Porion’s Evaporator

Apart from the mechanical contrivances which are referred to
in various parts of this work, in which their application is
explained, it will be necessary to direct attention to certain
machines and appliances which are adopted at some of the more
advanced paper-mills in this country and in America; but since
the various makers of paper-makers’ machinery are constantly
introducing improvements to meet the requirements of the
manufacturer, we must refer the reader to these firms for fuller
information than can be given in the limited scope of this
treatise. Many of the improvements in paper-making machinery
consist in modifications–sometimes of a very important nature–in
the construction of certain parts of a machine, whereby the
efficiency of the machine as a whole is in some cases considerably
augmented. Without offering any critical remarks upon the merits
of the respective improvements which have been introduced, it
will be sufficient to direct attention to the manufacturer’s own
description of the principal features of the special mechanical
contrivance which he produces for the use of the paper-maker. It
may also be said that innumerable patents have been obtained for
various improvements in machinery, or parts of machines, engines,
etc., which can readily be referred to at the Library of the Patent
Office, or any of the public libraries throughout the Kingdom.

[Illustration: Fig. 43.]

=Bentley and Jackson’s Drum-Washer.=–This drum-washer, for use in
the rag-engine, is shown in Fig. 43. It has cast-iron ends, strong
copper buckets, shaft, stands, lifting-gear, and driving-wheel,
but instead of the drum being covered with the ordinary strong
brass backing-wire, it is covered with their improved “honey-comb”
_backing-plates_, over which the fine wire is wrapped as usual. The
honey-comb backing consists of tough rolled brass or copper plates,
curved to suit the diameter of the drum, and secured to its ends by
cross-bars. It is practicably indestructible, strengthens the drum,
and by maintaining its cylindrical form, adds considerably to the
durability of the fine covering-wire.

[Illustration: Fig. 44.]

=Drying Cylinders.=–These cylinders, by the same firm, for which
patents were obtained in 1872 and 1887, are made with concave and
convex ends, the latter type being shown in Fig. 44. The cylinder
body is made of hard cast-iron, turned and polished on outside
surface. The ends and trunnions are of tough cast iron, turned
to fit into their places, and there secured by bolts and nuts by
a patented method, whereby no bolts (excepting for the manhole)
are put through the metal, an unbroken surface is preserved, and
the annoyance of leakage through the bolt-holes is avoided. A
manhole and cover is fitted to all cylinders 3 feet in diameter
and upwards, and a water-lifter and pipe to remove the condensed
steam. The trunnions are bored to receive nozzles or junctions
for admitting steam, and the whole, when completed, is carefully
balanced and tested by steam pressure to 35 lbs. per square inch.
The firm state that they have made cylinders from 2 to 10 feet in
diameter by this system.

[Illustration: Fig. 45.]

=Self-acting Dry Felt Regulator.=–This contrivance, which is
manufactured by Messrs. Bentley and Jackson, is represented in
front and side elevation in Fig. 45. A is the framing of the
paper-machine, B the felt-rollers, C the dry felt; D is a slide
carrying one end of the felt guide-roller B; C is a shaft across
the machine, with a pulley F, two-keyed on one end, and a bevel
pinion two-keyed on the other end. The pulley F and pinion H are
keyed together, and run loose upon the shaft G; I is a bevel-wheel,
gearing into the pinions H and 2. The wheel I is connected by
a spindle and a pair of bevel-wheels to a screw E, which works
through a threaded bush. When the machine is at work, if the felt
C should run on one side, it will pass between the pulley F and
the guide-roller B, causing the pulley to revolve, and turning the
screw E in the threaded bush, thereby moving the slide fixing D and
the guide-roller B, which causes the felt to run back. Should the
felt run to the other side, it will run in contact with the pulley
F 2, and thus reverse the motion of the guide-roller B.

[Illustration: Fig. 46.]

=Paper-cutting Machine.=–This machine (Fig. 46), which is
manufactured by the same firm, is constructed to cut from one to
eight webs simultaneously, in sheets of any required length, from
8 to 60 inches. It is built on the “Verny” principle, and its
operation is as follows:–The webs of paper from the reel-rolls
are carried by an endless felt, and the paper is drawn off the
rolls by travelling cast-iron gripper beams, which firmly grasp
the felt and the webs of paper to be cut, the travel of the beams
being equal to the length of the sheet of paper to be cut. When the
required length of the sheet is drawn from the rolls, a cast-iron
clamp, placed close to the dead cross-cut knife, descends and
firmly holds the paper until the movable cross-cut knife has cut
off the sheets, which fall on a second endless felt, and are placed
by the catchers in the usual manner. As soon as the sheets are cut,
the clamp is released, and the travelling-grippers are again ready
to seize the paper and repeat the operation.

[Illustration: Fig. 47.]

=Single Web Winding Machine.=–This machine (Fig. 47) is constructed
for preparing webs of paper for continuous printing-presses. The
roll of paper to be prepared is carried by brass bearings having
vertical and horizontal screw adjustments attached to standards
mounted on a slide, and movable by a screw transversely on the
machine to accommodate the deckle edges. The paper web is taken
through a pair of iron draw-rolls, carried by brass bearings,
fitted in cast-iron stands; there are two pairs of ripping-knives
with bosses, springs, and collars, mounted on turned wrought-iron
shafts running in brass bearings carried by cast-iron stands; a
wrought-iron leading-roll and carrying brackets fitted with brass
bushes; a copper measuring roll counter, geared to indicate up to
10,000 yards, with disengaging apparatus to cease measuring when the
paper breaks; a friction-drum 2 feet in diameter, made of wood,
mounted on cast-iron rings, and a wrought-iron shaft, all carefully
turned and balanced; two cast-iron swivelling arms, with brass
sliding bearings to carry the mandrel on which the prepared web is
to be wound, with screws, struts, wheels and shaft to regulate the
angular pressure of the roll of paper against the wood drum,
according to its weight and the quantity of paper.

[Illustration: Fig. 48.]

[Illustration: Fig. 49.]

=Cooling and Damping Rolls.=–The illustration (Fig. 48) represents
an apparatus, constructed by Messrs. Bentley and Jackson, for
cooling and damping paper after leaving the drying cylinders
and before passing through the calenders. It consists of two
brass rolls bored and fitted with cast-iron ends, brass nozzles,
and regulating taps, through which the rolls are supplied with
a constant flow of water. The rolls are carried by cast-iron
standards, fitted with brass steps and cast-iron caps. Jets of
steam are blown on each of the rolls from a perforated copper pipe
running parallel with, and at a little distance from, the body of
the roll. The steam is condensed on the cold surfaces of the brass
rolls, and absorbed by the web of paper, which passes around and in
contact with their surfaces, and is consequently damped on _both_
sides. The perforated steam-pipes are enclosed by copper hoods,
to prevent the steam from spreading, and the supply of steam is
regulated by ordinary brass valves or cocks. The rolls are geared
together by a pair of spur-wheels, and driven by a pulley of
suitable diameter.

[Illustration: Fig. 50.]

=Reversing or Plate-glazing Calender.=–This machine, which is
shown in Figs. 49 and 50, is also made by the firm referred to, and
consists of two hammered iron rolls, each about twelve inches in
diameter, of any suitable length, carefully turned and carried by
strong cast-iron standards, fitted with bell-metal steps. The top
roll is provided with setting-down blocks and brasses, compound
levers and weights to regulate the pressure required. The two rolls
are geared together by strong shrouded wheels, and driven by a
strong cast-iron spur-wheel and pinion, a driving-shaft, fast and
loose pulleys, carried by cast-iron stands and pedestals fitted
with brass steps. The machine is fitted with two metal feed-tables,
and a self-acting apparatus for returning the sheets to the rolls,
and a handle-lever, slide-bar, and strap-forks for starting and
reversing.

