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The engineer's and mechanic's encyclopædia, comprehending practical illustrations of the machinery and processes employed in every description of manufacuture of the British Empire .. (Volume 2) online

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The name of separation is given to a new process for the extraction of silver
from lead, invented by Mr. H. L. Pattinson, of Newcastle-upon-Tyne, and
patented by him in the year 1833. It depends upon the very curious fact dis-
covered by Mr. Pattinson, that when lead, containing a portion of silver, is
melted in a suitable vessel, and very slowly cooled, with constant stirring, at a
certain temperature, small particles or crystals of solid lead begin to form in
the mass cf liquid lead, which, being heavier than the liquid lead, sink to the


bottom of the vessel, and may be removed by means of a perforated iron ladle.
The particles or crystals thus separated, have the appearance of a very brilliant,
coarse-grained metallic powder ; and, on examination, are found to contain a
much smaller proportion of silver than the original lead. Mr. Pattinson also
discovered the converse of this, that, when solid lead, containing silver, is
slowly and carefully heated under favourable circumstances (as in the chamber
of a reverberatory furnace, supported on bars of iron at a distance from the
brick- work on all sides) at a certain temperature, drops of melted lead begin to
separate from it, which, on examination, are found to contain more silver than
the original lead. These principles are applied in the following manner to th
extraction of silver from lead, as detailed in the specification of the patent
alluded to.

" I melt a quantity of lead in an iron pot, and, after skimming off the impu-
rities, I allow it to cool slowly, taking care to break off and mix with the fluid
mass from time to time, the parts that may congeal on the sides of the pot ;
when the temperature has become sufficiently reduced, small solid particles of
lead, resembling crystals, begin to appear on the surface, and in the mass of
melted metal ; which solid particles', or crystals, as they continue to form, sink
down to the bottom of the pan, and, in a little time, are found in considerable
quantity. I then take an iron ladle, perforated with a number of holes, with
which I remove these small particles or crystals of solid lead, allowing the fluid
portion to drain out from among them into the pan. I then place the crystals
(either in the ladle used to remove them from the pan, or in another suitable per-
forated vessel) in the chamber of a reverberatory furnace, which is made for the
purpose unusually large ; and, in this chamber, when heated to a proper tempera-
ture, I drain or melt out from among the small solid particles or crystals, a further
quantity of fluid lead, leaving the residual lead in the ladle, or other vessel,
almost entirely deprived of its silver ; after which, this residual lead is with-
drawn from the furnace, melted in another pot, and cast into pieces for sale.
The lead which drains out from among the crystals in the reverberatory fur-
nace, is, from time to time, added to the lead in the pan whence the crystals
are taken ; and in this way I proceed until the original lead submitted to the
operation is reduced to about one-third, which, containing nearly the whole of
the silver held by the original lead, is afterwards refined in the usual way."

We are informed, that in practice it is found better to confine the process to
mere crystallization of the lead, without draining it in the manner described
above. The poor lead obtained by the first crystallization is melted and crystal-
lized a second time ; and, if necessary, this poor lead is crystallized a third
time, or until it is almost entirely deprived of its silver. The number of crystalli-
zations necessary, depends upon the amount of silver held by the original lead ;
but by two or three crystallizations, lead, containing ten or twelve ounces of
silver per ton, can be separated into one part rich lead, and four or five parts
poor lead ; the latter holding no more than four to six pennyweights of silver
per ton. This process is now in extensive operation in the various lead dis-
tricts of the kingdom.

SILVERING. The art or act of covering certain substances; as metal,
wood, paper, leather, parchment, &c. with silver, so as to give them the appear-
ance of that metal. Silver leaf is laid on much in the same way as gold leaf,
for which see GILDING.

