158 parts of chromic acid yield 106 parts of chlorine. The chloride of
chromium is again precipitated with carbonate of lime, and by ignition
converted into chromate of lime. Only three eighths of the chlorine
contained in the hydrochloric acid is given up, whilst manganese yields
one half.
7. Hargreaves proposes to evaporate a solution of protochloride of iron to
dryness, and then to heat the dried substance in a current of air, at a
temperature of about the melting point of zinc, by which means perchloride
of iron and free chlorine would be obtained. Thielbierge's suggestion
consists in passing air over protochloride of iron, and so giving rise to
peroxide of iron and chlorine. This, like Hargreaves' proposition,
possesses the disadvantage of furnishing the chlorine very largely diluted
with air and nitrogen.
8. Jessie de Mothney. This chemist has proposed a continuous process which
is as follows:--Peroxide of manganese either alone or mixed with lime is
put into a retort, which, when heated to redness, has a current of
hydrochloric acid gas passed into it. A disengagement of chlorine and
steam takes place, and there remains in the retort a mixture of
undecomposed peroxide of manganese with chlorides of manganese and
calcium. The retort containing the undecomposed peroxide and chlorides
being still kept at a red-heat, air or oxygen is passed over them, the
result being that the manganic chloride is decomposed at once.
The chlorine liberated by this last operation is conveyed into vats
containing a mixture of lime and manganous oxide, which substances have
been previously formed by the decomposition of the manganous chloride by
lime, the soluble chloride of calcium having been run off. Sesquioxide of
manganese and hypochlorite of calcium are formed in the vats, and these
two, reacting on each other, give rise to peroxide of manganese and
chloride of calcium. With fresh hydrochloric acid this latter product
yields more chlorine for use in the chambers. Magnesia may be substituted
for lime.
9. Dunlop. This process, which may be regarded as the first practical
method for utilising the whole of the exhausted manganese residues, and
rendering them capable of reapplication in the production of chlorine, was
devised by Mr Dunlop in 1855, since which time it has been in use in the
alkali works of the Messrs Tennant, at St. Rollox, Glasgow. The operation
consists in precipitating the chloride of manganese in the still liquor by
carbonate of calcium; the resulting manganese carbonate being decomposed
by heat. The liquors are previously mixed with a little milk of lime,
which frees them from ferric oxide, alumina, and silica.
Being allowed to stand until these and all other insoluble matters are
precipitated, the clear solution containing the chloride of manganese is
mixed with finely divided chalk, when the following reaction ensues:--
MnCl_{2} + CaCO_{3} = MnCO_{3} + CaCl_{2}.
The resulting milky liquid is then run into large iron boilers, through
each of which passes horizontally an iron shaft furnished with a number of
projecting arms. This shaft having been put into revolution so as to keep
the contents of the boilers agitated, steam is admitted into them under a
pressure of from two to four atmospheres, and by the combined effects of
heat and pressure the decomposition of the manganese chloride by the
calcium carbonate is accomplished in about four hours. The manganese
carbonate is then allowed to subside, the calcium chloride solution is
drawn off, the precipitate carefully washed, and thrown up in heaps on an
inclined surface to drain. When partially dried the carbonate of manganese
is placed in small low wagons, made of sheet-iron, supported on rollers,
and slowly drawn through a furnace by means of a chain. The furnace holds
forty-eight of these little wagons. The furnace is 50 feet long, 12 feet
wide, and 10 feet high. "A fire-brick flue runs down the centre of the
bottom of the furnace, and is connected at the far end with two return
metal pipes, which lie on each side of the flue. A uniform heat at about
660° F. is maintained in the furnace, in which four lines of rails are
laid for the small wagons to run along. The half-dried substance loses all
its moisture and part of its carbonic acid as the wagons pass along the
first line of rails, and as they return down the second line a further
escape of carbonic acid ensues, and eventually the expulsion of all the
acid, and the peroxidation of the manganese is completed during the
passage of the wagons on the third and fourth lines." The operation lasts
about forty-eight hours, the substance gradually changing in colour from
white to brown, and lastly to black.
The ends of the furnace are closed by loose hanging doors, so as to ensure
the entrance of a sufficient supply of air. The fire-place is situated
below the floor of the furnace, and requires very careful watching. The
resulting product is a mixture of oxides of manganese, and contains about
72 per cent. of peroxide of manganese.
9_a._ A. Dunlop. Another process designed by Mr Dunlop, and also in use at
Messrs Tennant's, is as follows:--Nitrate of sodium (Chilian nitre) and
chloride of sodium are decomposed by being heated in cast-iron cylinders
with sulphuric acid. The gaseous products are made to pass through leaden
Woulff's bottles containing sulphuric acid, which absorbs the nitric
peroxide formed, and allows the passage of the chlorine into the chambers.
The reaction may be represented by the following equation:--
NaCl + NaNO_{3} + H_{2}SO_{4} = Cl + NO_{2} + Na_{2}SO_{4} + H_{2}O.
The sulphuric acid charged with nitric peroxide is used in the manufacture
of chamber acid.
10. Weldon. _a._ The process by which the greater part of the chlorine
employed in the manufacture of bleaching compounds is now obtained and
which has hitherto proved the most practical is that of Mr Walter Weldon.
We have the authority of Mr Kingzett, in his work on 'The Alkali Trade,'
for the statement, that out of 90,000 tons of bleaching powder made in
Great Britain in 1874, 50,000 were procured by Weldon's method; and
turning to the Continent we find the process largely adopted in Germany,
France, and Belgium. The utilisation and regeneration of the residual
product left in the still after the evolution of the chlorine which it
will be presently seen is accomplished by the above process, is not the
only advantage accruing from it, since it has also been the means of
removing an extensive source of contamination of many of our streams and
rivers, into which the then useless chloride of manganese was thrown
previous to Mr Weldon's invention. It is true that the only waste product
formed in the course of the operations, viz., chloride of calcium, is got
rid of by being run into the nearest waters, but it is stated by the
Rivers Pollution Commission, beyond making these harder, no other
objectionable effect is caused by it.
Mr Weldon's process is based upon the fact, that if protoxide of manganese
be suspended in a solution of chloride of calcium, and an excess of lime
be added, the protoxide will become readily converted into peroxide if air
be forced into the liquor. It had long been known that it was possible to
convert into a peroxide the protoxide of manganese obtained by treating
the residual still liquors with an equivalent of lime, but all attempts to
reduce this knowledge to practical account had proved unsuccessful until
Mr Weldon attempted it.
Mr Weldon made the important discovery, that whilst protoxide of manganese
is by itself, when treated in the wet way with air, only capable of being
converted into peroxide, at the greatest, to the extent of one half; the
addition to the protoxide so treated of a certain quantity of lime
converted the whole of it into peroxide in less than a twentieth the time
required to peroxidise half the protoxide if lime were absent. It will be
seen that it is the employment of an _excess_ of lime which constitutes
the success of Mr Weldon's process, which is as follows:--
The residual liquors remaining in the still after the chlorine has been
evolved by the action of hydrochloric acid on peroxide of manganese, and
in which chloride of manganese is by far the predominating constituent,
are run into a receptacle termed the _neutralising well_, which is usually
six feet in depth by twenty in diameter. In this well the free
hydrochloric acid of the still-liquor is neutralised by the addition of
limestone or chalk, which at the same time serves to decompose the soluble
ferric and aluminic chlorides present in the liquid, and to precipitate
them as insoluble oxides. During this process the contents of the well are
kept in a state of brisk agitation by means of a suitable stirrer. After
this treatment the now neutral liquor consists of chlorides of manganese
and calcium in solution, of a small quantity of suspended ferric and
aluminic oxides and chalk. It additionally contains also in suspension a
by no means small quantity of sulphate of lime, derived from the sulphuric
acid always present in varying amount in the commercial hydrochloric acid
used.
From the neutralising well the liquor is pumped to a height of some forty
feet into tanks, called the _chloride of manganese settlers_, in which
after from two to four hours it deposits the solid matters suspended in
it, the supernatant clear liquor assuming a pale rose-coloured appearance.
The next operation is to draw off by means of syphons, which can be
lowered or raised in the settlers to any desired level, this clear liquid,
containing the chlorides of manganese and calcium, into a vessel called
the _oxidizer_; this latter being an iron cylinder, of from eight to
twelve feet in diameter, and from twenty-two to thirty-five feet deep. Two
pipes go down nearly to the bottom of the oxidizer; the larger one being
used for conveying a blast of air from a blowing engine, and the smaller
for the injection of steam. The introduction of steam is only had recourse
to in case the liquor when drawn into the oxidizer should not have the
requisite temperature, viz. 130° or 140° Fahr. Immediately above the
oxidizer a reservoir containing milk of lime is placed. A great deal
depends upon the careful preparation of the milk of lime, since on the
degree of fineness in which the lime is added to the manganese chloride in
solution depends the rapidity with which it acts in the oxidizer. The milk
of lime is kept constantly agitated, to ensure its being of uniform
consistency, and should contain from 15 lbs. to 20 lbs. of hydrate of
lime in every cubic foot of the mixture.
