Michael Faraday.

Experimental researches in chemistry and physics online

. (page 22 of 49)
Online LibraryMichael FaradayExperimental researches in chemistry and physics → online text (page 22 of 49)
Font size
QR-code for this ebook

but a brown substance, heavy, adhesive like honey or treacle,
and in certain cases even almost solid. From the circumstances
of the experiments, no hesitation could arise in concluding that
a spontaneous chemical change had taken place ; and it does
not seem at all unlikely that a similar change, or one to a
much greater extent, may have occurred suddenly during the
rapid alteration in the mechanical condition of the gas in Mr.
Gordon's experiment ; the most condensable of the substances
in the mixture of elastic matters which constitute oil-gas, being
perhaps those which are most altered, and in that case Mr.
Gordon's account of the phenomena would be correct.

Transference of Heat by change of Capacity in Gas*.

MANY of the copper vessels in which gas is compressed at the
Portable-Gas Works are cylinders from two to three feet in
length, terminated by hemispherical ends. These are attached
at one end to the system of pipes by which the gas is thrown
in, and being so fixed, the communication is opened ; it fre-
quently happens, that gas previously at the pressure of thirty
atmospheres in the pipes and attached recipients, is suddenly
allowed to enter these long gas-vessels, at which time a curious
effect is observed. That end of the cylinder at which the gas
enters becomes very much cooled, whilst, on the contrary,
the other end acquires a considerable rise of temperature.
This effect is produced by change of capacity in the gas ; for,
as it enters the vessel from the parts in which it was previously
confined, at a pressure of thirty atmospheres it suddenly ex-
pands, has its capacity for heat increased, falls in temperature,
and consequently cools that part of the vessel with which it
first comes in contact ; but the part which has thus taken heat
from the vessel being thrust forward to the further extremity
of the cylinder by the successive portions which enter is there
compressed by them, has its capacity diminished, and now
gives out that heat, or a part of it, which it had the moment
before absorbed ; this it communicates to the metal of that
part of the gas-vessel in which it is so compressed, and raises

* Quarterly Journal of Science, xxiii. 474.

On Labarraque's Disinfecting Soda Liquid. [1827.

its temperature. Thus the heat is actually taken up by the
gas from one end of the cylinder, and conveyed to the other,
occasioning the difference of temperature spoken of. The
effect is best observed when, as before stated, the gas, at a
pressure of thirty atmospheres, is suddenly let into the vessels :
the capacity of the recipients is such, that the pressure usually
sinks to about ten atmospheres.

Experiments on the nature of Labarraque's Disinfecting Soda

Liquid *.

1. THE following experimental investigations relate to the
nature of that medicinal preparation which M. Labarraque
has lately introduced to the world, and named Chloride of
oxide of Sodium. They were occasioned by the accounts
which were given of this and other substances of similar power
to the Members of the Royal Institution, at two of their Friday
evening meetings ; the value of the preparation, the uncertainty
of its nature, and the inaccuracy of its name, all urging the

2. In the first instance the inquiry was directed to the
nature of the action exerted by chlorine gas upon a solution of
carbonate of soda, questions having arisen in the minds of
many, whether it was or was not identical with the action
exerted by the same gas on a solution of the caustic alkali, and
whether carbonic acid was evolved during the operation or not.
Chlorine gas was therefore carefully prepared, and after being
washed was sent into a solution of carbonate of soda, in the
proportions directed by M. Labarraque : i. e. 2800 grains of
crystallized carbonate of soda were dissolved in 1*28 pint of
water; and being put into a Woulfe's apparatus, two-thirds
of the chlorine evolved from a mixture of 967 grains of salt
with 750 grains of oxide of manganese, when acted upon by
967 grains of oil of vitriol, previously diluted with 750 grains
of water, were passed into it; the remaining third being partly
dissolved in the washing water, and partly retained in the open
space of the retort and washing vessel. The operation was
conducted slowly, that as little muriatic acid as possible might

* Quarterly Journal of Science, xxiv. 84.

1827.] On Labarraque's Disinfecting Soda Liquid. 223

be carried over into the alkali. The common air ejected from
the bottle containing the solution was collected and examined;
but from the beginning to the end of the operation not a par-
ticle of carbonic acid was disengaged from the solution,
although the chlorine was readily absorbed. Ultimately a
liquid of a very pale yellow colour was obtained, being the
same as M. Labarraque's soda liquor, and with which the
investigations were made that will hereafter be described.