[Illustration: Fig. 51.]

=Plate-planing Machine.=–This machine, which is manufactured by
Messrs. Bryan Donkin and Co., of Bermondsey, is shown in Fig. 51.
By its aid the plates of rag-engines can be sharpened without being
taken to pieces. The slide of the machine is made exactly like the
roll-bar planing machine (see below), and is so arranged that it
can easily be taken off and used for sharpening roll-bars.

[Illustration: Fig. 52.]

[Illustration: Fig. 53.]

=Roll-Ear Planing Machine.=–In the accompanying engraving (Fig.
52) is shown an apparatus fitted to a rag-engine for sharpening
rag-engine roll-bars, and it will be seen that by means of it the
operation can be performed without removing the roll from its
usual position. The edges of the bars are first planed by a tool
supplied by the manufacturers to render the whole cylindrical
before sharpening them; the bevelled sides are then planed by
suitable tools, two of which accompany the apparatus. This method
of sharpening renders the bars uniform in shape, the roll is kept
in better working order, and it can be dressed in considerably less
time, and at less expense, than can be done by chipping by hand.

=Washing-Cylinder for Rag-Engine.=–The illustration at Fig. 53
represents the machine as manufactured by Messrs. Bryan Donkin and
Co. It is so made that the water is delivered on the driving side
of the rag-engine, thus avoiding any trough across the engine, and
admitting of the midfeather being thin, as is usual in cast-iron
engines. It is all self-contained, and the driving apparatus is
wholly on the outside of the engine. The raising and lowering are
effected by a worm and worm-wheel, so that the cylinder will stop
at any point required.

[Illustration: Fig. 54.]

=Bleach Pump.=–In the accompanying engraving (Fig. 54) is shown
a pump, manufactured by Bryan Donkin and Co., which is arranged
expressly for the purpose of pumping up bleach-liquor. Each pump
is all self-contained, and merely requires a drum and strap to
drive it. The live and dead riggers upon the pump allow it to be
started and stopped at pleasure. “In all paper-mills,” say the
manufacturers, “the bleach-liquor should be used over and over
again, not only to save bleach, which amounts to a considerable sum
in the course of a year, but also to keep the paper clean.”

[Illustration: Fig. 55.]

[Illustration: Fig. 56.]

=Three-Roll Smoothing-Presses.=–The engraving (Fig. 55) shows a
damp smoothing-press, with rolls for smoothing the paper between
the two sections of drying cylinders of a paper-machine. The makers
are Messrs. Bryan Donkin and Co. A three-roll smoothing press, for
smoothing the paper at the end of a paper-machine, also by the same
makers, is shown in Fig. 56.

[Illustration: Fig. 57.]

=Back-water Pump.=–The engraving (Fig. 57) shows a pair of back or
size-water pumps, manufactured by Bertrams, Limited. The barrels
are of cast-iron, lined with copper. The suction and discharge
valves are each contained in a chamber with covers, so that every
valve could be easily got at by simply releasing the cover. The
valve-seats are of brass, with brass guards and rubber clacks.
The plungers are of brass, with cup-leathers. All is fitted up
on a cast-iron sole-plate, with tall standards, disc-cranks, and
driving-pulley between frames.

[Illustration: Fig. 58.]

=Web-glazing Calender.=–Fig. 58 represents Bertrams’ web-glazing
calender, with steam-engine attached. The illustration shows the
machine in front elevation. The steam-engine is specially designed
for this class of work, having two cylinders 10 inches in diameter
by 16 inches stroke, fitted on a double-hooded sole-plate, with
double-throw crank-shaft, fly-wheel, two eccentrics, wrought-iron
piston-rods, connecting-rods and valve-rods, steam and exhaust
branch pipes with one inlet valve, lubricators, and the cylinders
cased with teak legging and brass hoops.

[Illustration: Fig. 59.]

=Reeling Machine.=–One form of reeling machine manufactured by
Bertrams, Limited, is shown in Fig. 59, and is used for slitting
and re-reeling webs of paper, especially where large webs are
requisite for web-calendering, web-printing, and suchlike. The reel
of paper from the paper-machine is placed on a sliding-carriage
arrangement, the brackets of which are planed and fitted to a
planed sole, with wedge or dove-tail corners, and controlled by
screws, hand-wheel, etc., so that the reel can quickly and easily
be moved forward or backward to suit any unequal reeling that may
have taken place on the paper or the machine. A hot cast-iron is
provided for mending breaks in the web, and a measuring-roll and
counter is also applied. The machine has an important application
of drawing-in or regulating rolls of cast iron, with arrangement
of expanding pulley for regulating the tension on the paper.
Slitting-knives, regulating, dancing, or leading-rolls, of cast
iron, etc., are applied for separating the edges and guiding the
webs after they are slit. The reeling is performed by a 3-feet
diameter drum, cross-shafts, and arms, to which regulating heads
are fitted, so that several webs can be run up at one operation.

[Illustration: Fig. 60.]

=Web-Ripping Machine.=–This machine, which is manufactured
by Messrs. Bentley and Jackson, is shown in Fig. 60, and is
constructed to divide webs of paper into two or more widths.
It consists of two brass bearings on cast-iron standards, with
screw adjustments, a break-pulley and friction-regulator, all
mounted on cast-iron slides, movable transversely by means of a
screw, geared-wheels, shaft and hand-wheel; a wood guide-roll,
about 7 inches diameter, with wrought-iron centres, carried by
brass bearings with screw adjustment; three skeleton drums, each
2 feet in diameter, on wrought-iron shafts, carried by brass
bearings, and driven by spur-wheels and pinions; two wrought-iron
leading-rolls, with brass bearings and cast-iron stands; a pair
of strong wrought-iron ripper shafts with circular steel knives,
bosses, springs, and collars; cast-iron stands and brass bearings,
spur-wheels and driving-pulley; two (or more) changeable wood
drums 1 foot 6 inches in diameter, each with wrought-iron shaft
and catch-box, carried by brackets fitted with brass steps for
easily changing, driven by wrought-iron shafts with pedestals and
friction-pulleys, 2 feet in diameter, with regulating screws and
lock-nuts, all carried by strong cast-iron framing and standards,
and driven by a wrought-iron driving-shaft, with fast and loose
driving-pulleys, strap-fork and levers for starting and stopping.

[Illustration: Fig. 61.]

