John Almon.

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8. placement in a precisely similar jar mounted as rep*
resented in fig. S. The mouth of this jar is closed
by a ground glass plate, which is tubulated, as is
shown in detail by fig. 4. This tub- 4,

ulature a^ain is closed by a rubber
stopper, through which pass first, the
dehvery tube, which reaches the bot-
tom of the jar, and secondly an over-
flow tube which merely passes
through the stopper, and which in
the experiment should be connected
by a nexible hose with a ventilator.
W hen a larger amount of chlorine is
desired the first jar may be connected
with a second, and that with a third, etc, all mounted
in the same way, and' the exit tube from the last
jar leading to a ventilator as before. When the
jars are full the tubulated stoppers with tiieir con-
nections are removed and a plain glass cover substituted. This
simple form of apparatus will be found very useful in all exper-
iments on gases heavier than the air.

During me process of electrolysis the dass will see that the
two gases are evolved in nearly the same proportions, the col-
ored gas rising in one jar as rapidly as the water falls in the
other. The narrowness of the jar prevents to a great degree
tiie diffusion of the chlorine, ana a piece of white paper placed

* Th6 pktimtm wire it ywj eafily welded to the foil on a smoothed siirfiMe of a
lamp of quick lime which lerres as ao anvil. The two haying been placed toffether
in the reqnired position on this support are first intensely heated at the pomtsto
be united, with a blow-pipe fiame, and then a quick Uow with a matt namnMr
eomplstee the work.




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m J. P. Cooke^ Jr.^ on Lecture ExperimemU,

behind the jar, will make tbe line between the colored gas and
the air visible to a considerable distance. When the jars aie
fall, tbe qualities of tbe two gases may be made evident by ap-

Sropriate experiments. As is well known, the gases will not be
elivered in atomic proportions, until the liquid acid is saturated
witb chlorine. It is best therefore not to empty tbe cell after
the experiments, but, having removed the rubber stoppers with
their attachments, to close tbe nioutb with tbe ground glass
stoppers, and the apparatus will then be ready for tbe next oc*
casion. It is also b^ to interpose a small wash bottle contain-
ing sulphuric acid, between the cell and tbe chlorine jar, for
this will not only dry the gas but also equalize the hydrostatic
pressure on the two delivery tubes. Decomposing cells like
that represented in fig. 1, and all other forms of glassware de-
scribed in this paper are made by the New England Olass Ca,
of East Caifibridge, and can be ordered Uirough any of the
dealers in philosophical apparatus in Boston. A much simpler
deoomposinff cell, although not quite so efficient an apparatus,
can be made with a common IT tube supported on a wooden
stand and mounted with rubber stoppers, delivery tubes and
platinum electrodes in every respect like the other.

Tbe second point to be illustrated in regard to hydrochloric
acid is, that it consists of equal volumes of its constituent gases;
and although by our first experiment^ if made in the way we
have described, it is shown that the gases are evolved in nearly
Cjqual proportions, yet a second experiment is reouired to estab-
lish the aosolute truth* of this important fact. The apparatus
we use for this purpose is represented in fig. 6, and the details
of the several parts are shown in fig. 6. The two gases are
evolved together from a simple decomposing cell, shown more
in detail in fig. 9, but in connection with another apparatus, and
the connection of the battery with the two electrodes, is here
made as before shown in fig. 2. The mixed gases pass through
a small drying tube filled with pumice moistened with oil of vit-
riol, into an absorption tube whose construction is shown in de-
tail by fig. 6. As the gaseous mixture is decidedly lighter than
air, it is conducted to the top of the absorption tube through
the small quill tube, and overflows through the short tube Ins-
low. Both of these should pass air-tight through the rubber
stopper, which closes the mouth of the large absorption tube and

* We bert of oootm leare out of Tiew the snaftU diflforeooe which ariset from
th« fact that the gases do not absolutely obej Mariotte's kw and are therefore an-
equally coDdeusM eren by the atmospheric pressure. The Tolumes of the two
gases would undoubtedly lie exactly equal uooer greatly diminished preesore, but
under the pressure of the air, the Tolume of tbe molecular weight of chlorine is
about |4v IMS than the corresponding Tolume of the molecular weight of hydrogen.
adlAirBnoe by ao sieaDs iBappnoiabls in accurate experiments.



