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gives no accurate results for the determination of
nickel. According to the experiments of Krauss,
the method is available for the determination of cobalt,
where, however, the oxidation is better efiieded with
hydrogen peroxide.

(To be contiaaed).



ON A NEW QUANTITATIVE SEPARATION
OF MANGANESE AND ZINC.

By PAUL JANNA8CH and J. F. McGREGORY

Thb new method of separating manganese and zinc
described below depends on the easy and complete
conversion of the former metal into manganese hydro-
peroxide, whilst the sine compounds undergo no changes.
Carnot was the first who precipitated the manganic salts
alone by hydrogen peroxide, and thus determined the
manganese quantitatively.

As one of^ the writers more than two years ago made
numerous preliminary experiments concerning the oxid-
ising adion of hydrogen peroxide, and has recognised it
as a remarkably efiScient oxidising agent in his new
method for the determination of sulphur, he thought it
advisable not to delay any longer to commence a series
of quantitative separations by means of this reagent. The
first of these separations is here communicated.

In their first experiments they set out with solutions of
the mixed sulphates, acidulated with dilute hydrochloric
acid (5 — 10 c.c), adding a moderate excess of strong
ammonia, and then effedmg the precipitation with hydro-
gen peroxide with prolonged heating on the water-bath.
Here considerable quantities of zinc oxide were invariably
found accompanying the manganese precipitate. In an
especial case where the manganese precipitate had been
left covered upon the water- bath for more than four hours,
the manganese separated was found to contain 0*0822

frm. ZnO. (The quantities taken had been 0*5380 grm.
InS04,5H20, and 0*5602 grm. ZnS04,7HaO.) That
precipitations of zinc were conneded with the expulsion
of the excess of ammonia appeared from the solutions
filtered from the manganese precipitate, which, on ei&n-
centration, soon became turbid from the separation of
white flocks, which subseqtiently, however, re-dissolved.
When we afterwards heated on the water-bath ibr a
very short time only (the other conditions remaining as
before), the results were considerably better, so that the
mean proportion of manganous oxide was found by 2*5
per cent too high, a value which could be reduced by 0*5
per cent by washing the manganese precipitate with
dilute ammonia. Thoroughly satisfadory results were
only obtained by considerably increasing the proportion
of ammonium chloride and ammonia in the liquid to be
precipitated with hydrogen peroxide, and working after-
wards exadly according to the following diredions — a
mixture of 0*5 grm. manganese sulphate, and the same
weight of zinc sulphate are placed in a Berlin-ware capsule
in 75 — 100 c.c. water. The capsule must be large enough
to hold conveniently 600 c.c. water. The solution is
acidified with a little dilute hydrochloric acid, and a large
quantity (at least 100 cc), of a solution of ammonium
chloride at 15 — 20 per cent is added. Finally, the liquid
is rendered strongly alkaline by the addition of 60—100



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i256



Certain Points in the Estimation of Barium.



fCBBMICALNBWt

I Blagr 99t 1891.



C.C. Strong ammonia, when no brown colouration of man-
ganic hy£oxide ought to take place.

The solution thus prepared and covered with a glass
capsule is at once mixed with an excess of hydrogen
peroxide (50 — 60 c.c. free from barium chloride), and all
the manganese is thus completely precipitated. It must
here be noted that at the end of the precipitation the
liquid suddenly boils up and spirts in consequence of the
oxygen gas liberated. The precipitate thus obtained is
heated for 10—15 minutes on a boiling water-bath until
the precipitate settles well after stirring. It is then
coUeded upon a roomy filter. The residue of manganic
oxide adhering to the porcelain is removed from the
capsule by means of a feather and rinsing with hot water
and a little ammonia, and at last the precipitate is washed
with boiling ammoniacal water and afterwards with hot
water alone until a drop of the filtrate evaporated upon
platinum foil leaves no trace of a residue. The manganese
precipitate can be incinerated in a platinum or porcelain
crucible without previous desiccation, and is then ignited
in the blast flame until the weight is constant. A repeti-
tion of the precipitation is perfeAly unnecessary. Nor is
it necessary to dissolve the precipitate in hydrochloric
acid and re- precipitate the manganese as a carbonate.