3. An experiment was then instituted, in which the effect of
excess of chlorine, upon a solution of carbonate of soda of the
same strength as the former, was rendered evident. The
solution was put into two Woulfe's bottles, the chlorine well
washed and passed through, until ultimately it bubbled through
both portions without absorption of any appreciable quantity.
As soon as the common air was expelled, the absorption of the
chlorine was so complete in the first bottle, that no air or gas
of any kind passed into the second, a proof that carbonic acid
was not liberated in that stage of the experiment. Continuing
the introduction of the chlorine, the solution in the first bottle
gradually became yellow, the gas not being yet visible by its
colour in the atmosphere above the solution, although chlorine
could be detected there by litmus paper. Up to this time no
carbonic acid gas had been evolved ; but the first alkaline
solution soon acquired a brighter colour, and now carbonic
acid gas began to separate from all parts of it, and passing
over into the second bottle, carried a little chlorine with it.
The soda solution in the first bottle still continued to absorb
chlorine, whilst the evolution of carbonic acid increased, and
the colour became heightened. After some time the evolution
of carbonic acid diminished, smaller quantities of the chlorine
were absorbed by the solution, and the rest passing into the
atmosphere in the bottle, went from thence into the second
vessel, and there caused the same series of changes and actions
that had occurred in the first. The solution in the first bottle
was now of a bright chlorine yellow colour, and the gas bubbled
up through it as it would through saturated water.

4. When the chlorine had saturated the soda solution in the
second bottle, and an excess of gas sufficient to fill several large
jars had been passed through the whole apparatus, the latter
was dismounted, the solutions put into bottles and distinguished

224* On Labarraque's Disinfecting Soda Liquid. [1827.

as the saturated solutions of carbonated soda ; they were of a
bright greenish yellow colour, and had an insupportable odour
of chlorine.

5. The saturated solution (4) was then examined as to the
change which had been occasioned by the action of the chlo-
rine. It bleached powerfully, and apparently contained no
carbonated alkali ; but when a glass rod was dipped into it
and dried in a warm current of air, the saline matter left, when
applied to moistened turmeric paper, reddened it considerably
at first, and then bleached it ; and this piece of paper being
dried and afterwards moistened upon the bleached part, gave
indications of alkali to fresh turmeric paper.

6. A portion of the saturated solution (4) being warmed,
instantly evolved chlorine gas, then assumed a dingy appear-
ance, and ultimately became nearly colourless ; after which it
had an astringent and saline taste. Being evaporated to dry-
ness at a very moderate temperature, it left a saline mass con-
sisting of much common salt, a considerable quantity of chlorate
of soda, and a trace of carbonate of soda. This mixture had
no bleaching powers. The dingy appearance, assumed in the
first instance, was found to be occasioned by a little manganese
which had passed over into the solutions, notwithstanding the
care taken in evolving and washing the gas.

7. From these experiments it was evident that when chlorine
was passed in excess into a solution of carbonate of soda (3),
the carbonic acid was expelled, and the soda acted upon as if
it were caustic, a mixture of chloride of sodium and chlorate
of soda being produced ; with the exception of the small por-
tion of carbonate of soda which, it appears, may remain for
some time in the solution in contact with the excess of chlorine
at common temperatures, without undergoing this change.
The quantities of chloride of sodium and chlorate of soda were
not ascertained, no doubt being entertained that they were in
the well-known proportions which occur when caustic soda is

8. The Labarraque's soda liquor which had been prepared
as described (2), was now examined relative to the part the
chlorine played in it, or the change the alkali had undergone,
and was soon found to be very different to that which has just
been described, as indeed the experiments I had seen made

1827.] On Labarraque's Disinfecting Soda Liquid. 225

by Mr. Phillips* led me to expect. The solution had but little
odour of chlorine ; its taste was at first sharp, saline, scarcely
at all alkaline, but with a persisting astringent biting effect
upon the tongue. When applied to turmeric paper, it first
reddened and then bleached it.

