E.

EARTHS. (_Terres_, Fr.; _Erden_, Germ.) Modern science has demonstrated

that the substances called primitive earths, and which prior to the

great electro-chemical career of Sir H. Davy, were deemed to be

elementary matter, are all compounds of certain metallic bases and

oxygen, with the exception of silica, whose base, silicon, being

analogous to boron, has led that compound to be regarded as an acid; a

title characteristic of the part it extensively performs in neutralizing

alkaline bodies, in mineral nature, and in the processes of art. Four of

the earths, when pure, possess decided alkaline properties, being more

or less soluble in water, having (at least 3 of them) an acrid alkaline

taste, changing the purple infusion of red cabbage to green, most

readily saturating the acids, and affording thereby neutro-saline

crystals. These four are _baryta_, _strontia_, _lime_ (_calcia_), and

_magnesia_. The earths proper are five in number; _alumina_, _glucina_,

_yttria_, _zirconia_, and _thorina_. These do not change the colour of

infusion of cabbage or tincture of litmus, do not readily neutralize

acidity, and are quite insoluble in water. The alkalies are soluble in

water, even when carbonated; a property which distinguishes them from

the alkaline earths. _Lithia_ must for this reason be considered to be

an alkali. See the above substances in their alphabetical places.

EAU DE COLOGNE. This preparation has long possessed great celebrity, in

consequence chiefly of the numerous virtues ascribed to it by its

venders; and is resorted to by many votaries of fashion as a panacea

against ailments of every kind. It is however nothing more than

aromatized alcohol, and as such, an agreeable companion of the toilet.

Numerous fictitious recipes have been offered for preparing _eau de

Cologne_; the following may be reckoned authentic, having been imparted

by Farina himself to a friend.

Take 60 gallons of silent brandy; sage, and thyme, each 6 drachms;

balm-mint and spearmint, each 12 ounces; calamus aromaticus, 4 drachms;

root of angelica, 2 drachms; camphor, 1 drachm; petals of roses and

violets, each 4 ounces; flowers of lavender, 2 ounces; flowers of

orange, 4 drachms; wormwood, 1 ounce; nutmegs, cloves, cassia lignea,

mace, each 4 drachms. Two oranges and two lemons, cut in pieces. Allow

the whole to macerate in the spirit during 24 hours, then distil off 40

gallons by the heat of a water bath. Add to the product:

Essence of lemons, of cedrat, of balm-mint, of lavender, each 1 ounce 4

drachms; neroli and essence of the seed of anthos, each 4 drachms;

essence of jasmin, 1 ounce; of bergamot, 12 ounces. Filter and preserve

for use.

Cadet Gassincourt has proposed to prepare _eau de Cologne_ by the

following recipe: Take alcohol at 32° B., 2 quarts; neroli, essence of

cedrat, of orange, of lemon, of bergamot, of rosemary, each 24 drops;

add 2 drachms of the seeds of lesser cardamoms, distil by the heat of a

water bath a pint and a half. When prepared as thus by simple mixture of

essences without distillation, it is never so good.

EAU DE LUCE, is a compound formed of the distilled oil of amber and

water of ammonia.

ELEMI, is a resin which exudes from incisions made during dry weather

through the bark of the _amyris elemifera_, a tree which grows in South

America and Brazil. It comes to us in yellow, tender, transparent lumps,

which readily soften by the heat of the hand. They have a strong

aromatic odour, a hot spicy taste, and contain 12-1/2 per cent. of

ethereous oil. The crystalline resin of elemi has been called _Elémine_.

It is used in making lacquer, to give toughness to the varnish.