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/• p. Cooke^ Jr,y on Lecture Experiments.



193



which should therefore have a bearing on the glass of at least
half an inch. It will be noticed that while the overflow tube



WvJ



is straight, the delivery tube is bent so that its open
end is four or five inches above the mouth of the ab-
sorption tube. Rubber stoppers, or rather caps, must
also be provided, bv which the open ends both of the delivery
and the overflow tubes may be closed at the right time. These
are made by boring with a cork-borer nearly through an ordinary
stopper and then pulling out the rubber core with a pair of
pincers. The absorption tube should now be divided into two
parts of equal capacity by means of rubber rings having how-
ever a length of three or four inches at the lower end for the
absorbent liquid.

The absorption tube having b^n i)repared as described and
filled with the mixed gases, the experiment is made in the fol-
lowing way. The apparatus is first rapidly depressed in a solu-
tion of caustic soda (of the ordinary strength used in the lab-
oratory) until the liquid rises in the tube to the level of the first
rin^. The open end of the delivery tube is now quickly closed
with the ruboer cap, and then the end of the overflow tube is
closed in the same way — the second rubber cap having been pre-
viously dropped upon the bc)ttom of the glass vessel containing
the soda solution so as to be ready for the purpose. The tube,
now perfectly air tight^ is removed from the liquid and the solu-
Am. Joub. Sci.^Sbcond Ssbixs, Vol. XLIV, No. 18L— Sept., 1867.
25



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104 /. P» Cooke^ Jr., on Ltcture Experimenis. *

tion of soda turned backward and forward through its entire
length antil the chlorine is wholly absorbed. The end of the
overflow tube is now opened dnder water colored blue with lit-
mus, which, as it rushes in, will be instantaneously bleached,
indicating the presence of chlorine. The tube must now be
immerq^ in the water until the level of the liquid is the same
within and without, when it will be found that just one-half of
the gas has been absorbed. We have now proved that one-half
of the volume of gas evolved during the electrolysis of hydro-
chloric acid consists of chlorine, and it only remains to show
that the remaining half still left* in the tube is hvdrc^n. For
this purpose the delivery tube may be connected with a water
faucet and the gas burnt as it is forced out through the overflow
tube.

We have now proved first, that hydrochloric acid is composed
of hydrogen and chlorine ; secondly, that these gases are present
in equal proportions by volume, and in order to complete our
demonstration of the constitution of this typical compound, we
have only to prove that when these equal volumes unite to form
HCl there is no condensation. This we may do either synthet-
icallv or analytically.

The svnthetical experiment is made b^ filling the absorption
tube as before with the mixed gases obtained by the electrolysis
of hydrochloric acid, taking great care, as also in the previous
experiment, that the tube should be perfectly diy. It will of
course be necessary to have two of these tubes if both exper-
iments are to be made in the same lecture. The tube thus filled
is to be exposed for some time to bright diffused sun-li^ht, and
afterwards directly to the sun-beam until perfect combination
results. If the glass is quite thick, and the rubber stopper b
forced in very tight, the gases may even be exploded in the
tube without danger, although this form of the experiment is
always attended with some risk. When the gases are in either
way thoroughly combined, the end of the exit tube is first
opened under mercury, in order to prove that no condensation
has taken place, and afterwards under water colored blue by
litmus, when a very rapid absorption takes place, and the red-
dening of the water will indicate that HCl has in fact been
formed.

The analytical experiment is made by decomposing HCl gas
by means of sodium amalgam. For this purpose the carefully
dried gas is first collected over mercury in a perfectly dry tube.
This tube we assume is graduated, or at least divided into two
parts of equal capacity. The tube full of gas is now slipped
over the mouth of a rubber cap, which has been previously
filled with the amalgam, see fig. 5 (lefl side of the wooa cut), and
sunk in the mercury trough until the liquid is just level with



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/. p. Cooke, Jr., on Lecture Experiments. 195

the brim. This cap, which is easily made from the " stopper
cord," should be capable of holding ten or twenty cubic centi*
meters of the amalgam, and should tightly clasp the tube. More-
over for this purpose the solid amalgam, above described, should
be reduced with mercury to the consistency of a thin paste.
The amalgam is now to be shaken up in the tube for several
minutes until the decomposition is complete, and then the mouth
of the tube may be opened under mercury. The liquid will
rise to supply the place of the chlorine which has been aosorb^,
and on sinking the tube in the mercury trough until the level is
the same within as without, it will appear that exactly one-half of
the volume has disappeared. As this, however, would require a
deep cistern of mercury, and as the interior surface of the tube
is left in such a very dirty condition as to obscure the resu}t, we
prefer to transfer the tube to a jar of water, which, when the
cap is removed, at once displaces the mercury and washes out
the interior, without sensibly impairing the accuracy of the ex*
periment.