A charge of the clear liquor having been drawn into the oxidizer, and
raised if necessary to the requisite temperature, the blowing in of air is
begun, whilst at the same time the milk of lime is run into the oxidizer
as rapidly as possible, the flow of milk of lime being only discontinued
when a sample of the filtrate drawn off, by means of a tap placed near the
bottom of the oxidizer, ceases to give the manganese reaction when mixed
with a solution of bleaching powder. This reaction consists in the
production of a purple colour caused by the formation of permanganate of
calcium. More milk of lime is then added, when the contents of the
oxidizer are found to consist of a thin white mud, composed of a solution
of calcium chloride, holding in suspension a mixture of protoxide of
manganese and lime. The injection of air being continued the white mud
rapidly becomes darker in colour, and soon changes into a thin black mud
composed of solution of calcium chloride, holding in suspension certain
compounds of peroxide of manganese partly combined with protoxide of
manganese, but chiefly with lime, which compounds Mr Weldon terms
"_manganites_." Mr Weldon suggests that the manganites so formed may be
regarded as salts in which the basic radical is calcium or manganese, and
the acid radical MnO_{3}; and may be represented by the formulæ CaMnO_{3},
and MnMnO_{3}; and possibly also CaMnO_{2} (MnO_{2})_{2}. "The quantity of
lime which has to be put into the oxidizer before the filtrate from a
sample of its contents ceases to yield the manganese reaction varies very
considerably. Recently precipitated protoxide of manganese dissolves very
appreciably in neutral solution of chloride of calcium, its solution
therein comporting itself with reagents exactly like solutions of
manganese salts. It dissolves also in solution of oxychloride of calcium,
that is to say, in solution of chloride of calcium containing dissolved
lime; its solution in oxychloride of calcium not giving the ordinary
manganese reactions."
"Hence even if all portions of the lime added to the chloride of manganese
in the oxidizer were capable of acting on chloride of manganese equally
readily, manganese could not cease to be so in solution as to be
detectible by ordinary reagents, until more than an equivalent of lime had
been added--that is to say, until enough had been added not only to
decompose all the chloride of manganese, but also to form a certain
quantity of oxychlorate of calcium. It is never the case, however, that
all portions of the lime used are capable of acting on the chloride of
manganese with equal readiness. The lime used always contains a larger or
smaller proportion of particles coarser than the rest, which coarser
portions cannot of course act so rapidly as the finer ones; and as the
decomposition of the chloride of manganese requires to be completed as
quickly as possible, those portions of the lime which will not act upon it
instantly are scarcely allowed time to act upon it at all.
"These coarser portions of the lime thus contribute very little to the
decomposition of the manganese, though they afterwards dissolve completely
in the hot solution of chloride of calcium, and then play their full part
in the reactions which take place during the subsequent blowing. The
proportion of lime which thus does not act on the chloride of manganese
varies with the source of the lime, and with the manner in which it is
prepared, so that the quantity of lime which has to be added to a charge
of chloride of manganese liquor in the oxidizer, before the filtrate from
a sample of the resulting mixture ceases to become coloured on the
addition of solution of bleaching powder, varies from about 1·1 to 1·45
equivalent.
"The further quantity of lime which is added after that point has been
reached is now usually so much as to raise the total quantity to about 1·5
to 1·6 equivalents, being from one half to six tenths in excess of the
quantity which actually takes part in the decomposition of the chloride of
manganese."[239]
[Footnote 239: 'Chemistry, Theoretical, Practical, and Analytical, as
applied to the Arts and Manufactures,'--Mackenzie & Co.]
As previously stated, Mr Weldon found that if only so much lime is
employed as is necessary to precipitate the manganese, not more than half
the protoxide of manganese will be converted into the peroxide, and that
even this result will be accomplished very tardily. And, as has been
already mentioned, a greater and more rapid yield of protoxide can only be
obtained by using a larger proportion of lime. Any excess, however, of
lime over that absolutely required for the peroxidation of the protoxide
of manganese must be sedulously avoided, since a superabundance of lime
leads to the formation of compounds that are not readily peroxidised.
Should such compounds be formed, it is necessary to destroy them, and this
may be done by the addition of a fresh quantity of chloride of manganese.
The objectionable compounds in question are lime and protoxide of
manganese, which are known in the process under the name of "bases;" and
the reason why it is desirable to prevent as much as possible their
formation will become evident when it is remembered that they cannot
furnish chlorine when treated with hydrochloric acid, but that they merely
dissolve in this latter.
The injection of air into the oxidizer, which constitutes the blowing
operation, varies from two to four hours.
The quantity required to be blown in is chiefly dependent upon the depth
of the oxidizer, and upon the amount of protoxide of manganese contained
in a given volume of the charge.
The greater the depth of this latter the more rapidly does the
peroxidation take place; and the greater the number of molecules of
protoxide in a given volume of the charge, the larger is the total surface
presented to the action of injected air, and consequently the greater is
the proportion of the oxygen absorbed.
"In one instance 175,000 cubic feet of air were blown in during five
hours, and of the oxygen contained in this, 14·8 per cent. (equal to
rather more than 4 cwt.) was absorbed in the production of 22 cwt. of
peroxide of manganese."[240]
[Footnote 240: Weldon.]
The expenditure of mechanical power in forcing the air into the oxidizer
averages between seven and eight horse-power for every 100 lbs. of
peroxide of manganese obtained. In theory, to produce the quantity of
chlorine contained in a ton of bleaching powder containing 37 per cent. of
chlorine, 1020 lbs. of peroxide of manganese would be required; but it is
found in practice that instead of this quantity of peroxide giving the
above result, 1100 lbs. are needed.
"The consumption of lime averages 14 cwt. per ton of bleach. By this
process 1 ton of bleach is made, using 2832 lbs. of hydrochloric acid,
generated by the decomposition of 47·5 cwt. of salt, viz. a quantity which
theoretically yields 3334 lbs. of hydrochloric acid. There is therefore a
loss of acid of 15 per cent. The loss of manganese varies from 4 to 10 per
cent. The whole of the lime is lost, and two thirds of the total chlorine
(in combination with calcium) contained in the acid used.[241]
[Footnote 241: Kingzett.]
When sufficient air has been blown into the oxidizer, the contents which
consist of a solution of chloride of calcium, holding in suspension
peroxide and protoxide of manganese and lime, are run into one of a range
of settling tanks placed below the level of the oxidizer. These tanks are
known as _mud settlers_. In these the manganese mud is left to deposit
until about half its volume has become clear. It generally requires 3 or 4
hours to deposit. The clear part, which consists of chloride of calcium,
being then decanted by means of a swivel-pipe, is usually thrown away. The
mud remaining in the settlers, which contains in a cubic foot from 4 lbs.
to 5 lbs. of peroxide of manganese, is now in a fit condition to be placed
in the still, where it is to be exposed to the action of the hydrochloric
acid. The stills, which are made of slabs of hard siliceous sandstone or
of Yorkshire flagstones, and are usually in the shape of an octagonal
prism, are about 8 feet square, and 10 feet in depth. Mr Kingzett says
"the new Weldon stills are polygonal in shape, about 12 feet across, and 7
feet to 8 feet deep." Contrary to the course formerly followed, when
native manganese was used in the Weldon process, the still is charged with
hydrochloric acid first, and the manganese mud is run in upon the acid in
a small, steady stream, the flow of which can be regulated by a stopcock.
Steam being carefully admitted into the still at the same time, the mud
dissolves very rapidly in the acid, and the chlorine is evolved in an even
current, the force and flow of which is dependent upon and can be very
accurately regulated by the admission of the mud.
The time occupied before the reaction between the acid and the manganese
is completed varies in different works from two to six hours. At the end
of this time the contents of the still are run off into the well placed
below it, and are afterwards submitted to the various operations already
described, which we have seen to accomplish the regeneration of the
residue and effect its reconversion into peroxide of manganese. The
process is a continuous one, and theoretically the original quantity of
manganese should be capable of being used over and over again for an
unlimited number of operations. In practice, however, there is always
found to be a loss of a small per-centage of manganese, arising from some
of the chloride of manganese being carried down by the sulphate of lime
and the ferric and aluminic oxides in the settlers, and not being
thoroughly recovered when the deposit is washed; for, though an exhaustive
washing of the precipitated matters could be easily managed, the bulk of
the wash waters would render the recovery of the chloride of manganese
from them a non-paying affair. This loss of chloride varies according to
the statements of different manufacturers from 2 to 10 per cent.
It is stated that not only is the chlorine yielded by Mr Weldon's process
of very pure quality, and the bleaching powder manufactured from it very
high of strength and excellence; but that over from 20 to 25 per cent.
more bleach is obtained from a given quantity of hydrochloric acid, when
artificial peroxide of manganese is used instead of the native. This
advantage is chiefly owing to the artificial manganese (of the manganese
mud) from its physical condition being much more accessible than the
native form of manganese to the action of the hydrochloric acid, and from
its dissolving in the acid so much more readily and thoroughly, and
neutralising as much as from 95 to 99 per cent. of it, a much larger
amount than the native ores are capable of neutralising.
Again, the bleaching powder produced by the above process stands not only
very high in point of strength, but varies very little in the amount of
chlorine it contains, as may be gathered from the following table, which
shows the average strength for thirteen consecutive weeks of the bleaching
powder made at six large and different manufactories:--
-------------------------------------------------
| FACTORY.
WEEK. |-----------------------------------------
| I. | II. | III. | IV. | V. | VI.