EBULLITION. (Eng. and Fr.; _Kochen_, Germ.) When the bottom of an open

vessel containing water is exposed to heat, the lowest stratum of fluid

immediately expands, becomes therefore specifically lighter, and is

forced upwards by the superior gravity of the superincumbent colder and

heavier particles. The heat is in this way diffused through the whole

liquid mass, not by simple communication of that power from particle to

particle as in solids, called the _conduction_ of caloric, but by a

translation of the several particles from the bottom to the top, and the

top to the bottom, in alternate succession. This is denominated the

_carrying_ power of fluids, being common to both liquid and gaseous

bodies. These internal movements may be rendered very conspicuous and

instructive, by mingling a little powdered amber with water, contained

in a tall glass cylinder, standing upon a sand-bath. A column of the

heated and lighter particles will be seen ascending near the axis of the

cylinder, surrounded by a hollow column of the cooler ones descending

near the sides. That this molecular translation or loco-motion is almost

the sole mode in which fluids get heated, may be demonstrated by placing

the middle of a pretty long glass tube, nearly filled with water,

obliquely over an argand flame. The upper half of the liquid will soon

boil, but the portion under the middle will continue cool, so that a

lump of ice may remain for a considerable time at the bottom. When the

heat is rapidly applied, the liquid is thrown into agitation, in

consequence of elastic vapour being suddenly generated at the bottom of

the vessel, and being as suddenly condensed at a little distance above

it by the surrounding cold columns. These alternate expansions and

contractions of volume become more manifest as the liquid becomes

hotter, and constitute the _simmering_ vibratory sound which is the

prelude of ebullition. The whole mass being now heated to a pitch

compatible with its permanent elasticity, becomes turbulent and

explosive under the continued influence of fire, and emitting more or

less copious volumes of vapour is said to boil. The further elevation of

temperature, by the influence of caloric, becomes impossible in these

circumstances with almost all liquids, because the vapour carries off

from them as much heat in a latent state as they are capable of

receiving from the fire.

The temperature at which liquids boil in the open air varies with the

degree of atmospheric pressure, being higher as that is increased, and

lower as it is diminished. Hence boiling water is colder by some degrees

in bad weather, or in an elevated situation, with a depressed barometer,

than in fine weather, or at the bottom of a coal-pit, when the barometer

is elevated. A high column of liquid also by resisting the discharge of

the steam raises the boiling point. In _vacuo_, all liquids boil at a

temperature about 124° F. lower than under the average atmospheric

pressure. For a table of elasticities, see VAPOUR. Gay Lussac has shown

that liquids are converted into vapours more readily or with less

turbulence, when they are in contact with angular or irregular, than

with smooth surfaces; that they therefore boil at a heat 2° F. lower in

metallic than in glass vessels, probably owing to the greater polish of

the latter. For example, if into water about to boil in a glass matras,

iron filings, ground glass, or any other insoluble powder be thrown,

such a brisk ebullition will be instantly determined, as will sometimes

throw the water out of the vessel; the temperature at the same time

sinking two degrees F. It would thence appear that the power of caloric,

like that of electricity, becomes concentrated by points.

The following table exhibits the boiling heats, by Fahrenheit’s scale,

of the most important liquids:--

Ether, specific gravity 0·7365 at 48° 100°

Carburet of sulphur, 113

Alcohol, sp. grav. 0·813 Ure, 173·5

Nitric acid, 1·500 Dalton, 210

Water, 212

Saturated solution of Glauber salt, Biot, 213-1/3

do. do. Acetate of lead do. 215-2/3

do. do. Sea salt do. 224-1/3

do. do. Muriate of lime, Ure, 285

do. do. do. 1 + water 2, do. 230

do. do. do. 35·5 + do. 64·5, do. 235

do. do. do. 40·5 + do. 59·5, do. 240

Muriatic acid, sp. grav. 1·094 Dalton, 232

do. do. 1·127 do. 222

Nitric acid, do. 1·420 do. 248

do. do. 1·30 do. 236

Rectified petroleum Ure, 306

Oil of turpentine do. 316

Sulphuric acid, sp. grav. 1·848 Dalton, 600

do. do. 1·810 do. 473

do. do. 1·780 do. 435

do. do. 1·700 do. 374

do. do. 1·650 do. 350

do. do. 1·520 do. 290

do. do. 1·408 do. 260

do. do. 1·300+ do. 240

Phosphorus do. 554

Sulphur do. 570

Linseed oil do. 640

Mercury Dulong, 662

do. Crighton, 656

Saturated solution of

acetate of soda, containing 60 per cent. Griffiths, 256

do. Nitrate of soda, 60 do. 246

do. Rochelle salt, 90 do. 240

do. Nitre, 74 do. 238

do. Muriate of ammonia, 50 do. 236

do. Tartrate of potash, 68 do. 234

do. Muriate of soda, 30 do. 224

do. Sulphate of magnesia, 57·5 do. 222

do. Borax, 52·5 do. 222

do. Phosphate of soda, ? do. 222

do. Carbonate of soda, ? do. 220

do. Alum, 52 do. 220

do. Chlorate of potash, 40 do. 218

do. Sulphate of copper, 45 do. 216

EDULCORATE, (_Edulcorer_, Fr.; _Aussüssen_, Germ.) is a word introduced

by the alchemists to signify the sweetening, or rather rendering

insipid, of acrimonious pulverulent substances, by copious ablutions

with water. It means, in modern language, the washing away of all

particles soluble in water, by agitation or trituration with this fluid,

and subsequent decantation or filtration.

EFFERVESCENCE. (Eng. and Fr.; _Aufbrausen_, Germ.) When gaseous matter

is suddenly extricated with a hissing sound during a chemical mixture,

or by the application of a chemical solvent to a solid, the phenomenon,

from its resemblance to that of simmering or boiling water, is called

effervescence. The most familiar example is afforded in the solution of

sodaic powders; in which the carbonic acid gas of sesquicarbonate of

soda, is extricated by the action of citric, or tartaric acid.

