Arnold Bennett.

Chemical news and journal of industrial science online

. (page 42 of 88)
Online LibraryArnold BennettChemical news and journal of industrial science → online text (page 42 of 88)
Font size
QR-code for this ebook


alcohol, to precipitate the greater poitioo of the remaining
sodium bisulphite. 50 parts of water are now added with
a sufficiency of sodium chloride to form a concentrated
solution. Again set aside in an open-mouthed glass jar,
covered with bibulous paper, for seven or eight days, a
deposition of the dye in a crystalline state, together with
sulphite of calcium, will take place, which latter, owing
to its insolubility in water, may be removed by filtration.

The alizarin-blue S is separated from any unaltered
substance left in the original stoppered vessel by solution,
and added to the brine, now purified from lime salts, and
once more set aside to crystallise, the final purification
being effeded in a beaker containing alcohol and a small
percentage of water to remove the last traces of sodium
chloride, coUeding the crystals on a filter-paper and drying
at ordinary temperatures.

The needle-shaped crystals are of a deep red. Dilute
solutions are of a pale sherry colour, changing, with the
addition of a few drops of ammonia, to a green, which
immediately gives way to magenta and every shade of
purple, till oxidation is complete, when it assumes a blue
colour, the absorption spedtrum of which is continuous
and strongest in the least refrangible end, presenting the
appearance of extending into the infra-red.

Plates immersed in a solution containing i : zo,ooo and
z per cent of ammonia give the most perfed results the
day after preparation, but rapidly deteriorate unless kept
quite dry.

With a slit yvq^ inch in width, and an exposure of forty

* Rtad before the Royal Society, March u, 1891.



minutes, results have been obtained in the region of
Great A of the 2nd order, which possess all the detail and
definition usually so charaderistic of the violet end.
Numerous lines are sharply depided which were pre-
viously not known to exist. W.l. 8400 has been reached,
giving almost equal detail.

The process for the preparation of pure coerulin S is a
slight modification of the preceding. The results obtained,
as well as the acinic curve, are almost identical. The
pure substance is almost white ; dilute solutions pass
rapidly from pale yellow to a bright green ; a trace of
ammonia produces an olive- green.

For several samples of paste I am indebted to the kind-
ness of Messrs. Schott, Segner, and Co., of Manchester,
agents to the Badische Anilin- und Soda-Fabrik, Lud-
wigshafen, who hold the patent rights for the manufaAure
of alizarin-blue S. It is hoped this company may be
induced to manufadure this substance free from the
minute crystallisable impurities which render it unsuitable
for use in investigations of such delicate nature.



DISCUSSION ON THE THEORY OF.

SOLUTION.*

(Continued from p. 13 1).

Professor Ostwald read the following communication
"On the Eledrical Behaviour of Semipermeable Mem-
branes ** : —

If we fill two glass beakers with copper sulphate solu-
tion, put in them two copper wires conneded with a
couple of Leclanch^ cells, and a galvanoscope, and close
the circuit by a siphon filled with any eledrolyte, which
is prevented from mixing with the copper sulphate by
covering the ends of the siphon with parchment ps^per, no
phenomenon of special interest is to be noticed. We have
an ele^rolytic circuit without polarisation, as used bv
Paalzow for the determination of the specific condudivf-
ties of liquids. By varying the liquid in the siphon only
the total resistance of the circuit varies, and polarisation
does not generally occur. If we fill the siphon with
potassium ferrocyanide, nothing novel seems to go on at
the first glance. But if we remember that on the contad
of copper salts with fe'rocyanides a seniipirmtabU mem*
brang of copper ferrocyanide is formed, through which,
according to the observations of Traube, no copper salt
can diffuse, we are led to a somewhat strange question.
The fad that no copper salt can pass through the mem*
brane is evidence that the copper ions existing in the salt
solution are likewise unable to pass. But as the eledri-
city in eledrolytes travels only with the ponderable ions,
we are met by the alternative either that the refusal of
the copper (and ferrocyanide) ions to pass through the
membrane will cause the current wholly to stop, or that
the eledricity will deposit the copper ions on the mem-
brane and itself alone pass through. The semipermeable
membrane must in the first case ad as an imsulaior; in
the second case it must ad as a mttallic diaphragm. Both
these cases are so unexpeded that the described expert*
ment at once acquires a special interest.

