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(Concluded from p. 48).

The surface waters used to supply London from tie
Thames or the Lea are filtered by the method of con-
tinuous filtration, a surface of one hundred acres beiiig
required for the purpose. The thickness of sand 6ifftn



* From A Paper read January 15, 1590. Reprinted in part firpm tbe
Journal of tht Astociatton of EttgiHtmng SocUtiet,

Digitized by VJ^^^^V IV^



CHilrtcAt NbWb, I
Jan. 30, 1891. f



Filtration of Natural Waters,



57



with the different companies supplying the city with
water, from two feet at the East London and Grand
Jundion Companies to fonr and a half feet at the Chelsea
Company, and the rate of filtration per hour in imperial
gallons pisr square foot of filtering surface is two and
one-sixth with the Lambeth Company, to one and a half
gallons with the Southwark and Vauxhall Company.
Two and a half gallons, or five vertical inches an hour
(which is seldom attained), is considered the maximum
consistent with good clarification. Complete analyses
are made of the water supplied to the metropolis by the
different companies. Some of the determinations, as for
instance colour, and the amount of permanganate to
oxidise the organic matter are made daily ; other chemical
determinations are made weekly. The monthly deter-
minations made by Dr. Percy P. Prankland, of the
baderia in the waters of the different companies have
been inspended since December, z888. The average
reduftion of the number of micro-organisms present in
the waters of the Thames and Lea, was in 1887 97*6 per
cent in the case of the Thames, and 93*9 in the case of
the Lea. **If,'* sayi the report on the metropolitan
supply for December, z88S, ** these figures could be
accepted as at all representing the degree of security

J liven to consumers of the waters of those rivers by pre-
Iminary filtration, it is evident that the views on this
subjeA acquired by a consideration merely of the results
of comparative chemical analysis of filtered and unfiltered
waters would have to be considerably modified, and the
charader of the water supply would be correspondingly
raised in the public estimation. Further, if the results
obtained from month to month could be relied on as an
index to the effed of filtration m eliminating objedion-
able matters from the water, the baderiologtcal method
would seem to afford a delicate and easily applied test of
the working efficiency of the filter."

The average numbers of baderia in the water of the
Thames is generally less than in the Spree at Berlin;
thus during the year ending December, 1887, the highest
number in November was 81,000, and the lowest in June
was aaoo, the average for the year being 21,492.

The only filtering plant in this country that I know of
which at all compares with the plants in Europe, is that
at Pou^hkeepsie, where the Hudson River, water is con-
verted mto good clear water, though not absolutely free
from colour. Mr. Fowler, the superintendent of the
works, writes me with regard to the details oi the filtra-
tion : — ** Our usual rate of filtration is about six inches
per hour, vertically, and this we regard as the maximum
of efficiency, although we can sometimes do good work,
BO far as clarifying is concerned, at double that rate, and
at other times are unable to do good work at one half
that rate, although the latter condition is exceptional.
Very much depends upon the condition of the water in
the river. The depth of water on the sand varies from
one to three or four feet, and the difference of level
between the surface of the water on the beds and that in
the intermediate basins is usually two to four or five
feet."

The rapid filtration of water through coarse gravel is
not unfi-equently carried out at water works to remove
the larger particles floating in the water. When a filter
of this kind is cleaned, it is surprising to see the amount
of fine dirt of all kinds that has been intercepted by the
coarse material. Filters of this charader do not pretend
to purify the water in the sense of removing baderia or
in oxidising the organic matter, but they are useful just
to the extent to which they clarify the water and thereby
imjprove its appearance.

The American system of filtering large quantities of
water may be said to be the mechanical filters working
under pressure. These filters are composed of four or
five feet of moderately fine sand (some have also a
mixture of coke), enclosed generally in boiler-iron cases.
They work with tremendous rapidity, sometimes over a
hundred vertical feet an hour, but forty feet is said by



some to be the highest rate consistent with good filtration.
In this system alum is generally added to the water as a
coagulent. Its effed in very small amount is quite
remarkable — say a grain to a gallon, or even less— in
retaining the solid matters of the water in the sand of
the filter. The alum is decompNosed by the carbonates in
the water, and hydrate of alumina is precipitated. This
is a gelatinous and slimy substance, and immediately
surrounds the alga, clay, and anything else that may be
suspended in the water, and the sand retains this coagu-
lated mass. Alumina has also the effed of taking the
colour out of water, so that clear, colourless water may'
be obtained by this process from swampy waters full of
growing algs with almost incredible rapidity.