EFFLORESCENCE, (Eng. and Fr.; _Verwittern_, Germ.) is the spontaneous

conversion of a solid, usually crystalline, into a powder, in

consequence either of the abstraction of the combined water by the air,

as happens to the crystals of sulphate and carbonate of soda; or by the

absorption of oxygen and the formation of a saline compound, as in the

case of alum schist, and iron pyrites. Saltpetre appears as an

efflorescence upon the ground and walls in many situations.

EDGE-TOOLS. See CUTLERY and STEEL.

EGGS, HATCHING. See INCUBATION, ARTIFICIAL.

EIDER-DOWN, is a kind of precious down, so called because it is obtained

from the EIDER-duck. These birds build their nests among precipitous

rocks, and the female lines them with fine feathers plucked from her

breast, among which she lays her five eggs. The natives of the districts

frequented by the eider-ducks let themselves down by cords among the

dangerous cliffs, to collect the down from the nests. It is used to fill

coverlets, pillows, cushions, &c.

ELAINE is the name given by Chevreul to the thin oil, which may be

expelled from tallow, and other fats, solid or fluid, by pressure either

in their natural state, or after being saponified, so as to harden the

_stearine_. It may be extracted also by digesting the fat in 7 or 8

times its weight of boiling alcohol, spec. grav. 0·798, till it

dissolves the whole. Upon cooling the solution, the stearine falls to

the bottom, while the elaine collects in a layer like olive oil, upon

the surface of the supernatant solution, reduced by evaporation to one

eighth of its bulk. If this elaine be now exposed to a cold temperature,

it will deposit its remaining stearine, and become pure. See FAT, OILS,

and STEARINE.

ELASTIC BANDS. (_Tissus Elastiques_, Fr.; _Federharz-zeige_, Germ.) The

manufacture of braces and garters, with threads of caoutchouc, either

naked or covered, seems to have originated, some time ago, in Vienna,

whence it was a few years since imported into Paris, and thence into

this country. At first the pear-shaped bottle of Indian rubber was cut

into long narrow strips by the scissors; a single operative turning off

only about 100 yards in a day, by cutting the pear in a spiral

direction. He succeeded next in separating with a pair of pincers the

several layers of which the bottle was composed. Another mode of

obtaining fine threads was to cut them out of a bottle which had been

rendered thin by inflation with a forcing pump. All these operations are

facilitated by previously steeping the caoutchouc in boiling water, in

its moderately inflated state. More recently, machines have been

successfully employed for cutting out these filaments, but for this

purpose the bottle of caoutchouc is transformed into a disc of equal

thickness in all its parts, and perfectly circular. This preliminary

operation is executed as follows: 1. the bottle, softened in hot water,

is squeezed between the two plates of a press, the neck having been

removed beforehand, as useless in this point of view; 2. the bottle is

then cut into two equal parts, and is allowed to consolidate by cooling

before subjecting it to the cutting instrument. When the bottle is

strong enough, and of variable thickness in its different points, each

half is submitted to powerful pressure in a very strong cylindrical

mould of metal, into which a metallic plunger descends, which forces the

caoutchouc to take the form of a flat cylinder with a circular base. The

mould is plunged into hot water during the compression. A stem or rod of

iron, which goes across the hollow mould and piston, retains the latter

in its place, notwithstanding the resilience of the caoutchouc, when the

mould is taken from the press. The mould being then cooled in water, the

caoutchouc is withdrawn.

The transformation of the disc of caoutchouc into fine threads is

performed by two machines; the first of which cuts it into a riband of

equal thickness in its whole extent, running in a spiral direction from

the circumference to the centre; the second subdivides this riband

lengthwise into several parallel filaments much narrower but equally

thick.

[Illustration: 366 367 368]

The following _figs._ 366, 367, 368. represent the machine for cutting

the spiral riband. The disc D, placed horizontally, turns round its

vertical axis, so as to present its periphery to the edge of a knife C,

formed like a circular blade, whose plane is perpendicular to that of

the bases of the disc. This knife turns round its centre, which is

fixed. The rotatory motion of the disc forces the knife to penetrate

further and further into its mass, and the motion of the knife itself

makes it cut the riband more easily. It is obvious, that if the disc

alone revolved, the motionless knife could act only by pressure, and

would meet with an enormous resistance. A third movement becomes

necessary. In proportion as the disc is diminished by the removal of the

spiral band, the centre of this disc must advance upon the knife, in

order that the riband may have always the same breadth. The inspection

of _fig._ 368. will make the accordance of the three motions

intelligible.