For the determination of the zinc in the filtrate after
removal of the manganese, there is the choice of two
methods. In one, the boiling ammoniacal solution is
precipitated with ammonium sulphide, and the precipitate
is filtered after heating for an hour on the water-bath.
As the washing of the precipitated zinc sulphide involves
much inconvenience it is advisable to pour through the
filter only the liquid in the beaker, and then return the
filter with the unwashed precipitate into the beaker which
contains only small quantities of zinc sulphide. The
precipitate is then dissolved in dilute hydrochloric acid
with the aid of heat, and the zinc is precipitated by
sodium carbonate in presence of only a small quantity of
ammoniacal salt. It must be noted that zinc carbonate
precipitated in this manner may contain a small impurity
of silica.

In the other method the zinc solution is evaporated to
dryness on the water-bath in a large platinum capsule
(stirring is not necessary towards the end) ; the residual
saline mass is heated to 125—150" in the air-bath for
about an hour, and the ammoniacal italts are expelled by
heating on an asbestos plate over the gas-flaine. The
saline masses which adhere to the sides must be occasion-
ally pushed down to the bottom of the capsule with a
stout platinum wire. An exposure of the ammonium
salts diredly over the flame is not admissible, as losses of
zinc might possibly happen. The non-volatile residue is
dissolved in hot water and a couple of drops of hydro-
chloric acid, the solution is filtered and precipitated at a
boil with sodium carbonate in a Berlin-ware capsule.

This method of separating manganese and zinc
possesses various advantages. 'l*he manganese is rapidly
precipitated, and the filtration and washing are so easy
that a determination of manganese in presence of zinc
can be easily carried out within two hours. The weighing
of the zinc does not involve any circumstantialities.
These distinguishing properties of manganese precipitated
with hydrogen ptroxide have already induced the authors
to attempt other separations in the same manner. They
are already in a position to announce that manganese and
nickel, and probably cobalt, can be separated in the same
manner. As they are at present examining the behaviour
of the alkaline potassium cyanides of cobalt, nickel, and
manganese with hydrogen peroxide, they will give full
reports on all these possible separations of manganese,
zinc, cobalt, and nickel.— yoMm.yiir PrakL Chtmis^ New
Series, Vol. xliii., p. 402.



Oxides of Salts of Chrome.— M. Prud'homme.—
An examination of chromium hydroxide, chloride, chlor-
ates, and sulphites from a tindorial point of view.— Af on.
Sci, Qu4S„ No. 584.



LONDON WATER SUPPLY.
Report on thb Composition and Quality of Daily
Samples of the Water Supplied to London
FOR THE Month Ending April 30TH, 1891.

By WILLIAM CROOKES, F.R.S.;

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

and C.MEYMOTT TIDY. M.B., P.C.S., Barrister-at-Law,

Profeseor of Chemistry and of Forensic Medicine at the London

Hospital: Medical Officer of Health for Islincton.



To General A. Db Courcy Scott, R.A.,
Watir Examimr^ Mttropolis Watgr Act, 1871.

London May 8tb, 1891.
Sir, — We submit herewith the results of our analyses
of the 1 82 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 tsJcing their supply from the Thames and Lea.

In Table I. we have recorded the analyses in detail of
samples, one taken daily, from April ist to April
30th 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 XVIII.

We have recorded in Table II. the tint of the several
samples of water, as determined by the colour-meter
described in a previous report.

In Table III. we have recorded the oxygen required to
oxidise the organic matter in all the samples submitted
to analysis.

Of the i8a samples examined, the whole were found
to be clear, bright, and well filtered.

Throughout the month o^ April the condition of the
water supply to the Metropolis continued to be entirely
satisfadofy, in reaped alike to freedom from turbidity,
from colour-tint, and from excess of organic matter.
Thus, in the case of the Thames-derived supply, the mean
ratio of brown to blue tint was as 13*9 to ao ; the mean
amount of oxygen required for oxidation, 0*055 grain per
gallon ; the mean amount of organic carboo, 0*155 part in
100,000 parts ; and the maximum amount in any sinele
sample examined, 0*190 part in 100,000 parts of uie
water, — numbers wnich, it will be seen, correspond very
closely with those recorded as expressing the results
furnished by the previous month's supply.

We are, Sir,

Youi obedient Servants,

William Crookss.
William Odlino.
C. Mbymott Tidy.



ON CERTAIN POINTS IN THE ESTIMATION

OF BARIUM AS THE SULPHATE.*

By F. W. MAR.