=Roeckner’s Clarifier.=–In this apparatus, of which an
illustration is given in Fig. 61, Mr. Roeckner has taken advantage
of the fact that if a column of liquid is ascending very slowly and
quietly within a vessel, it will not be able to carry up with it
the solid particles which it contains, which will gradually fall
back and sink to the bottom under the action of gravity, without
ever reaching the top of the vessel, provided this be of sufficient
height. The illustration shows the arrangement of the apparatus on
a small scale; the liquor to be clarified is run into a well or
reservoir _b_; into this dip a wrought-iron cylinder _c_, which is
open at the lower end, but hermetically closed at the top by means
of the casing _d_. From this casing air can be withdrawn through a
pipe, _h_, by means of an air-pump _i_. As soon as this is done the
liquid will begin to ascend the cylinder _c_, and if the height of
this is below that to which the water will rise at the atmospheric
pressure (say 25 feet), the liquid will ascend until it fills
the cylinder and the casing. Into the pocket at the side of the
casing there dips a pipe _g_, which passes out through the opposite
side of the casing, descends below the level of the water in the
tank, and ends in a discharge-cock. When this cock is opened, the
cylinder _c_ and the pipe _g_ form between them a syphon, of which,
however, the descending leg is of very small diameter compared with
the ascending leg. In consequence, the liquid will rise in the
cylinder _c_ very slowly. The sediment it contains will sink back
and collect in the bottom of the tank _b_, and clear water will
flow out at the outlet. A sludge-cock at the bottom of the tank
allows the solid matter to be drawn off at intervals and conveyed
to any convenient place for drying, etc.[30] For drawing clear
water from a river, the clarifier would simply be placed in the
river, dipping 2 or 3 inches into it below the lowest water-level.
The clear water will then be drawn through the clarifier, while
the heavier matters will fall down and be carried away by the
river current. It is stated that this has proved a great advantage
to a paper-mill which used a river, and had, prior to its use,
been much troubled through the dirt being pumped with the water.
The clarifier to receive the waste from paper-machinery, or from
washings in the engines, can be placed in any convenient corner,
and by its action the water can be re-used, and the otherwise lost
fibres collected, without its action ever being stopped.

[Illustration: Fig. 62.]

=Marshall’s Perfecting Engine.=–This engine, a longitudinal
section of which is shown in Fig. 62, has been introduced into
this country by Messrs. Bentley and Jackson, and is described
in _Industries_[31] as follows:–“The machine, which is the
invention of Mr. F. Marshall, of Turner’s Falls, Mass., U.S.A.,
is used in one of the processes of paper manufacture, and has for
its purpose the more effectual drawing of the pulp fibre, the
clearance of knots from the pulp previous to its delivery on to the
paper-making machine, and the saving of time in the treatment of
the material. As will be seen in the illustration (Fig. 62), the
machine consists essentially of a cast-iron conical casing, bored,
and fitted with about two hundred elbowed steel knives, G, placed
in sections. At the large end of this conical casing is placed a
movable disc, also fitted with about two hundred and ten steel
knives, F, and capable of adjustment by means of a screw, worm,
worm-wheel, and hand-wheel, E. The revolving cone and disc are of
cast iron, fitted with straight steel knives firmly keyed upon a
hammered iron shaft, and carefully balanced to prevent vibration.
The knives of the revolving cone and disc are brought into contact
with the stationary knives by means of the hand-wheel, E, and
the disc-knives can be independently adjusted by means of the
hand-wheel C, which actuates a screw on the conical casing by means
of the worm and worm-wheel shown. The machine is driven by means
of a pulley A, and the whole machine is mounted on a cast-iron
base-plate. The pulp material enters the engine in the direction
indicated by the arrow, B, at the small end of the cone, and is by
the rotary and centrifugal action of the revolving cone, propelled
to its large end, and during its passage is reduced to a fine pulp
by the action of the knives. It then passes through the knives,
F, of the stationary and rotating discs, by which the fibres are
further crushed or split up, all knots or strings rubbed out, and
the pulp effectually cleared previous to its exit through the
passage D.” We are informed that the machine is capable of treating
from 900 lbs. to 1,200 lbs. of pulp per hour. The power required to
drive it is estimated at from 40 i.h.p. to 50 i.h.p. when making
300 revolutions per minute. This, however, is dependent on the
amount of friction caused between the surfaces of the fixed and
revolving knives. The flow space occupied is 12ft. 6in. in length,
and 4ft. in width. The perfecting machine, in its complete form, is
shown in Fig. 63.

=Recovery of Soda.=–Probably one of the most important
improvements in modern paper-making, at least from an economical
point of view, is the process of recovering one of the most costly,
and at the same time most extensively used, materials employed in
the manufacture–soda. While not a great many years since (and
in some mills is still the case even now), it was customary to
allow the spent soda liquors resulting from the boiling of various
fibres to run into the nearest rivers, thus not only wasting a
valuable product, but also polluting the streams into which they
were allowed to flow, means are now adopted by which a considerable
proportion of the soda is recovered and rendered available for
further use. The means by which this is effected are various,
but all have for their object the expulsion of the water and the
destruction of the organic matters dissolved out of the fibrous
substances in the process of boiling with caustic soda solutions.
One of the main objects of the various methods of recovering the
soda from spent liquors is to utilise, as far as practicable, all
the heat that is generated from the fuel used, whereby the process
of evaporation may be effected in the most economical way possible.
The principle upon which the most successful methods are based is
that the flame and heat pass over and under a series of evaporating
pans, and through side flues, by which time the heat has become
thoroughly utilised and exhausted. When all the water has been
expelled, the resulting dry mass is ignited and allowed to burn
out, when the black ash that remains, which is carbonate of soda,
is afterwards dissolved out, and the alkaline liquor causticised
with lime in the usual manner. According to Dunbar, 8 cwt. of
recovered ash and 4½ cwt. of good lime will produce 900 gallons
of caustic ley at 11° Tw. The liquor is then pumped into settling
tanks, from which it is delivered to the boilers when required.

[Illustration: Fig. 64.]

=Evaporating Apparatus.=–An ordinary form of evaporator for the
recovery of the soda is shown in Fig. 64. It consists of a chamber
A, of the nature of a reverberatory furnace, lined with fire-brick,
the bottom of which is slightly hollowed. Above this is a tank
B containing the liquor, which is run down into the chamber as
required by means of a pipe C, provided with a tap. At one end of
the chamber is a furnace D, the flame of which passes through
the chamber and over the surface of the liquor lying upon the
floor, heating the chamber, evaporating, and at last incinerating,
its contents, and at the same time warming the liquor in the
tank above, and evaporating some of its water. The products of
the combustion in the furnace, and of evaporation, pass by the
flue into a chimney, and escape thence into the air. There is a
door E in the side of the furnace near the level of the floor of
the chamber, and this is opened from time to time to enable the
workmen to stir and move about the contents of the chamber, and
finally, when the process is sufficiently advanced, to draw out
the residue. The first effect produced is the reduction of the
liquor to the consistence of tar. Later on, a white crust, which
is the incinerated material, forms on the surface, and is drawn
on one side by the workmen, so as to allow of fresh crust being
formed. When all the charge has become solid it is drawn. The
charge is usually withdrawn before the conversion into carbonate is
completed; it is then raked out into barrows and placed in a heap,
generally in a shed or chamber, open on one side, but sometimes in
a closed brick-chamber or den, where the combustion continues for
several weeks. The result is the fusion of the material into a grey
rocky substance, which consists chiefly of carbonate and silicate
of soda.

Various modifications of the esparto evaporator and calciner have,
however, been introduced since the recovery of soda has become more
general, and are in use at various works, all having for their
main object the economising of fuel and the utilising of the waste
heat of the fire, which in the old-fashioned calciner goes up the
chimney and is lost. The leading principle, of all of them is to
use the waste heat in concentrating the liquor preparatory to its
being run into the part where the calcination is to be effected.
This is done by so extending and widening out the flue as to cause
the heated air and flame, after they have performed their function
in the calcination, to pass over or under their layers of liquor,
lying upon shelves or floors in such a way that the liquor shall
become more and more concentrated as it approaches the calciner by
successive steps or gradations.[32]–_Dr. Ballard._

[Illustration: Fig. 65.]

