To construct a printing machine which shall throw off two sides at a
time with exact register, that is, with the second side placed precisely
upon the back of the first, is a very difficult problem, which was
first practically solved by Messrs. Applegath and Cowper. It is
comparatively easy to make a machine which shall print the one side of a
sheet of paper first, and then the other side, by the removal of one
form, and the introduction of another; and thus far did Mr. König
advance. A correct register requires the sheet, after it has received
its first impression from one cylinder, to travel round the peripheries
of the cylinders and drums, at such a rate as to meet the types of the
second side at the exact point which will ensure this side falling with
geometrical nicety upon the back of the first. For this purpose, the
cylinders and drums must revolve at the very same speed as the carriage
underneath; hence the least incorrectness in the workmanship will
produce such defective typography as will not be endured in
book-printing at the present day, though it may be tolerated in
newspapers. An equable distribution of the ink is of no less importance
to beautiful letter-press. See _figs._ 921. 922.
The machines represented in _figs._ 923, 924, 925, are different forms
of those which have been patented by Messrs. Applegath and Cowper. That
shown in _figs._ 923. and 925. prints both sides of the sheet during its
passage, and is capable of throwing off nearly 1000 finished sheets per
hour. The moistened quires of blank paper being piled upon a table A,
the boy, who stands on the adjoining platform, takes up one sheet after
another, and lays them upon the feeder B, which has several linen girths
passing across its surface, and round a pulley at each end of the
feeder; so that whenever the pulleys begin to revolve, the motion of the
girths carries forward the sheet, and delivers it over the entering
roller E, where it is embraced between two series of endless tapes, that
pass round a series of tension rollers. These tapes are so placed as to
fall partly between, and partly exterior to, the pages of the printing;
whereby they remain in close contact with the sheet of paper on both of
its sides during its progress through the machine. The paper is thus
conducted from the first printing cylinder F, to the second cylinder G,
without having the truth of its register impaired, so that the
coincidence of the two pages is perfect. These two great cylinders, or
drums, are made of cast iron, turned perfectly true upon a self-acting
lathe;[47] they are clothed in these parts, corresponding to the
typographic impression, with fine woollen cloth, called _blankets_ by
the pressmen, and revolve upon powerful shafts which rest in brass
bearings of the strong framing of the machine. These bearings, or
plummer blocks, are susceptible of any degree of adjustment, by set
screws. The drums H and I are made of wood; they serve to conduct the
sheet evenly from the one printing cylinder to the other.
[47] I have witnessed with much pleasure the turning of these great
cylinders in Messrs. Cowper’s factory at Manchester.
[Illustration: 923 924 925]
One series of tapes commences at the upper part of the entering drum E,
proceeds in contact with the right-hand side and under surface of the
printing cylinder F, passes next over the carrier-drum H, and under the
carrier-drum I; then encompassing the left-hand side and under portion
of the printing drum G, it passes in contact with the small tension
rollers _a_, _b_, _c_, _d_, _fig._ 925., and finally arrives at the
roller E, which may be called the commencement of the one series of
endless tapes. The other series may be supposed to commence at the
roller _h_; it has an equal number of tapes, and corresponds with the
former in being placed upon the cylinders so that the sheets of paper
may be held securely between them. This second series descends from the
roller _h_, _fig._ 925., to the entering drum E, where it meets and
coincides with the first series in such a way that both sets of tapes
proceed together _under_ the printing cylinder F, _over_ H, _under_ I,
and _round_ G, until they arrive at the roller _i_, _fig._ 923., where
they separate, after having continued in contact, except at the places
where the sheets of paper are held between them. The tapes descend from
the roller _i_, to a roller at _k_, and, after passing in contact with
rollers at _l_, _m_, _n_, they finally arrive at the roller _h_, where
they were supposed to commence. Hence two series of tapes act invariably
in contact, without the least mutual interference, as may be seen by
inspection of the _figs._ 923, 924, 925.
The various cylinders and drums revolve very truly by means of a system
of toothed wheels and pinions mounted at their ends. Two horizontal
forms of types are laid at a certain distance apart upon the long
carriage M, adjoining to each of which there is a flat metallic plate,
or inking table, in the same plane. The common carriage, bearing its two
forms of type and two inking tables, is moved backwards and forwards,
from one end of the printing machine to the other, upon rollers attached
to the frame-work, and in its traverse brings the types into contact
with the sheet of paper clasped by the tapes round the surfaces of the
printing cylinders. This alternate movement of the carriage is produced
by a pinion working alternately into the opposite sides of a rack under
the table. The pinion is driven by the bevel wheels K.