The method of silvering copper is as follows: take of tartar and common salt,
each two drachms, half a drachm of alum, fifteen or twenty grains of silver, pre-
cipitated from nitric acid by copper ; mix these well together, and with the
mixture rub the surface of the copper, and it will have the appearance of silver;
after the loose powder is brushed off, the surface may be polished with a piece
of leather. Pins are silvered by boiling them with tin-filings and tartar. The
birckles, studs, plates, &c. of harness are silvered by the following cheat) a^d
easy process : take half an ounce of silver that has been precipitated t'mm
aqua-fortis by copper; muriate of ammonia and common salt, of each two ouv.ces,
and one drachm of corrosive murinte of mercury ; triturate these together, and
form them into a paste with water After boiling the substances to be silvered


with tartar and alum, they are to be rubbed with the above preparation, then to
be made red hot, and afterwards polished. This silvering may be effected by
using the argentine precipitate above mentioned, with borax and mercury, and
causing it to adhere by fusion. To silver the dial-plates of clocks, the scales of
barometers, thermometers, &c., and all other metallic plates of similar descrip-
tion, rub upon them a mixture of muriate of silver, tartar, and sea-salt, and
afterwards wash off the saline matter with water. This silvering is not durable,
but it may be improved by heating the article, and repeating the operation once
or oftener, if it be thought necessary. The following amalgam is used for
silvering the interior surface of hollow glass globes : fuse together two parts by
weight of bismuth, one part of lead, and one of pure tin ; when this is nearly
cold, add four parts of mercury, and fuse the whole over a gentle heat. The
glass globe being thoroughly clean, introduce into it a paper funnel, which
reaches to the bottom, and pour in the liquid amalgam. At a proper tempe-
rature it will adhere to the glass, which, by being turned and shaken, will thus
have its interior surface completely covered, and any remainder of the amalgam
may be poured out when the operation is completed.

SIZE. A kind of weak glue, used in many trades ; it is made of the shreds
and parings of leather, parchment, or vellum, boiled in water, and strained.
Common size is made of leather, boiled in water till it becomes of a viscid con-
sistence. If it is wanted in painting for nicer purposes, it should be prepared
by taking any quantity of the shreds or cuttings of glovers' leather, and putting
to each pound a gallon of water ; let these be boiled for six or eight hours,
supplying water, so that it may not diminish to less than two quarts ; then
strain the hot fluid through a flannel, and afterwards evaporate it, till it is of
the consistence of a jelly when cold. The size used in burnish gilding, and
made of cuttings of parchment, is prepared much after the same manner.

Gold-she is directed to be made thus : " Of gum-anime and asphaltum,
take each one ounce; minium litharge of gold and amber, of each half
an ounce ; reduce all into a very fine powder, and add to them four ounces
of linseed oil and eight ounces of drying oil ; digest them over a gentle fire
that does not flame, so that the mixture may only simmer, but not boil, lest it
should run over and set the house on fire ; stir it constantly with a stick till all
the ingredients are dissolved and incorporated, and do not leave off stirring till
it becomes thick and ropy ; after being sufficiently boiled, let it stand till it is
almost cold, and then strain it through a coarse linen cloth, and keep it for use.
To prepare it for working, put what quantity you please in a horse-muscle shell,
adding as much oil of turpentine as will dissolve it; and making it as thin as
the bottom of your seed-lac varnish, hold it over a candle, and then strain it
through a linen rag into another shell ; add to these as much vermillion as will
make it of a darkish red ; if it is too thick for drawing, thin it with some oil of
turpentine. The chief use of this size is for laying on metals. The best gold-
size for burnishing is thus made : take fine bole, what quantity you please ;
grind it finely on a piece of marble, then scrape into it a little beef suet ; grind
all well together, after which mix in a small proportion of parchment-size, with
a double proportion of water, and it is done."

Silver-size is made of tobacco-pipe clay in fine powder, into which is scraped
some black-lead and a little Genoa soap ; all is then ground together with
parchment, as already directed.

SKATES. Small sledges fastened to the shoes or boots of a skater, by which
he is enabled to slide, and make evolutions with great ease, grace, and rapidity,
over ice. They are made of ribs of steel or iron fixed to wooden soles, and are
provided with straps and buckles to fasten them, and with small pointed pegs
to prevent them slipping from their just position. As the exercise of skating is
highly agreeable to young persons, and they can rarely be employed in this
country but for a very small portion of the year, a substitute for them was
provided a few years ago by Mr. Tyers, of Piccadilly, by which persons may
rapidly glide over any level surface, though not with equal facility as upon ice.
This contrivance is represented in the following cut, and simply consists of a
ingle iiue of little wheels, placed one before the other, instead of a solid piece


of metal, the body being carried forward by the rolling of the former instead of
the sliding of the latter; but the exercise to the body is very nearly the same,
and is a very healthy recreation.