The knife C is placed upon a shaft or axis A, which carries a pulley,

round which a belt or cord runs which drives the whole machine. This

knife is six inches in diameter. In order that by being kept cool it may

cut the caoutchouc better, it is plunged at its lower part into a trough

B, full of water; a stopcock R, serves to empty this trough.

The shaft A bears a pinion p, which takes into a wheel R, placed upon

the shaft A´; upon which there is cut a worm or endless screw, V, V.

This worm bears a nut E, which advances as the screw turns, and carries

with it a tie L, which in its turn pushes the disc D, carried upon a

shoulder constantly towards the knife. This shoulder is guided by two

ears which slide in two grooves cut in the thickness of the table. The

diameter of the pinion p is about one fifth of that of the wheel R; so

that the arbour A turns five times less quickly than the arbour A; and

the fineness of the screw V contributes further to slacken the movement

of translation of the disc.

When the disc is all cut down, the shoulder, the tie, and the nut, are

brought back to their original position by lifting the nut, which is

hinged on. The disc is fixed upon the shoulder by means of sharp points,

and an upper washer. The shoulder and the washer have a very small

diameter, in order that the knife may, in cutting down the disc, advance

as near as possible to the centre.

The rotatory movement of the disc and its shoulder, is given by an

endless screw W, W, which governs a pinion _p´_, provided with 10 teeth,

and carried by the shaft A, upon which the shoulder is mounted. The

arbour A´ of this endless screw receives its motion from the first shaft

A, by means of the wheels S and S´ mounted upon these shafts, and of an

intermediate wheel S´´. This wheel, of a diameter equal to that of the

shaft A´´, is intended merely to allow this shaft to recede from the

shaft A. The diameter of the wheel of this last shaft is to that of the

two others in the ratio of 10 to 8.

[Illustration: 369]

_Second machine for sub-dividing the ribands._ _Fig._ 369.--The riband

is engaged between the circular knives, C, C, which are mounted upon the

rollers R, R; thin brass washers keep these knives apart at a distance

which may be varied, and two extreme washers mounted with screws on each

roller maintain the whole system. The axes of these rollers traverse two

uprights M, M, furnished with brasses, and with adjusting screws to

approximate them at pleasure. The axis of the lower roller carries a

wheel _r_, which takes into another smaller wheel _r´_, placed upon the

same shaft as the pulley P, which is driven by a cord. The diameter of

the wheel _r_ is three times greater than the wheel _r´_. The pulley P

is twice the size of the wheel _r´_; and its cord passes round a drum B,

which drives the rest of the machine.

The threads when brought to this state of slenderness, are put

successively into tubs filled with cold water; they are next softened in

hot water, and elongated as much as possible in the following

manner:--They are wound upon a reel turned quickly, while the operative

stretches the caoutchouc thread with his hand. In this way it is

rendered 8 or 10 times longer. The reels when thus filled are placed

during some days in a cold apartment, where the threads become firm, and

seem to change their nature.

This state of stiffness is essential for the success of the subsequent

operations. The threads are commonly covered with a sheath of silk,

cotton, or linen, by a braiding machine, and are then placed as warp in

a loom, in order to form a narrow web for braces, garters, &c. If the

gum were to exercise its elasticity during this operation, the different

threads would be lengthened and shortened in an irregular manner, so as

to form a puckered tissue. It is requisite therefore to weave the

threads in their rigid and inextensible, or at least incontractile

condition, and after the fabric is woven to restore to the threads of

caoutchouc their appropriate elasticity. This restoration is easily

effected by passing a hot smoothing iron over the tissue laid smoothly

upon a table covered with blanket stuff. See BRAIDING MACHINE.

ELECTIVE AFFINITY, (_Wahlverwandtschaft_, Germ.) denotes the order of

preference, so to speak, in which the several chemical substances

_choose_ to combine; or really, the gradation of attractive force

infused by Almighty Wisdom among the different objects of nature, which

determines perfect uniformity and identity in their compounds amidst

indefinite variety of combination. The discussion of this interesting

subject belongs to pure chemistry. See DECOMPOSITION.

ELEMENTS (Eng. and Fr.; _Grundstoffe_, Germ.) The ancients considered

fire, air, water, and earth, as simple substances, essential to the

constitution of all terrestrial beings. This hypothesis, evidently

incompatible with modern chemical discovery, may be supposed to

correspond, however, to the four states in which matter seems to exist;

namely, 1. the unconfinable powers or fluids,--caloric, light,

electricity; 2. ponderable gases, or elastic fluids; 3. liquids; 4.

solids. The three elements of the alchemists, salt, earth, mercury,

were, in _their_ sense of the word, mere phantasms.

In modern science, the term _Element_ signifies merely a substance which

has not yet been resolved by analysis into any simpler form of matter;

and it is therefore synonymous with undecompounded. This class

comprehends 54 different bodies, of which no less than 41 are metallic.