The mechanism for supplying the ink, and distributing it over the forms,
is one of the most ingenious and valuable inventions belonging to this
incomparable machine, and is so nicely adjusted, that a single grain of
the pigment may suffice for printing one side of a sheet. Two similar
sets of inking apparatus are provided; one at each end of the machine,
adapted to ink its own form of type. The metal roller L, called the
_ductor_ roller, as it draws out the supply of ink, has a slow rotatory
motion communicated to it by a catgut cord, which passes round a small
pulley upon the end of the shaft of the printing cylinder G. A
horizontal plate of metal, with a straight-ground edge, is adjusted by
set screws, so as to stand nearly in contact with the ductor roller.
This plate has an upright ledge behind, converting it into a sort of
trough or magazine, ready to impart a coating of ink to the roller, as
it revolves over the table. Another roller, covered with elastic
composition (see _suprà_), called the vibrating roller, is made to
travel between the ductor roller and the inking table; the vibrating
roller, as it rises, touches the ductor roller for an instant, abstracts
a film of ink from it, and then descends to transfer it to the table.
There are 3 or 4 small rollers of distribution, placed somewhat
diagonally across the table at M, (inclined only 2 inches from a
parallel to the end of the frame,) furnished with long slender axles,
resting in vertical slots, whereby they are left at liberty to revolve
and to traverse at the same time; by which compound movement they are
enabled to efface all inequality in the surface of the varnish, or to
effect a perfect distribution of the ink along the table. The table
thus evenly smeared, being made to pass under the 3 or 4 proper inking
rollers N, _fig._ 924., imparts to them an uniform film of ink, to be
immediately transferred by them to the types. Hence each time that the
forms make a complete traverse to and fro, which is requisite for the
printing of every sheet, they are touched no less than eight times by
the inking rollers. Both the distributing and inking rollers turn in
slots, which permit them to rise and fall so as to bear with their whole
weight upon the inking table and the form, whereby they never stand in
need of any adjustment by screws, but are always ready for work when
dropped into their respective places.
Motion is given to the whole system of apparatus by a strap from a steam
engine going round a pulley placed at the end of the axle at the back of
the frame; one steam-horse power being adequate to drive two double
printing machines; while a single machine may be driven by the power of
two men acting upon a fly-wheel. In Messrs. Clowes’ establishment, in
Stamford-street, two five-horse engines actuate nineteen of the above
described machines.
The operation of printing is performed as follows:--See _fig._ 926.
The sheets being carefully laid, one by one, upon the linen girths, at
the feeder B, the rollers C and D are made to move, by means of a
segment wheel, through a portion of a revolution. This movement carries
on the sheet of paper sufficiently to introduce it between the two
series of endless tapes at the point where they meet each other upon the
entering drum E. As soon as the sheet is fairly embraced between the
tapes, the rollers C and D are drawn back, by the operation of a weight,
to their original position, so as to be ready to introduce another sheet
into the machine. The sheet, advancing between the endless tapes,
applies itself to the blanket upon the printing cylinder F, and as it
revolves meets the first form of types, and receives their impression;
after being thus printed on one side, it is carried, over H and under I,
to the blanket upon the printing cylinder G, where it is placed in an
inverted position; the printed side being now in contact with the
blanket, and the white side being outwards, meets the second form of
types at the proper instant, so as to receive the second impression, and
get completely printed. The perfect sheet, on arriving at the point _i_,
where the two series of tapes separate, is tossed out by centrifugal
force into the hands of a boy.
[Illustration: 926]
The diagram, _fig._ 926. shows the arrangement of the tapes, agreeably
to the preceding description; the feeder B, with the rollers C and D, is
seen to have an independent endless girth.
[Illustration: 927]
The diagram, _fig._ 927. explains the structure of the great machine
contrived by Messrs. Applegath and Cowper for printing the _Times_
newspaper. Here there are four places to lay on the sheets, and four to
take them off; consequently, the assistance of eight lads is required.
P, P, P, P, are the four piles of paper; F, F, F, F, are the four
feeding-boards; E, E, E, E, are the four entering drums, upon which the
sheets are introduced between the tapes _t_, _t_, _t_, _t_, whence they
are conducted to the four printing cylinders 1, 2, 3, 4; T is the form
of type; I, I, are two inking tables, of which one is placed at each end
of the form. The inking apparatus is similar to that above described,
with the addition of two central inking rollers R, which likewise
receive their ink from the inking tables. The printing cylinders 1, 2,
3, 4, are made to rise and fall about half an inch; the first and third
simultaneously, as also the second and fourth. The form of type, in
passing from A to B, prints sheets at 1 and 3; in returning from B to A,
it prints sheets at 4 and 2; while the cylinder alternately falls to
give the impression, and rises to permit the form to pass untouched.