Water. — The points to be illustrated in the case of water or
rather of free steam are all indicated by the equation



HH | + |0 |=: | H^O



There is no more striking experiment in this connection than
the decomposition of water dv sodium, but as made in the usual
way the experiment is attenaed with no little danger. Sodium
in certain states explodes violently when brought in contact
with water, and after several accidents of this sort we have sub-
stituted the solid sodium amalgam above described with the
best results. We place an ounce or more of this amalgam in a
common gas flask and pour upon it water. The action is very
moderate and must be assisted by a gentle heat, but on heating
the flask with a gas lamp the gas is evolved rapidly and with
^eat regularity. We collect it over the pneumatic trough and
illustrate its properties in the usual way.

We illustrate the fact that water is composed of two volumes
of hydrogen to every one of oxygen by the electrolysis of di-
lute sulphuric acid, using for the purpose the decomposing cell,
fig. 1, already described. We collect the gases in two tall bell
glasses standing side by side on the shelf of the same pneumatic
trough. These bells are of course calibrated and the equal di-
visions marked by rubber rings. Six cells of Bunsen^s battery,
medium size, give a rapid evolution of gas.

Lastly we illustrate the fact, that when the elementary gases
unite to form aqueous vapor, three volumes are condensed to
two, by means of the eudiometer represented in fig. 7. This
apparatus is easily made with a common iron casting well known



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r



196 /. P. Cooke^ Jr., on Lecture Experiments.

to fteam fitters as a '' return bend." Any machinist wiU eanlj
adapt this casting to the required use by attaching to it, as shown
in the figure, a circular iron plate to serve as a stand, by also
^ screwing on to one side an or- s.

dinary " elbow joint," and at the
same time by carefully rimming
out the three apertures so as to pre-
sent smooth sur&ces for the ad-
hesion of the rubber stoppers.
Into one of the openings of the
'* return bend " we fasten with a
perforated rubber stopper, a com-
mon straight eudiometer tubey such
for examjMe as is ordinarily used
in Bunsen's method of gas anal-
ysis, while into the second open-
ing we &8ten in a similar way an
open glass tube. In the opening
of the elbow joint we secure with
& perforated rubber stopper as
beK>re, that convenient substitute
for a stop cock so well known to
chemists as a nipper tap. Last of ^:^
all we obtain from the dass house ^
a tubulated tube like tnat shown in fig. 8, of
such size that it will eover the eudiometer tube
and fit the upper end of the same rubber stop-
b per by which the last is secured in its place.
The upper end of this outer tube is also closed
with a perforated stopper, as shown in the fiff-
ure, and fine platinum wires, connecting wiUi
the wires of the eudiometer, pass between the stopper and the
glass. The lower end of the outer tube should not nt too tightly
around the rubber stopper so that it can easily be removed
when not wanted, moreover all the stoppers should be made of
such length that while perfectly tight, they can easily be removed
for cleaning the tubes.'^ These rubber joints, if well made, give
great flexibility to the apparatus and enable it to withstand
quite rough usage.

The eudiometer being thus mounted, mercury is first poured
into the open limb, which is then dosed with a rubber stoppw
and the mercury transferred by inclining the apparatus to the
closed limb, this process being repeated until the eudiometer

* It is also best to place around the upper end of the eudiometer tube a rubber
ring, <^te narrow, but sufliciently thick to fill the annular space whea tba ooter
tube 18 in its place, and alto perforated with a number ai small bdea, ao that r*^
steam or wupor, employed in Uie azperimenta, may pass £f»elj. Tliis rii^ <
the eudiometer tube and gives greater aotidltjr to Che apparatus.