=Roeckner’s Evaporator.=–This apparatus, an illustration of which
is shown in Fig. 65, is thus described by Dr. Ballard, medical
officer of the Local Government Board, who was specially appointed
by the board to investigate the effluvium nuisances which arise
in connection with certain manufacturing industries. “In this
apparatus there is above the calcining floor a series of shelves
or shallow pans, alternating in such a manner that the liquor
flowing from the tank above into the uppermost of them, flows,
after a partial evaporation, over the edge of the shelf into the
shelf or shallow pan next below, and in this way from shelf to
shelf, still becoming more and more concentrated until it reaches
the final floor, over which the flame from the actual fire plays,
and where the first part of the calcination is effected. The
heated air, in passing to the chimney, passes over each of these
shelves in succession, heating them and concentrating the liquor
upon them. There is between the lower shelves an arrangement for
causing the liquor to pass from the upper to the lower by means of
a pipe, instead of its running over the edge. At the top of all
is a covered tank, where the temperature of the liquor is raised
before it is run into the evaporator. In order to promote the
heating of the liquor in this tank, the lower part of the tank is
made to communicate by side pipes with tubes passing across the
evaporator near the fire, as, for instance, at the bridge and at
the further end of the calcining floor. In this way a circulation
of liquor is set up which serves to heat the liquor in the tank
more effectually. A pipe from the top of the tank leads to the
chimney-shaft, conducting any vapours into it. As the incinerated
crust forms it is raked on one side, and when sufficient of it has
accumulated it is drawn to an opening (provided with a damper) at
the side or end of the floor, and discharged down this opening
into a brick chamber below, which is inclosed by iron doors, and
from which a flue conducts the vapours that arise during the final
fusion through the fire in such a way as to consume them.” By
recent improvements Mr. Roeckner has constructed an apparatus for
condensing and rendering inoffensive the vapours eliminated from
the liquor during its evaporation on the successive shelves of his
evaporator.

=Porion’s Evaporator.=–This evaporator and incinerating furnace
much resembles in principle an ordinary reverberatory furnace,
except that it is provided with paddle agitators, which project the
liquid upwards, causing it to descend in a spray, thus increasing
the surface of the liquid coming in contact with the hot air and
current of smoke traversing the furnace. By this method the expense
of fuel is greatly reduced. The residue is in a state of ignition
when it is withdrawn from the furnace, and is piled in heaps so
that it may burn slowly. When the combustion is complete, the
resulting calcined mass is treated with water, and the carbonate
of soda formed is afterwards causticised in the usual way. About
two-thirds of the soda is thus recovered.

=The Yaryan Evaporator.=–Mr. Homer T. Yaryan, of Toledo, Ohio,
U.S.A., has introduced some important improvements in evaporating
apparatus, which have been fully recognised in America, and appear
to have been attended with success. The principle involved is that
of multiple effects, in which the evaporation takes place while
the liquid is flowing through heated coils of pipe or conduits,
and in which the vapour is separated from the liquid in a chamber,
at the discharge end of the coils, and is conducted to the heating
cylinder surrounding the evaporating coils of the next effect,
from the first to the last effect. The objects of the invention
are: (1) to provide extended vaporising coils or conduits and
increased heating surface for each liquid feed supply in the
heating cylinders, and provide improved means for feeding the
liquid, whereby each set or coil of vaporising tubes will receive
a positive and uniform supply of liquid without danger of the
feed ducts being clogged by extraneous matter; (2) to positively
control the amount of liquid fed by the pump to the evaporating
coils, and make it more uniform than heretofore, regardless of the
speed of the pump; (3) to provide improved separating chambers at
the discharge ends of the vaporising coils so as to better free
liquid and solid particles from the vapours; (4) to provide for
the successful treatment of the most frothy liquids by causing
the vapours carrying solid and liquid particles to pass through
catch-all chambers, where they are arrested and precipitated and
then returned to the evaporating coils; (5) to secure a more
positive flow and circulation of liquid from the evaporating
cylinder of one effect to another, under the influence of a better
vacuum than heretofore in multiple-effect vacuum evaporating
apparatus; (6) to provide for transferring a better concentrated
liquid into the separating chamber containing cooler concentrated
liquid in direct connection with the condenser and vacuum pump, so
as to equalise the temperature of the two liquids, and then draw
off both by one tail pump.

[Illustration: Fig. 66.]

[Illustration: Fig. 67.]

[Illustration: Fig. 68.]

[Illustration: Fig. 69. Fig. 70. Fig. 71.]

[Illustration: Fig. 72. Fig. 73. Fig. 74.]

The present invention comprises a series of important improvements
on an apparatus described by Mr. Yaryan in a former English patent,
No. 14,162 (1886), and covers a number of important modifications
in construction, whereby improved results are secured. It is only
necessary, therefore, to give the details of the new patent,
No. 213 (1888), since it embodies the latest improvements which
practical working of the apparatus has suggested. In reference to
the accompanying illustrations the following details are given:
Fig. 66 represents a side elevation of the apparatus; Fig. 67,
the front elevation; Fig. 68, a top plan view; Fig. 69, a vertical
section of a cylinder showing the evaporating coils and separating
chamber; Fig. 70 is a horizontal section; and Fig. 71, a vertical
section of the separating chamber shown in Fig. 69, both on
reduced scale; Fig. 72 is a broken section of the cylinders for
showing the connections of the liquid pipe from the first to the
third effect evaporator; Fig. 73 is a rear end view of a cylinder
with manifold, the feed pump and a sectional view of the feed
box and supply devices; Fig. 74 represents a sectional view, on
enlarged scale, of the manifold and a feed duct; Fig. 75 is an
inside view of a return bend-head; Fig. 76 an inside view of a
section of the head; Fig. 77, a vertical cross section thereof
on enlarged scale, and showing the partitions forming cells
for connecting the ends of the evaporating tubes; Fig. 78 is a
vertical longitudinal section of a catch-all chamber; Fig. 79, a
cross section thereof; Fig. 80 is a vertical longitudinal section
of new form of separating chamber; and Fig. 81 represents a side
view and Fig. 82 an end view of the cylinders for showing the pipe
connection between the separating chambers of the third and fourth
effect evaporators.

[Illustration: Fig. 75. Fig. 76. Fig. 77.]

[Illustration: Fig. 78. Fig. 79. Fig. 80.]

The evaporating cylinders are mounted upon a framework Y, supported
upon columns X X, or other suitable supports. The apparatus is
shown arranged as quadruple effect, with four connected cylinders,
but multiple effect apparatus may be constructed with an increased
number of cylinders up to ten or twelve. The heating cylinders
B^1 B^2 B^3 B^4, containing the evaporating tubes or coils, are
preferably arranged in the same horizontal plane, and are provided
at the discharge ends of the evaporating coils with separating
chambers, A^1 A^2 A^3 A^4, of enlarged diameter, and at the supply
ends of the coils with the coils with return bend ends, C^1 C^2
C^3 C^4. From each separating chamber, A^1, A^2, valve pipe D^1
D^2 D^3 leads into the shell of the next heating cylinder, as
B^2, B^3, B^4, and vapour pipe D^4 leads from the last separator
A^4 to the condenser H, and the vacuum pump H^1. A cylindrical
catch-all chamber E^1, E^2, E^3, E^4, is connected in each vapour
pipe between each separator and each successive heating cylinder,
as shown in Figs. 66, 67, and 68, and in detail in Fig. 75. Gauge
glass and liquid receiving chambers, G^1, G^2, G^3, G^4, connect
with the bottom of each separating chamber for receiving the
liquid as it is separated from the vapour, and a gauge glass _g_
is applied to each of such chambers. Liquid discharge and transfer
pipes _t_, _t^1_, having valves _h_, _h^1_, as best shown in Figs.
66, 68, and 72, lead respectively from chambers G^1, G^2, of the
first and second effect to the manifold feed pipes leading into the
cylinders B^3, B^4, of the third and fourth effect for the purpose
hereafter described. The main steam supply pipe F, having a safety
valve _f_ and stop valve _f^1_, Figs. 66, 67, and 68, connects with
the heating cylinder B^1 of the first effect. The evaporating tubes
1, 2, 3, 4, 5, are expanded or otherwise secured in the tube sheets
_d_ and _e″_ at opposite ends of the cylinders, and are properly
connected at the ends in sets of five to form coils. The outer rear
return-bend head C^1 C^2, etc., are provided on their insides with
numerous short intersecting partition plates _c_, forming single
and double cells, properly arranged for connecting the evaporating
tubes in sets of five, as shown in Figs. 75, 76, 77.