9. A portion of the solution (2) being boiled, gave out no
chlorine ; it seemed but little changed by the operation, having
the same peculiar taste, and nearly the same bleaching power
as before. This is a sufficient proof that the chlorine, though
in a state ready to bleach or disinfect, must not be considered
as in the ordinary state of solution, either in water or a saline
fluid ; for ebullition will freely carry off the chlorine under the
latter circumstances.

10. A portion evaporated on the sand-bath rather hastily,
gave a dry saline mass, quite unlike that left by the saturated
solution already described (6); and which, when dissolved, had
the same astringent taste as before, and bleached solution of
indigo very powerfully : when compared with an equal portion
of the unevaporated solution which had been placed in the
mean time in the dark, its bleaching power upon diluted sul-
phate of indigo was 30, that of the former being 76. Another
portion evaporated in a still more careful manner, gave a mass
of damp crystals, which, when dissolved, had the taste, smell,
and bleaching power of the original solution, with almost equal

11. These experiments showed sufficiently that the whole
of the chlorine had not acted upon the carbonate of soda to
produce chloride of sodium and chlorate of soda ; that much
was in a peculiar state of solution or union which enabled it
to withstand ebullition, and yet to act freely as a bleaching or
disinfecting agent ; and that probably little or none had com-
bined with the sodium, or been converted into chloric acid.
To put these ideas to the test, two equal portions of the
Labarraque solution were taken ; one was placed in a large
tube closed at one extremity, diluted sulphuric acid was
added till in excess, and then air blown through the mixture
by a long small open tube, proceeding from the mouth, for the
purpose of carrying off the chlorine ; the contents of the tube

* Phil. Mag. N. S. i. 376.

On Labarraque's Disinfecting Soda Liquid. [1827.

were then heated nearly to the boiling-point, air being con-
tinually passed through. In this way all the chlorine which
had combined with the carbonated alkali without decomposing
it, was set free by the sulphuric acid, and carried off by the
current of air and vapour, whilst any which had acted chemi-
cally upon the alkali would, after the action of the sulphuric
acid, be contained in solution as muriatic and chloric acids,
and from the diluted state of the whole, would not be removed
by the after process, but remain to be rendered evident by
tests. The other portion being diluted, had sulphuric acid
added also in excess, but no attempt was made to remove
the chlorine. Equal quantities of these two portions in the
same state of dilution were then examined by nitrate of silver
for the quantities of chlorine sensible in them, and it was
found that the latter portion, or that which retained the whole
of the chlorine thrown into it, contained above sixty times as
much as the former.

12 Now although it may be supposed that in the former
portion that part of the chlorine which, in acting energetically,
had produced chloric acid, could not be detected by the nitrate
of silver, yet more than a sixth of the small portion which
remains cannot be thus hidden ; and even that quantity is
diminished by the sulphuric acid present in excess, which
tends to make the chlorine in the chlorate sensible to nitrate
of silver : so that the experiment shows that nearly 59 parts out
of 60 of the chlorine in M. Labarraque's liquid are in a state of
weak combination with the carbonated alkali, and may be sepa-
rated by acids in its original condition ; that this quantity is
probably wholly available in the liquid when used as a bleaching
or disinfecting agent ; that little, if any, of the chlorine forms
chloride of sodium and chlorate of soda with the alkali of the
solution ; and that the portion of chlorine used in preparing the
substance which is brought into an inactive state, is almost in-
sensible in quantity.

13. The peculiar nature of this compound or solution, with
the results Mr. Phillips had shown me (8), obtained by evapo-
ration of a similar preparation to dry ness, induced me to try
the effects of slow evaporation, crystallization, heat, and air
upon it. In the first place, five equal portions of the solution
prepared by myself were measured out : two were put into

1S27.] On Labarraque's Disinfecting Soda Liquid. 227

stoppered bottles, two were put into basins and covered over
with bibulous paper, and one was put into a basin and left
open; all were set aside in an obscure place, and remained
from July 16th to August 28th. Being then examined, the
portions in the basins were found crystallized and dry; the
crystals were large and flat, striated and imperfect, resembling
those formed in a similar way from carbonate of soda. They
were not small and acicular, were nearly alike in the three
basins, and had effloresced only on a few minute points. A
part of one portion, when dissolved, gave a solution having an
alkaline taste, without any of the pungency of Labarraque's
liquid ; and when tested by turmeric paper, it reddened, but
did not bleach it.