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/• p. Caohtj Jr , on Lecture Experiments. 197

tube is full The excess of mercury is now drawn out of the
open tube by the tap and this tube having been removed the in-
strument is left as represented in fig. 9. The eudiometer is now
ready for receiving the mixed gases, which are passed up into it
from a simple decomposing cell, as shown in the figure, the ex-
cess of mercury overflowing into any ^
convenient vessel. Theo/>en^te6eisnow
replaced and the outer tube secured in '
position. It is next necessary to raise
the temperature of the eudiometer tube
to a point considerably above the boil-
ing point of water and maintain it at
this temperature during the rest of
the experiment. This is most conven-
iently done by passing through the
outer tube the vapor of amylic alcohol
(fousel oil,) which may be generated
in a flask placed at one side and con-
nected by a glass tube with the upper
end of the apparatus. The tubula-
ture at the lower end of the tube
should at the same time be dipped
iEto the mouth of a glass bottle into
which the alcohol may flow as fast as
the vapor is condensed, .and since the
latent neat of this vapor is very small,
this simple method of condensation
will be found amply sufficient. '

As soon as the temperature of the
eudiometer tube is constant, which can
easily be told, because the mercury
column will then remain at a constant

height, mercury must be poured into the open tube or with-
drawn from it by the nipper tap until the level is the same in
both limbs of the apparatus, it remains now only to note the
volume of the confined ^ and to explode it by passing an elec-
tric spark through the platinum wire already noticed, first, how-
ever, tightly closing the end of the open tube with its rubber
stopper. When the stopper is removed and the mercury col-
umns again brought to the same level it will be found that the
volume of the confined gas has been reduced one-third. The
result, however, is always a little too small, because aqueous
vapor, even at the boiling point of amylic alcohol, 1S2^ C, does
not exactly obey Mariotte s law, and is somewhat more con-
densed than the mixed gases by the atmospheric pressure. It
would be better to employ the vapor of a liquid having a still



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198 /• P. Cooke, Jr., on Lecture Experiments.

higher boiling point, but the results with amylic alcohol are
sufficiently accurate for a lecture experiment*
Ammoi^ia.— The points to be illustrated in the case of ammo-



nia are indicated by the equation H H H[+| N |= | hJ ^ j *



We demonstrate the composition of ammonia by the old
methods which are familiar to every teacher, synthetically by
passing a mixture of nitric oxyd and hydrogen over heated
platinum sponge as in the beautiful experiment of the late Dr.
Hare, and analytically by decomposing aqua ammonia either
by electrolysis or by means of chlorine. For the electrolysis
of ammonia the decomposing cell fig. 1 may be used, filling it
with the strongest aqua ammonia and adding a not too small
amount of sulphate ammonia in order to increase the condadang
power of the liquid. The reaction is less simple than in the
electrolysis either of water or of hydrochloric acid, bat as the
final results the gasses are evolved, very nearly at least, in ato-
mic proportions, three volumes of hydrogen to one of nitrogen.
They can be collected separately in graduated bells as in the
electrolysis of water. In decomposing ammonia by chlorine we
use with very satisfactory results the apparatus shown in fig. 6
and already described. For this use however a tube should be
selected so thin that water may be boiled in it without risk of
breaking the glass. The tube having been filled by displaoe-
ment with pure and dry chlorine ^as, we press down the lower
end into very weak aqua ammonia (eight measures of water to
one of the concentrated solution,) until the liquid flowing in
through the overflow tube rises to the height of the first rubber
ring. We now quickly close the delivery tube with its rubber
cap and allow the absorption to continue until the tube is about
half full of the ammonia water when we also close the overflow-
tube and shake up the liquid in the large tube until all cloadi-
ness has disappeared from the interior. The decomposition is
now complete but a considerable amount of the liberated nitre*
gen still remains dissolved in the liquid. To expel this we
heat the tube carefully over a gas lamp until the liquid within
begins to boil. On now transferrins the apparatus to the poea-
matic trough and opening the overflow tube under water it will
be found, when the tube cools, that just one- third of the original
volume is left and it can easily be shown that the residual gas

* Indeed we can obtain with free steam a result, whidi it suffidently oaar ih%
theory for aU purposes of illustration, only it is then important that both th*
mizea gases and tlie resulting yapor should be measured under a pretiure eon*
siderably lees than that of the atmosphere. For thb purpose a loqg eodicMnetflr
tube should be used and before each measurement the ieyel of the mercorf eboald
be adjusted so that it shall stand in the open tube from 10 to 15 incbet lower thaa
b the eudiometer. Of course the diflferenoe of Ieyel most be the iame mt bolb
measurements.