Five may be styled _Archæal_, from the intensity and universality of

their affinities for the other bodies, which they penetrate, corrode,

and apparently consume, with the phenomena of light and heat. These 5

are _chlorine_, _oxygen_, _iodine_, _bromine_, _fluorine_. Eight

elements are eminently inflammable when acted upon by any of the

preceding five, and are thereby converted into incombustible compounds.

The simple non-metallic inflammables are _hydrogen_, _azote_, _sulphur_,

_phosphorus_, _selenium_, _carbon_, _boron_, _silicon_.

The following table exhibits all the undecompounded bodies in

alphabetical order, with their prime equivalent numbers, atomic weights,

or reciprocal combining and saturating proportions, as given by

Berzelius, in reference to oxygen, reckoned 100,000.:--

_Table of undecompounded Bodies, or modern Chemical Elements._

A signifies Archæal; I, Inflammable; M, Metal.

Aluminium M. 171,167

Antimony -- 806,542

Arsenic -- 470,042

Azote I. 88,518

Barium M. 856,880

Bismuth -- 886,000

Boron I. 135,983

Bromine A. 489,150

Cadmium M. 696,970

Calcium -- 256,019

Carbon I. 76,437

Cerium M. 574,718

Chlorine A. 221,325

Chromium M. 351,819

Cobalt -- 369,991

Copper -- 395,695

Fluorine I. 116,900

Gold M. 1243,013

Hydrogen I. 62,398

Iodine A. 789,145

Iridium M. 1233,260

Iron -- 339,213

Lead -- 1294,489

Lithium -- 81,320

Magnesium -- 158,353

Manganesium -- 345,900

Mercury M. 1265,822

Molybdenum -- 598,525

Nickel -- 369,675

Osmium -- 1244,210

Oxygen A. 100,000

Palladium M. 665,840

Phosphorus I. 196,155

Platinum M. 1233,260

Rhodium -- 651,400

Selenium I. 494,582

Silicon -- 277,478

Silver M. 675,804

Strontium -- 547,285

Sulphur I. 201,165

Tantalum M. 1153,715

Tellurium -- 801,760

Thorinum -- 744,900

Tin -- 735,294

Titanium -- 303,686

Tungsten -- 1183,000

Uranium -- 2711,360

Vanadium -- 855,840

Yttrium -- 401,840

Zinc -- 403,226

Zirconium -- 420,238

ELUTRIATE. (_Soutirer_, Fr.; _Schlemmen_, Germ.) When an insoluble

pulverulent matter, like whitening or ground flints, is diffused through

a large body of water, and the mixture is allowed to settle for a

little, the larger particles will subside. If the supernatant liquid be

now carefully decanted, or run off, with a syphon, it will contain an

impalpable powder, which on repose will collect at the bottom, and may

be taken out to dry. This process is called elutriation.

EMBALMING. (_Embaument_, Fr.; _Einbalsamen_, Germ.) Is an operation in

which balsams (_baumes_, Fr.) were employed to preserve human corpses

from putrefaction; whence the name.

The ancient Egyptians had recourse to this process for preserving the

bodies of numerous families, and even of the animals which they loved or

worshipped. An excellent account of their methods is given in Mr.

Pettigrew’s work upon Mummies. Modern chemistry has made us acquainted

with many means of counteracting putrefaction more simple and

efficacious than the Egyptian system of salting, smoking, spicing, and

bituminizing. See PUTREFACTION.

EMBOSSING WOOD. (_Bossage_, Fr.; _Erhabenes Arbeit_, Germ.) Raised

figures upon wood, such as are employed in picture frames and other

articles of ornamental cabinet work, are usually produced by means of

carving, or by casting the pattern in plaster of Paris, or other

composition, and cementing, or otherwise fixing it on the surface of the

wood. The former mode is expensive; the latter is inapplicable on many

occasions. The invention of Mr. Streaker may be used either by itself,

or in aid of carving; and depends on the fact, that if a depression be

made by a blunt instrument on the surface of the wood, such depressed

part will again rise to its original level by subsequent immersion in

the water.

The wood to be ornamented having been first worked out to its proposed

shape, is in a state to receive the drawing of the pattern; this being

put on, a blunt steel tool, or burnisher, or die, is to be applied

successively to all those parts of the pattern intended to be in relief,

and, at the same time, is to be driven very cautiously, without breaking

the grain of the wood, till the depth of the depression is equal to the

intended prominence of the figures. The ground is then to be reduced by

planing or filing to the level of the depressed part; after which, the

piece of wood being placed in water, either hot or cold, the part

previously depressed will rise to its former height, and will then form

an embossed pattern, which may be finished by the usual operations of

carving.

For this invention the Society of Arts voted to Mr. Streaker their

silver Isis medal, and ten guineas.