In the leceived mode of precipitating barium as barium
sulphate, three conditions are carefully obsetved — absence
of excess of acid, slow mixing of the reagents and rest,
before filtration, of twelve hours, or until the precipitate
has completely subsided. Usually in this process, the
precipitate is thrown out in a finely-divided, milky con*
dition, and settles very slowly. My observation that the
precipitate, under certain circumstances, is formed in a
more crystalline condition and settles rapidly, led me to
investigate the conditions of so rapid a precipitation.
These quickly settling precipitates were noticed in the
first instance, in the aAion of sulphuric acid upon sola-

* Amtfiean JourmU o/Scunegt vol. xli.. April 1891. ContribatioM
from the Kent CbemicAl Laboratory of Yale College.— Vi.



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Certain Paints in the Estimation of Banum.



257



tions containing a very large amount of potassium
Chloride with hydrochloric acid in excess. In the course
of five or ten minutes the precipitate had completely
settled and was found to be in a distindly crystalline
condition, and much coarser than the usual form of
precipitated barium sulphate.

At the time it was thought that the cause of this rapid
subsidence was the alkaline salt present, and accordingly,
a series of experiments was made in which potassium,
•odium and ammonium hydroxides were added in varying
amounts to about 400 cm.* of water, hydrochloric acid
added to more than acidity (but not in measured amount),
0*5 grm. of barium chloride introduced, and precipitation
brought about by adding dilute sulphuric acid. Some-
times these precipiutes settled rapidly, but as often came
down in the familiar milky condition. Later, another
series of experiments, in which the different conditions
were more carefully regulated, was made thus : in 400
cm.* of water were dissolved 0*5 grm. of barium chloride,
10 cm.* of strong hydrochloric acid, and amounts of the
alkaline chlorides varying from 5 grms. to 0*05 grm., the
whole bei^g precipitated with 10 cm.* of a solution of
sulphuric acid made by diluting the concentrated acid
with three parts of water. These precipitates all settled
rapidly, and the variation in the amounts of alkali seemed
to exert no very marked influence. Finally, these experi-
ments seeming to point to hydrochloric acid as the
influential fador, a series of experiments was made to
test the effed of varying the amount of this acid. From
a solution containing in 400 cm.* 0*5 grm. of barium chlo-
ride and amounts of hydrochloric acid varying from i cm.*
to 50 c m.*, the barium was thrown out by means of 10
cm.* of dilute sulphuric acid. This series showed that the
hydrochloric acid had a very marked effed upon the pre-
apitation of the barium sulphate. When only one or two
c.c of hydrochloric acid were present, the precipitate
appeared immediately, in a milky condition, and settled
tfowly ; as the amount of acid was increased, a point
was soon reached where the precipitate was not so
quickly apparent, but settled out much more quickly and
in a coarser condition. With 10—15 cm.* of strong hydro-
chloric acid in the solution, the precipitate settled clear
in ten or twelve minutes, and was in excellent condition
for filtration. When the solution contained 50 cm.* of
the acid, the precipitate settled clear in five minutes.
Upon adding the sulphuric acid to such very acid solu-
tions, no {precipitate shows for a moment, but then it
separates in beautiful crystalline condition and falls
almost immediately. It can be safely filtered with or
without pressure in ten minutes. In one instance, in the
course of the experiments just detailed, a grms. of
barium chloride were precipitated in the presence of 30
cm.* of hydrochloric acid, the precipitate was allowed to
settle clear, and was then filtered and washed, the whole
operation being completed in seven minutes. This rapid
subsidence of the precipitate is seen in hot solutions onlv
^75" C. being the lowest temperature compatible with
the attainment of good results, and 85—90* better.

To ascertain whether small amounts of barium would
be precipitated in like manner from these acid solutions,
a series of experiments was made with solutions con-
taining in 400 cm.*, xo cm.* of hydrochloric acid, and 5,
JO, 15, 20, 25, 30, and 50 m.grms. of barium chloride,
precipitation being brought about as in the experiments
above. These solutions remained clear a few minutes,
and then a very transparent precipitate appeared, but in
no case was it as pronounced, as the more finely-divided
precipitate produced in a neutral solution containing 5
m.grms. of barium chloride by the same amount of sul-
phuric acid. However, by giving a circular motion to
the solution in the beaker, after about 20 minutes a small
conical heap of barium sulphate was colle^ed in each
case in the centre of the beaker.

Experiments were next undertaken to ascertain whether
barium is completely thrown out of solution when pre-
cipitated under the conditions related above. The barium '



salt used in all the experiments described below was
obtained by finely powdering seleAed crystals of barium
chloride and drying by pressure between blotting papers.
Portions of the same sample were used throughout. The
hydrochloric acid used was the chemically pure article
of commerce and had a specific gravity of 1*20. The
sulphuric acid used was obtained by diluting the pure
concentrated acid with three parts of water, and had a
specific gravity of 1*28.