By performing the experiment we find that the second
alternative holds good. The current becomes rapidly
weaker, and after ten minutes we can easily observe a
very marked polarisation current in inverse diredion to
the primary current. After some hours of current the
parchment paper containing the semipermeable membrane
on the positive side is coated with a layer of metallic
copper, and this is evidence that ths copptr ions are
filtered off by the temipermeabU membrane.

From this experiment it follows that the semipermeable
membrane really ads as a sieve, not only as regards com-
pounds, but also for ions, allowing some of them to pais



« British Association (Sedion B), Leeds Meeting, 1890

Digitized by VJI^^^



gle



158



theory of Solution.



r CiHBllICAL IVBWt,

i Aprils, x8gi.



and retaining others ; for we know, for example, that
potassium chloride can pass the membrane of copper
pnissiate, and therefore the ions K and CI do so, while
barium chloride and potassium ferrocyanide are retained.
In the two last-mentioned cases one of the ions has the
power of passing, but is retained by the other. At the
first moment the CI ions of the barium chloride will of
course go through the membrane, while the barium ions
stay behind. But by this separation a separation of posi-
tive and negative eledricity also takes place, and thereby
forces will arise tending to draw the CI ions back. Finally
a double layer of eledricity is formed, causing a potential
difference on both sides of the membrane, whose value
depends only upon the molecular concentration of the
eleArolyte, and in no way upon its nature.

If the formation of the double layer is prevented, free
diffusion of the passing ion takes place. By adding to
the barium chloride some salt whose metal can pass
through the membrane — for instance, some salt of potas-
sium — the CI ions at once will traverse the membrane,
but the same number of K ions must go along with them.
In this case, however, it may be assumed that the added
potassium salt undergoes a double decomposition with
the barium chloride, forming potassium chloride, which is
able to diffuse through the membrane. But we can also
cause the CI ions to pass by putting some diffusible nega-
tive ions on the outsidt of the membrane— for instance,
copper nitrate. Then we soon find chlorine outside and
a nitrate inside the membrane. In this case it is impos-
sible to assume a double decomposition, because both the
■alts are separated by the membrane, which prevents
the dififusion of the barium chloride, as well as of the
copper nitrate, and the explanation, by taking into
account free migrating ions, seems to be the only sufficient
one.

The above-mentioned double layers and potential
differences, occurring at semipermeable membranes, when
one of the ions of the eledrolyte is retained, are probably
the source of the potential differences and currents we
meet with in living matter, because the cells of organisms
are all coated with such semipermeable membranes. It
is perhaps not too rash to hope that the ancient mystery
of eleArical fishes will find its solution on these lines.

Referring to the discussion Professor Ostwald said —
Professor Fitzgerald has asked why the ions, when they
are free, do not separate by diffusion. The answer is that
they do. If we have a solution of HCl, for example,
consisting to a great extent of H and CI ions, in contadi
with pure water, the H ions, moving much faster than
the CI ions, take the lead in wandermg into the water.
But a separation of ele^ricity hereby takes place, and |
every ion being charged with a great amount of either
positive or negative eledricity, the eledrostatic forces
resulting from the initial separation soon prevent further
separation. Therefore water must take a positive poten-
tial against a solution of hydrogen chloride, and in general
water must show against every eleArolytic solution the
potential of the faster ion.

These considerations, which lead to the whole theory
of the potential differences between eledroly tes, were first
developed by W. Nernst (ZsUsch.f. phys, Chtm., ii., 613,
and iv., 129), who has confirmed them by various experi-
ments; and (uither by M. Planck ( IVtVif. Ann., xl., 561).
As far as I am aware, no theory of fluid-cells
(Plutiisk*itik$tten) had hitherto existed, and the possi-
bility ot developing one consistent with experiment from
the principles first stated by Arrbenius is strong evidence
in favour of his views.