Each of the lines marked _t_, consists of two endless tapes, which run
in contact at the parts shown, but separate at the entering drums E, and
at the taking off parts _o_, _o_, _o_, _o_. The return of the tapes to
the entering drum is omitted in the diagram, to avoid confusion of the
lines.
The sheets of paper being laid upon their respective feeding-boards,
with the fore edges just in contact with the entering drum, a small
roller, called the drop-down roller, falls, at proper intervals, down
upon the edges of the sheets; the drum and the roller being then
removed, instantly carry on the sheet, between the tapes _t_, downwards
to the printing cylinder, and thence upwards to _o_, _o_, _o_, _o_,
where the tapes are parted, and the sheet falls into the hands of the
attendant boy. This noble mechanism is so perfectly equipped, that it is
generally in full work within four minutes after the form is brought
into the machine-room. The speed of König’s machine, by which the
_Times_ was formerly printed, was such as to turn out 1800 papers per
hour; that of Applegath and Cowper throws off 4200 per hour, and it has
been daily in use during eight years.
PRUSSIAN BLUE, and PRUSSIATE OF POTASH, are two important articles of
chemical manufacture, which must be considered together. The first is
called by English chemists, _Ferrocyanodide of iron_, the _Cyanure
ferroso-ferrique_ of Berzelius; _Eisenblausaures eisenoxyd_, or
_eisencyanür_ + _eisencyanid_, Germ.; the second is called
_Ferrocyanodide of potassium_, the _Cyanure ferroso-potassique_ of
Berzelius; _Eisencyanür-kalium_, _cyaneisen_ + _cyankalium_, or
_Blausaures eisenoxydul-kali_, Germ.
Prussian blue (_Berliner-blau_, Germ.), is a chemical compound of iron
and cyanogen. When organic matters abounding in nitrogen, as dried
blood, horns, hair, skins, or hoofs of animals, are triturated along
with potash in a strongly ignited iron pot, a dark gray mass is
obtained, that affords to water the liquor originally called _lixivium
sanguinis_, or blood-lye, which, by evaporation, yields lemon-coloured
crystals in large rectangular tables, bevelled at the edges. This salt
is called in commerce, prussiate of potash, and has for its ultimate
constituents, potassium, iron, oxygen, and hydrogen, (the latter two in
such proportions as to form water), and the peculiar compound CYANOGEN,
the _blaustoff_ of the Germans.
These crystals consist, in 100 parts, of potassium 37·02, iron 12·82,
cyanogen 37·40, water 12·76; or, cyanide of potassium 61·96, cyanide of
iron 25·28, and water 12·76. They may be represented also by the
following composition: 44·58 of potassa, 38·82 of hydrocyanic or prussic
acid, and 16·60 of oxide of iron, in 100 parts; but the first appears to
be their true chemical constitution. Dry ferrocyanodide of potassium, is
a compound of, one atom of cyanide of iron, 54 = (28 + 26), and 2 atoms
of cyanide of potassium, 132, = ([26 × 2] + [40 × 2]); the sum being
186; hydrogen being 1·0 in the scale of equivalents. The crystals of
prussiate of potash are nearly transparent, soft, of a sweetish saline
and somewhat bitterish taste, soluble in 4 parts of water at 52° F., and
in 1 part of boiling water, but insoluble in alcohol. They are permanent
in the air at ordinary temperatures, but in a moderately warm stove-room
they part with 12-3/4 per cent. of water, without losing their form or
coherence, and become thereby a white friable anhydrous ferrocyanodide
of potassium, consisting of 42·44 potassium, 42·87 cyanogen, and 14·69
iron, in 100 parts.
This salt is an excellent reagent for distinguishing metals from each
other, as the following TABLE of the precipitates which it throws down
from their saline solutions will show:--
Metallic solutions. Colour of precipitate.
Antimony white.
Bismuth white.
Cadmium white, a little yellowish.
Cerium (protoxide) white, soluble in acids.
Cobalt green, soon turning reddish-gray.
Copper (protoxide) white, changing to red.
Do. (peroxide) brown-red.
Iron (protoxide) white, rapidly turning blue.
Do. (peroxide) dark blue.
Lead white, with a yellowish cast.
Manganese (protoxide) white, turning quickly peach or blood-red.
Manganese (deutoxide) greenish-gray.
Mercury (protoxide) white.
Do. (peroxide) white, turning blue.
Molybdenum dark brown.
Nickel (oxide) white, turning greenish.
Palladium (protoxide) green (gelatinous).
Silver white, turning brown in the light.