These filters are in very general use in paper mills and
other industrial works where a clear, colourless water Is
needed, and where a coloured turbid river water is the
only natural supply available. They have also been
introduced into some cities of considerable size, as, for
instance. Long Branch, Chattanooga, and Atlanta, and
they are said to give water that is satisfadory to those
who use it. The objedion to the system is the use of
alum. If all the alum used were decomposed in the few
seconds that it takes the water to pass through the filter,
so that no undecomposed alum passed into the filtered
water, there might be no objedion to its use, but this is
not always the case. Tbe amount of alum used is
ordinarily small, and it is claimed that if it even all went
into the filtered water it would not injure it for drinking.
This may be so, but the prejudice that exists against
drinking water which has been treated with ** chemicals "
is so strong that it is not likely that any system using a
coagulent in a soluble form will find general acceptance.
Under some conditions, when the water has high colour
with much suspended matter, the alum has to be in*
creased largely to give good results. I have known as
high as seventeen grains to the gallon to be used with a
very bad swampy water.

In this connedion should be mentioned the spongy iron
filter of Bischof, which gives most excellent results both
in taking out suspended matters from the water, including
the baderia, and also decreases the hardness of the water.
This filter has been used on the small scale in houses,
and also on the large scale in Antwerp, to decolourise and
otherwise purify the water of that city. The filter is
composed of finely-divided metallic iron made by re-
ducing iron ore by means of carbon at a temperature
below fusion. Its adion was not understood for a long
time, and the mystery that surrounded it was an
additional recommendation for it. The rationale of its
working seems to be this, namely, that the iron being in
a very finely-divided state is dissolved to a slight extent
by the combined adion of the oxygen and carbonic acid
in the water, and the ferrous carbonate thus produced is
further oxidised, forming hydrate of iron, and then this
ads as a coagulent just as the alumina hydrate does.
The system was said to be too expensive on a large scale,
and it has now been replaced at Antwerp by the Anderson
process, in which the dark water is made to pass through
a long revolving iron cylinder in which there is a large
quantity of fragments of cast iron. These fragments of
iron in their fridion one on the other are abraded, minute
particles are broken off which are dissolved in the way
above described. The water coming from the revolving^
cylinder is exposed to the air, the iron oxidises and pre*
cipitates, combines with the colouring matter in the
water, encloses the solid particles, and is then filtered
out through sand. The process is said to work satis-
fadorily and give clear, colourless water. There is no
objedion to this Use of iron as a coagulent, provided that
it is all oxidised and precipitated, and none is carried in
solution into the filtered water ; but this takes time.

Both alum and iron salts have a tendency to sterilise
water. Their adion may be both dired by killing the
baderia, and indired by removing them with the precipi-
tated alumina or iron hydrate. If a drop of a solution of

Digitized by VJ^^^^V iC



S8



Specific Gravity cj a Liquid.



fCttBJItCALKBllP«,
I Jan. JO, 1891.



«ium or of iron chloride be added to a gallon of turbid
watcir, it wiU become perfSedly clear in the coarse of a
few boors, the alumina or iron hydrate, which is formed
in the water, settling to the bottom and carrying all the
Mnpended matters with them. It has been proposed to
clarify Mississippi water by adding a very small quantity
of an iron solution to the water in the settling basins.

I have laid some weight oif the desirability of following
nature's processes in the purification of impure waters,
(^either the American system, with its mighty rush of
waters, or the European system, with its calm, steady,
ai)d deliberate fiow, finds any analogy in nature. In the
rapid-working mechanical filters a coagulent is used to
grasp and bold the suspended matter ; in the continuously
woiking filter beds the baAeria are put to a novel use in
retaining the solid matter on the sticky surface of the



Natttfe uses these methods also ; she removes colour
1^ means of clay in the soil and intercepts mechanically
in the badcria-laden soil all the solid matter in the water.



b«t she goes farther than this, and, giving the badtria

Mi playrMaks «p tlw oraaaic commnMids and leaves fN>

I of ttieir cxisceBGe behind. To do this, time is



** The baderia of nitrification,*' as Dr. Smart
has well said, in referring to the systems of rapid filtra-
tion, ** cannot be harnessed to the work of artificial
filtration."