-------|------|------|------|------|------|------
1st | 36·9 | 37·8 | 36·7 | 36·3 | 36·6 | 36·6
2nd | 36·1 | 36·8 | 36·7 | 36·2 | 35·1 | 37·4
3rd | 36·5 | 38·0 | 36·6 | 36·1 | 37·2 | 37·9
4th | 35·9 | 37·1 | 35·9 | 36·2 | 36·8 | 37·1
5th | 35·8 | 36·9 | 36·0 | 36·3 | 36·5 | 37·8
6th | 36·0 | 37·0 | 36·2 | 35·9 | 36·5 | 37·2
7th | 36·5 | 36·0 | 36·3 | 36·6 | 35·8 | 36·8
8th | 36·3 | 36·8 | 36·3 | 36·3 | 35·0 | 37·1
9th | 36·4 | 36·3 | 36·8 | 35·7 | 35·2 | 37·0
10th | 36·5 | 36·7 | 36·3 | 36·0 | 36·2 | 37·6
11th | 36·8 | 36·8 | 36·2 | 35·9 | 36·0 | 37·2
12th | 36·8 | 35·9 | 35·6 | 35·6 | 36·1 | 37·2
13th | 36·7 | 35·2 | 35·9 | 36·1 | 36·9 | 37·5
-------------------------------------------------
Spite of the expensive plant required to work Mr Weldon's process, it is
said to possess very decided advantages over the old methods as far as
regards cost of production.
In connection with Mr Weldon's process may be mentioned Mr Valentin's
modification of it, for which a provisional patent was taken out by this
latter gentleman. Instead of adding more lime, after the neutralised still
liquors have been precipitated by an equivalent of lime, as is done in the
above process, Mr Valentin adds a solution of potassium ferricyanide, and
air being blown in, the peroxidation of the manganese is effected much
more quickly than in Mr Weldon's process. It was also calculated that, by
Mr Valentin's method, bleaching powder could be produced at a cost of
about ten shillings per ton less than when made by Mr Weldon's.
For the successful working of Mr Valentin's process it is necessary that
the ferricyanide should be recovered, not only because of its cost, but
also because its presence gives rise to the production of cyanogen
compounds, which would enter the chamber with the chlorine. Hitherto no
economical plan for the recovery of the salt has been devised, and
consequently Mr Valentin's proposed modification of Mr Weldon's process
has failed to be adopted.
_b._ A second process for obtaining chlorine, called "_the magnesia
process_," has been devised by Mr Weldon. In the previous method, or
"_lime process_," two thirds of the chlorine contained in the hydrochloric
acid, as we have seen, is lost, passing away in the form of waste chloride
of calcium.
In the "magnesia process" all the chlorine is utilised, the acid employed
being made to yield the whole of its gas in the free state. The
regeneration of the manganese peroxide being likewise accomplished, and
the process being a continuous one, theoretically no loss of material
should take place.
Beyond the employment of liquor pumps, no machinery is requisite for
carrying out the operation, which, being very simple in its details,
requires the employment of little skilled and, consequently, expensive
labour. Further, the inventor claims for it the production of bleaching
powder at a less cost per ton than by any other process. The "magnesia
method" is worked as follows:--
The spent liquors of the still, consisting of chloride of manganese and
free hydrochloric acid, are neutralised with magnesite, or, as it is
sometimes called, Greek stone--a very pure native form of carbonate of
magnesia. Sometimes the magnesite is calcined, and the magnesia thus
obtained used instead.
The neutralisation may be effected either in the still itself, or in a
well made of cast iron. The liquid is next pumped into the settlers, in
which it deposits its ferric and aluminic oxides and sulphate of lime. The
clear liquor containing the chlorides of manganese and magnesia is then
run into an iron evaporating pan, where it is concentrated by boiling
until it reaches a temperature of between 300° and 320° F. At this point
the magnesium chloride begins to be decomposed by the water, and
hydrochloric acid is given off. When it has reached the above degree of
concentration, it is conveyed into a muffle furnace. This furnace is
divided into two compartments, separated by an iron door, which can be
opened or shut by means of a pulley placed outside. The desiccation of the
mass which is accompanied with the evolution of a little chlorine and a
large amount of hydrochloric acid, having been completed in one of the
divisions of the furnace, it is broken up by constant stirring into thin
cakes and raked into the second division, where it is gently heated with
access of air; when the operation is complete the residue which left the
first compartment as a mixture of manganese and magnesium chloride becomes
converted into manganate of magnesia (MgMnO_{3}), its chlorine having been
driven off partly in the free state and partly as hydrochloric acid. "As
long as water is present in the furnace hydrochloric acid is evolved, and
as the main evaporation takes place in the first division of the furnace,
it is chiefly hydrochloric acid that is there generated. In the second
division it is chiefly chlorine which is evolved, but it is, of course,
mixed with some hydrochloric acid. It is, indeed, doubtful whether much
manganese chloride is decomposed by the water so long as there remains
any chloride of magnesium, as this body is far more readily
decomposable."[242]
[Footnote 242: Kingzett.]
It is stated that all the manganese is not converted into peroxide in the
furnace, but that a certain portion of it is left as protoxide; which,
with the magnesia, constitutes the useless "bases." The completion of the
process is known when portions of the cake drawn from time to time from
the furnace cease to indicate any increase in the quantity of peroxide of
manganese.
The finely-divided black powder--manganate of magnesium--thus obtained,
after leaving the furnace and when sufficiently cold, is ready for the
stills--where, in contact with hydrochloric acid, it is again employed in
the generation of chlorine.
The chlorine leaves the furnace mixed with much hydrochloric acid,
nitrogen, and air. The gaseous mixture is drawn by a chimney draught
through the coke towers, as in the making of salt-cake. By this
contrivance the hydrochloric acid is recovered, yielding a solution strong
enough to react upon fresh manganese in the still. The diluted chlorine
may be made to ascend leaden towers, where it comes in contact with a
shower of milk of lime, which absorbs the gas and forms ordinary bleaching
liquid, whilst sometimes it is employed in the production of potassium
chlorate.
We have seen that the chlorine yielded by the "magnesia process" is partly
in the concentrated, and partly in the dilute condition. The ratio of
strong chlorine generated in the still to that of weak chlorine produced
in the furnace may be anything between one to one, and one to about four,
at pleasure.
"When working so as to obtain strong chlorine and weak chlorine in about
equal proportions, the quantity of the liquor to be boiled down per ton of
total bleaching powder made was about 105 cubic feet. As the proportion of
the weak chlorine increased, the quantity of liquor to be boiled down
diminished until, when the proportion of the weak chlorine to that of the
strong became as four to one, the quantity of liquor to be boiled down per
ton of total bleaching powder made was only about 40 cubic feet."[243]
[Footnote 243: 'Chemistry, Theoretical, Practical, and
Analytical,'--Mackenzie & Co.]
11. (Deacon.) As we have already seen, Vogel proposed to obtain chlorine
by the decomposition by heat of cupric chloride, and to reconvert the
resulting cuprous chloride into the cupric salt by treatment with
hydrochloric acid.
Chlorine may be produced by passing a mixture of gaseous hydrochloric acid
and air over heated bricks or other porous substances, a reaction which
Oxland unsuccessfully attempted to turn to account for the production of
chlorine for manufacturing purposes. The cause of failure appears to have
been the great heat necessary to effect the decomposition of the acid
atmospheric oxygen.
In the late Mr Deacon's process both Vogel's and Oxland's methods are
combined. He discovered that to be able to generate chlorine and water
from gaseous hydrochloric acid and air, a very much lower temperature than
that employed by Oxland was necessary, and he found that this diminished
temperature could be attained, if the gas and air to be decomposed were
passed over porous bricks saturated with a solution of sulphate of copper,
and heated to a temperature of 700° to 750° F.
Beyond this point he found the heat ought not to be carried; for at 800°
the cupric chloride formed begins to volatilise, and to condense in the
cooler parts of the apparatus (presently to be described), thereby
interfering with the draught through it, and delaying the working, since
its removal becomes necessary. It was found that below 400° the reaction
does not take place. Experience has demonstrated that the best temperature
to effect this decomposition is 625° F.
The hydrochloric acid obtained either from a soda furnace or evolved from
an aqueous solution is immediately mixed with a quantity of air containing
an excess of oxygen over that required for liberating all the chlorine
from the evolved hydrochloric acid, and passed through heated U-shaped
tubes of cast-iron, from which the gaseous mixtures obtain the necessary
temperature. The original plant was so contrived that the heated gases
were conveyed from the U-shaped tubes into a series of nine towers made of
iron or other suitable material. Entering by a pipe at the bottom of the
first tower, and passing on to the second, the gases came into contact
with a series of ordinary agricultural drain pipes of small bore arranged
with vertical spaces, these pipes being saturated with a solution of
sulphate of copper and sulphate of soda, it being subsequently found that
this latter addition increased the efficacy of the copper sulphate, as
well as its power to resist decomposition. From the first two towers of
the series the mixed gases traversed the remaining ones, where they
encountered small pieces of common brick, fire brick, or burnt clay also
impregnated with the copper and soda sulphates, after reacting upon which
they passed out of the apparatus, called the '_decomposer_,'
In the more recently made decomposers we believe the nine towers were
abolished, and one chamber substituted for them, the drain-pipes being at
the same time abandoned for pieces of brick and clay marbles.
A decomposer upon this latter principle is said to have been in use for
several months at a factory in Berlin, and to have worked perfectly
satisfactorily. After leaving the decomposer, the gaseous mixture, which
now consists of chlorine, water, nitrogen, unconsumed oxygen, and
undecomposed hydrochloric acid, after being cooled, is passed through
water, by which means it is deprived of its hydrochloric acid.