Tantalum yellow, dark burned colour.
Tin (protoxide) white, (gelatinous).
Do. (peroxide) yellow, do.
Uranium red-brown.
Zinc white.
No precipitations ensue with solutions of the alkaline or earthy salts,
except that of yttria, which is white; nor with those of gold, platinum,
rhodium, iridium, osmium, (in concentrated solutions,) tellurium,
chromium, tungstenium. All the precipitates by the ferrocyanodide of
iron, are double compounds of cyanide of iron with cyanide of the metal
thrown down, which is produced by the reciprocal decomposition of the
cyanide of potassium and the peculiar metallic oxide present in the
solution. The precipitate from the sulphate of copper has a fine brown
colour, and has been used as a pigment; but it is somewhat transparent,
and therefore does not cover well. The precipitate from the peroxide
salts of iron is a very intense prussian blue, called on the continent,
Paris blue. It may be regarded as a compound of prussiate of protoxide
and prussiate of peroxide of iron; or as a double cyanide of the
protoxide and peroxide of iron, as the denomination _cyanure
ferroso-ferrique_ denotes. In numbers, its composition may be therefore
stated thus: prussic or hydrocyanic acid, 48·48; protoxide of iron,
20·73; peroxide of iron, 30·79; or cyanogen, 46·71; iron, 37·36; water,
15·93; which represent its constitution when it is formed by
precipitation with the prussiate of potash or a salt of iron that
contains no protoxide. If the iron be but partially peroxidized in the
salt, it will afford a precipitate, at first pale blue, which turns dark
blue in the air, consisting of a mixture of prussiate of protoxide and
prussiate of peroxide. In fact, the white cyanide of iron (the prussiate
of the pure protoxide), when exposed to the air in a moist condition,
becomes, as above stated, dark blue; yet the new combination formed in
this case through absorption of oxygen, is essentially different from
that resulting from the precipitation by the peroxide of iron, since it
contains an excess of the peroxide in addition to the usual two cyanides
of iron. It has been therefore called _basic_ prussian blue, and, from
its dissolving in pure water, _soluble_ prussian blue.
Both kinds of prussian blue agree in being void of taste and smell, in
attracting humidity from the air when they are artificially dried, and
being decomposed at a heat above 348° F. The neutral or insoluble
prussian blue is not affected by alcohol; the basic, when dissolved in
water, is not precipitated by that liquid. Neither is acted upon by
dilute acids; but they form with concentrated sulphuric acid a white
pasty mass, from which they are again reproduced by the action of cold
water. They are decomposed by strong sulphuric acid at a boiling heat,
and by strong nitric acid at common temperatures; but they are hardly
affected by the muriatic. They become green with chlorine, but resume
their blue colour when treated with disoxidizing reagents. When prussian
blue is digested in warm water along with potash, soda, or lime,
peroxide of iron is separated, and a ferroprussiate of potash, soda, or
lime remains in solution. If the prussian blue has been previously
purified by boiling in dilute muriatic acid, and washing with water, it
will afford by this treatment a solution of ferrocyanodide of potassium,
from which by evaporation this salt may be obtained in its purest
crystalline state. When the powdered prussian blue is diffused in
boiling water, and digested with red oxide of mercury, it parts with all
its oxide of iron, and forms a solution of bi-cyanodide, improperly
called prussiate of mercury; consisting of 79·33 mercury, and 20·67
cyanogen; or, upon the hydrogen equivalent scale, of 200 mercury, and 52
= (26 × 2) cyanogen. When this salt is gently ignited, it affords
gaseous cyanogen. Hydrocyanic or prussic acid, which consists of 1 atom
of cyanogen = 26, + 1 of hydrogen = 1, is prepared by distilling the
mercurial bi-cyanide in a glass retort with the saturating quantity of
dilute muriatic acid. Prussic acid may also be obtained by precipitating
the mercury by sulphuretted hydrogen gas from the solution of its
cyanide; as also by distilling the ferrocyanide of potassium along with
dilute sulphuric acid. Prussic acid is a very volatile light fluid,
eminently poisonous, and is spontaneously decomposed by keeping,
especially when somewhat concentrated.
Having expounded the chemical constitution of prussian blue and
prussiate of potash, I shall now treat of their _manufacture upon the
commercial scale_.