Secondly, Professor Fitsgerald seeks for the source of
energy required for the separation of, #.^., CI and H by
dissolving HCl in water. This question is in accordance
with the widely-spread assumption that a great expen-
diture of work must be done to effeA this separation. As
a great amount of heat is developed by forming HCl from
its elements it seems evident that the same amount of |
energy mast be restored to the elements in separating



them. This is quite true if common hydrogen and chlorine
were formed, but the ions H and CI, existing in the
aqueous solution of hydrogen chloride, are by no means
identical with the so-called free elements. To use a word
to which chemists are accustomed, the ions H and CI are
allotropic forms of these elements, similar to yellow and
red phosphorus, and contain very different amounts of
energy from those which they contain in their common
state of hydrogen and chlorine gases. Therefore it is
impossible to say anything d priori about the evolution or
absorption of energy conne^ed with the change from
HCl gas to positively charged H ions and negatively
charged CI ions ; we must interrogate fads ; and these
teach us that the ions generally contain much less energy
than the elements in the common state, and therefore a
great amount of energy is not called for in the trans-
formation of, e.g., HCl into the free ions H and CI.

The elements in the state of ions being charged with
great amounts of eledricity, the very different tendency
of the elements to assume the state of ions can be con-
veniently called their different affinity for eledricity.
This expression is of course only Afaqon de parler, but it
gives a good description of the behaviour of the elements.
The adiion, for example, of zinc on cupric sulphate solu-
tion, containing the ions Cu and SO4. depends on the
greater tendency of the zinc to form ions; therefore the
zinc tears the positive electricity necessary for its exist-
ence as an ion from the copper ions, and deposits the
latter as uneledrical, i,e,, common metallic copper. The
SO4 ions, being no closer connected with the zinc than
with the copper, ad only as, owing to their negative
charges, they render possible the existence of an equal
number of positive ions, no matter of what nature. '

If I am right Professor Fitzgerald is now ready to
acknowledge the views of Arrhenius as possible ones, but
he assumes that the fads explained by these views can
also be explained by some other views, of which he has
given some specimens. It is, of course, impossible to
deny this. But as the theory of Arrhenius has done its
work up to the present, and the new theory has yet its
way to make, the former seemb to have certain claims to
be preferred. As the theory of Arrhenius has shown
itself to be consistent with a very great number of fade,
in the most various branches uf physics and chemistry,
the new theory must of necessity lead in all these cases
to the same result as that of Arrhenius. Then the scien-
tific world will have the wonderful spedacle of two
theories, starting from different points of view, but leading
everywhere to the same result. Science will then possess
a twofold means of further investigation of some of its
most difficult problems; a state of matters that cannot be
too urgently wished for by all who have devoted their
powers to such investigations.

In reply to Mr. Pickering's remark that the indudion
experiment upon eledrolytic solutions described by me is
opposed to the first principles of science, especially to the
first law of thermodynamics, I wish only to remind him
that by canying out the common ledure experiment with
two metallic balls and a charged body, we can get from
the balls a spark, and therefore also an amount of energy.
As no one hitherto has found in this experiment a con-
tradidion to the law of the conservation of energy, I can
leave the defence of my experiment to all teachers who
annually perform this experiment in their ledures.

Professor Lodge has asked if the experiment in ques-
tion has been carried out, and in what manner. The
description of a series of such experiments has been given
in the Zeitschr. /. phys. Chem., iii., 1889, p. zao. The
easiest way to demonstrate the liberation of ions in elec-
trolytes by indudion is to fill a glass jar covered on the
outside with tinfoil with dilute sulphuric acid, to conned
the outside with a source of positive eledricity, and to
insert in the sulphuric acid an earthconneded capillary
eledrode, t.«., a short Lippmaon eledromeier. The very |

minute bubbles of hydrogen developed by eledrostattcal {

adions can then easily be observed in the capillary tube



Digitized by



Google



Cbbm icAX. Nbws, i
Apnl 3, X891. I



Theory oj Solution.



150



00 the boundary of the mercury and the sulphuric acid by
help of a microscope.

Professor Armstrong has declared that the dissociation
theory of eledrolytes is unacceptable to chemists. As
fir as I am aware, there exists nowhere a real contra-
didion between chemical/af /s and the dissociation theory,
but this theory only runs against all the time-honoured
fgelings of chemists. As feelings, although very powerful
things, are at least variable with time and custom, it is to
be expensed that they will change sooner or later. The
time is not very long past when the assumption that, in
the vapour of ammonium chloride, hydrochloric acid and
ammonia, which have ** so great an affinity for each
other,** should exist separate from one another ran in
quite the same manner against the feelings of chemists.
Now we are accustomed to this conception, and in the
same manner chemists will speak in a year or two as
quietly of the free ions as they now speak of the uncom-
bined mixture of hydrochloric acid and ammonia in the
gaseous state.