SKEET. ^. long sort of scoop, used to wet the sides of a ship, in order to
keep them cool, and prevent them from splitting by the heat of the sun : it is
also employed in small vessels, to wet the sails, to render them more efficacious
in light breezes ; in large ships the same operation is usually effected by the

SKELETON (in its common signification), all the bones of a dead animal,
dried, cleansed, and disposed in their natural situation. The term is, however,
applied by mechanics to the principal framing or external configuration of
various things; as the skeleton of a house, which implies merely the walls,
rafters, roof, &c., as left from the hands of the bricklayer. Skeleton keys are
thin, light keys, with almost the whole substance of the bits filed away, so that
they may the more easily escipe the opposition presented by the wards in
ordinary locks.

SKIFF. A small, light boat resembling a yawl.

SLAG. Vitrified cinders.

SLAKE. The saturating of quick-lime with water, which, when effected,
is called slaked-lime, and is in the state of a powder ; chemically termed the
hydrate of lime ; containing one part water to two of lime.

* SLAKIN. A term used by smelters to express a spongy, semi-vitrified sub-
stance, which they mix with the ores of metal, to prevent their fusion : it is
the scoria, or scurn, separated from the surface of a former fusion of metals.

SLAM. The refuse of alum works, often employed as a manure in combi-
nation with sea-weed and lime.

SLAP- DASH. A provincial term, more commonly called by builders
rough-casting ; it is a composition of lime and coarse sand reduced to a liquid
form, and applied to the exterior of walls as a preservative.

SLEDGE. A kind of carriage without wheels, which is made so as to slide,
or skate as it were, over the ground.

SLEEPERS. Wooden or stone blocks, firmly imbedded in the ground, to
sustain the pressure of a railway and its load, and to steady the connexions of
the rail ; the term sleeper is also applied to many other, though somewhat
similar objects.

SLICK. The ore of any metal, but particularly gold, when it has been
pounded and prepared for further working.

SLIDING, in Mechanics, is when the same point of a body moving along
a surface, describes a line without revolving.

SLIP A place lying with a gradual descent on the banks of a river or
harbour, and rendered convenient for ship-building. See a description of an
improved one, under the article SHIP, denominated Clark's Radiating Railways.

SLOOP. A small vessel furnished with one mast, the main sail of which v
attached to a gaff above, to the mast on its foremost edge, and to a boom below
It differs from a cutter by having a fixed steering bowsprit, and a jib-stay ; the
sails are also less in proportion to the size of the vessel.

SLUICE. A frame of timber, stone, or other matter, serving to retain and
raise the water of a river, &c., and, on occasion, to let it pass. Such is the
sluice of a mill, which stops and collects the water of a rivulet, &c., to let it
fall, at length, in the greater plenty upon the mill wheel ; such also are those
used as vents, or drains, to discharge water off land. See TIDE-MILL, WATER-
WHEEL, &c.

VOL. II. 4 Q

6? 4


SMACK. A small vessel, commonly rigged as a sloop or hoy ; used chiefly
.n the coasting and fishing trade.

SMALT. A combination of glass with the oxide of cobalt, in the state of a
very fine blue powder. See ZAFFRE and COBALT.

SMELTING. The operation of fusing ores, in order to separate the metals
from the other minerals by which they may be combined.

SMOOTHING IRONS are of various kinds. The box iron is a polished
iron box, of a form nearly triangular, and provided with a sliding door, through
which is put a red-hot heater. The flat, or sad iron, which is in more general
use, is simply a heater of cast iron, with a polished flat face, and a handle
above ; this, however, is only heated to a degree that wiU not scorch the linen
'to be operated upon by it. Mr. Taylor, of Birmingham, has recently introduced
an improvement upon the latter, by which it partakes of the properties of the
former. Fig. 1 represents the lower part of the iron, hollow inside, and having a
stub or block of iron cast to the face, on which is screwed a button. Fig. 2
is the heater, with a square hole in the middle, through which the stub in Fig. I
passes. Fig. 3 is the upper part and handle of the flat iron, having also a square


Fig. 2.

Fig. 4.

hole in it ; so that when this is placed over the former two, the button passes
through both, and is made fast by giving it half a turn, by means of the heater
handle, Fig. 4. This handle also serves for taking the heater out of the fire, and
putting it to the iron, or the reverse operation, by thrusting its extremity into a
hole in the heater, made for that purpose. This invention, for which Mr. Taylor
obtained a patent, forms a cheap substitute for the box iron.