The rate at which nature works may be expressed in
the amount of rainfall. If we Uke the rainfall at fifty
inches, and assume that even half of this sinks into the

Sound (a very high estimate), we have twenty- five
. chef yearly on a square foot of surface. The amount
9f water which gpes through the Berlin filters, at a rate
of four inches an hour, is more than 1250 times this
emount. If we wish to imitate the process by which
oatare makes its springs, we must pour the water from
river or lake which we wish to filter intermittently on
the surface of ground which is favourable for this pur-
pose. The favourable conditions are these :~The ground
must be sufficiently porous to allow the ready flow of
water through it, and it must have such relations to the
strata bekiw as will enable us to colled the water at
some lower level. It would not profit us much to pour the
water on to a gravel bed if we could not find it again
after it had been filtered. If the natural conditions for
this purpose are not favourable, drains would have to be
put in at suitable depths to colled the filtered water.
Water purified in this wa;^ would in no wiee differ from
natural spring water, provided that the amount of water
applied did not exceed the capacity of the filtering
area.

The question o^ the maintenance of the purity of the
water supplies of large cities, which are dependent upon
lurface waters, is daily becoming more urgent in this
country as the population becomes more dense on the
colledmg areas, and the protedion of streams against
pollution becomes more and more difficult. The radical
remedy in such cases is to take water from another and,
usually, more distant region, which, it is probable, will
never become thickly settled. But in filtration, both in-
termittent and continuous, when intelligently conduded,
we have a substitute which can give as clear, colourless,
and, we have good reason also to suppose, safe drinking
water.



The Prodtttflion of Higher Alcohols Daring the
Alcoholic Fermentation. — L. Lehdet. — In view of
the author's results, it is impossible to admit that the
higher alcohols are exclusively produced by the normal
fermentation of sugar, and their formation must be chiefly
•oaght for elsewhere. Their origin may be traced to the
development of a micro-organism, the adfon of which at
the outset of fermentation is smothered by the ad ion of
the yeast, but which resumes its adivity when the yeast
has completed its iMk^-^CompttrRindHs, vol. cxii.. No. a.



THE SPECIFIC GRAVITY OF A UqUtl>,

A FUNCTION OF ITS BOILINOPOINt

AND MOLECULAR WEIGHT.

By A. B. RICHARDSON, AiMc.liiit.Bl«d.Biis.



Thb boiling-point of a liauid is to some extent d^endeol
upon the molecular weight of that liquid. This fad tB
best observed in the case of the homologous series in or-
ganic chemistry, in which a fairly constant rise in the
boiling-point occurs for a constant increase of molecolar
weight. Nevertheless, between sptcific gravity and tile
temperature of ebullition, no definite relations seem to
have been observed.

If, by a new mode of procedure, some connedion ^
.and to exist between these two quantities— ^be"
point and specific gravity— there Is no reasoa 4o t



found to exist between these two quantities— ^beBiea*
gravity— there Is no leasQa 4o 4odM
that a material aid would be leadeeed to the tol etioo mi



the flsore important probleas, naineily, the depeodenoe of
specific gravity epoa molecular weight. In this fiapeiv
only ^wse liquids which possess a specific gravity greater
than unity have been examined.

Under what conditions must a liquid be placed that te
specific gravity may appear as a fundion of its boiling«'
point ? The boiling- points, pure and simple, apparently
have no connedion whatever with the specific gravities
and thus some other temperature must be considered.
Imagine the case of a liquid heated to temperatures Ux
above its builing-point. Also conceive that ebullition has
by some means been prevented. Under such, circum-
stances it is palpable that the specific gravity of the liquid
will have much decreased, takmg it for granted that the
liquid would continue expanding. At some temperature,
constant for each liquid, the specific gravity would at
lait assume unit value. Here then is a new condition of
Hquid matter, namely, the temptfature at which tMidb
given liquid attains unit specific gravity.

To arrive at these temperatures two measurements are
required for every liquid. We must know (1) the specific
gravity at some given temperature, and (2) the rate of tx-
pansion between o** and the boijing-point.

In the following tables these temperatures have been
calctilatcd for a few liquids. The spiecific gravities ani
rates of expansion were taken from Professor Thorpe^s
paper on a|«ecific volume {yanrH* Cktm. Boe^t 1S80).

in this table m s molecular weight, T s anit specific
gravity temperature (Centigrade), T«a absolute tempera-
ture of unit specific gravity, I « boiling-point -(Centigrade),
and ta »> absolute temperature of boiling.

With inorganic compounds we have the following re-
sults. (See Table, p. 60).