But it should not be forgotten that a great many purely
chemical fadls — in the first place the great generality and
regularity of the chemical readions of eledrolytes as used
in analytical chemistry, in opposition to the variability
and irregularity of the behaviour of non-eledrolytes,
especially of organic bodies— have found their first
explanation in the theory of eledrolytic dissociation. The
objedion against this theory, that if the ions of salts exist
in a free state this would not be any ground for the law
of constant proportion between acid ions and metals, is
easily refuted. For, according to Faraday's law, all
chemically equivalent amounts of positive and negative
ions are charged with equal amounts of eledricity; in an
eledrically neutral solution, as all ordinary solutions are,
I there cannot but exist an exa(5l equivalent number of

positive and negative ions. We see, therefore, the law of
Faraday conneded in the closest manner with Richter*s
law of chemical eouivalents; if the one holds good, the
other must also hold good, and vice versd.

Professor Armstrong has asked why water does not split
into ions, while hydrogen chloride, a body similar to
water, does. But has Professor Armstrong forgotten that
liquid hydrogen chloride, like pure water, is an insulator
for the eledric current, as was found long ago by Gore,
an observation afterwards confirmed by Bleekrode ? It
has been stated by F. Kohlrausch that* at ordinary tem-
peratures no pure liouid is a good eledrolyte. The theory
of Arrhenins is still m this point the only one which ex-
plains this strange fad; pure liquids do not condud,
because their molecules have no space to resolve them-
selves into ions.

It is therefore not improbable that water would condud
eledroljTtically if we could find a suitable solvent for it.
An investigation in this diredion would be of very great
interest, but not without grave difficulties.

To a certain, but very small extent, water too contains
ions, namely, H and OH. This is shown by the hydro-
lytic adion of water on the salts of weak acids and bases,
the amount of H or OH ions dissociated from these acids
or bases being in such cases comparable with the amount
of the same ions in water. Then the latter ads as a
very weak acid or base, and the adion follows the common
law of masses, as J. Walker has shown (ZtHsch.f, phys,
Chim,, iv., 319).

(To be continued).



STUDIES ON THE EARTHS OF THE CERIUM

AND YTTRIUM GROUP.*

By A. BETTENDORFF.

Tbb material for the following researches was orthite,
obtained from the establishments of Dr. Marquart, of
Bonn, and Dr. Schuchardt, of Goerlitz, and said to have



• From Liebig^s AnnaUn



been derived from Stromboe, near Arendal, and from
Hitteroe. From the analysis of Angstrom and Cldve, it
appears that all the orthites contain varying quantities of
the earths of the cerium and yttrium groups, in which con-
siderable quantities of thoria are also present.

The rare earths of the orthite were separated according
to the known methods which are also used for the decom-
position of cerite. To remove the cerium and thorium
oxide, the author used the process given by Debraye
{Comptes Rendus, xcvi., 828). The nitrates of the earths are
fused with six parts of potassium nitrate, a method which
is expeditious and gives excellent results. The cerium
compound is so completely removed that on treating the
hydroxides of the earths with chlorine gas no trace can
be discovered. On the other hand, very small quantities
only of the other earths remain in the cerium oxide. After
the removal of this oxide and of thoria, the earths of
both groups are separated by means of potassium sul-
phate.

This separation has hitherto been effeded exclusively
by Mosandet's method. The author has introduced a
modification which has an influence upon the complete
separation of the two groups. The cerium group contains
certain oxides, the double potassium sulphates of which
are only precipitated from a saturated solution of potas-
sium sulphate very slowly and on vigorous agitation. The
separation is therefore undertaken by preference in corked
bottles which are filled with a solution of potassium sul-
phate, saturated when hot, and allowed to cool. The
bottom of the bottle is then coated with a firmly adherent
saline crust. If the separation is to take place without
shaking, the bottle, after the introdudion of the chlorides
or nitrates of the earths, is completely filled with the
saturated solution of potassium sulphate, corked up, and
inverted; these are the conditions prescribed by Mosander.
In the other case, the bottles are only filled partially.
When both the groups have been separated, and the earths
have been set free from the double sulphates, the separa-
tion of the two constituents is commenced.