[Illustration: Fig. 81. Fig. 82.]

The heads are pierced with holes _c′_ for connecting the liquid
supply pipes M of the manifolds L. The inner return-bend head T in
the separating chambers are formed like heads C^1 C^2, etc., with
intersecting partition plates _x_, and are provided with discharge
openings _t″_ for every fifth tube, as shown in Fig. 69. Tube sheet
_d_ is made of considerably larger diameter than cylinders B^1
B^2, etc., and acts as a vibrating diaphragm, to accommodate the
expansion and contraction of the tubes. The separating chambers may
be constructed with dash plates _b_ _b_, two or more in number,
having openings _g′_ _g′_ alternately upon opposite sides for the
passage of vapour, and opening _a′_ at the bottom for the passage
of liquid, as shown in Fig. 80. Here a tube sheet _z_ is provided
near the openings of the evaporating tubes, and in such sheet are
set numerous small horizontal tubes _n_, which discharge against a
vertical arresting plate _b′_ set near their open ends. Water and
solid matter are impelled against the plate and thereby arrested
and caused to flow down to the bottom of the chamber. The liquid
feed apparatus consists of a supply tank K, stand-pipe J, feed box
K^1, double pump I, manifold L, and connecting pipes and valves.
The liquid to be evaporated flows from tank K, through pipe _k_, to
stand-pipe J and box K^1, the flow being constant and uniform, and
of the desired quantity, by means of a valve _k′_ having a lever
handle _r′_ which is connected by a cord or chain passing over a
pulley _j_ with float _q_ in stand-pipe J. The valve opening in
pipe _k_ being properly adjusted by means of the float, etc., the
liquid is admitted to the stand-pipe J while the column of liquid
is automatically maintained at any desired height and pressure
regardless of the quantity in the supply tank, by means of the
float _q_, which, as it rises, tends to close valve _k′_, and as
it falls, to open the valve. From the bottom of the stand-pipe J,
nozzle _j′_ discharges a constant and uniform stream of liquid into
feed box K^1. The suction pipe I″ of pump I extends into box K^1,
where it terminates in a turned-down nozzle provided with valve _i_
having a lever handle and float _z_. As a given amount of liquid is
constantly running into the box, should the pump run too fast the
float lowers, partially closing the valve and lessening the amount
of liquid drawn at each stroke of the pump, and preventing air from
being drawn in, since the end of the suction pipe is always sealed
by the liquid. The liquid is forced by pump I into the manifolds
L, from which it flows through the contracted ducts _l_ into the
enlarged feed pipes _m_, as shown in Figs. 73 and 74. Ducts _l_ are
of about one-half inch diameter, and the upper and lower sections
thereof are connected by a union coupling, one portion of which
_l′_ has a reducer with opening one-quarter inch diameter, more or
less, according to the amount of liquid it is desired to feed.

The catch-all chambers E^1 E^2, etc., Figs. 66, 78, and 79, are
provided each at its inlet end _e_, with tube sheet _o_ extending
across its diameter a short distance in front of the opening of
vapour pipe D^1, and in such sheet are fixed numerous longitudinal
tubes _p_ extending to near the opposite head _e′_, so that vapours
carrying watery or solid particles are impelled against the head
and arrested. Liquid and solid matter, arrested in the catch-all
chambers, flow through pipes _v v′_ _v″_ down into the fluid
transfer pipe _t t′_ (Figs. 67, 68, and 72), and thence into the
evaporating coils and through pipe _v‴_ directly to the tail pump
W, Fig. 67. By use of the catch-all chambers the most frothy
liquids can he readily and economically managed. A liquid transfer
pipe _s_, having a valve _h″_, leads directly from receiving
chamber G^3 of the third effect to the separating chamber A^4 of
the fourth effect, the latent heat being carried off in the vapours
drawn by the vacuum pump H^1 into the chamber H, and the finished
liquid of both effects is drawn off through pipe _w_ by one and
the same tail pipe pump W. The water of condensation accumulating
in the heating cylinders B^1 B^2, etc., is transferred from one
to the other through connecting pipes _u u′ u″_ having valves
_y_, shown in Figs. 66, 67, and 68; and finally from cylinder B^4
through pipe _u‴_ directly into condenser H. The specification of
the patent, which those interested will do well to consult, next
describes the operation of the apparatus.

=American System of Soda Recovery.=–Mr. Congdon gives an
exhaustive description[33] of the method of recovering soda
in the United States, from whose interesting paper we extract
the following:–The spent liquors are delivered to the Yaryan
evaporator from the pans at a density of 6° to 7° B. at 130°
F. Here they are concentrated to 34° to 42° at 140° F. At this
density they are fed into furnaces of a reverberatory type, where
they are burnt to a cherry-red heat; and the ash then raked out.
This ash, which averages 50 per cent. of soda, is weighed in iron
barrows on suitable scales, and wheeled into the leaching-room
for lixiviation. The system of leaching, as it is termed in the
States, is conducted as follows:–Iron tanks are used, with
suitable piping, that allows pumping from one tank to another, and
also to pump from any one of them up to the causticising tanks in
the alkali-room. There is also a water-line by which water may be
pumped into any of the tanks, and there is a spout used in washing
away the black ash sludge. The leaching-tanks have false bottoms
of 2in. by 2in. stuff, placed crosswise, over which is a layer of
gravel, on which lies a layer of straw, by which the liquor is
filtered. The gravel is removed every few days, and the straw
with every charge. When one of the tanks is filled with black ash,
it is “wet down” with the stored liquor (the strongest of the
stored weak liquors), and also with the strongest weak liquors
from the tanks, and with weak liquors obtained from these tanks by
pumping water upon them and keeping them full. This is all pumped
up to the causticising-tank until the strength is reduced to 2°
or 1½° B. The remaining liquor is then drained into a tank known
as the “clear-liquor” tank, owing to there being no black ash in
it. The liquor from the next weakest pan is then pumped upon the
pan containing the black ash, and the next weakest liquor pumped
upon this. The weaker pans are then in succession pumped upon
the stronger, and the water pumped upon these, and thus a very
perfect washing is obtained. The sludge left behind is nothing but
charcoal, with a slight trace of carbonate of soda. Mr. Congdon
illustrates the above system thus. The tanks stand as follows:–

No. 1. Clear liquor, 1° to 2° B. (strongest).

No. 2. Black ash sludge (weaker than No. 3).

No. 3. Black ash, after sending up to causticising-tank (strongest
sludge).

No. 4. Fresh black ash.

No. 5. Weaker than No. 2 (sludge only).

No. 6. Weaker than No. 5 (sludge and weakest liquor).

The method of procedure is as follows:–

Liquor from No. 3 drained into No. 1 (now full).

No. 6 pumped on to No. 2 (No. 6 sludge thrown away).

Liquor from No. 2 drained upon No. 3.

Water put on No. 5.

No. 5 pumped upon No. 2 (No. 5 sludge thrown away).