14. One of these portions, that had effloresced least, was se-
lected, and being dissolved, was compared in bleaching power
upon diluted sulphate of indigo, with one of the portions of
solution that had been preserved in bottles. The former had
scarcely any visible effect, though sulphuric acid was added to
assist the action ; a single measure of the indigo liquor coloured
the solution permanently blue, whereas seventy-seven such
measures were bleached by the portion from the bottle. Hence
the process of slow crystallization had either almost entirely
expelled the chlorine, or else had caused it to react upon the
alkali, and by entering into strong chemical combination as
chloride and chlorate, had rendered it inert as a bleaching or
disinfecting agent.

15. From the appearance of the crystals there was no reason
to expect the latter effect ; but to put the question to the proof,
one of the evaporated portions, and one of the fluid portions
contained in the bottles, were acted upon by sulphuric acid,
heat, and a current of air, in the manner already described (11),
to separate the chlorine that had not combined as chloride or
chlorate. They were then compared with an equal portion of
the solution, which retained all its chlorine, nitrate of silver
being used as before ; the quantity of chloride indicated for the
latter portion was 60 parts ; whilst that of the fluid portion
deprived of as much free chlorine as could be, by sulphuric
acid and blowing, was 6 parts ; and for the evaporated and
crystallized portion, similarly cleared of free chlorine, only
1*5 part.

228 On Labarraque's Disinfecting Soda Liquid. [1827.

16. This result, as compared with the former experiment of
a similar kind (11), showed, that though reaction of the chlo-
rine on the carbonate had taken place in the evaporated por-
tion, it was only to a very slight extent, since the chlorine was
almost as much separated from it by the process altogether, as
it had been from the recent preparation by sulphuric acid,
blowing and heat. The experiment showed also that there
was a gradual reaction of the chlorine and alkali in the fluid
preparation, proceeding to a greater extent than in the evapo-
rated portion ; for chlorine, equal to five parts, was found by
the nitrate of silver to remain. Hence this preparation is one
which deteriorates even in the small space of forty-three days.
Whether the effect will proceed to any great extent, prolonged
experiments only can show.

17. From an experiment made upon larger quantities of the
Labarraque liquor, it would appear that the force of crystal-
lization alone is sufficient to exclude the chlorine. A quantity
was put into an evaporating basin, and left covered over with
paper from July 16th to August 28th. Being then examined,
a few large crystals were found covered over with a dense
solution ; the whole had the innocuous odour of Labarraque's
fluid, and the fluid the usual acrid, biting taste. The crystals
being separated, one of the largest and most perfect was chosen,
and being well wiped on the exterior, and pressed between folds
of bibulous paper, was rubbed down in water, so as to make a
saturated solution. This had no astringent taste like that of
Labarraque's fluid, or the mother-liquor, but one purely alka-
line; and when applied to turmeric paper, reddened, but did
not bleach it. Equal portions of this saturated solution and
of the mother-liquor were then compared in bleaching power,
acid being added to the former to assist the effect : it was found,
notwithstanding that portions of mother-liquor must have ad-
hered to the crystal, that its solution had not "^st part the
power of the mother-liquor. This, in conjunction with the
other experiments, is a striking instance of the manner in which
the carbonate of soda acts, as a simple substance, with the
chlorine in the solution. The crystal itself had never been in
contact with the air : but whether it should be considered as
the excess of carbonate of soda only which crystallized; or
whether it is essential to the formation of these crystals that

1S27.] On Labarraque's Disinfecting Soda Liquid. 229

chlorine should simultaneously be given off into the air ; or
what would take place, if the water were abstracted without
the evolution of chlorine, I have not determined.

18. Notwithstanding the perfect manner in which the chlo-
rine may be thus separated by crystallization and slow evapo-
ration to dryness, yet it is certain that by quick evaporation a
substance apparently quite dry may be obtained, which yet
possesses strong bleaching power. In one experiment, where,
of two equal portions, one had been evaporated in the course
of twenty-four hours to dryness upon the warm part of a sand-
bath, it, when compared with the former, had not lost more
than one-third of its bleaching power.