It is next made to ascend a tower, where, meeting with a stream of
sulphuric acid running over coke, it is deprived of its water. The
chlorine (diluted with nitrogen and oxygen) is now ready for the lime
chamber.
One great objection urged against the adoption of the above process, viz.,
that in consequence of the large volume of the evolved gases enormously
large chambers for the preparation of the bleaching would be
necessitated, seems to have been met by passing the gas through a series
of chambers, in which the first contains nearly finished bleaching powder;
the second, lime in a less saturated condition; and so on, until the last
chamber contains merely slaked lime.
The following table, exhibiting the amount of chlorine contained in
different batches of bleaching powder made by Deacon's process, is
extracted from 'Chemistry, Theoretical, Practical, and Analytical,'
published by Mackenzie:--
----------+-----------+----------+-----------
| Strength. | | Strength.
----------+-----------+----------+-----------
July 14 | 36·0 | July 22 | 34·3
" 15 | 34·8 | " " | 36·5
" " | 36·1 | " 24 | 36·8
" 17 | 36·4 | " " | 37·5
" " | 36·0 | " 25 | 36·1
" 18 | 37·2 | " " | 36·7
" " | 37·9 | " " | 36·8
" 19 | 37·2 | " 26 | 36·2
" " | 37·0 | " " | 36·9
" 20 | 37·9 | " 27 | 36·9
" " | 36·7 | " " | 35·5
" 21 | 36·0 | " 28 | 37·2
" " | 35·3 | " " | 37·0
" " | 37·7 | " " | 36·75
----------+-----------+----------+-----------
Writing on this process in his late work, 'The Alkali Trade,' Mr Kingzett
says:--"The process bearing Mr Deacon's name was first brought before the
public at the British Association Meeting in 1870.
"It excited at that time much attention, and indeed for some period it was
doubtful whether it would not rival or even displace the Weldon process.
Further experience, however, discovered difficulties in the practical
working of this beautiful method, which exercise a deteriorating influence
on its value, and lessen its applicability. Although several plants have
been erected in connection with this mode of manufacturing chlorine, most
of them have been since abandoned, and at the present time most of the
chlorine is manufactured according to the process of Mr Weldon."
Dr Jurisch, in a communication to 'Dingler's Polytechnic Journal,' 1876,
remarks that when Deacon's process was first taken up within a short time
by more than twelve English and two German establishments, the view was
generally entertained that the balls of clay steeped in solution of copper
would ensure an uninterrupted production of chlorine gas for a year or
two, if not longer. Before many months had elapsed complaints were heard
of the action of the balls. He, therefore, undertook to determine what can
be the cause of these balls declining so rapidly in their efficacy. His
conclusion is, that the true cause of this speedy decrease in the
decomposition is due to sulphuric acid, which passes through the
interstices of the clay-balls mixed with the other gases. This injurious
action, according to Hasenclever and Sartori, is probably to be explained
by the following reaction:--The vapour of sulphuric acid in contact with
sulphate of alumina at a dull red-heat, as is found in the balls, is
resolved into sulphurous acid, watery vapour, and oxygen; the sulphurous
acid thus formed is reoxidised at the expense of the free chlorine, is
again decomposed, and thus keeps up a destructive circulation in the
apparatus, which reduces or totally checks the chlorine.[244]
[Footnote 244: Extracted from the 'Chemical News.']
_Prices of Bleaching Powder_ (CLAPHAM).
In 1805 £120 0 0 per ton.
" 1810 84 0 0 "
" 1815 80 0 0 "
" 1820 47 0 0 "
" 1825 27 0 0 "
" 1830 23 0 0 "
" 1832 21 0 0 "
" 1835 23 0 0 "
" 1840 21 0 0 "
" 1846 18 0 0 "
" 1850 13 15 0 "
" 1855 10 15 0 "
" 1857 13 10 0 "
" 1860 11 0 0 "
" 1868 10 12 0 "
_Prop., Uses, &c._ Chlorine is a gas possessing a yellowish-green colour,
and a pungent, suffocating odour. It is one of the heaviest substances
that are gaseous at ordinary temperatures, being nearly 2-1/2 heavier than
atmospheric air; sp. gr. 1·47. It is soluble to a considerable extent in
water, that liquid at 60° Fahr. absorbing about twice its volume. It is
non-inflammable, but its union with some of the elements is attended with
the phenomena of combustion; thus, phosphorus, copper leaf, powdered
antimony and arsenic, and several other substances thrown into chlorine
immediately inflame. Under a pressure of 4 atmospheres it is condensed
into a yellow, limpid liquid. Moist chlorine gas cooled to 32° Fahr.
condenses into yellow crystals, containing 35-1/2 parts of chlorine and 90
parts of water. The most remarkable property of chlorine is its power of
destroying almost all vegetable and animal colours, and the putrid odour
of decomposing organic matter; hence its value as a bleaching agent, and
as a disinfectant and fumigator. When first proposed as a bleaching agent
by Berthollet, it was used much the same way as sulphur is now in
bleaching woollen goods; afterwards a solution of the gas in water was
employed, but the final improvement was Tennant's patent of combining the
gas with lime to form "chloride of lime." With the bases chlorine forms an
important series of compounds called chlorides.
_Tests._ Free chlorine is readily distinguished from other gases by its
colour, suffocating odour, and bleaching properties. The aqueous solution
dissolves gold leaf, and with nitrate of silver gives a white, curdy
precipitate.
=CHLORINE STILLS.= The accompanying figure represents a section of one of
the earlier forms of still used in the preparation of chlorine.
[Illustration: FIG. 1.]
These stills were sometimes made of strong sheet lead, the lower part of
which was enclosed in a jacket of cast iron, into which steam was forced,
by which means the contents of the still were heated. The steam was
injected from an ordinary boiler through the pipe H, and the materials,
after the decomposition had been completed, were drawn off by the pipe G.
The four openings, C, D, E, F, were secured by water lutes, capable of
bearing a pressure greater than that required in the chamber where the
saturation took place. In some cases the lower half of the still was made
of cast iron, and fitted into a groove made in the upper part, the two
sections being united by means of a strong cement. In the latter case the
heating of the still was effected by a naked fire applied to the bottom.
Into the orifice C the said materials employed were introduced, whilst the
acid was poured through the opening F. The gas evolved passed off through
the pipe E to the purifier and chamber, where it was absorbed by the lime,
and converted into bleaching powder, and the shaft of the agitator passed
up through D.
The use of the leaden stills survived for a longer time in France than in
this country. In some parts of Germany large glass globes with long necks
were employed, in which the chlorine was generated from a mixture of
hydrochloric acid and manganese. But these were only applicable in cases
where comparatively small quantities of bleaching powder were to be
manufactured. When the chlorine is obtained from a mixture of manganese,
common salt, and sulphuric acid, the apparatus, being required to
withstand a greater heat, is made entirely of metal.
[Illustration: FIG. 2.]
In fig. 2. _a a_ represents a shallow iron pan, fitted with the tube _b_,
for the purpose of emptying the contents of the leaden cylinder _d d_.
This iron vessel serves as the lower part of the cylinder _d d_, the top
of which is provided with an opening for a funnel syphon tube, for the
introduction of the acid, and another opening, _f_, for the manganese. The
entire apparatus stands on a flue leading from the furnace.
[Illustration: FIG. 3.]
The foregoing drawing represents a vessel for the manufacture of chlorine
on a large scale, and is extensively used in Germany.
It consists of a cylindrical vessel of sandstone, the lower half of which,
A, is carved out of a single block; the upper half, B, also of one piece,
fits into the lower by means of a grooved joint, the two parts being
united by means of a cement made of clay and boiled linseed oil. About six
inches from the bottom the cylinder widens by 2 inches, and the rim thus
formed carries a perforated bottom, C, upon which the manganese is
deposited in large lumps. The tube D, likewise of stone, passes beneath
the perforated bottom, and is at the other end joined to the steam-tube E.
The steam must therefore, when introduced, enter the cylinder through the
perforations of the false bottom. The top of the cylinder is closed by a
lead cover, K, which is fastened down by means of iron clamps; this lid
has an aperture, G, and the tubes E, F, H, pass through it; tube E serves,
as already stated, for the introduction of the steam; tube F is for the
delivery of chlorine; the bent tube, H, which ends in a funnel, for the
introduction of the hydrochloric acid; and the opening G for throwing the
lumps of manganese into the cylinder. The solution of manganese chloride,
resulting from the action of the hydrochloric acid upon the manganese, is
removed through I, which is kept closed by a wooden stopper whilst the
reaction proceeds.
See also, under CHLORINE, the description of WELDON'S stills, and of
DEACON'S apparatus.
=CHLORITE.= A salt in which the hydrogen of chlorous acid, HClO_{2}, is
replaced by a metal or other basic radical. See CHLOROUS ACID.
=CHLOROCHROMIC ACID.= CrOCl. _Syn._ CHLOROCHROMIC ANHYDRIDE. _Prep._
Bichromate of potassium, 3 parts; common salt, 3-1/2 parts; are intimately
mixed together, put into a glass retort, and oil of vitriol, 9 parts,
added; heat is next applied and maintained as long as dense, red vapours
are given off. The product in the receiver is a heavy, deep-red liquor,
greatly resembling bromine in appearance. Water resolves it into
hydrochloric and chromic anhydride.
=CHLORODYNE.= See PATENT MEDICINES.