1. _Of blood-lye_, the phlogisticated alkali of Scheele. Among the
animal substances used for the preparation of this lixivium, blood
deserves the preference, where it can be had cheap enough. It must be
evaporated to perfect dryness, reduced to powder, and sifted. Hoofs,
parings of horns, hides, old woollen rags, and other animal offals, are,
however, generally had recourse to, as condensing most azotized matter
in the smallest bulk. Dried funguses have been also prescribed. These
animal matters may either be first carbonized in cast-iron cylinders, as
for the manufacture of _sal ammoniac_ (which see), and the residual
charcoal may be then taken for making the ferroprussiate; or the dry
animal matters may be directly employed. The latter process is apt to be
exceedingly offensive to the workmen and neighbourhood, from the
nauseous vapours that are exhaled in it. Eight pounds of horn (hoofs),
or ten pounds of dry blood, afford upon an average one pound of
charcoal. This must be mixed well with good pearlash, (freed previously
from most of the sulphate of potassa, with which it is always
contaminated,) either in the dry way, or by soaking the bruised charcoal
with a strong solution of the alkali; the proportion being one part of
carbonate of potassa to from 1-1/2 to 2 parts of charcoal, or to about
eight parts of hard animal matter. Gautier has proposed to calcine three
parts of dry blood with one of nitre; with what advantage to the
manufacturer, I cannot discover.
[Illustration: 928]
The pot for calcining the mixture of animal and alkaline matter is
egg-shaped as represented at _a_, _fig._ 928, and is considerably
narrowed at the neck _e_, to facilitate the closing of the mouth with a
lid _i_. It is made of cast iron, about two inches thick in the belly
and bottom; this strength being requisite because the chemical action of
the materials wears the metal fast away. It should be built into the
furnace in a direction sloping downwards, (more than is shown in the
figure,) and have a strong knob _b_, projecting from its bottom to
support it upon the back wall, while its shoulder is embraced at the
arms _c_, _c_, by the brickwork in front. The interior of the furnace is
so formed as to leave but a space of a few inches round the pot, in
order to make the flame play closely over its whole surface. The
fire-door _f_, and the draught-hole _z_, of the ash-pit, are placed in
the posterior part of the furnace, in order that the workmen may not be
incommoded by the heat. The smoke vent _o_, issues through the arched
top _h_ of the furnace, towards the front, and is thence led backwards
by a flue to the main chimney of the factory. _d_ is an iron or stone
shelf, inserted before the mouth of the pot, to prevent loss in
shovelling out the semi-liquid paste. The pot may be half filled with
the materials.
The calcining process is different, according as the animal substances
are fresh or carbonized. In the first case, the pot must remain open, to
allow of diligent stirring of its contents, with a slightly bent flat
iron bar or scoop, and of introducing more of the mixture as the
intumescence subsides, during a period of five or six hours, till the
nauseous vapours cease to rise, till the flame becomes smaller and
brighter, and till a smell of ammonia be perceived. At this time, the
heat should be increased, the mouth of the pot should be shut, and
opened only once every half hour, for the purpose of working the mass
with the iron paddle. When on opening the mouth of the pot, and stirring
the pasty mixture, no more flame rises, the process is finished.
If the animal ingredients are employed in a carbonized state, the pot
must be shut as soon as its contents are brought to ignition by a
briskly urged fire, and opened for a few seconds only every quarter of
an hour, during the action of stirring. At first, a body of flame bursts
forth every time that the lid is removed; but by degrees this ceases,
and the mixture soon agglomerates, and then softens into a paste. Though
the fire be steadily kept up, the flame becomes less and less each time
that the pot is opened; and when it ceases, the process is at an end.
The operation, with a mass of 50 pounds of charcoal and 50 pounds of
purified pearlash, lasts about 12 hours, the first time that the furnace
is kindled; but when the pot has been previously brought to a state of
ignition, it takes only 7 or 8 hours. In a well-appointed factory, the
fire should be invariably maintained at the proper pitch, and the pots
should be worked with relays of operatives.
The molten mass is now to be scooped out with an appropriate iron
shovel, having a long shank, and caused to cool in small portions, as
quickly as possible; but not by throwing it into water, as has sometimes
been prescribed; for in this way a good deal of the cyanogen is
converted into ammonia. If it be heaped up and kept hot in contact with
air, some of the ferrocyanide is also decomposed, with diminution of the
product. The crude mass is to be then put into a pan with cold water,
dissolved by the application of a moderate heat, and filtered through
cloths. The charcoal which remains upon the filter possesses the
properties of decolouring syrups, vinegars, &c., and of destroying
smells in a pre-eminent degree. It may also serve, when mixed with fresh
animal coal, for another calcining operation.
As the iron requisite for the formation of the ferrocyanide is in
general derived from the sides of the pot, this is apt to wear out into
holes, especially at its under side, where the heat is greatest. In this
event, it may be taken out of the furnace, patched up with iron-rust
cement, and re-inserted with the sound side undermost. The erosion of
the pot may be obviated in some measure by mixing iron borings or cinder
(hammerschlag) with the other materials, to the amount of one or two
hundredths of the potash.