Another kind of irons, called Italian irons, are much used for the same pur-
poses. This is a hollow cylinder, with a spherical end, the other end being open
for placing in the interior a cylindrical or somewhat tapered red-hot heater; it
is mounted upon a stand, and the small articles of linen are gently pressed by
a sliding motion over the heated surface. A variety of modifications of this
apparatus may be seen in the ironmongers' shops, some double and some treble :
but there is one that was patented by a Mr. Nicholson, of Lambeth, that seems
to demand some notice here ; the use of separate heaters being therein obviated
by the burning of a lamp in a hollow cone, the apex of which supports the
irons, and communicates the heat of the flame of the lamp thereto. Muoh
ingenuity has likewise been expended in the fabrication of irons for crimping
and rolling linen between cylinders, with corrugated and plain surfaces, con-
taining, in the interior, heaters, and worked by cranks and wheels ; but as most
of our readers will probably think that we have already devoted sufficient space
to the affairs of the laundry, where this machinery may easily be seen, and its
uses demonstrated, we refer the ardent inquirer to the laundress herself for
further particulars.

SMUT, in Agriculture, a disease to which wheat is peculiarly liable, by which
it becomes contaminated with a sooty looking powder, which sometimes destroys
the whole substance of the grain. Many contrivances called smut-machines,
have been, at different times, invented to cleanse wheat, before grinding, from
this serious defect ; but they have proved only partially successful in their

SOAP. 675

operation, owing, we conceive, to the process simply consisting of violent agita-
tion, which cannot be effective in removing the hollow damaged grain from the
mass, although it may drive off much of the loose or external foulness.

SNATCH-BLOCK. A block having an opening in one of its sides, wherein
to fix the bight of a rope occasionally. This is by some termed a rouse-about
block. See BLOCKS.

SNOW. The frozen vapours of the atmosphere ; its whiteness is owing to
the small particles in which it is divided, for ice, when pounded, becomes
equally white.

SNOW. A vessel equipped with two masts, resembling the main and fore-
masts of a ship, and a third small mast just abaft the main- mast, carrying a
small sail similar to a ship's mizzen.

SNOW-PLOUGH. A simple machine operating like a plough, but upon a
larger scale, for clearing away the snow from roads. It usually consists of
boards framed together, forming an angular figure, the point of which enters
the snow, which is thrown by the boards to the sides of the road, leaving a fur-
row similar to those in a ploughed field.

SNUFF. A scented powder, the use of which is too well known. The
stalks of tobacco leaves, ground small, are the basis of all snuffs ; and the various
kinds derive their names from the whims of the manufacturers, who combine
with them those odoriferous substances by which they are distinguished,

SOAP. A name given to those bodies which are compounds of the alkalies
with fat and the fixed oils. The earths, and the other metallic oxides also, com-
bine with fat and oils, forming neutral compounds. The former have been called
earthy, and the latter metallic soaps. The soaps formed by the alkalies have
the distinguishing character of being soluble in water and alcohol. The earthy
soaps are perfectly insoluble : and since any of the earths have a stronger attrac-
tion for oil than the alkalies, the alkaline soaps are alvvaj's decomposed by the
earths. This occasions the cuvdy appearance when soap is used with water con-
taining any earthy or metalJic salt: it is from this quality that waters are said
to be hard. Soap was imperfectly known to the ancients. It is mentioned by
Pliny as made of fafc and ashes, and as an invention of the Gauls. Aretaeus and
others inform us, that the Greeks obtained their knowledge of its medical use
from the Romans. Its virtues, according to Bergius, are detergent, resolvent,
and aperient ; and its use recommended in jaundice, gout, calculous complaints,
and in obstructions of the viscera. Many have boasted of its good effects in
urinary calculous affections, especially when dissolved in lime water, by which
its efficacy is considerably increased ; for it thus becomes a powerful solvent of
mucus, which an ingenious modern author supposes to be the chief agent in the
formation of calculi ; it is, however, only in the incipient state of the disease
that these remedies promise effectual benefit, though they generally abate the
more violent symptoms where they cannot remove the cause. With Boerhaave,
soap was a general medicine ; for as he attributed most complaints to viscidity
of the fluids, lie, and most of the Boerhaavian school, prescribed it in conjunc-
tion with different resinous and other substances, in gout, rheumatism, and
various visceral complaints. Soap is also externally employed as a resolvent,
and gives name to several officinal preparations.