19. With the desire of knowing what effect carbonic acid
would have on Labarraque's fluid, and whether it possessed
in a greater or smaller degree the power of ordinary acids to
expel the chlorine, portions of the solution were put into two
Woulfe's bottles, and a current of carbonic acid gas passed
through them. The gas was obtained from sulphuric acid
and whitening in a soda-water apparatus, and was well washed
in water. The stream of gas brought away small portions of
chlorine with it, but they were not sensible to the smell, and
could only be detected by putting litmus paper into the cur-
rent. An immense quantity of gas, equal to nearly 1300 times
the volume of the fluid, was sent through ; but yet very little
chlorine was removed, and the bleaching powers of the fluid
were but little diminished, though it no longer appeared alka-
line to turmeric paper. Air was then passed through the solu-
tion in large quantity ; it also removed chlorine, but apparently
not quite so much as carbonic acid.

20. One other experiment was made upon the degree in
which the carbonate of soda in Labarraque's liquor resisted
decomposition by the chlorine, even at high temperature. Two
equal portions of the fluid were taken, and one of them boiled
rapidly for fifteen minutes ; both were then acted upon by sul-
phuric acid, blowing and heat, as described (11), and the two
were then tested by nitrate of silver, to ascertain the quantity
of chlorine remaining : it was nearly three times as much in
the boiled as in the unboiled portion ; and by comparing this
with the results before obtained (11), it will be seen, that after
boiling for a quarter of an hour, not more than a twentieth

230 Anhydrous Crystals of Sulphate of Soda. [1828.

part of the chlorine had acted upon the alkali to form chloride
and chlorate.

21. It would seem as if I were unacquainted with Dr. Gran-
ville's paper upon this subject, in the Quarterly Journal of
Science, p. 371, were I to close my remarks without taking
any notice of it. Unfortunately Dr. Granville has mistaken
M. Labarraque's direction, and by passing chlorine, to " com-
plete saturation," through the carbonate, instead of using the
quantities directed, has failed in obtaining Labarraque's really
curious and very important liquid ; to which, in consequence,
not one of his observations or experiments applies, although
the latter are quite correct in themselves.

Royal Institution, Sept. 3, 1827.

Anhydrous Crystals of Sulphate of Soda*.

IF a drop of a solution of sulphate of soda be placed upon
a glass plate and allowed to evaporate spontaneously, it will
leave crystals which may be distinguished by their form and
ultimate efflorescence, as being the salt in question. Most of
the potash and soda salts may be distinguished as to their base
by such an experiment. They are easily converted into sul-
phates by a drop or two of sulphuric acid and ignition, and
then, being dissolved and tried as above, will yield crystals
which may be known by their forms, and more especially
by their efflorescence if of soda, and their unchangeable state
if of potash. This test is, however, liable in certain circum-
stances to uncertainty, arising from a curious cause. If the
drop of solution on the glass be allowed to evaporate at common
temperatures, then the efflorescence takes place and the dis-
tinction is so far perfect ; but if the glass plate with the drop
upon it be placed upon a warm part of a sand-bath or hot iron
plate, or in any other situation of a certain temperature, con-
siderably beneath the boiling-point of the solution, the crystals
which are left upon evaporation of the fluid are smaller in
quantity, more similar in appearance to sulphate of potash, and
finally do not effloresce. Upon examining the cause of this

* Quarterly Journal of Science, xxv. 223,

1829.] On the Manufacture of Optical Glass. 231

difference, I found they were anhydrous ; consequently in-
capable of efflorescing, and indeed exactly of the same nature
as the crystals obtained by Dr. Thompson from certain hot
saturated leys*.

Hence it would appear that a mere difference in the tempe-
rature at which a solution of sulphate of soda is evaporated,
will cause the formation of hydrated or anhydrous crystals at
pleasure, and that whether the quantity of the solution be large
or small. This, indeed, might have been expected from that
which takes place when hydrated crystals of sulphate of soda
are carefully melted ; a portion dissolves, and a portion sepa-
rates, the latter in an anhydrous state*. I find that, if it were
desirable, crystallized anhydrous sulphate of soda might easily
be prepared for the market; though, as the pure salt is now
but little used, it is not likely this condensed form will be re-
quired. Whenever a soda salt is to be distinguished from one
of potash, in the manner above described, this effect of tempe-
rature must be carefully guarded against.

Online LibraryMichael FaradayExperimental researches in chemistry and physics → online text (page 22 of 49)