The above lixivium is not a solution of pure ferroprussiate; it contains
not a little cyanide of potassium, which in the course of the process
had not absorbed the proper dose of iron to form a ferrocyanide; it
contains also more or less carbonate of potash, with phosphate,
sulphate, hydrogenated sulphuret, muriate, and sulpho-cyanide of the
same base, as well as phosphate of lime; substances derived partly from
the impure potash, and partly from the incinerated animal matters.
Formerly that very complex impure solution was employed directly for the
precipitation of prussian blue; but now, in all well regulated works, it
is converted by evaporation and cooling into crystallized ferroprussiate
of potash. The mother-water is again evaporated and crystallized,
whereby a somewhat inferior ferroprussiate is obtained. Before
evaporating the lye, however, it is advisable to add as much solution of
green sulphate of iron to it, as will re-dissolve the white precipitate
of cyanide of iron which first falls, and thereby convert the cyanide of
potassium, which is present in the liquor, into ferrocyanide of
potassium. The commercial prussiate of potash may be rendered chemically
pure by making its crystals effloresce in a stove, fusing them with a
gentle heat in a glass retort, dissolving the mass in water,
neutralizing any carbonate and cyanide of potash that may be present
with acetic acid, then precipitating the ferroprussiate of potash by the
addition of a sufficient quantity of alcohol, and finally crystallizing
the precipitated salt twice over in water. The sulphate of potassa may
be decomposed by acetate of baryta, and the resulting acetate of potassa
removed by alcohol.
2. _The precipitation of prussian blue._--Green sulphate of iron is
always employed by the manufacturer, on account of its cheapness, for
mixing with solution of the ferroprussiate, in forming prussian blue,
though the red sulphate, nitrate, or muriate of iron would afford a much
richer blue pigment. Whatever salt of iron be preferred, should be
carefully freed from any cupreous impregnation, as this would give the
pure blue a dirty brownish cast. The green sulphate of iron is the most
advantageous precipitant, on account of its affording protoxide, to
convert into ferrocyanide any cyanide of potassium that may happen to be
present in the uncrystallized lixivium. The carbonate of potash in that
lixivium might be saturated with sulphuric acid before adding the
solution of sulphate of iron; but it is more commonly done by adding a
certain portion of alum; in which case, alumina falls along with the
prussian blue; and though it renders it somewhat paler, yet it
proportionally increases its weight; whilst the acid of the alum
saturates the carbonate of potash, and prevents its throwing down
iron-oxide, to degrade by its brown-red tint the tone of the blue. For
every pound of pearlash used in the calcination, from two to three
pounds of alum are employed in the precipitation. When a rich blue is
wished for, the free alkali in the prussian lye may be partly saturated
with sulphuric acid, before adding the mingled solutions of copperas and
alum. One part of the sulphate of iron is generally allowed for 15 or 20
parts of dried blood, and 2 or 3 of horn-shavings or hoofs. But the
proportion will depend very much upon the manipulations; which, if
skilfully conducted, will produce more of the cyanides of iron, and
require more copperas to neutralize them. The mixed solutions of alum
and copperas should be progressively added to the lye as long as they
produce any precipitate. This is not at first a fine blue, but a
greenish gray, in consequence of the admixture of some white cyanide of
iron; it becomes gradually blue by the absorption of oxygen from the
air, which is favoured by agitation of the liquor. Whenever the colour
seems to be as beautiful as it is likely to become, the liquor is to be
run off by a spigot or cock from the bottom of the precipitation vats,
into flat cisterns, to settle. The clear supernatant fluid, which is
chiefly a solution of sulphate of potash, is then drawn off by a syphon;
more water is run on with agitation to wash it, which after settling is
again drawn off; and whenever the washings become tasteless, the
sediment is thrown upon filter sieves, and exposed to dry, first in the
air of a stove, but finally upon slabs of chalk or Paris plaster. But
for several purposes, prussian blue may be best employed in the fresh
pasty state, as it then spreads more evenly over paper and other
surfaces.
A good article is known by the following tests: it feels light in the
hand, adheres to the tongue, has a dark lively blue colour, and gives a
smooth deep trace; it should not effervesce with acids, as when
adulterated with chalk; nor become pasty with boiling water, as when
adulterated with starch. The Paris blue, prepared without alum, with a
peroxide salt of iron, displays, when rubbed, a copper-red lustre, like
indigo. Prussian blue, degraded in its colour by an admixture of free
oxide of iron, may be improved by digestion in dilute sulphuric or
muriatic acid, washing, and drying. Its relative richness in the real
ferroprussiate of iron may be estimated by the quantity of potash or
soda which a given quantity of it requires to destroy its blue colour.