The values of T were calculated from the equation for
liquid expansion, y^^i^ai^^bt*'^^ci^. The values of a,
b, and c are given, in the paper above mentioned, for all
temperatures between 0° and the boiling-point for each
liquid. The equations are here assumed to hold true for
temperatures abo94 the boiling points. Curves I. and II.
are obtained by plotting the values of specific gravity as
abscissae, and temperatures of unit specific gravity as
ordi nates, from Tables I. and II. respedively. The curves
show that specific gravity is a fundion of the temperature
of unit specific gravity. Since the rates of expansion of
the various liquids are so extremely variable, no such
relation could have been predided.

The values of -. are very uniform, and many of them

m

closely approximate to the number a. It seems extremely

probable that if a large number of liquids were examined,

they might admit of division into groups, such that for

T
each group a constant valne of . virould be obtained.

m

Such a division would at first be purely empirical. The
reason of such a grouping would possibly appear wheo a



Digitized by



Googk



Jao. 30, 1891. I



specific Gravity of a Liquid.



59



Digitized by



Google



do



London Water Supply.



f CtftMICAL NBWt^

1 Jmn. 30, 1891.



Molecoltr

FormaU. wdgbt.

CaH.OCl 78*5

CHaCHCla 987

CHaCla 847

CCI3COH Z47

CCI4 X53-4

CCUCOCI 182

COfOJCU X64

CCljCHCla 2027

CCUBr Z98

SaH4lCl X90-5

CaH^Bra z88

CHB'3. a53

ICl 162*5

CHCI3 Z19

Bra •• • 160



Table


h'-Organu


Compounds,




nit specific


Specific


Boiling


T


avity temp.


gravity.


poinu


m


84*


»*I3773


507'


1-07


'35


X'20394


59*9


1-37


198


1-37776


41-6


23


220


1-5448


97-2


»-5


271


X-63I95


767


»-7


322


x*6564


X18


176


326


x-69225


ziz'9


2


393


170893


X591


1-9


425


2-05496


X04-07


2-15


506


2-X61439


140


2-6


518


2-21324


131-45


2-8


646


2-83413


151-2


2-56


730


3*z822


xoi*3


4*49


246


x-52657


61*2


2-07


619


3*18828


60


3-8



I

x-65
2-27

4-75
2-2

3-5
2-8
2-9
2-47

^V
3-6

3-9
4*3
7-2

4*02

10-3



If
I-I3

x-23

x-49

«-33
1-56
1-52

x-55
x-55
1-85
z-88
1-95

2'l6

2-68

1-55
2-68



Pomiila. m,

CSa 76

PClaCaHsO 146*7

SiC]4 X69-4

SOCla.'.' .*.' •'•' .*.* 1x8*7

POCIj X53

TiCh x^

vods m

POBfCIa X97'7

AtF^ X32

PBrs • 271

SOaCIa X35

QH.PCIa 1787

PSCI3 X69

SSCla X35

S11CI4 •• •• •• •• 279

CrOaCla •• •• .. 202*7

SOaOHCl 1x6-5



T.

1x2
210

244
287
297
345
390
440
490
635
793

283
304
361
402
438
494
503



Table II.

Specific gravity.

1*292x5

X-30526

1*52408

X -6x275

X-67673

X-7IX6

x-76o88

1-8653
2*12065
2-6659
2-923 IX

X708X4

x-3428

x-6682

x-7094

2-2787

X-96X

x-78474



4604
1x7-5
57*57
7595
78-8
X07-23

136-4
X27-X9

X37-6

6o'4

X72-9

6995
224-6
X25-07
138-12
X13-89
XX5-9
X55-3



»-47

x-4

1-45

2*X

2-5

2*2
2'06
25
2*5

4-8
37

2*1

17
2*X
2*2

x-57

2*4

43



t


ta


2-44


X*2I


x*8


X-24


4-2


1-5


3-78


x-6


377


1-62


3-2


x-62


2-8


x-62


346


x-78


3-6


2-46


10-5


2-72


4-6


2*39


3-05


r63


x-36


z*x6


2*85


1*59


a-9


1-64


3-8


x-84


4-26


x-95


3-2


2*82



■nflBcient number of examples had been examined. We
should thus have the following conditions :^

Specific gravity 00 temperature of unit specific gravity.
Temperature of unit specific gravity 00 molecular weight

(because « approaches constant value), and hence specific

gravity 00 molecular weight.
Lastly, there is a greater uniformity between the values

of -1 than between those of - , and consequently all that
has been said with regard to values of 1 applies with



Moreover, it should
Ta.



even greater force to values of 3-S.

ta

be remarked that the numbers representing^* regarded

ta
In general, increase with increasing specific gravities, and
In faA usually assume values Viry ctouly approximating
thi actual specific gravitiis themstlvis.