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/. p. Cooke, /n, on a new form of Eudiometer. 199

is nitrogen. Hence, it follows, since chlorine always combines
with its own volume of hydrogen, that ammonia contains only
one volume of nitrogen to every three volumes of hydrogen,
the point to be proved. To complete this series of illustrations
it only remains to show that in ammonia gas the four volumes
are condensed to two. For this purpose some dry ammonia ^
is passed up into the eudiometer tube as in fig. 9. The side
tube is then replaced as in fig. 7, the mercury level adjusted and
the position marked with a rubber ring. A stream of electric
sparks from a Btihmkorfl* coil is now passed through the gas, so
arranging the connections that the sparks may traverse the
whole length of the gas column, and the amount of gas should
be small enough to render this possible. The decomposition
proceeds somewhat slowly, but after sujfficient time on readjust-
ing the level it will be found that the volume of the gas has
doubled. Besides the experiments described above, there are
many others, to which these same forms of apparatus are appli*
cable; but these will suggest themselves to every teacher ana it
is not therefore necessary to enter into further details.

JBudtomeier. — ^The eudiometer described above, although origi-
nally contrived for the lecture table has proved to be of still
greater value in the laboratory, in all processes of gas analysis
for which such an instrument is required. It is not only very
cheap, simple, and easil;^ repaired, but also equallv as accurate
as the the most complicated apparatus. It can be used in a
room of the most variable temperature ; for by passing a cur-
rent of water, or of steam, as the case may require, through the
outer tube the temperature of the eudiometer tube may be easily
maintained absolutely constant. The various gases are passed
in as shown in fig. 9 and through the same opening the reagents
used in the processes of analysis are readily introduced. By
replacing the open tube as in fig. 7, and bringing the two mer-
cury columns to the same level, the residual volumes may always
be read off under the atmospheric pressure and at a constant tem-
perature, indicated by a tnermometer placed in the annular
space between the tubes. Or on the other hand by varying the
height of the mercury column in the outer tube we may reduce
the gas to the same volume and measure the difference of ten-
sion according to the method of Begnault. This form of eudi-
ometer is especially adapted for the admirable methods of gas
analysis devised by Bunsen. The absorbent balls used by him
are most readily introduced when the apparatus is arranged as
shown in fig. 9 and the volume of aqueous vapor formed afi«r
combustion may easily be measured by replacing the current of
cold water through the outer tube by a current of free steam.
In this case it will be best to measure the gas under as great a
difference of pressure as possible, in order to ensure that all the



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900 J. F* Coofe, Jr^ on a newftrm of Emdiameier.

water is vaporized and also in order to avoid the somewhat un-
certain correction arising from the diflerenoe of temperatuie of
the two limbs of the apparatus. This correction, which in most
cases is insignificant, oecomes important when steam is nsed,
and it is dien best to measure direct! v the diflEbrence of level be*
tween the mercury in the open mouth of the iron dstem, fi^. 9,
and that in the tube. This we do by the millimeter divisions
on the eudiometer tube with the aid of a very simple contri-
vance. A split rinff of blackened sheet brass, carrying a bent
steel wire, is slipped down over the outer tube until the end of
the wire iust touches the surface of the mercury. The vertical
heiffht of this simple measure being known we have only to
add to it the hei^nt of the mercury column above the upper
edge of the ring m order to know the exact difference of level
Of course care must be taken when the measurement is made
that the mercury column is vertical, but it is unnecessary to
dwell on such obvious precautions, which are essentially the
same with this apparatus as those so fully detailed by Bunsen in
his work on *' Gbsometry." It is obvious moreover that the
number of these corrections is considerably diminished in using
this apparatus as compared with the ordinary mercury pneu-
matic trough, and besiaes the convenience and comfort of work-
ing in a warm room, it has the additional recomendation that it
xeouires a very small amount of mercury.

The above apparatus as represented in fig. 9 may also be
used with great advantage in Gay Lussac's process of determin-
ing the density of vapors. The method of using it is obvious
to any one who is jbmiliar with the process. After a weighcKi
amount of the liquid under examination enclosed in a thin glass



Online LibraryJohn AlmonThe American journal of science and arts → online text (page 74 of 102)