Sulphuretted hydrogen passed through prussian blue diffused in water,
whitens it; while prussic acid is eliminated, sulphur is thrown down,
and the sesquicyanide of iron is converted into the single cyanide. Iron
and tin operate in the same way. When prussian blue is made with two
atoms of ferrocyanide of potassium, instead of one, it becomes soluble
in water.
For the mode of applying this pigment in dyeing, see CALICO-PRINTING.
_Sesquiferrocyanate of potash_, is prepared by passing chlorine gas
through a solution of ferrocyanide of potassium, till it becomes red,
and ceases to precipitate the peroxide salts of iron. The liquor yields,
by evaporation, prismatic crystals, of a ruby-red transparency. They are
soluble in 38 parts of water, and consist of 40·42 parts of
sesquicyanide of iron, and 59·58 of cyanide of potassium. The solution
of this salt precipitates the following metals, as stated in the
table:--
Bismuth pale yellow.
Cadmium yellow.
Cobalt dark brown red.
Copper (protoxide) red brown.
Do. (peroxide) yellow green.
Iron, protoxide salts of blue.
Manganese brown.
Mercury (protoxide) red brown.
Mercury (peroxide) yellow.
Molybdenum red brown.
Nickel yellow green.
Silver red brown.
Tin (protoxide) white.
Uranium red brown.
Zinc orange yellow.
PUMICE-STONE (_Pierre-ponce_, Fr.; _Bimstein_, Germ.); is a spongy,
vitreous-looking mineral, consisting of fibres of a silky lustre,
interlaced with each other in all directions. It floats upon water, is
harsh to the touch, having in mass a mean sp. grav. of 0·914; though
brittle, it is hard enough to scratch glass and most metals. Its colour
is usually grayish white; but it is sometimes bluish, greenish, reddish,
or brownish. It fuses without addition at the blowpipe into a white
enamel. According to Klaproth, it is composed of, silica, 77·5; alumina,
17·5; oxide of iron, 2; potassa and soda, 3; in 100 parts. The acids
have hardly any action upon pumice-stone. It is used for polishing
ivory, wood, marble, metals, glass, &c.; as also skins and parchment.
Pumice-stone is usually reckoned to be a volcanic product, resulting,
probably, from the action of fire upon obsidians. The chief localities
of this mineral are, the islands of Lipari, Ponza, Ischia, and Vulcano.
It is also found in the neighbourhood of Andernach, upon the banks of
the Rhine, in Teneriffe, Iceland, Auvergne, &c. It is sometimes so
spongy as to be of specific gravity 0·37.
PUOZZOLANA, is a volcanic gravelly product, used in making hydraulic
mortar. See CEMENTS and MORTARS.
PURPLE OF CASSIUS, _Gold purple_ (_Pourpre de Cassius_, Fr.;
_Gold-purpur_, Germ.); is a vitrifiable pigment, which stains glass and
porcelain of a beautiful red or purple hue. Its preparation has been
deemed a process of such nicety, as to be liable to fail in the most
experienced hands. The following observations will, I hope, place the
subject upon a surer footing.
The proper pigment can be obtained only by adding to a neutral muriate
of gold a mixture of the protochloride and perchloride of tin. Every
thing depends upon this intermediate state of the tin; for the
protochloride does not afford, even with a concentrated solution of
gold, either a chesnut-brown, a blue, a green, a metallic precipitate,
or one of a purple tone; the perchloride occasions no precipitate
whatever, whether the solution of gold be strong or dilute: but a
properly neutral mixture, of 1 part of crystallized protochloride of
tin, with 2 parts of crystallized perchloride, produces, with 1 part of
crystallized chloride of gold (all being in solution), a beautiful
purple-coloured precipitate. An excess of the protosalt of tin gives a
yellow, blue, or green cast; an excess of the persalt gives a red and
violet cast; an excess in the gold salt occasions, with heat (but not
otherwise), a change from the violet and chesnut-brown precipitate into
red. According to Fuchs, a solution of the sesquioxide of tin in
muriatic acid, or of the sesquichloride in water, serves the same
purpose, when dropped into a very dilute solution of gold.