The black ash is treated thus:–

No. 4, full of black ash, is wet down with Nos. 1, 2, and 3, and
pumped up to the causticising-tank.

Water is pumped out to Nos. 2 and 3, and then drained upon No.
4, the liquor still being pumped up from No. 4 while the water
is being pumped upon Nos. 2 and 3, which are kept full. This is
continued until the liquor tests only 2° to 1° B.

No. 4 is now drained upon No. 1.

No. 3 pumped upon No. 4, and this drained into No. 1 (now full).

No. 3 pumped upon No. 5.

Water pumped upon No. 2 (No. 2 the next to be thrown away).

No. 5 is by this time full of fresh black ash, and the same process
is carried out with No. 4.

In a manufacture such as paper-making, which involves the
consumption of enormous quantities of materials of variable
quality, as soda ash, caustic soda, and bleaching powder, for
example, it will be readily seen that some means should be at the
command of the consumer who does not avail himself of the services
of a practical chemist at his works, by which he can ascertain the
_actual_ value of the various substances he uses. An art which, up
to a certain point in its progress, is mainly a chemical operation,
it would undoubtedly be more safely and economically conducted when
supervised by persons well acquainted with chemical principles
and reactions, and less dependent upon individual judgment, than
is, perhaps, too frequently the case. Under such supervision more
perfect uniformity of results–a consideration of the greatest
importance in a manufacture of this kind–would be ensured.

[Illustration: Fig. 83. Fig. 84. Fig. 85.]

=Examination of Commercial Sodas.=–The methods of determining the
percentage of real alkali in the commercial products which have
received the name of _Alkalimetry_ are fortunately of a simple
character, and such as a person of ordinary intelligence and
skill can readily manipulate and render thoroughly reliable by
exerting the necessary care. He must, however, be provided with a
few indispensable appliances, which will be described, and with
these he should make several trials upon various samples until
he finds that his results are uniform and his manipulation easy
and reliable. He will require a chemical balance,[34] capable of
weighing to the tenth of a grain; a few glass “beakers” (Fig.
83) of various sizes, capable of holding from four to eight or
ten ounces of fluid; several glass stirrers; a bottle of litmus
solution, made by dissolving litmus in hot water; books of litmus
and turmeric papers; and several glass flasks (Fig. 84) of various
sizes, capable of holding from four to eight ounces. Besides these
accessories, certain measuring instruments, termed _alkalimeters_
or _burettes_, are employed, of which either of the two following
may be employed. These instruments are of glass, and hold up to 0
or zero exactly 1,000 grains. The scale is graduated in a hundred
divisions, which are again subdivided into tenths. Bink’s burette
is shown in Fig. 85, and Mohr’s burette in Fig. 86. The latter,
being provided with a stand, enables the operator to add the test
liquor–with, which the burette is charged–drop by drop, when the
alkaline solution to be tested is near the point of saturation,
without engaging the hands.

[Illustration: Fig. 86. Fig. 87.]

=Mohr’s Alkalimeter.=–This useful instrument (Fig. 86) and the
method of using it is thus described by Mohr:–“I have succeeded
in substituting for expensive glass stop-cocks an arrangement
which may be constructed by any person with ease, which remains
absolutely air and water-tight for an indefinite period, which
may be opened and regulated at will by the pressure of the
fingers, and which costs almost nothing. It consists of a small
piece of vulcanized indiarubber tube, which is closed by a clamp
of brass wire (Fig. 87). The ends of this clamp, which I call a
pressure-cock, are bent laterally at right angles in opposite
directions and furnished with knobs, so that when both ends are
pressed the clamp is opened, and a single drop or a continuous
current of liquid may be allowed to escape at pleasure. The
measuring-tube is a straight glass cylinder, as uniform as
possible, graduated to 0·2 or 0·1 cubic centimètres, and somewhat
contracted at its lower end, so as to fit into the indiarubber
tube. A small piece of glass tube inserted below the pressure-cock
forms the spout. The pressure-cock has the advantage of not
leaking, for it closes itself when the pressure of the fingers
is removed. The measure, furnished with the pressure-cock, is
fastened upon an appropriate stand, which can be placed at any
required height. When used, it is filled above the zero point with
test liquor, the cock opened for an instant, so as to let the
air escape from the spout, and the level of the solution is then
adjusted. This is done by bringing the eye level with the zero
point, and applying a gentle pressure to the cock until the liquid
has sunk so low that the inferior curve of the liquid touches the
graduation like the circle of a tangent; the cock is then closed,
and at the same moment the liquid remains at zero, and continues to
do so for weeks if evaporation is prevented. The test-measure being
normally filled, the experiment may be commenced; this is done
sitting, while the filling of the measure is done standing.

“The weighed sample of alkali is first placed in a beaker-glass,
and the test-liquor is allowed to flow into it by gently pressing
the cock. Both hands are set at liberty, for when the pressure-cock
is released it closes of itself. The volumetric[35] operation may
be interrupted at pleasure, in order to heat the liquid, shake it,
or do whatever else may be required. The quantity of liquid used
may be read off at any moment, and in repeating an experiment,
the limit of the quantity used before may be approached so near
that the further addition of liquid may be made drop by drop.”
The test-acid to be used _volumetrically_–that is, with the
alkalimeter, has a specific gravity of 1·032 at 60° F., and 1,000
grains by measure contain exactly 40 grains of real or anhydrous
(that is, without water) sulphuric acid.

The chemical principles involved in the process of alkali-testing
may be thus briefly stated:–According to the laws of chemical
combination defined by the atomic theory of Dalton, all substances
combine in _definite_ proportions or “equivalents”; thus, 1 part by
weight of _hydrogen_ combines with 8 parts by weight of _oxygen_
to form water. The equivalent number of hydrogen, therefore, is
1, and of oxygen 8, and that of water 9. Again, 3 equivalents of
oxygen combine with 1 equivalent of sulphur (16) to form sulphuric
acid; thus, sulphur 16, oxygen 24, equals anhydrous sulphuric
acid 40; therefore 40 is the _equivalent_ or combining number of
this acid, and it cannot be made to unite with alkalies or other
bases in any other proportion. For example, 40 _grains_ by weight
of _pure_ sulphuric acid will neutralise exactly 53 grains of
_dried carbonate of soda_, 31 grains of _pure anhydrous soda_, or
40 grains of _hydrate of soda_ (caustic soda). This being so, it
is only necessary to have exactly 40 grains of _real_ sulphuric
acid in 1,000 grains of water to form a _test-acid_, which, when
employed to neutralise an alkaline solution, will show, by the
proportion of dilute acid used to saturate the alkali, the absolute
percentage present in the sample.