The soaps used in the manufactures and domestic economy, are made with the
fixed alkalies, combined with different kinds of fat and oil. These, in the manu-
facture of soap, are divided into two principal varieties, viz. hard and soft. The
alkali employed for hard soap is soda, generally obtained from the different sea
vegetables, and called by different names, according to the name of the plant,
in different countries. Most of the algae, but particularly the fucus and salsola,
afford soda by burning. The vegetables are first dried, and then burnt in pits
formed with loose stones. The earthy matter, and the soda, with some neutral
salts, fuse into a crude mass, in which state it is sold. This substance is fur-
nished in great abundance from the Highlands of Scotland, under the name of
kelp, and from Alicant, in Spain, under the name of barilla. In France it is
known by the name of varec ; this being the name of the plant from which it
is generally produced there. It is commonly, however, in this state that it

676 SOAP.

comes to the soap-maker, varying frequently in its value, and often occasioning
much uncertainty in its employment. It should be the first business, therefore,
of the manufacturer, to assay the substance from which he gets his alkali, even
before he purchases it. When the exact value of the alkali is known, it is then
to be treated as follows, to prepare it for mixing with the fat. The kelp, or
barilla, is first to be pounded, and then mixed with one-fifth its weight of quick
lime, in a large vat. These vats are generally three or four in number to each
boiler. Besides these vats for the infusion of crude alkali, each of them has a
cavity made under it. The bottom of each vat is even with the ground, the
under cavity being sunk below, and is intended to receive the liquor which runs
from a plug-hole in the upper vat, when the infusion has gone on to a certain
extent. One of these vats, with its under reservoir, is sufficient for one boiling f
but they are generally all at work, in order to give time for the solution of the
alkali from the crude mass. In charging a vat, the barilla, kelp, or potash, and
sometimes mixtures of these, are first coarsely powdered and mixed with quick-
lime, also coarsely powdered ; some water is then thrown upon these, to slake the
lime. In the side of the vat some straw is first placed about the plug-hole, to
prevent bits from passing through. The vat is now charged, and water poured
upon the materials till it stands considerably above the solid mass ; after stand-
ing several hours the plug is withdrawn, to let out the solution into the lower
reservoir. The plug is now returned, and fresh water poured upon the mate-
rials. Some, or all of the first ley is now removed into one of the other lower
reservoirs before the second infusion is drawn off. This is done that the soap-
boiler may always have at command two leys of different degrees of strength,
as, in the course of every boiling, he finds it necessary to use sometimes the
weak, and, at other times, the strong. The number of waters to be added to
the materials, depends upon the judgment of the workman, who, by his taste,
can tell when the water has dissolved the whole of the alkali. The ley being
ready to lade out of the reservoir, which is near to the boiler, the tallow or oif,
first weighed, is put in. When it is sufficiently melted, the workman begins by
adding the ley and stirring the mixture. The alkali and the oil soon begin to
unite, forming a milky fluid. As more ley is added, and the stirring continued,
the liquid thickens. This is continued generally for thirty hours, and frequently
more, till small portions of the soap, taken out from time to time, assume a
proper consistence, which the workman, by constant experience, understands.
He now adds a quantity of common salt, which has the effect of separating the
watery part from the soap, which contains a portion of neutral salts, that existed
in the crude alkali, especially when more than enough has been added. The
fire has now to be withdrawn, and the mass left to cool. The watery part will
be found at the bottom, and requires to be drawn out by a pump, which is a
fixture ou the side of the boiler. When this has been removed the fire is re-
kindled, and if the mass does not melt freely, a little water is added. As soon
as the whole becomes liquid, and is made uniform by agitation with woodeu
poles, the fire is again withdrawn, and the mass allowed to a/ssume a propeir
consistence for lading. It is laded into square moulds ; these are composed

Online LibraryLuke HebertThe engineer's and mechanic's encyclopædia, comprehending practical illustrations of the machinery and processes employed in every description of manufacuture of the British Empire .. (Volume 2) → online text (page 99 of 135)