=Chlorodyne= (Dr Browne's). Acid muriat. conc., 5 parts; ether,
chloroform, tinct. cannab. Ind., tinct. capsici, of each 10 parts;
morphia, prussic acid, of each 2 parts; oil of peppermint, 1 part; syrup,
50 parts; tinct. hyoscyami, tinct. aconiti, of each 3 parts.
=Chlorodyne, English.= A filtered mixture of 5 grammes tinct. aromat., 4
grammes tinct. opii simp., 1 gramme morph. mur., 10 grammes aq. amygd.
amar., 80 grammes syrup of liquorice, 1 gramme extract of liquorice, 40
grammes 90 per cent. spirit of wine, 5 drops oil of peppermint, 10 drops
ether, 30 drops chloroform.
=CHLOROFORM.= CHCl_{3}. _Syn._ TERCHLORIDE OF FORMYLE, FORMYL-CHLORIDE;
CHLOROFORMYL, TRICHLOROMETHANE, CHLOROFORMUM, L. A remarkable fluid
discovered by Liebig in 1830, and independently by Soubeiran in 1832, and
carefully examined in 1834 by Dumas. In 1842 its action upon animals was
investigated by Dr M. Glover, and in 1847 it was introduced to the medical
profession as an anæsthetic agent by Dr Simpson of Edinburgh.
It was first obtained by the action of caustic alkali upon chloral, but it
is more easily prepared by distilling alcohol or wood spirit with chloride
of lime. It may also be procured from wood spirit, acetone, oil of
turpentine, and several essential oils, as well as from amylic alcohol,
acetic acid, tartaric acid, and phenol; when these different bodies are
severally subjected to the action of chloride of lime. When chlorine is
made to act on marsh gas, or when chloral is treated with an alkali,
chloroform is also produced.
_Prep._ 1. Chloride of lime (in powder), 4 lbs.; water, 12 lbs.; mix in a
capacious retort or still, add of rectified spirit, 12 fl. oz., and
cautiously distil as long as a dense liquid, which sinks in the water it
passes over with, is produced; separate this from the water, agitate it
with a little sulphuric acid, and, lastly, rectify it from carbonate of
barium.
2. Chloride of lime, 4 lbs.; water, 10 pints; rectified spirit, 1/2 pint;
proceed as last, using a spacious retort that the mixture will only 1-3rd
fill, and the heat of a sand bath. When ebullition commences remove the
fire as quickly as possible, lest the retort be broken by the suddenly
increased heat, and let the solution distil into a receiver as long as
there is nothing which subsides, the heat being restored if it be at all
needed. Add to the distilled liquid four times as much water, and shake
the whole well together; next cautiously separate the heavier part as soon
as it has subsided, and to this add chloride of calcium, broken into
fragments, 1 dr.; and shake occasionally during an hour; finally, let the
fluid again distil from a glass retort into a glass receiver.
3. Hydrate of lime, 1 part, is suspended in cold water, 24 parts, and
chlorine passed through the mixture until nearly the whole of the lime is
dissolved; hydrate of lime, q. s. just to restore the alkaline reaction of
the liquid, is then added; and, afterwards, rectified spirit of wine or
wood spirit, 1 part, is mixed in; the whole, after repose for 24 hours in
a covered vessel, is cautiously distilled as before.
4. (B. P.) Take of chlorinated lime 10 _lbs._; rectified spirit, 30 fluid
ounces; slaked lime, a sufficient quantity; water, 3 gallons; sulphuric
acid, a sufficient quantity; chloride of calcium in small fragments 2
_oz._; distilled water, 10 fluid ounces. Place the water and the spirit in
a capacious still, and raise the mixture to a temperature of 100° F. Add
the chlorinated lime, and 5 _lbs._ of the slaked lime, mixing thoroughly.
Connect the still with a condensing worm, encompassed by cold water, and
terminating in a narrow-necked receiver; and apply heat so as to cause
distillation, taking care to withdraw the fire the moment that the process
is well established. When the distilled product measures 50 fluid ounces
the receiver is to be withdrawn. Pour its contents into a gallon bottle,
half filled with water; mix well by shaking, and set it at rest for a few
minutes, when the mixture will separate into two strata of different
densities. Let the lower stratum, which contains crude chloroform, be
washed by agitating it in a bottle with 3 fluid ounces of the distilled
water. Allow the chloroform to subside, withdraw the water, and repeat the
washing with the rest of the distilled water, in successive quantities of
3 oz. at a time. Agitate the washed chloroform for five minutes in a
bottle with equal volume of sulphuric acid, allow the mixture to settle,
and transfer the upper stratum of liquid to a flask, containing the
chloride of calcium, mixed with 1/2 oz. of slaked lime, which should be
perfectly dry. Mix well by agitation. After the lapse of an hour connect
the flask with a Liebig condenser, and distil over the pure chloroform by
means of a water bath. Preserve the product in a cool place in a bottle
furnished with an accurately ground stopper. The lighter liquid which
floats on the crude chloroform after its agitation with water, and the
washings with distilled water, should be preserved and employed in a
subsequent operation. Sp. gr. 1·456.
_Prop., &c._ Liquid; transparent; colourless; odour fragrant, ethereal,
and apple-like; taste ethereal, sweetish, but slightly acrid; soluble in
2000 parts of water; mixes in all proportions with alcohol and ether;
dissolves (readily) bromine, camphor, caoutchouc, gutta percha, iodine,
oils, resins, wax, and several other like substances; boils at 141·8°
Fahr.; kindles with difficulty; burns, when strongly heated, with a
greenish flame; and communicates a dull, smoky-yellow colour to the flame
of alcohol. Sp. gr. 1·48 (1·497, Miller); density of vapour 4·2. The
vapour has the remarkable property of rendering a person breathing it
temporarily insensible to pain.
Chloroform is frequently adulterated with alcohol and ether; and owing to
careless manipulation, is also sometimes contaminated with other
substances, as chloral, hydrochloric acid, free chlorine, aldehyde and
certain chlorinated oils. These latter compounds are not only the most
objectionable and prejudicial of the impurities found in chloroform, but
if present in it to any appreciable extent, they render its anæsthetic
administration not only inefficient, but frequently absolutely dangerous.
These deleterious chlorinated oily compounds may be removed by agitation
with strong sulphuric acid, or by distillation from it. Chloroform made
from wood spirit is said to be more impure than that from alcohol. When
pure it is free from colour, and of a pleasant odour. It is not perfectly
soluble in water; and does not turn the colour of litmus red. Rubbed on
the skin it quickly evaporates, scarcely leaving any odour. Dropped into
water, it falls to the bottom and remains bright and limpid; but if it
contain alcohol the surface of the drop becomes opaline. If the same
experiment be made with diluted sulphuric acid, sp. gr. 1·44, the drop of
pure chloroform will fall to the bottom; but that which contains spirit,
if not shaken, will float or remain suspended in the acid solution. When
contaminated with heavy hydrocarbon oils, a drop evaporated from the palm
of the hand leaves behind a strong smell. Hydrochloric acid and free
chlorine are detected by the ordinary tests.
Mr Shuttleworth, writing to the 'Canadian Pharmaceutical Journal,'
says:--"In regard to the restoration of chloroform which has become
spoiled, I would recommend that the chloroform be well agitated with a
dilute solution of hyposulphite of soda.
"It should then be separated by means of a glass funnel from the
supernatant liquid, and again washed; this time with simple water. After
being separated the chloroform should be passed through filtering paper to
free it from traces of moisture, when it will be found much improved and
comparatively sweet, good enough in any case for external use.
"There are, of course, certain other impurities of chloroform which the
hyposulphite will not remove. These are of a more stable character, and as
they possess a higher boiling point than chloroform, may be separated by
distillation, or by treatment with sulphuric acid in the usual manner."
_Uses, Action, &c._ Chloroform is anodyne, antispasmodic, sedative,
stimulant, and anæsthetic. In small doses (5 to 12 or 15 drops, in water,
mixed with a little syrup or mucilage) it is employed in spasmodic
disorders, and as a stimulant and diaphoretic. It is now chiefly used as
an anæsthetic to produce insensibility to pain during surgical operations.
The dose for inhalation is 1 fl. dr., which is repeated, in a few minutes,
if no effect is produced, until 3 fl. dr. have been thus exhibited; the
effects being carefully watched, and the source of the chloroform vapour
removed as soon as a sufficient degree of anæsthesia is produced, or any
unpleasant symptoms develop themselves.
Chloroform in large doses depresses the heart's action, and causes
profound coma, and death. It is therefore dangerous in all cases
complicated with diseases of the heart or brain, or any visceral
affections of a congestive character.
The treatment of asphyxia from chloroform is--the horizontal position,
cold affusion to the head and spine, artificial respiration, and, if
possible, either the application of electricity, or the inhalation of
protoxide of nitrogen or oxygen gas, largely diluted with atmospheric
air.
_Concluding Remarks._ The preparation of chloroform is not unattended with
danger, and frequently miscarries in careless or inexperienced hands. This
arises chiefly from the violent reaction which immediately follows the
application of the heat. The common plan is attended with danger of
explosion, or of the liquid in the still being forced over into the
receiver, owing to the extraordinary rapidity with which the vapours are
eliminated, and the ingredients, in consequence, swell up. A method which
is successfully adopted on the large scale is to employ a very broad and
shallow capsule-shaped still, having a flat rim round it, with a head or
capital furnished with a corresponding rim at its lower part. In use, a
flat, endless band of vulcanised india rubber is placed between the two
rims, which are then held air-tight together by means of small, iron
clamps. The application of heat is also delayed for some time after the
admixture of the spirit with the other ingredients, and the process is
interrupted as soon as the first violence of the reaction has subsided, by
which time the whole product of chloroform will have passed over into the
receiver. If the distillation is continued beyond this point, the
remaining product is water. On the small scale, a very capacious,
flat-bottomed retort or cucurbit should be employed. A similar condenser
may be used to that noticed under ether.