The author has used the method of the partial decom-
position of the nitrates, as it permits larger quantities to
be worked up in a relatively short time. It is easily
pradicable to melt up the nitrates of the yttrium earths
to a clear liquid, as their point of fusion is low and remote
from their decomposition heat. Small quantities of the
nitrates of the cerium earths can also be melted to a trans-
parent liquid in a platinum crucible on an open fire. But
if we attempt to operate on larger quantities, it appears
that long before complete fusion is effeded a part of the
mass is decomposed, with separation of oxide and basic
nitrate. Under these conditions the access of heat is not
in harmony with the thermic condudivity of the solid
nitrate, whence the portions lying nearest to the fire are
melted and decomposed before the entire mass enters into
fusion. This defed may be remedied by placing the
platinum crucible containing the nitrates in a porcelain
crucible in such a manner that there remains everywhere
between the two an interval of from z to a m.m. As the
porcelain crucible is very apt to crack, it is wrapped round
with some rings of platinum wire, after which hundreds
of fusions can be undertaken in it. In this manner large
quantities of nitrate can be fused to a clear liquid, and, if
heated more strongly, begin to decompose. As soon as
small crystalline leaflets of basic nitrate appear on the
surface of the melt, the contents of the crucible are poured
into a large platinum capsule. The cold mass forms a
perfedly clear solution in zo parts of water ; and, on
boiling, basic nitrate separates from the solution in dense
flocks, which are easily removed by filtration. From the
concentrated filtrate a second separation is then obtained,
and so further. .

The earths, freed from cerium oxide and precipitable by
potassium sulphate, after the last portions of the yttrium
earths had been removed had an equivalent of RO«iog*o
to zio*2. It is readily pradicable to remove all lanthanum
by systematic fradional precipitation of the nitrates of



Digitized by



Google



i6d



Milk Analysis by the Asbestos Method.



\ Aprils, 189X.



these oxides. Small quantities of didymium oxide are
still present, but the produd has a high degree of puriiy,
as is proved by the equivalent of the oxide ROSZ0876.

The separation is carried so far that in the basic
nitrates ultimately obtained no lanthanum lines can be
obtained in the spark - spe^rum of the chloride. The
united basic nitrates, when completely freed from La,
furnish a brown oxide with the equivalent of RO s zi3'2
to 114*0. They contain all the didymia and samaria
bands, larger or smaller quantities of gadolinia or terbia,
according as the separation of the yttrium earths by
means of potassium sulphate has been effeded by
Mosander's process, or by the modification above
described.

The author now communicates the observations made
whilst obtaining pure lanthanum compounds from the
above-mentioned mixtures ROa 10876.

A further purification by a systematic fraAionated de-
composition of the nitrates on fusion presents serious
difficulties. Though the melting -pomt has become
rather high, it is pradicable, by the process above
described, to obtain a clear melt from which leaflets of
basic citrate separate ; but, on cooling, the congealed
mass is scattered about as dust — the more, the richer it
is in lanthanum nitrate — sometimes with such force that
considerable quantities are lost. This phenomenon was
observed by Berzelius, and is described in his ** Lehr-
buch."

It is more advantageous to apply the method described
by Aner von Welsbach, which depends on the circum-
stance that in a solution of the mixed didymium and
lanthanum - ammonium nitrates, the double salt of
lanthanum first crystallises out, being much less soluble.
Auer von Welsbach condudls this separation in a strong
nitric solution. The author — as his preparation contained
but little didymium — found it more convenient to allow
crystallisation to take place in a solution as neutral as
possible.

(To b« contiooed).



MILK



ANALYSIS BY THE
METHOD.*



ASBESTOS



By FRANK T. SHUTT, M.A., F.LC, F.C.S.

To render complete the results of feeding experiments
conduced at the Central Experimental Farm with
thoroughbred stock, a comparatively large number of
analyses of milk is required to be made. At the outset of
this work, therefore, a process was sought by which the
composition of the milk (i.«., total solids and fat) could be
accurately and rapidly ascertained.

After working Adams's, Wanklyn's, the plaster-of-paris,
•and, and other methods, a trial was made of the asbestos
method as described by Thomas Macfarlane, F.R.S.C.,
Chief Analyst, Department Inland Revenue, in a paper
read before this Society in May, 1887. This process



Online LibraryArnold BennettChemical news and journal of industrial science → online text (page 42 of 88)