Fig. 19.— The Stanhope Water Softener (Clarifying Tower).
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THE SOFTENING OF HARD WATER 265
over others in the market, especially for treating waters
containing magnesia salts. The chemicals used (lime and
soda ash) are boiled with water and then mixed with the
hard water, contained in a tank, by means of a steam
" trajector." After thorough mixing, steam and air are forced
by a " blower " through perforations in a series of pipes laid
close to the bottom of the tank. This stirs up the mud and
diffuses it throughout the water, and when the liquid is
allowed to rest precipitation is very rapid. In from thirty
minutes to one hour the water is almost perfectly clear and
can be drawn off. By using duplicate tanks, one quantity of
water can be treated whilst that in the other is undergoing
clarification. Water which contains magnesia compounds,
after precipitation, still contains a little carbonate of magnesia,
which rapidly blocks up the boiler " injector." To obviate
this the water, when being drawn off from the settling tank
into the storage tank, is dosed with carbonic acid gas by aid
of a blower. The carbonic acid is derived from the combus-
tion of coke in a special stove. The water when sufficiently
carbonated no longer deposits in the tubes. By this process
the labour involved is as great for softening 2000 gallons as
20,000, but with large quantities the expense for labour is
said not to exceed Jd. per 1000 gallons. Some waters are
found to clarify much more rapidly if a little alum be added,
together with the other chemicals, and this the inventors
recommend in such cases.
The cost for chemicals required to soften waters of various
qualities is given in the following table by Messrs. Archbutt
and Deeley, and is quoted here, since the chemicals used in
this process are the same, both in quality and quantity, as
those used in other processes which are designed to soften
water containing both lime and magnesia. It will be observed
that the cost increases rapidly with the amount of sulphates
present, especially sulphate of magnesia, since such water can
only be softened by use of soda ash as well as lime. In each
case the hardness is reduced to from^T to 5°.
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266
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THE SOFTENING OF HARD WATER 267
The Maignen "Filtre Rapide" Co. are the makers of a
plant which softens and filters the water automatically.
By means of a small motor worked by the flow of the
water to be softened, the proper amount of " Anti-calcaire "
is added, and mixture takes place in a small tank. From
this the water flows to another tank, where most of the sedi-
ment is deposited. Finally it traverses one of their rapid
filters and reaches the storage tank in a completely clarified
condition.
Although certain of the processes described would appear
to require very little personal attention, according to the
statements of the inventors, yet, if uniformly satisfactory
results are to be obtained, there must be constant supervision.
The treated water must be repeatedly examined to ascertain
that neither too little nor too much of the lime or other
chemicals is being added. If too little, the water will not
be properly softened, and if too much, the water will be
rendered alkaline, and the magnesia will not be removed.
When the amount of lime added is a little less than the
theoretical quantity required to precipitate wholly the lime
and magnesia salts, the two carbonates separate in a form
which settles well, and the softened water filters readily.
When the full theoretical amount is used, or a slight excess,
the carbonates deposit slowly, and in a form which rapidly
clogs the filters. Even after passing the filter, more magnesia
continues to separate for from twelve to twenty-four hours.
When spring or deep -well waters are being softened, the
best proportions of lime water and spring or well water having
been once determined, it only remains to examine the water
occasionally to see that these proportions are being main-
tained, and that the lime water is uniform in strength. If
the lime water be not saturated with lime it will be too weak,
whereas, if by undue agitation it is not only saturated, but
contains lime in suspension, it will be too strong. With
river waters the case is often different. The composition
may vary considerably with the season, and, if a tidal river,