In the first series the barium salt was dissolved in about
400 cm.* of water, 15 cm.* of hydrochloric were added,
and precipitation was brought about by adding 10 cm.*
of the dilute sulphuric acid. The precipitates were fil-
tered, after standing about ten minutes, upon asbestos
felts in perforated platinum crucibles.





BaCU'2H|0 taken.


BaSO« foond.


Bnor.




Grm.


Grm.


Grm.


z.


05002


0*4760


0*0016


2.


0*5042


0*4812


0*0006


3-


0*5038


0*4786


0*0025


4.


0*5002


0*4760
0*4812


0*0016


5.


05046


0*oou6


6.


0*5038


0*4804


O'0006



The results of these determinations indicate plainly a
loss of barium sulphate, but inasmuch as the felts used
had been made very thin and it had been subsequently
observed that a small quantity of the sulphate could be
colleAed in one of the filtrates of the series by giving a
circular motion to the water, it was thought that the thm-
ness of the felts might offer an explanation of the loss
and of the varying results of the series. The following
series was, therefore, made in exadly the same manner,
except that care was taken to have the felts carefully
made and reasonably thick.



7-
8.

9-
zo.



BaCl,aH,0
Grm.

0*50x4
0*2227
0*5003
0*5046



BaSO« found.
Grm.

0*4785
0*2Z22

0*4773
o*48z4



Brror.
Grm.

0*0004-
0*0005-
0*0004-
0*0004-



These results are uniform, and indicate a trifling loss
only ; though in the filtrates of these experiments also a
very slight, but, as it proved upon re-filtering, unweigb-
able amount of the sulphate could be coUeAed. The pre-
cipitate in the last of these experiments was filtered off
almost immediately after precipitation, and before it had
completely subsided. In another case the whole opera-
tion, including the three weighings necessary, was con-
duced to a finish in forty-five minutes.

In spite of the appearance of the trifling deposit in the
filtrate, the deficiency in barium sulphate in these deter-
minations was not greater than should be expeded from
the accepted solubility of that salt in water. To ascertain
the tfftd of strongly acid solutions upon the solubility of
barium sulphate, the following determinations were
made : —

In experiment zi the same amounts of the sulphuric
and hydrochloric acids, 10 cm.* and Z5cm.* respedively,
were used as before, but the total volume was reduced to
zoo cm.*. In Z2 and Z3 the same total volume as before,
400 cm.*, was used, but this volume contained 150 cm.*
of the strong hydrochloric acid instead of 15 cm.*, as in
the preceding experiments.





BaCU-2H,0 taken.
Grm.


BaSO« found.
Grm.


Error.
Grm


ZI.
Z2.
'3.


0*5016
0*5004
o*5oox


0*4888
0*4779
0*4776


0*0002
0*0000
0*0000



It appears from these experiments that, as in the pre
cedinp; series, the solubility of barium sulphate in solutions
constituted as described is not increased by the free
hydrochloric acid, and that the effed upon the solubility



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Certain Points in the Estimation o/Ba$ium.



(Cbsmicai. 1Ib««,
If ajr i9f i^«



when this acid is present in great strength is to make the
precipitate rather more insoluble, if anything, than it is
m water. In this connexion, it should be remarked that
experiments of Fresenius,* together with somewhat
similar experience gained by the writer in another line of
work not included in this account, point to the faA that
the presence of an excess of sulphuric acid is an important
condition of this high degree of insolubility. The exad
amount of such excess has not been determined, but the
amount used in the foregoing experiments seems to be
sufficient.

In the preceding experiments barium chloride was used
in considerable quantity. The following determinations
were made to ascertain whether very much smaller
quantities of barium would come down as completely and
as soon, or whether J t is necessary to let the precipitations
stand longer before filtration. In these experiments the
barium salt was measured from a standard solution con-
tainiflg 200 m.grms. of the chloride to the litre. The
amounts of hydrochloric and sulphuric acids, 15 con,* and
zo cm.* retpedively, and the whole volume of the solu-
tion was the same as in the former experiments.





BaC1«-2H,0


BaSO«


Time in mtnates






ta&Q.


foand.


between predpi-


Error.




Grin.


Grm. tation and filtration.


Grm.


X4-


0*0030


0*0024


120


0*0004


15-


0*0050


0*0046


150


0*0002


z6.