=CHLOROFORMIC ANODYNE= (George Harley) is said to be an alcoholic tincture
of opium with prussic acid and chloroform.
=CHLOROHYPONITRIC GAS= (NOCl) and =CHLORONITROUS GAS= (N_{2}O_{2}Cl_{4}
are two peculiar compounds, formed when nitric acid and hydrochloric acid
are mixed.
=CHLOROMETER.= _Syn._ CHLORIM'ETER. An instrument or apparatus employed in
chlorometry. The chlorometers in common use are graduated measures and
tubes precisely similar to those used in ACIDIMETRY, ALKALIMETRY, &c.
=CHLOROMETRY.= _Syn._ CHLORIM'ETRY. The estimation of the available
chlorine in the bleaching powder of commerce, which is valued and sold in
this country by its per-centage of that element. The plans generally
adopted are applicable to the so-called chlorides of soda and potassa, as
well as to the ordinary bleaching powder, chloride of lime. Most of them
depend on the oxidising effect of water when undergoing decomposition
through the action of chlorine.
_Dalton's Process._ The test solution is prepared as follows:--Pure
protosulphate of iron (previously dried by strong pressure between the
folds of cloth or bibulous paper), 78 gr., are dissolved in distilled
water, 2 oz., and a few drops of hydrochloric or sulphuric acid added.
This quantity of protosulphate requires for complete peroxidation just the
quantity of oxygen liberated by 10 gr. of chlorine; in other words, the
solution exhibits the indirect effect produced by exactly 10 grains of the
bleaching element.
Exactly 50 gr. of the sample of chloride of lime to be examined are next
weighed, and well mixed in a glass or wedgwood mortar with tepid water, 2
oz.; and the mixture poured into a graduated tube or chlorometer. The tube
is next filled up to 0, or zero, with the washings of the mortar, and the
whole well mixed, by placing the thumb over the orifice and shaking it.
The solution of chloride of lime, thus formed, is next gradually and
cautiously added to the solution of sulphate of iron, previously noticed,
until the latter is completely peroxidised, which may be known when it
ceases to be affected by a solution of red prussiate of potash. When a
drop of the latter test, placed upon a white plate, ceases to give a blue
colour on being touched with the point of a glass stirrer or rod dipped in
the liquor under examination, enough of the solution of the chloride has
been added. The number of measures thus consumed must now be carefully
read off from the graduated scale of the chlorometer, from which the
richness of the sample may be estimated as follows:--As 100 of the
chlorometer divisions contain exactly 50 gr. of the chloride under
examination, each measure will contain only 1/2 gr., and, consequently,
the number of measures consumed will represent half that number of grains
of the chloride examined; and the weight of the chloride thus used will
have contained 10 gr. of chlorine--the constant quantity of that substance
required to peroxide the test solution of sulphate of iron. Thus:--If 80
measures of the liquor in the chlorometer have been consumed, this
quantity will represent 40 gr. of chloride of lime, and 10 gr. of
chlorine. By dividing 1000 by this number, the per-centage of chlorine
will be obtained. In the present instance this would be--
1000
---- = 25%
40
_Crum's Process._ Equal weights of water and hydrochloric acid are mixed
together, and cast-iron borings digested in the diluted acid until
saturation is complete; a large excess of iron being purposely employed,
and the liquid kept at the heat of boiling water for some time. One
measure of the solution, marking 40° on Twaddell's scale (sp. gr. 1·200),
is then mixed with an equal quantity of acetic acid (sp. gr. 1·048). This
forms the test-liquid. When mixed with 6 or 8 parts of water it is quite
colourless, but chloride of lime occasions the production of peracetate of
iron, which gives it a red colour.
The above proof-solution is next poured into 12 two-oz. vials, of exactly
equal diameters, to the amount of 1/9th of their capacity; these are
filled up with bleaching liquid of various strengths; the first at 1/12th
of a degree of Twaddell, the second 2/12ths, and so on up to 12/12ths of
1°. They are then well corked up, and, after agitation, arranged side by
side on a tray, furnished with holes to receive them. (See _engr._) To
ascertain the strength of an unknown sample of bleaching liquor, the
proof-solution of iron is put into a phial, exactly similar to the 12
previously used, and in precisely the same proportion (1/9th). The phial
is then filled up with the bleaching liquor, well shaken, and placed
beside that one of the 12 already prepared which it most resembles in
colour. The number on that phial expresses the strength of the sample
under examination, in twelfths of a degree of Twaddell's hydrometer.
[Illustration]
_Obs._ The preceding method is admirably suited for weak solutions, such
as are employed for bleaching textile fabrics, and is well adapted (from
its simplicity) to the purposes of practical men. Indeed, it is quite
astonishing to see with what ease and accuracy it is applied by unlettered
operatives. This gives it great practical value. It has been for some time
in extensive use in the bleaching houses of Scotland.
TABLE _exhibiting the quantity of Bleaching Liquid, at 6° on_ TWADDELL'S
_scale_ (_sp. gr._ 1·030), _required to be added to a weaker liquor, to
raise it to the given strengths. Adapted from_ MR CRUM'S _table by_ MR
COOLEY.
-----------------------------------------------
| | Proportions required.
Strength | Required |-----------------------
of Sample | Strength. | Given | Liquor
in 1/12°. | | Sample. | at 6°.
-----------+-----------+-----------+-----------
| | Parts. | Part.
Water. | 8/12° | 8 | 1
1 | " | 9-1/4 | 1
2 | " | 11 | 1
3 | " | 13-1/2 | 1
4 | " | 17 | 1
5 | " | 23 | 1
6 | " | 35 | 1
7 | " | 71 | 1
Water. | 6/12° | 11 | 1
1 | " | 13-1/2 | 1
2 | " | 17 | 1
3 | " | 23 | 1
4 | " | 35 | 1
5 | " | 71 | 1
Water. | 4/12° | 17 | 1
1 | " | 23 | 1
2 | " | 35 | 1
3 | " | 71 | 1
Water. | 3/12° | 23 | 1
1 | " | 35 | 1
2 | " | 71 | 1
------------------------------------------------
According to Mr Crum, the range of strength within which cotton is "safe"
is very limited. A solution at 1° of Twaddell's scale (sp. gr. 1·005) is
not more than safe, while one at 1/2° is scarcely sufficiently strong for
the first operation on stout cloth, unless it is packed more loosely than
usual.
_Gay-Lussac's Indigo Process._ One part of the best indigo is dissolved in
9 parts of strong sulphuric acid by the aid of a gentle heat; this
solution is then mixed with distilled water, in such proportion that 1
volume of chlorine gas shall exactly decolour 10 volumes of this solution.
Each measure so decoloured is called a degree, and each degree is divided
into fifths. 5 gr. of the best chloride of lime, dissolved in 500 gr.
measures of water, possess the above power, and indicate 10° or proof; or
in other words, will decolour 10 times its volume of the indigo solution.
_Obs._ This method of chlorometry is objectionable, and liable to error,
from the indigo solution altering by keeping. When, however, the proper
precautions are used, it may be safely trusted for weak bleaching liquors.
_Arsenious Acid Process._ This depends on the conversion, by oxidation, of
arsenious acid into arsenic acid, in the presence of chlorine and water.
To prepare the test-liquor, pure arsenious acid, 100 gr., are dissolved in
about 4 fl. oz. of pure hydrochloric acid (free from sulphurous acid), and
the solution diluted with water until, on being poured into a graduated
10,000 grains-measure-glass, it occupies the volume of 7000 grains measure
marked on the scale. Each 1000 grains measure of this liquid now contains
14·29 gr. of arsenious acid; corresponding to 10 gr. of chlorine, or
1/10th gr. of chlorine for every division or degree of the scale of the
chlorometer.
100 gr. of the chloride of lime to be examined are next dissolved in water
as before, and poured into a tube graduated up to 2000 grains measure. The
whole is now well shaken, in order to obtain a uniformly turbid solution,
and half of it (1000-grains-measure) transferred to a graduated
chlorometer, which is, therefore, thus filled up to 0°, or the zero of the
scale, and contains exactly 50 gr. of the chloride of lime under
examination; whilst each degree or division of the scale contains only 1/2
gr.
1000 grains measure of the arsenious acid test-liquor are now poured into
a glass beaker, and a few drops of solution of sulphate of indigo added in
order to impart a faint but distinct blue colour to it; the glass is then
shaken so as to give a circular movement to the liquid, and whilst it is
whirling round, the chloride-of-lime solution from the chlorometer is
gradually and cautiously added, until the blue tinge given to the
arsenious acid test-liquor is destroyed; care being taken to stir the
mixture well during the whole process, and to stop as soon as the
decolorisation is completed.
Let us suppose now that, in order to destroy the blue colour of the 1000
grains measure of the arsenious acid test-liquor, 90 divisions or degrees
of the chloride-of-lime solution have been employed. These 90 divisions,
therefore, contained the 10 gr. of chlorine required to destroy the colour
of the test-solution; and since each division represents 1/2 gr. of
chloride of lime, 45 gr. of chloride of lime (10 gr. of chlorine) were
present in the 90 divisions so employed, from which the per-centage
strength may be ascertained. For--
45 : 10 : : 100 : 22·22
The chloride of lime examined, therefore, contained 22-1/4 per cent,
(nearly) of chlorine.