EMBOSSING CLOTH. Mr. Thomas Greig, of Rose Bank, near Bury, patented an

invention, in November 1835, which consists in an ingenious construction

of machinery for both embossing and printing silk, cotton, woollen

cloth, paper, and other fabrics, in one or more colours, at one

operation.

[Illustration: 370 370*]

_Figs._ 370, 370* represent three distinct printing cylinders of copper,

or other suitable material, A, B, C, with their necessary appendages for

printing three different colours upon the fabric as it passes through

the machine: either of these cylinders A, B, or C, may be employed as an

embossing cylinder, without performing the printing process, or may be

made to effect both operations at the same time.

The fabric or goods to be operated upon being first wound tightly upon a

roller, that roller is to be mounted upon an axle or pivot, bearing in

arms or brackets at the back of the machine, as shown at D. From this

roller the fabric _a a a a_ is conducted between tension rails, and

passed under the bed cylinder or paper bowl E, and from thence proceeds

over a carrier roller F, and over steam boxes not shown in the drawing,

or it may be conducted into a hot room, for the purpose of drying the

colours.

The cylinders A, B, and C, having either engraved or raised surfaces,

are connected to feeding rollers _b b b_, revolving in the ink or

coloured troughs _c c c_; or endless felts, called sieves, may be

employed, as in ordinary printing machines, for supplying the colour,

when the device on the surface of the cylinders is raised: these

cylinders may be furnished with doctors or scrapers when required, or

the same may be applied to the endless felts.

The blocks have adjustable screws _g g_, for the purpose of bringing the

cylinders up against the paper bowl, with any required degree of

pressure: the cylinder B is supported by its gudgeons running in blocks,

which blocks slide in the lower parts of the side frames, and are

connected to perpendicular rods _i_, having adjustable screw nuts.

The lower parts of these rods bear upon weighted levers _k k_, extending

in front of the machine; and by increasing the weights _l l_, any degree

of upward pressure may be given to the cylinder B.

The colour boxes or troughs _c c c_, carrying the feeding rollers _b b

b_, are fixed on boards which slide in grooves in the side frames, and

the rollers are adjusted and brought into contact with the surface of

the printing cylinders by screws.

If a back cloth should be required to be introduced between the

cylindrical bed or paper bowl E, and the fabric _a a a_, as the ordinary

felt or blanket, it may, for printing and embossing cotton, silk, or

paper, be of linen or cotton; but if woollen goods are to be operated

upon, a cap of felt, or some such material, must be bound round the

paper bowl, and the felt or blanket must be used for the back cloth,

which is to be conducted over the rollers H and I.

For the purpose of embossing the fabric, either of the rollers A, B, or

C, may be employed, observing that the surface of the roller must be

cut, so as to leave the pattern or device elevated for embossing

velvets, plain cloths, and papers; but for woollens the device must be

excavated, that is, cut in recess.

The pattern of the embossing cylinder will, by the operation, be

partially marked through the fabric on to the surface of the paper bowl

E; to obliterate which marks from the surface of the bowl, as it

revolves, the iron cylinder roller G is employed; but as in the

embossing of the same patterns on paper, a counter roller is required to

produce the pattern perfectly, the iron roller is in that case dispensed

with, the impression given to the paper bowl being required to be

retained on its surface until the operation is finished.

In this case the relative circumferences of the embossing cylinder, and

of the paper bowl, must be exactly proportioned to each other; that is,

the circumference of the bowl must be equal, exactly, to a given number

of circumferences of the embossing cylinder, very accurately measured,

in order to preserve a perfect register or coincidence, as they continue

revolving between the pattern on the surface of the embossing cylinder,

and that indented into the surface of the paper bowl.

The axle of the paper bowl E, turns in brasses fitted into slots in the

side frames, and it may be raised by hand from its bearings when

required, by a lever _k_, extending in front. This lever is affixed to

the end of a horizontal shaft L, L, crossing the machine seen in the

figures, at the back of which shaft there are two segment levers P, P,

to which bent rods Q, Q, are attached, having hooks at their lower ends,

passed under the axle of the bowl. At the reverse end of the shaft L, a

ratchet-wheel _r_, is affixed, and a pall or click mounted on the side

of the frame takes into the teeth of the wheel _r_, and thereby holds up

the paper bowl when required.

When the iron roller G, is to be brought into operation, the vertical

screws _t_, _t_, mounted in the upper parts of the side frames, are

turned, in order to bring down the brasses N, which carry the axle of

that roller and slide in slots in the side frames.