Curve III. represents this relation. Although these
curves are represented as straight lines, it will at once be
evident that they could, with equal right, be regarded as
sinuous, similar to those of Curves I. and II. (Points on
Curve I. are expressed by the multiplication sign ; those
on Curve II. by the addition sign).

Nothing can be definitely decided until many and more
varied liquids have been examined. Consequently this
paper can avail nothing except to indicate a possible
source of a more intimate conne^on between the physical
properties of liquids.



LONDON WATER SUPPLY.
Report on the Composition and Quality op Daily
Samples of the Water Supplied to London
FOR THE Month Ending December 3XST, X890.

By WILLIAM CROOKBS, F.R.S.;

WILLIAM ODLINO. M.B., F.R.S., F.R.C.P.,
ProfeMor of Chemistry at the Univertitv of Oxford ;

and C.MBYMOTT TIDY.M.B., F.C.S., Barriiter-at-Law,

Profeisor of Chemistrir and of Forensic Medicine at the LoadoB

Hospital i Medical OiBcer of Health for lalinfton.

To General A. De Courcy Scott, R.A.,
Water Examiner ^ Metropolis Water Act, iSyu

London Janoary 9th, 1891.
Sir, — We submit herewith the results of our analyses
of the X33 samples of water colleded by us during the past
month, at the several places and on the several days indi-
cated, from the mains of the seven London Water Com-
panies taking their supply from the Thames and Lea.

In Table L we have recorded the analyses in detail of
samples, one taken daily, from December xst to December
3xst inclusive. The purity of the water, in reaped to
organic matter, has been determined by the Oxygen and
Combustion processes ; and the results of our analvses by
these methods are stated in Columns XIV. to XVIIL

We have recorded in Table IL the ^nt of the several
samples of water, as determined by l^e colour-meter
described in a previous report. \

In Table IIL we have recorded the oxygen required to

Digitized by VJvb^^V l^



CnrncALNfwt,!

JM. 30,1891. f



Chemical Notices from Foreign Sources.



6x



oxidiM the organic matter in all the samples submitted
to analysis.

Of the 133 samples examined, the whole were found to
be clear, bright, and well filtered.

It will be noticed that from the X5th to the 3xst of the
month, the regular examination of samples drawn from
the stand-pipes day by day, was largely interfered with by
the prevailing frost, which, while ^considerable also in
severity, has not for many years past been equalled in
duration, beginning as it did on December gth, and con-
tinuing, pradically without intermission, well into the
present 3rear. That this wholly exceptional frost, though
offering impediments to the process of filtration and re-
tarding the rate of filtration, did not interfere with its
thoroughness, is shown by the circumstance that no one
sample of water, alike among those included in the
Tables, and among numerous supplementary samples
submitted to examination, was found otherwise than free
from colour and turbidity. Moreover, in respedt to
chemical charaders generally, the water supply for
December was found to compare favourably even with
the supply of the previous summer and autumn months,
as shown in the following Table of results afforded by
the water distributed by the Companies taking their
supply from the Thames :^

Ratio of Ox^cea Organic Organic

brown to required for carbon per carbon per

blue tint. oxidation. 100,000. 100,000.

Meant. Meani. Meant. Maxima.

June •• •• 12*0:20 0*049 0*150 0*166

July •• .. i6'i:ao 0*056 0*153 0*185

August. •• 17*1:20 0*065 0*150 0*175

September*. 11*5:20 0*044 o*>47 0*170

Odober .. 10*4:20 0*040 0*136 o'xoo

November.. 13*1:20 0*045 0*142 0*258

December •• 14*8:20 0*045 0*136 0*148

It came to our notice, however, that some of the
Thames-derived water distributed during the later part of
December, and at the commencement oithe present year,
manifested, in the case of certain particular samples, an
unpleasant faint taste associated in yet fewer instances
with a corresponding odour. From our analysis of
different samples, we were able to satisfy ourselves
definitely that the occurrence of this taste and smell, both
evanescent, did not depend on any contamination of the
water with animal matter ; and from a consideration of
the exceptional meteorological conditions prevailing of
combined frost, fog, and snow, and from our examination
of various samples of snow and snow-water, we are in-
clined to attribute the occurrence in question to an ad-
mixture with the main supply of a small proportion of
water furnished by the melting of heavily fog-laden snow,
such as some of that which we had the opportunity of
experimenting on.

We are. Sir,

Your obedient Servants,

William Crookbs.

William Odlino.

C. Meymott Tidy.



CHEMICAL NOTICES FROM FOREIGN



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