Buisson prepares gold-purple in the following way. He dissolves, first,
1 gramme of the best tin in a sufficient quantity of muriatic acid,
taking care that the solution is neutral; next, 2 grammes of tin in aqua
regia, composed of 3 parts of nitric acid, and 1 part of muriatic, so
that the solution can contain no protoxide; lastly, 7 grammes of fine
gold in a mixture of 1 part of nitric acid, and 6 of muriatic, observing
to make the solution neutral. This solution of gold being diluted with
3-1/2 litres of water (about 3 quarts), the solution of the perchloride
of tin is to be added at once, and afterwards that of the protochloride,
drop by drop, till the precipitate thereby formed acquires the
wished-for tone; after which it should be edulcorated by washing, as
quickly as possible.
Frick gives the following prescription:--Let tin be set to dissolve in
very dilute aqua regia without heat, till the fluid becomes faintly
opalescent, when the metal must be taken out, and weighed. The liquor is
to be diluted largely with water, and a definite weight of a dilute
solution of gold, and dilute sulphuric acid, is to be simultaneously
stirred into the nitro-muriate of tin. The quantity of solution of gold
to be poured into the tin liquor must be such, that the gold in the one
is to the tin in the other in the ratio of 36 to 10.
Gold-purple becomes brighter when it is dry, but appears still as a
dirty-brown powder. Muriatic acid takes the tin out of the fresh-made
precipitate, and leaves the gold either in the state of metal or of a
blue powder. At a temperature between 212° and 300° Fahr., mercury
dissolves out all the gold from the ordinary purple of Cassius.
Relative to the constitution of gold-purple, two views are entertained:
according to the first; the gold is associated in the metallic state
along with the oxide of tin; according to the second, the gold exists as
a purple oxide along with the sesquioxide or peroxide of tin. Its
composition is differently reported by different chemists. The
constituents, according to--
Gold. Tin oxide.
Oberkampf, in the purple precipitate, are 39·82 60·18
violet ditto 20·58 79·42
Berzelius 30·725 69·275
Buisson 30·19 69·81
Gay Lussac 30·89 69·11
Fuchs 17·87 82·13
If to a mixture of protochloride of tin, and perchloride of iron, a
properly diluted solution of gold be added, a very beautiful purple
precipitate of Cassius will immediately fall, while the iron will be
left in the liquid in the state of a protochloride. The purple thus
prepared keeps in the air for a long time without alteration. Mercury
does not take from it the smallest trace of gold,--_Fuchs’ Journal für
Chemie_, t. xv.
PURPLE OF MOLLUSCA, is a viscid liquor, secreted by certain shell-fish,
the _Buccinum lapillus_, and others, which dyes wool, &c. of a purple
colour, and is supposed to be the substance of the Tyrian dye, so highly
prized in antient Rome for producing the imperial purple. See DYEING.
PURPURIC ACID, is an acid obtained by treating uric or lithic acid with
dilute nitric acid. It has a fine purple colour; but has hitherto been
applied to no use in the arts.
PURPURINE, is the name of a colouring principle, supposed by Robiquet
and Colin to exist in madder. Its identity is questionable.
PUTREFACTION, _and its Prevention_. The decomposition of animal bodies,
or of such plants as contain azote in their composition, which takes
place spontaneously when they are exposed to the air, under the
influence of moisture and warmth, is called putrefaction. During this
process, there is a complete transposition of the proximate principles,
the elementary substances combining in new and principally gaseous
compounds. Oxygen is absorbed from the atmosphere, and converted into
carbonic acid; one portion of the hydrogen forms water with the oxygen;
another portion forms, with the azote, the carbon, the phosphorus, and
the sulphur respectively, ammonia, carburetted, phosphuretted, and
sulphuretted hydrogen gases, which occasion the nauseous smell evolved
by putrefying bodies. There remains a friable earthy-looking residuum,
consisting of rotten mould and charcoal. Vegetables which contain no
azote, like the ligneous part of plants, suffer their corresponding
decomposition much more slowly, and with different modifications, but
they are finally converted into vegetable mould. In this process, the
juices with which the plants are filled first enter into the acetous
fermentation under the action of heat and moisture; the acid thereby
generated destroys the cohesion of the fibrous matter, and thus reduces
the solids to a pulpy state. In the progress of the decomposition, a
substance is lastly produced which resembles oxidized extractive, is
soluble in alkalis, and is sometimes called _mould_. This decomposition
of the plants which contain no azote, goes on without any offensive
smell, as none of the above-named nauseous gases are disengaged. When
vegetable matters are mixed with animal, as in the dung of cattle, this
decomposition proceeds more rapidly, because the animalized portion
serves as a ferment to the vegetable. Vegetable acids, resins, fats, and
volatilized oils, are not of themselves subject to putrefaction.
The object of the present article is to detail the principles and
processes, according to which, for various purposes in the arts, the
destruction of bodies by putrefaction may be prevented, and their
preservation in a sound state secured for a longer or a shorter time.