The cylinders A, B, and C, are represented hollow, and may be kept at

any desired temperature during the operation of printing, by introducing

steam into them; and under the colour boxes _c_, _c_, _c_, hollow

chambers are also made for the same purpose. The degree of temperature

required to be given to these must depend upon the nature of the

colouring material, and of the goods operated upon. For the purpose of

conducting steam to these hollow cylinders and colour boxes, pipes, as

shown at _v_, _v_, _v_, are attached, which lead from a steam boiler.

But when either of these cylinders is employed for embossing alone, or

for embossing and printing at the same time, and particularly for some

kinds of goods where a higher temperature may be required, a red-hot

heater is then introduced into the hollow cylinder in place of steam.

If the cylinder B, is employed as the embossing cylinder, and it is not

intended to print the fabric by that cylinder simultaneously with the

operation of embossing, the feeding rolling _b_, must be removed, and

also the colour box _c_, belonging to that cylinder; and the cylinders

A, and C, are to be employed for printing the fabric, the one applying

the colour before the embossing is effected, the other after it. It is

however to be remarked, that if A, and C, are to print colours on the

fabric, and B, to emboss it, in that case it is preferred, where the

pattern would allow it. A and C, are wooden rollers having the pattern

upon their surfaces, and not metal, as the embossing cylinders must of

necessity be.

It will be perceived that this machine will print one, two, or three

colours at the same time, and that the operation of embossing may be

performed simultaneously with the printing, by either of the cylinders

A, B, or C, or the operation may be performed consecutively by the

cylinders, either preceding or succeeding each other.

The situations of the doctors, when required to be used for removing any

superfluous colour from the surface of the printing cylinder, are shown

at _d_, _d_, _d_; those for removing any lint which may attach itself,

at _e_, _e_, _e_. They are kept in their bearings by weighted levers and

screws, and receive a slight lateral movement to and fro, by means of

the vertical rod _m_, which is connected at top to an eccentric, on the

end of the axle of the roller H, and at its lower end to a horizontal

rod mounted at the side of the frame; to this horizontal rod, arms are

attached, which are connected to the respective doctors; and thus by the

rotation of the eccentric, the doctors are made to slide laterally.

When the cylinders A, B, or C, are employed for embossing only, those

doctors will not be required. The driving power is communicated to the

machine from any first mover through the agency of the toothed geer,

which gives rotatory motion to the cylinder B, and from thence to the

other cylinders A, and C, by toothed geer shown in _fig._ 370.

EMBROIDERING MACHINE. (_Machine à broder_, Fr.; _Steckmaschine_, Germ.)

This art has been till of late merely a handicraft employment,

cultivated on account of its elegance by ladies of rank. But a few years

ago M. Heilmann of Mulhausen invented a machine of a most ingenious

kind, which enables a female to embroider any design with 80 or 140

needles as accurately and expeditiously as she formerly could do with

one. A brief account of this remarkable invention will therefore be

acceptable to many readers. It was displayed at the national exposition

of the products of industry in Paris for 1834, and was unquestionably

the object which stood highest in public esteem; for whether at rest or

in motion, it was always surrounded with a crowd of curious visiters,

admiring the figures which it had formed, or inspecting its movements

and investigating its mechanism. 130 needles were occupied in copying

the same pattern with perfect regularity, all set in motion by one

person.

Several of these machines are now mounted in France, Germany, and

Switzerland. I have seen one factory in Manchester, where a great many

of them are doing beautiful work.

The price of a machine having 130 needles, and of consequence 260

pincers or fingers and thumbs to lay hold of them, is 5000 francs, or

200_l._ sterling; and it is estimated to do daily the work of 15 expert

hand embroiderers, employed upon the ordinary frame. It requires merely

the labour of one grown-up person, and two assistant children. The

operative must be well taught to use the machine, for he has many things

to attend to: with the one hand he traces out, or rather follows the

design with the point of the pantograph; with the other he turns a

handle to plant and pull all the needles, which are seized by pincers

and moved along by carriages, approaching to and receding from the web,

rolling all the time along an iron railway; lastly, by means of two

pedals, upon which he presses alternately with the one foot and the

other, he opens the 130 pincers of the first carriage, which ought to

give up the needles after planting them in the stuff, and he shuts with

the same pressure the 130 pincers of the second carriage, which is to

receive the needles, to draw them from the other side, and to bring them

back again. The children have nothing else to do than to change the

needles when all their threads are used, and to see that no needle

misses its pincers.

This machine deserves particular attention, because it is no less

remarkable for the happy arrangement of its parts, than for the effects

which it produces. It may be described under four heads: 1. the

structure of the frame; 2. the disposition of the web; 3. the

arrangement of the carriages; and 4. the construction of the pincers.