0*0050


1 0*0023
1 0*0043


^


0*0025
0*0005


iJ:


0*0050


0*0031


5


0*0016


0*0050


0*0040


10


0*0007


19.


0*0X00


0*0078


zo


0*0017


20.


o*ozoo


0*0085


X5


O'OOZO


az.


o*ozoo


0*0083


3<>


o*ooia


aa.


o*ozoo


00087


60


0*0007



From these reatilts it would appear that the precipita-
tion^ in the presence of hydrochloric acid to the amount
indicated, -does not take place so rapidly when the amount
of the, ba^um salt is' small, but that two or three hours
are snfficieiit for reasonably complete separation of the
precipitate in any case.

In all the experiments described above there was no
attempt at a gradual admixture of the reagents, but they
were measured out and at once added to the solutions,
the whole being well stirred. From the results obtained
it appears to be established, as regards the usual pre-
cautions in precipitating barium by means of sulphuric
acid, that, contrary to former usage, it is highly advan-

•tageous to have. the solution strongly acid with hydro-
chloric acid ; that it is not necessary to add the reagents

'drop by drop, but that the whole quantity required to
•complete the reaction may be added at once ; that

.^ordinarv quantities of barium salts, in presence of a con-
aiderable excess of svlphuric and hydrochloric acids, are
precipitated completely and at once, but that when only
A few m.grms« are present the precipitate requires more
time to separate under the same conditions. Two or

< three hours are, however, sufficient, and in no case is the
excessive time of twelve hours required.

In the light of the fad demonstrated in the preceding
account, that hydrochloric acid may be introduced freely,
and without detriment to the quantitative exaAness of
the precipi|ation of barium in the form of sulphate from
pure solutions, it seemed desirable to look somewhat into
the question as to what the influence of a large excess of
hydrochloric acid might be upon the well-known con-
taminating effed of alkaline salts present during precipita-
tion, especially as it is customary to attempt the purifica-
tion of barium sulphate thrown down in the reverse of this
process — the determination of sulphuric acid by means of
.a soluble barium rait — by digestion of the washed pre-
cipitate in hydrochloric acid. The following series of
experiments was undertaken with this end in view. The



details are shown in the tabular statement, precipitation
being effeded in the presence of free acid and the alkaline
salt.





BaCL*2H.O

taken.


BaSO«




HClin




foand.


Error.


•olution.




Grm.


Grm.


Grm.


Cm.s.


23.


0*5092


0*5032


0*0169+


IZO


24.


0*5027


0*4907


0*01074-


ZO


25.


0*5026


0*4944


00154+


ZOO


26.


0*5045


0*4939


0*0Z22 +


ZO


27.


0*5020


0*4931


0*0137 +


ZO


28.


0*5013


0*4849


o*oo6i +


zo



* ZHi, fur Anal. Chmn,, vol. is., p. 6a.



salts

present.

Gmia.

KCIO3 3

f 3
KCl 5

•f 5

•> 5
NaCl 5



From the results it is plain that, whatever may be the
efifed of digesting the washed precipitate in hydrochloric
acid, the presence of this acid m large excess during pre-
cipitation in the presence of alkaline salts, does not pre-
vent contamination of the precipitate. On the contrary,
the greatest contamination seems to have occurred in
those cases in which the acid was present to the largest
degree, but in view of the slight variation in contamination
as compared with the great differences in the amount of
acid employed, it does not appear probable that the in-
crease of acid has very much to do with the amount of
contamination.

It likewise seemed to be a matter of some interest in
this connexion, to investigate the process by which it ' is
currently supposed (Fres. '* Quant. Anal.," vol. i., p. 5^)
that barium sulphate carrymg alkaline salts may oe
efiedually purified, viz., by the solution of the washed
precipitate in strong sulphuric acid and re-precipitatidn
by water. Accordingly the determinations of the following
series were undertaken. The barium sulphate, precipitated
from solutions containing 5 grms. of potassium chloride
and zo con.* of hydrochloric acid, was coUe^ed upon a
filter, either paper or asbestos, and, after burning the
paper or removing the j^recipitate from the asbestos (by
tapping the crucible which held it and brushing out with
a camel's hair brush), was dissolved by warming with con-
centrated sulphuric acid in a large porcelain crucible aiyl,
after cooling, poured into water containing Z5 cm.* to 20
cm.* of hydrochloric acid. The water into which the
solutions in strong acid was poured was warmed with a
view to diminish the milkiness of the precipitate, but care



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