_Obs._ This method is extremely simple and trustworthy when properly
employed; but to ensure accuracy, certain precautions must be adopted.
Instead of pouring the test-liquor into the solution of the sample (as in
alkalimetry), the solution of the sample must be poured into the
test-liquor.
Vogel found that in a normal solution of arsenious acid that had been
prepared for using in the above process, half the quantity of the
arsenious acid became oxidised to arsenic acid in the course of about a
year. He therefore recommends that the standard solution, if kept for some
time, should be tested by a magnesium salt. The formation of a precipitate
would show the solution had undergone such a change, as to render it unfit
for volumetric estimations.
_Penot's Process._ This is a modification of the previous process. For the
arsenious acid solution arsenite of soda is substituted, and for the
indigo solution a colourless iodised paper, which is turned blue by the
smallest quantity of free acid. The paper is prepared in the following
manner:--1 gram of iodine, 7 grams of carbonate of soda, 3 grams of
starch, and a quarter of a litre of water are mixed. When the solution
becomes colourless it is diluted to half a litre; in this fluid, white
paper is soaked. The arsenical fluid is prepared by dissolving 4·44 grams
of arsenious acid, and 13 grams of crystallised carbonate of soda in 1
litre of water. This solution is added by means of a burette to the
solution of chloride of lime intended to be tested (10 grams of the sample
to 1 litre) the completion of the reaction being known by the paper
remaining uncoloured.
Lunge says that the same piece of moist iodine test paper may be made use
of repeatedly, since the spots produced by testing usually disappear after
about twenty-four hours if exposed to the air. The paper must, however, be
kept away from dust.
_Wagner's Process._ This method is based upon the fact that a solution of
chloride of lime separates the iodine from a weak (1 to 10) and slightly
acidified iodide-of-potassium solution, the iodine being quantitatively
estimated by means of hyposulphite of soda:--
Iodine 21, } {Iodine of sodium, 2NaI,
Hyposulphite of } yield {Tetrathionate of sodium, Na_{2}S_{4}O_{6},
soda, 2Na_{1}SO_{3} } {Water, 5H_{2}O.
+5H_{2}O,
The test is performed as follows:--100 c. c. =1 gram of bleaching-powder
solution, obtained by dissolving 10 grams of chloride of lime in 1 litre
of water, are mixed with 25 c. c. of solution of iodide of potassium
acidified with dilute hydrochloric acid. The resulting clear, deep
brown-coloured solution is treated with hyposulphite of soda solution
until quite colourless. The hyposulphite of soda solution is composed of
24·8 grams of that salt to 1 litre of water; 1 c. c. of this solution
neutralises 0·0127 grams of iodine, and 0·00355 grams of chlorine.
_Otto's Process._ This method is based upon the following data. Two
molecular weights of protosulphate of iron when brought into contact with
chlorine, in presence of water, and free sulphuric acid, give one molecule
of persulphate of iron, and two molecules of hydrochloric acid, the
process consuming one molecule of chlorine. Two molecules of crystallised
sulphate of iron = 556, correspond to 71·0 of chlorine, or in other terms
0·7839 grams of the crystallised sulphate correspond to 0·1 gram of
chlorine.
_Bunsen's Process._ This consists in adding iodide of potassium to the
bleaching-powder liquor, acidulating the mixture with hydrochloric acid,
and running the solution of arsenite of soda into it till only a yellow
tint shows itself. A little starch paste is now added, and the arsenite
solution cautiously introduced drop by drop, till the blue colour just
disappears. The solutions must all be standardised. To preserve the starch
paste Mohr advises the addition to it of a little chloride of zinc.
_Mr Davies_ uses glycerin as a solvent for the arsenious acid. He prepares
a standard solution as follows:--13·95 grains of arsenious acid in 40 c.
c. of glycerin and fitted up to 1 litre. Every c. c. corresponds to 0·1
grain of chlorine. Indigo sulphate solution is used as an indicator, and
the bleaching liquor is run into the glycerin solution until the blue
colour of the latter is changed to a brownish yellow.
_Dr Ure's_ as follows:--Liquor of ammonia, of a known strength, tinged
with litmus, is added to a solution of a given weight of the chloride
under examination, until the whole of the chlorine is neutralised, which
is known by the colour being destroyed. From the quantity of ammonia
consumed the strength of the sample is estimated.
The value of bleaching powder is estimated in England, America, and
Germany by degrees corresponding to the per-centage of available chlorine
contained in a sample of chloride of lime by weight; but in France the
degrees denote the number of litres of chlorine gas at 0° c. and 760° Mm.
Bar., which 1 kilo of bleaching powder can evolve. In the following table
the chlorometrical degrees of France and England are contrasted:--
French. English.
63 20·02
65 20·65
70 22·24
75 23·83
80 25·42
85 27·01
90 28·60
100 31·80
105 33·36
110 34·95
115 36·54
120 38·13
125 39·72
126 40·04
The per-centage may be calculated by multiplying the French degrees by the
coefficient 0·318.
=CHLOROCARBONIC ACID.= (COCl_{2}). _Syn._ PHOSGENE GAS, CARBONIC
OXYDICHLORIDE. This compound may be produced by the direct combination of
equal volumes of carbonic oxide and chlorine gases under the influence of
sunlight (whence its name of "phosgene gas"), when the mixture gradually
becomes colourless, and contracts to half its original volume.
Chlorocarbonic acid has a peculiar pungent smell, and fumes strongly when
exposed to moist air, the moisture of which it decomposes, producing at
the same time hydrochloric and carbonic acids.
It is sometimes employed in chemical research for the removal of hydrogen
from organic compounds, and the substitution of carbonic oxide, or its
elements for the hydrogen.
=CHLOROPHYLL.= The green colouring matter contained in the leaves, stalks,
unripe fruit, and juices of most plants.
=CHLORO'SIS.= _Syn._ GREEN SICKNESS. A disease which principally affects
young unmarried females.
_Symp._ Languor, listlessness, fatigue after the least exercise,
palpitation of the heart, flatulency, indigestion, acidity of stomach and
bowels, constipation (generally), appetite for unnatural food, general
debility, &c. As the disease advances, the skin at first pale, assumes a
peculiar greenish tint, the respiration becomes affected, the feet and
legs swell, and various organic affections of the viscera ensue. During
the early stages of this disease the catamenia are usually pale and
scanty, and return at irregular intervals, and as it progresses they
disappear altogether.
_Treat._ This should be tonic and restorative. That recommended under
ANÆMIA may be adopted with advantage. See also APPETITE, ATROPHY.
=Chlorosis, Electuary for--Female Electuary.= A greenish-black thick
syrup, consisting of sugar, bayberries, carbonate of iron, iron filings,
and water. (Buchner.)
=Chlorosis Powder--Female Powder=--consists of a mixture of anise, sugar,
and 14 per cent. of iron filings. (Wittstein.)
=Chlorosis Powder--Female Powder=, according to Schott and Strauss, is a
mixture of violet root, gum Arabic, and a tasteless green powder with 33
per cent. of steel filings. According to Hager, it is composed of 2 parts
ferri pulvis, with 3 parts powdered sweet-flag root.
=Chlorosis Powder--Female Powders.= Steel filings, starch powder, and knot
grass, of each 1 part, Florentine orris root, 4 parts.
=Chlorosis Powder--Female Powders.= A mixture of 1 part steel filings and
2 parts of a vegetable powder composed of gum Arabic, Florentine orris,
knot grass, &c. (Egb. Hoyer.)
=Chlorosis Water= (Dr Ewich) contains in 10,000 parts 11 of sodium
carbonate, 9 of sodium chloride, 1-1/2 sodium sulphate, 7 calcium
carbonate, and 1·2 iron carbonate with an excess of carbonic acid.
(Hager.)
=CHLOROUS ACID.= HClO_{2}. _Syn._ ACIDUM CHLORO'SUM, L. _Prep._ From
chlorate of potassium, 4 parts; arsenious anhydride, 3 parts; nitric acid,
12 parts; (diluted with) water, 4 parts; heated together in a glass flask,
furnished with a bent tube, and placed in a water bath. It must be
collected in the same way as chlorine, or passed into water, when it forms
a solution of chlorous acid.
_Prop., &c._ Chlorous acid is a greenish-yellow gas, non-condensable by a
freezing mixture of salt and ice, but liquefiable by extreme cold. The
aqueous solution undergoes gradual decomposition, yielding chloric acid
and chlorine. Chlorous acid possesses powerful oxidising and bleaching
properties; with the bases it forms salts called CHLORITES. These are all
soluble in water, and bleach like the acid. They may be recognised by the
evolution of chlorous acid gas when acted on by an acid. The use of the
arsenious acid is to deoxidise the nitric acid employed in the process.
Tartaric acid, or other deodorising agent, may be substituted for it.
=CHOC'OLATE.= _Syn._ CHOCOLA'TA, L.; CHOCOLLATI, Mexican; CHOCOLAT, Fr. A
beverage or paste made from the roasted seeds of the _Theobroma Cacao_, or
COCOA. Strictly speaking, the term "chocolate" is applicable to all
genuine preparations of cocoa, but it is now generally used to distinguish
those which contain sugar, and, commonly, flavouring substances. Of late
years great attention has been paid to the manufacture of chocolate in
England; our principal makers now import the finest descriptions of cocoa,
and produce varieties of the manufactured article which are scarcely
inferior to those of their French rivals. The different kinds of cocoa,
and the processes of roasting, sweating, &c., are described under COCOA,
to which article we refer the reader also for particulars respecting the
chemistry of chocolate.
