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NA TURE
543
THURSDAY, JUNE 22, 1911.
PROBLEMS OF POTABLE WATER.
Modern Methods of Water Purification. By J. Don
and J. Chisholm. Pp. xvi + 368. (London :
Edward Arnold, 1911.) Price 15s. net.
HEN Mr. Don read his paper on “The Filtra¬
tion and Purification of Water for Public
Supply ” before the Institute of Mechanical Engineers
in January, 1909, it was generally thought that a very
useful addition had been made to the literature on
this subject, and in following this up with the volume
under review, which is in effect an amplification of
the former publication, the authors have done a great
service to those whose duty it is to provide a pure
and efficient supply of water for domestic purposes.
Following a general introduction, the first chapter
deals with the sources of supply. The possible pollu¬
tions that may be expected are fully discussed, and
some most useful information is given of the best
means of detecting, and, as far as may be, prevent¬
ing them.
Obviously, all water destined for domestic purposes
cannot be taken from sources unimpeachable, both
as to purity and constancy of supply, and the next
two chapters in the book deal with the first steps
towards remedying these evils under the general
heading of “ Storage.”
The main inference that is to be drawn from this
section is that, in addition to ensuring constant and
adequate supply from sources which depend largely
on the rainfall over a limited catchment area, storage
undoubtedly has a very marked effect in purifying
and rendering harmless an otherwise polluted and
dangerous water. The work of numerous investi¬
gators is quoted in support of this contention, parti¬
cularly the valuable researches of Dr. Houston on
the storage of water from the rivers Thames and
Lea, published in his reports as Director of Water
Examination to the Metropolitan Water Board.
The result of these researches are very lucidly
summed up by the authors in the following sen¬
tences :—
“ 1. The microbes of disease, and those which are
indicative of sewage (B. coli) perish rapidly in stored
water. In about three weeks, generally speaking,
the safety change is complete, and the dangers
imminent from sewage pollution minimised.
“2. After being impounded for two or three weeks
the water is in a better state from a chemical point
of view, seeing that there is a well marked decrease
of ordinary ammonia, oxygen consumed, oxidised
nitrogen, lime salts, and occasionally of albuminoid
nitrogen.
“ 3. Storage deprives the raw water of nearly all
its sediment, and therefore serves to prolong the life
of the filter beds.”
There is one danger, however, occurring sometimes
after prolonged storage, which should not be lost
sight of; that is the abnormal development in the
reservoir of algae and other minute vegetable growths
at certain seasons of the year. These growths not
no. 2173, VOL. 86]
only cause great inconvenience by rapidly choking
the filter beds, but certain species give rise to exceed¬
ingly unpleasant odours and tastes in the water, which
cannot usually be got rid of by filtration. A remedy
for these evils, however, is suggested in the book,
namely, the addition of exceedingly small doses of
copper sulphate, which, it is stated, not only will
cause the death of myriads of these organisms, but
if added in anticipation of a rapid development will
prevent the growth taking place. The use of hypo¬
chlorites is also recommended.
Following on this exhaustive and extremely valu¬
able discussion of storage, the authors devote a large
section to the question of filtration. There are three
chapters devoted to this subject, entitled respectively,
“Sand Filtration” “The Management of Sand
Filters,” and “ Mechanical Filters.”
Under the first heading elaborate and exceedingly
interesting and instructive explanations are given of the
theory of sand filtration, which bring out very con¬
clusively the precautions which are necessary to ensure
efficient purification. The action of a sand filter
appears to be threefold; first, the mechanical strain¬
ing of the grosser suspended matter, this causes a
film or skin composed of silt, algal, and bacteria to
form on the surface of the sand; secondly, the living
algse in this skin seem to have a power of consuming
the bacteria which come within their orbit, thus re¬
taining many of the minute organisms which would
otherwise pass through the interstices between the
sand grains. The third action is brought about by
the slimy or gelatinous film which forms round the
grains of sand in the lower layers of the bed; this
has the power not only of retaining most of those
microbes and minute particles of matter which escape
the filmy skin, but also by a process of adsorption, of
acting on the organic matter dissolved in the water,
“mineralising” it, and converting it into innocuous
nitrates, sulphates, and carbonic acid.
It is pointed out that to ensure all these actions
taking place properly it is necessary that the rate of
filtration should be slow (about 4 inches per hour) and
uniform, as an irregular flow causes disturbance to
the microbes adhering to the slimy coating of the
sand grains.
All the operations in connection with the manage¬
ment of filters are dealt with under this heading, and
details are given of their construction. Descriptions
are given of many of the elaborate processes em¬
ployed in different parts of the world, and the chapter
concludes with a discussion on the use of coagulants
for the rapid sedimentation of matter in suspension,
and also for the formation of an artificial filtering
skin. This leads up to an important chapter on
mechanical filters, which are rapidly gaining favour
in various parts of the world. Numerous appliances
are described, differing chiefly in matters of detail.
The general features are the use of a much greater
head of water or of artificial pressure, and the use
of an artificial skin produced by the addition of alum,
and, if necessary, lime or some other alkali, if the
water has not sufficient natural alkalinity to precipi¬
tate the alumina. The filtering medium employed
S
©1911 Nature Publishing Group
544
NATURE
[June 22, 1911
consists of sand or crushed quartz, and in some cases
layers of some such oxidising material as polarite or
oxidium are used, in addition to sand, as in the
Candy filter.