=Preparation of the Test-Acid or Standard Solution.=–As there is
some trouble involved in the preparation of the test-liquor, it
is advisable to prepare a sufficient quantity at a time to last
for many operations. It may be readily made by mixing 1 part of
concentrated sulphuric acid with 11 or 12 parts of _distilled
water_, the mixture being made in what is termed a “Winchester”
bottle, which holds rather more than half a gallon, and is provided
with a glass stopper. The acid solution must be _adjusted_ or
brought to the proper strength after it has cooled down to 60°
F.; and it should be _faintly tinged_ with litmus, which will
give it a pinkish hue. The acid, to be of the proper strength,
should _exactly_ neutralise 53 grains of pure carbonate of soda,
previously calcined at a red heat, or 31 grains of pure anhydrous
soda. To prepare the anhydrous carbonate of soda, a few crystals of
carbonate of soda are placed in a Berlin porcelain crucible, and
this must be heated over a spirit-lamp or Bunsen burner. When all
the water of crystallisation has become expelled, the calcination
is continued until the mass is at a bright red heat, when the
vessel may be allowed to cool. 53 grains of the calcined carbonate
are now to be carefully weighed, and next dissolved in a glass
beaker, in about 2 ounces of distilled water. The alkalimeter is
now to be charged with the test-acid to the level of zero, and (if
Mohr’s burette be used) the beaker containing the alkaline solution
is to be placed upon the stand immediately beneath the exit-tube.
Now press the knobs of the pressure-cock, and allow a portion
of the liquor to flow into the beaker. When the effervescence
which immediately sets up subsides, make further additions of the
test-liquor from time to time, until the effervescence becomes
sluggish, at which period the acid must be added with greater
caution. When the solution approaches saturation it acquires a
purplish tint (due to the litmus with which the acid is tinged),
which it retains until the point of saturation is reached, when it
suddenly changes to a pink colour. After each addition of the acid
the solution should be stirred with a thin and clean glass rod;
and before the final change from purple to pink, the end of the
glass rod should be applied to a strip of blue litmus paper, when,
if the moistened spot touched assumes a red colour, the saturation
is complete; if, on the contrary, the paper is unchanged, or has a
violet or reddish hue, add the test-liquor, one or two drops at a
time, with continued stirring, until a drop of the solution applied
with a glass rod reddens litmus paper, when the saturation is
finished. If any test-liquor remain in the burette, this indicates
that there is excess of acid in the test-liquor; consequently more
distilled water must be added to the bulk, the burette emptied
and refilled with the reduced liquor, and another 53 grains of
anhydrous carbonate of soda treated as before, until 1,000 grains
of the acid liquor _exactly_ neutralise the solution. Should the
whole contents of the burette in the first trial be used before
saturation is complete, a little more sulphuric acid must be put
into the Winchester or test-acid bottle, and a 53-grain solution
of carbonate of soda treated as before. A very little practice
will enable the operator to adjust his test-liquor with perfect
accuracy; and, to prevent mistakes, the bottle should be labelled
“Test-acid,” and always be kept closed by its stopper.

=Sampling Alkalies.=–Soda-ash of commerce is usually packed in
wooden casks, and in order to obtain a fair average sample from a
large number of these casks, which may represent one consignment,
it is important to take small samples, as near the centre of each
cask as possible, from as many of the casks as time will permit.
Each sample, as drawn from the cask, should be at once placed
in a rather wide-mouthed bottle furnished with a well-fitting
cork. Each sample should be numbered and marked with the brand
which distinguishes the cask from which it was taken. The duty
of sampling should be placed in the hands of a person of known
integrity and intelligence.

When about to test a sample of soda-ash, the contents of the bottle
should first be emptied upon a sheet of dry paper, and the larger
lumps then crushed to reduce the whole to a coarse powder, and
this must be done as quickly as possible to prevent absorption of
moisture from the atmosphere. 100 grains of the alkali must now
be accurately weighed and put into a glass flask (Fig. 84), and
the remainder of the alkali returned to the bottle and the vessel
securely corked. About half an ounce of distilled water is then to
be put into the flask and gentle heat applied, with an occasional
shaking, until the alkali is all dissolved. The flask is then to
be set aside for a few minutes, until any insoluble matter present
has subsided, when the clear liquor is to be carefully poured into
a beaker glass; the sediment must be washed several times with
small quantities of distilled water, and the washings added to
the solution in the beaker. This washing is of great importance
and must be performed several times, or until the last washing
liquor produces no effect upon yellow turmeric paper, which even
slight traces of alkali will turn a brown colour. So long as this
brown tint is given to the turmeric paper the presence of alkali
is assured, and the washing must be continued. It is important,
after each washing, to pour off the last drop of the liquor above
the sediment, by which the operation is more effectual, and is
effected with less water than when this precaution is not observed.
In order to ensure perfect accuracy in the result, every particle
of the washings must be added to the contents of the beaker-glass
in which the assay is to be made.

=The Assay.=–The alkalimeter is first to be filled with the
test-acid exactly to the line 0 or zero of the scale as described,
and the beaker containing the solution to be tested then placed
immediately beneath the dropping tube of the instrument; a thin
glass rod should be placed in the beaker as a stirrer. The acid
liquor is then allowed to flow gradually into the alkaline
solution (which should be repeatedly stirred with the glass rod),
by pressing the knobs of the pressure-cock, until the solution
assumes a purple tint, which it will retain until the exact point
of saturation has been arrived at, when, as before stated, it
will suddenly change to a pink colour. Before the latter stage is
reached the beaker should be placed over a spirit lamp or Bunsen
burner, and the liquid heated to expel the carbonic acid which is
evolved, and partly absorbed by the solution during the process of
saturation. When the neutralisation is complete, the alkalimeter
is allowed to repose for a few moments, so that the acid liquor
may drain from the interior of the glass tube into the bulk of the
fluid, and the quantity of test-acid used is then determined by
reading off the number of divisions of the alkalimeter that have
been exhausted, every one of which represents 1/100th part, or 1
per cent. of _alkali_, whenever the _equivalent weight_ is taken
for assay. Every 1/10th part of an alkalimeter division represents
1/10th of 1 per cent., and the result is thus obtained without
the necessity of any calculation. The following table shows the
_equivalent_ or combining proportions of soda with 40 grains of
real (that is, anhydrous) sulphuric acid:–

Are
equivalent
to
40 grains of sulphuric acid } 31 grains soda (anhydrous).
1,000 grains of dilute } 40 grains hydrate of soda (pure
sulphuric acid (sp. gr. 1·033) } caustic soda).
1,000 grains of dilute } 53 grains carbonate of soda
sulphuric acid (water-grain } (anhydrous).
measure) sp. gr. 1·032 } 143 grains crystallized
} carbonate of soda.

Mr. Arnot recommends the following method for alkali testing: “The
sample, which should be a fair average of the drum or cask from
which it is drawn, should, in the case of caustic soda, be quickly
crushed into small fragments, and returned to the stoppered bottle
in which it was collected for testing. It need not be finely
ground, and, indeed, should not be, as it very readily attracts
moisture from the air. The contents of the drum are usually pretty
uniform, and the crushing recommended will give the operator
a sample quite fit to work upon. Samples of soda-ash and soda
crystals will, of course, be fairly representative of the casks
from which they are drawn. One hundred grains of the prepared
sample must be weighed out upon a watch-glass or slip of glazed
paper, and transferred to a porcelain basin, with at least half a
pint of boiling water. The watch-glass is preferable for caustic
soda, and the weighing in the case of that agent must be done
expeditiously. While the sample is dissolving the burette will be
charged with the standard acid. To the soda solution a few drops
of solution of litmus, sufficient to colour it distinctly, will
be added. The acid will then be run into the blue soda liquor;
at first, within reasonable limits, this may be done rapidly,
but towards the close of the operation the acid must be added
cautiously, and the solution kept well stirred. In the case of
caustic, when the blue has distinctly changed to red, the operation
may be considered completed, and the measures may be read off the
burette; and this is, without calculation, the result required.
When the soda in the sample is a carbonate, the blue colour of the
litmus will be changed to pink before all the soda is neutralised,
owing to a portion of the liberated carbonic acid remaining in
the solution; this must be eliminated by placing the basin over a
Bunsen burner and boiling the solution. The blue colour will thus
be restored, and more acid must be added, repeating the boiling
from time to time, until the red colour becomes permanent. It is
sometimes necessary to filter the soda solution before testing;
this applies specially to recovered soda, and, although in a less
degree, to soda-ash.” When the soda solution is filtered, it will
be necessary to thoroughly wash out the liquor absorbed by the
filtering paper, the washings being added to the bulk of the liquor
as before. The best plan is to allow the soda solution to stand
for some time until all the sediment has deposited, and then to
pour off as much of the liquor as possible, and then to wash the
sediment into a very small filter, in which it will receive further
washing, until no trace of alkali can be detected in the last wash
water.