_Prep._ The cocoa nibs[245] are ground in a mill consisting of stone or
metal rollers, which are usually heated either by charcoal fires or by
steam, so as to soften or melt the natural fat.[246] The warm, smooth
paste which passes from the mill is then placed in a mixing mill, and
incorporated with refined sugar, and usually vanilla or other flavouring
substance. The trituration is continued until the whole paste is converted
into an entirely homogeneous mass, which is finally shaped, by means of
suitable moulds, into various forms, as blocks, loaves, tablets, lozenges,
&c.
[Footnote 245: The bruised, roasted seeds, freed from husk and membrane.]
[Footnote 246: Cacao- or cocoa-butter.]
_Obs._ Chocolate, prepared as above, without the addition of aromatics, is
known in the trade as PLAIN CHOCOLATE. The Spaniards flavour it with
vanilla, cloves, and cinnamon, and frequently scent it with musk and
ambergris. With these additions it is termed SPANISH CHOCOLATE. In
general, they add too large a quantity of the last four articles. The
Parisians, on the contrary, use little flavouring, and that principally
vanilla. They employ the best kinds of cocoa, and add a considerable
quantity of refined sugar. So prepared, it is called FRENCH CHOCOLATE.
_Proportions._ 1. FRENCH CHOCOLATE:--The proportions used for the best
description are said to be--2 beans of vanilla, and 1 lb. of the best
refined sugar, to every 3 lbs. of the choicest cacao nuts.
2. SPANISH CHOCOLATE:--The following forms are said to be commonly
adopted:--
_a._ Caracas cocoa, 11 lbs.; sugar (white), 3 lbs.; vanilla, 1 oz.;
cinnamon (cassia), 1/4 oz.; cloves, 1/2 dr.
_b._ Caracas cocoa, 10 lbs.; sweet almonds, 1 lb.; sugar, 3 lbs.; vanilla,
1-1/4 oz.
_c._ Caracas cocoa, 8 lbs.; island cocoa, 2 lbs.; white sugar, 10 lbs.;
aromatics, as above.
_d._ Island cocoa, 7 lbs.; farina, q. s. to absorb the oil. Inferior.
3. VANILLA CHOCOLATE. _Syn._ CHOCOLAT À LA VANILLE, Fr. A variety of
French or Spanish chocolate highly flavoured with vanilla. The following
proportions have been recommended:--
_a._ Caracas cocoa, 7 lbs.; Mexican vanilla, 1 oz.; cinnamon, 1/2 oz.;
cloves, 3 in no.
_b._ Best chocolate paste, 21 lbs.; vanilla, 4 oz.; cinnamon, 2 oz.;
cloves, 1/2 dr.; musk, 10 gr.
_Obs._ The vanilla used in making chocolate is reduced to powder by
rubbing it with a little sugar before adding it to the paste.
_Pur., &c._ The chocolate commonly sold in England is prepared from the
cake left after the expression of the oil, and this is frequently mixed
with the roasted seeds of ground peas, and maize or potato flour, to which
a sufficient quantity of inferior brown sugar, or treacle and mutton suet,
is added to make it adhere together. Inferior sweet almonds are also
employed in the same way.
Since the above paragraph was written there has been a vast improvement in
English chocolates, though the cheaper sorts of certain makers are still
much adulterated. Genuine chocolate should dissolve in the mouth without
grittiness, and should leave a peculiar sensation of freshness; after
boiling it with water the emulsion should not form a jelly when cold, for
if it does starch or flour is present. The presence of animal fat may
generally be detected by a cheesy or rancid flavour. See COCOA.
_Qual., &c._ Chocolate is nutritive and wholesome if taken in moderation,
but is sometimes apt to disagree with weak stomachs, especially those that
are easily affected by oily substances or vegetable food. When this is the
case, by adopting the simple plan recommended under BUTTER, chocolate may
generally be taken with impunity, even by the dyspeptic. The quantity of
aromatics mixed with the richer varieties of chocolate improve the
flavour, but render them more stimulant and prone to produce nervous
symptoms and head complaints.
Chocolate is taken in the solid form, or made into a beverage; or,
combined with sugar, is made into various articles of confectionery.
CHOCOLATE FOR THE TABLE is prepared by slicing or scraping very finely the
required quantity into a jug, and adding to it a small quantity of boiling
water. This is worked into a thin, smooth paste, and the jug immediately
filled up with boiling milk-and-water. A froth is produced by the same
means that eggs are beaten up. The operation of "milling," performed by
rapidly twirling a notched cylinder of wood in the emulsion, raises the
froth very quickly. Sugar may be put in with the scraped chocolate, or
added afterwards at pleasure.
Chocolate should never be made for the table before it is wanted, because
beating it again injures the flavour, destroys the froth, and separates
the body of the chocolate, the oil of the nut being observed, after a few
minutes' boiling, or even standing long by the fire, to rise to the top.
This is one of the principal reasons why chocolate offends the stomach.
Preparations of chocolate, intended either as nutritious articles of food
for convalescents, or as vehicles for medicine, are common among the
pharmacop[oe]ial and magistral formulæ of the Continent. The following are
a few examples:--
=Chocolate, Aromat'ic.= _Prep._ (Weiglebt.) Cocoa beans and sugar, of each
16 oz.; cinnamon, 1/2 oz.; cloves, 2 dr.; cardamoms and vanilla, of each 1
dr.
=Chocolate, Car'rageen.= See CHOCOLATE, WHITE (Nos. 1 and 2).
=Chocolate, Chalyb'eate.= _Syn._ FERRUGIN'EOUS CHOCOLATE; CHOCOLA'TA
CHALYBEA'TA, C. MAR'TIS, L. _Prep._ 1. (Trousseau.) Spanish chocolate, 16
oz.; carbonate of iron, 1/2 oz.; mix, and divide into 1-oz. cakes. One at
a time; in anæmia, amenorrh[oe]a, chlorosis, &c.
2. (Pierquin.) Iodide of iron, 2 dr.; chocolate, 16 oz. For 1/2-oz. cakes;
as above, and in scrofulous and glandular affections.
=Chocolate, Guarana'.= _Syn._ PAULLIN'IA CHOCOLATE; CHOCOLA'TA PAULIN'IÆ,
C. GUARAN'Æ, L. _Prep._ From guarana and white sugar, of each 1 oz.,
triturated together, and afterwards thoroughly mixed with good plain
chocolate, 18 oz. Recommended as a restorative in debility, chlorosis, and
other diseases of debility, especially those of a nervous character.
=Chocolate, Ice'land Moss.= _Syn._ CHOCOLA'TA CETRAR'IÆ ISLAND'ICÆ, C.
LICHEN'IS, L. _Prep._ 1. (P. C.) Simple chocolate (P. C.), 32 parts;
sugar, 29 parts; dried jelly of Iceland moss, 11 parts; mix.
2. (Cadet.) Chocolate, 4 lbs.; sugar, 2 lbs.; Iceland moss (freed from its
bitter, and powdered), 1-1/2 lb.; tragacanth and cinnamon, of each 4 oz.;
water, q. s.; to be beaten in a warm mortar, or ground with a muller on a
warm slab to a paste. Recommended in pulmonary affections, general
debility, weakness of stomach, &c. See COCOA (Iceland Moss).
=Chocolate, Pur'gative.= _Syn._ CHOCOLA'TA PUR'GANS, C. CATHAR'TICA, L.
_Prep._ 1. Jalap, 1 oz.; chocolate, 9 oz.; mix, and divide into 1-dr.
cakes.--_Dose_, 1 to 2 cakes, as a purge.
2. Jalap, 2 oz.; calomel and sugar, of each 1 oz.; triturate together,
then add chocolate, 20 oz.; for 1-dr. cakes.
3. Scammony, 2 dr.; chocolate, 3 oz.; for 1 dozen cakes. The last two are
given in worms.--_Dose_ (for an adult), 1 cake, taken fasting.
=Chocolate, Sal'ep.= _Syn._ SAL'OOP CHOCOLATE; CHOCOLA'TA CUM SAL'EP, L.
_Prep._ 1. (P. C.) Chocolate, 16 oz.; powdered salep, 1/2 oz.
2. (Cadet.) Cacao paste and sugar, of each 1 lb.; powdered salep, 1 oz.
Arrowroot chocolate and tapioca chocolate are made in the same manner.
(See _below_.)
=Chocolate, Sim'ple.= _Syn._ HYGIEN'IC C., HOM[OE]OPATH'IC C.; CHOCOLA'TA,
C. SIM'PLEX, C. SALU'TIS, L.; CHOCOLAT DE SANTÉ, Fr. _Prep._ (P. C.)
Caracas and Maragnan cocoa, of each 96 lbs.; sugar, 160 lbs.; cinnamon, 1
oz. (to 2 oz.); triturated together in the usual manner, and formed into
cakes or powder.
=Chocolate, Vanil'la.= _Syn._ CHOCOLA'TA CUM VANIL'LA, L. _Prep._ 1. (P.
C.) Chocolate (plain,--P. C.), 16 oz.; vanilla, 1/2 dr.