The advantages of this method of filtration seem
to be the much more rapid rate at which the water
can be passed through the filters, and consequently
the much smaller area which they occupy, and the
ease and rapidity with which they can be cleaned
by mechanical means. This effects a great saving of
labour, and also does away with the workmen coming
in contact with the filtering medium. As regards
efficiency, it would appear that these filters are at
least as efficient as ordinary sand filters.
After two very useful chapters on “The Purification
of Water by Ozone ” and “ Water Softening and
Household Appliances,” two chapters follow on the
testing of water. They consist of a discussion of the
bacteriological, chemical, and microscopic examina¬
tion of the raw and filtered waters and the inferences
to be drawn from them.
The bacteriological tests suggested, and the methods
of applying them are, however, somewhat open to
criticism, and need revision in subsequent editions,
and the suggestion that these tests should be under¬
taken by the water managers themselves (unless
specially qualified) is also perhaps not of the happiest.
To anyone acquainted with the bacteriological and
chemical analysis of water, it will be apparent that
unless these tests are carried out by skilled operators
errors of execution and judgment are likely to crop
up. The growing necessity of dealing with impure
and polluted sources of supply renders frequent and
careful analysis imperative, and the example of the
Metropolitan Water Board and some of the Con¬
tinental and American water undertakers in appoint¬
ing a staff of qualified analysts might well be fol¬
lowed by other bodies.
As the authors point out, the interpretation of the
results of analysis depend largely on local conditions,
yet they give a table of the standards of purity re¬
quired in Britain and America, which, by the way,
are not applicable to a very large number of water
supplies, and they do not state from what source
these standards, in so far as they apply to British
supplies, are obtained.
In the remaining chapters, the book deals with
problems of distribution, and, in addition to engineer¬
ing problems, several pages are devoted to the de¬
velopment of such growths as crenothrix in the mains
and the action of peaty waters on lead. This latter
subject was exhaustively investigated by Dr. Houston
about fifteen years ago, on behalf of the Local
Government Board, and the authors quote exten¬
sively from his work; the two kinds of action, plumbo-
solvency and erosion, although attributed to different
causes, are frequently caused by the same water.
The authors have surely misunderstood Dr. Hous¬
ton’s work when they state (on p. 324) that erosion,
which results in the formation of the hydroxide of
lead, has probably no consequences obnoxious to the
consumer, for they go on to say that the hydroxide
scales away and mixes with the current. The section
no. 2173, VOL. 86]
concludes with a general discussion on public health in
relation to water supply, and an account is given of
several outbreaks of cholera and typhoid fever, which
have been attributed to that cause. It should have
been pointed out, however, that in the case of the
epidemics at Belfast, mentioned on p. 348, the water
supply was completely exonerated by the Health Com¬
mission appointed to inquire into the matter.
The arrangement of the book is exceedingly good,
the type clear, and the numerous diagrams and photo¬
graphs make the descriptions of the various appliances
verv easy to understand. As appendices there are
some useful tables of filtration constants and other
engineering data, and a concise and well-arranged
bibliography of works on water purification.
Denison B. Byles.
GERMAN AND FRENCH BOOKS ON
CRYSTALLOGRAPHY.
(1) Lehtbuch der Kristallphysik (mit Ausschluss der
Kristalloptik). By Prof. W. Voigt. Pp. xxiv + 964.
(Leipzig and Berlin : B. G. Teubner, 1910.) Price
30 marks.
(2) Legons de Cristallographie. By G. Friedel. Pp.
v + 310. (Paris : A. Hermann et Fils, 1911.) Price
10 francs.
(3) Die Kristallgruppen nebst ihren Beziehungen zu
den Raumgittern. By Prof. E. Sommerfeldt. Pp.
vii + 79 (Dresden : T. Steinkopff, 1911.) Price 3
marks.
(i)'T'HIS treatise is based upon the lectures delivered
4 for some years past by Prof. Voigt at the
University of Gottingen, and it concentrates also into
a single volume of 964 pages the original work in phys¬
ical crystallography other than optical contributed in
numerous memoirs during the course of a long and
active career. Prof. Voigt’s name is, perhaps, most
familiar from his work on the elasticity of crystals
and their piezo- and pyro-electrical properties. These
branches of physical crystallography are well repre¬
sented in the book before us, and the only criticisms
that suggest themselves are that Prof. Voigt has not
given us more experimental details and illustrations
of the interesting forms of apparatus employed in
the researches, and that British work in this branch
of science, especially the thermal expansion and elas¬
ticity of crystals, is not referred to. The result of
these omissions is that in the first place the book
presents a somewhat forbiddingly mathematical
aspect, the theoretical and mathematical side vastly
predominating and entirely overshadowing the prac¬
tical experimental side of the subject, and that in the
second place a certain narrowness of outlook is in¬
evitable.
Having said so mucn, however, and remembering
that Prof. Voigt’s chair is that of theoretical physics,
the thorough manner in which the subject is dealt
with inside these somewhat narrow lines cannot fail
to impress the reader. The most valuable considera¬
tion is, moreover, that we have here brought together
for us the facts and theories for which hitherto in¬
vestigators and students have had to search through
the numerous original papers of Prof. Voigt. The
©1911 Nature Publishing Group