=Estimation of Chlorine in Bleaching Powder.=–It is desirable that
the manager or foreman of a paper-mill should have at his command
some ready means by which he may test the percentage of chlorine
in samples of bleaching powder, or chloride of lime, delivered at
the mill, not alone to enable him to determine the proportions to
be used in making up his bleaching liquors, but also to ensure his
employers against possible loss in case of inferior qualities being
delivered at the mill. Bleaching powders being purchased according
to percentage, it is absolutely necessary that the purchaser should
have this determined to his own satisfaction before either using
or paying for the material. Good chloride of lime should contain
35 per cent. of available chlorine, but the powder should not be
accepted which contains less than 32 per cent. There are several
methods of estimating the percentage of chlorine in bleaching
powder, which is composed of hypochlorite of lime, chloride of
calcium, and hydrate of lime, the latter substances being of no
service in the bleaching process.

According to Fresenius, in freshly prepared and perfectly normal
chloride of lime, the quantities of hypochlorite of lime and
chloride of calcium present stand to each other in the proportion
of their equivalents. When such chloride of lime is brought into
contact with dilute sulphuric acid, the whole of the chlorine it
contains is liberated in the elementary form. On keeping chloride
of lime, however, the proportion between hypochlorite of lime
and chloride of calcium gradually changes: the former decreases,
the latter increases. Hence from this cause alone, to say nothing
of original difference, the commercial article is not of uniform
quality, and on treatment with acid gives sometimes more, and
sometimes less, chlorine. As the value of bleaching powder depends
entirely upon the amount of chlorine set free on treatment with
acids, chemists have devised very simple methods of determining the
available amount of chlorine in any given sample, these methods
having received the name of _chlorimetry_. The method of Fresenius
is generally considered both practicable and reliable.

=Fresenius’ Method= of preparing the solution of bleaching powder
to be tested is as follows:–Carefully weigh out 10 grains of
the sample, and finely triturate it in a mortar with a little
cold water, gradually adding more water; next allow the liquor to
settle, then pour the liquid into a litre flask, and triturate
the residue again with a little water, and rinse the contents of
the mortar carefully into the flask, which should then be filled
with water up to the graduated mark. Now shake the milky fluid
and proceed to examine it while in the turbid state; and each
time, before measuring off a fresh portion, the vessel must be
again shaken to prevent the material from depositing. The results
obtained with the solution in its turbid condition are considered
more accurate and reliable than when the clear liquid alone is
treated, even though the deposit be frequently washed. This may be
proved, Fresenius says, by making two separate experiments, one
with the decanted clear liquor, and another with the residuary
turbid mixture. In an experiment made in his own laboratory
the decanted clear fluid gives 22·6 of chlorine, the residuary
mixture 25·0, and the uniformly mixed turbid solution 24·5. One
cubic centimètre of the solution of chloride of lime so prepared
corresponds to 0·01 gramme of chloride of lime.

=Gay-Lussac’s Method.=–This method, which is known as the
_arsenious acid process_, has been much adopted for the
determination of chlorine in bleaching powders, and is conducted as
follows:–

_The Test-liquor._–This is prepared by dissolving 100 grains of
_pure_ arsenious acid in about 4 ounces of pure hydrochloric acid,
and the solution is to be diluted with water until, on being poured
into a graduated 10,000 grains measure-glass, it occupies the
volume of 700 grains measure marked on the scale. Each 1,000 grains
measure of this liquid now contains 14·29 grains of arsenious acid,
corresponding to 10 grains of chlorine, or 1/10 grain of chlorine
for every division or degree of the scale of the chlorimeter, for
which purpose a Mohr’s burette of the above capacity may be used,
or a graduated tube of the form shown in Fig. 85 may be employed.

_Testing the Sample._–100 grains of the chloride of lime to
be tested are next dissolved in water, and poured into a tube
graduated up to 2,000 grains measure. The whole must be well shaken
in order to obtain a uniformly turbid solution, and half of it
(1,000 grains measure) transferred to a graduated chlorimeter,
which is, therefore, thus filled up to 0°, or the zero of the
scale, and contains exactly 50 grains of the chloride of lime
under examination, whilst each degree or division of the scale
contains only ½ grain. 1,000 grains measure of the arsenious acid
test-liquor are now poured into a glass beaker, and a few drops of
a solution of sulphate of indigo added, in order to impart a faint,
but distinct, blue colour to it; the glass is then to be shaken
so as to give a circular movement to the liquid, and whilst it is
whirling round the chloride of lime solution from the chlorimeter
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 with a glass rod during the whole process, and to
stop as soon as the decoloration is complete. We will assume that
in order to destroy the blue colour of 1,000 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 grains of chlorine required to destroy the colour
of the test solution; and since each division represents ½ grain
of chloride of lime, 45 grains of chloride of lime (10 grains of
chlorine) were present in the 90 divisions so employed, from which
the percentage strength may be ascertained:–

For 45 : 10 :: 100 : 22·22.

The chloride of lime examined, therefore, contained 22¼ per
cent. (nearly) of chlorine. 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. If the contrary
plan were adopted the hydrochloric acid of the test-liquor would
liberate chlorine gas so fast that much would be lost, and the
result rendered incorrect. By pouring, on the contrary, the
chloride of lime solution into the arsenious acid solution the
chlorine is disengaged in small portions at a time, and meets with
an abundance of arsenious acid to react on. The mixture of chloride
of lime should also be employed turbid.

=Estimation of Alumina in Alum Cake, etc.=–Mr. Rowland Williams,
F.C.S., in a paper read before the Chemical Society in June,
1888, describes a method of estimating the alumina in alums,
alum cakes, and sulphate of alumina, by which he obtained more
accurate results than are obtained by the ordinary ammonia method
of estimation. After pointing out several objections to the method
of precipitating the alumina by ammonia, he proceeds:–“There
is another method for the estimation of alumina which is not so
well known as the above. This is by means of sodium thiosulphate.
Having had a very extensive and successful experience of this
process, I can recommend it with confidence. Considerable practice
is, however, necessary in order to secure good results, as
certain conditions must be carefully attended to, otherwise the
precipitation will be incomplete. The estimation is made in a
moderately dilute solution. In the case of alum cake and sulphate
of alumina I dissolve 400 grains in water, filter, dilute to 10,000
grains. I use 1,000 grains of this solution (equal to 40 grains of
the sample) for estimating the alumina. If any free acid is present
it is neutralised by a few drops of carbonate of soda solution,
and the whole diluted to about 8 ounces measure. A large quantity
of crystallized thiosulphate of soda is then added, and the liquid
boiled for at least half-an-hour, constantly replacing the water
lost by evaporation. By the end of that time all the alumina will
be precipitated in a finely-divided form, along with more or less
free sulphur. The precipitate is then filtered off and washed well
with boiling water. The filtration and washing take place very
rapidly, and may generally be accomplished in about twenty minutes,
this being a great saving of time in comparison with the long and
tedious washing by decantation, which is necessary in the case of
gelatinous alumina. Before filtration, it is advisable to add a
drop or two of carbonate of soda solution, lest the liquid should
have become slightly acid during boiling.”

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