1. The structure of the frame. It is composed of cast-iron, and is very

massive. _Fig._ 371. exhibits a front elevation of it. The length of the

machine depends upon the number of pincers to be worked. The model at

the exposition had 260 pincers, and was 2 metres and a half (about 100

inches or 8 feet 4 inches English) long. The figure here given has been

shortened considerably, but the other proportions are not disturbed. The

breadth of the frame ought to be the same for every machine, whether it

be long or short, for it is the breadth which determines the length of

the thread to be put into the needles, and there is an advantage in

giving it the full breadth of the model machine, fully 100 inches, so

that the needles may carry a thread at least 40 inches long.

_Disposition of the piece to be embroidered._--We have already stated

that the pincers which hold the needles always present themselves

opposite to the same point, and that in consequence they would

continually pass backwards and forwards through the same hole, but the

piece is displaced with sufficient precision to bring opposite the tips

progressively of the needles, every point upon which they are to work a

design, such as a flower.

[Illustration: 371]

The piece is strained perpendicularly upon a large rectangular frame,

whose four sides are visible in _fig._ 371.; namely the two vertical

sides at F F, and the two horizontal sides, the upper and lower at F´

F´´. We see also in the figure two long wooden rollers G and G, whose

ends, mounted with iron studs, are supported upon the sides F of the

frame, so as to turn freely. These form a system of beams upon which the

piece destined to receive the embroidery, is wound and kept vertically

stretched to a proper degree, for each of these beams bears upon its end

a small ratchet wheel _g_, _g_; the teeth of one of them being inclined

in the opposite direction to those of the other. Besides this system of

lower beams, there is another of two upper beams, which is however but

imperfectly seen in the figure, on account of the interference of other

parts in this view of the machine. One of these systems presents the web

to the inferior needles, and the other to the upper needles. As the two

beams are not in the same vertical plane, the plane of the web would be

presented obliquely to the needles were it not for a straight bar of

iron, round whose edge the cloth passes, and which renders it vertical.

The piece is kept in tension crosswise by small brass templets, to which

the strings _g´´_ are attached, and by which it is pulled towards the

sides of the frame F. It remains to shew by what ingenious means this

frame may be shifted in every possible direction. M. Heilmann has

employed for this purpose the pantograph which draughtsmen use for

reducing or enlarging their plans in determinate proportions.

_b b´ f b´´_ (_fig._ 371.) represents a parallelogram of which the four

angles _b_, _b´_, _f_, _b´´_, are jointed in such a way that they may

become very acute or very obtuse at pleasure, while the sides of course

continue of the same length; the sides _b_, _b´_ and _b_, _b´´_ are

prolonged, the one to the point _d_, and the other to the point _c_, and

these points _c_ and _d_, are chosen under the condition that in one of

the positions of the parallelogram, the line _c d_ which joins them

passes through the point _f_; this condition may be fulfilled in an

infinite number of manners, since the position of the parallelogram

remaining the same, we see that if we wished to shift the point _d_

further from the point _b´_, it would be sufficient to bring the point c

near enough to _b´´_, or _vice versa_; but when we have once fixed upon

the distance _b´ d_, it is evident that the distance _b´´ c_ is its

necessary consequence. Now the principle upon which the construction of

the pantograph rests is this; it is sufficient that the three points

_d_, _f_, and _c_ be in a straight line, in one only of the positions of

the parallelogram, in order that they shall remain always in a straight

line in every position which can possibly be given to it.

We see in the figure that the side _b c_, has a handle B´´ with which

the workman puts the machine in action. To obtain more precision and

solidity in work, the sides of the pantograph are joined, so that the

middle of their thickness lies exactly in the vertical plane of the

piece of goods, and that the axes of the joints are truly perpendicular

to this plane, in which consequently all the displacements are effected.

We arrive at this result by making fast to the superior great cross bar

D´´ an elbow piece _d_², having a suitable projection, and to which is

adapted in its turn the piece _d´_, which receives in a socket the

extremity of the side _b_, _d_; this piece _d´_ is made fast to _d´´_ by

a bolt, but it carries an oblong hole, and before screwing up the nut,

we make the piece advance or recede, till the fulcrum point comes

exactly into the plane of the web. This condition being fulfilled, we

have merely to attach the frame to the angle _f_ of the parallelogram,

which is done by means of the piece F´´.

It is now obvious that if the embroiderer takes the handle B´´ in his

hand and makes the pantograph move in any direction whatever, the point

_f_ will describe a figure similar to the figure described by the point

_c_, and six times smaller, but the point _f_ cannot move without the

frame, and whatever is upon it moving also. Thus, in the movement of the

pantograph, every point of the web describes a figure equal to that

described by the point _f_, and consequently similar to that described

by the point _c_, but six times smaller; the embroidered object being

produced upon the cloth in the position of that of the pattern. It is

sufficient therefore to give the embroidering operative who holds the

handle B´´, a design six times greater than that to be executed by the

machine, and to afford him at the same time a sure and easy means of

tracing over with the point _c_, all the outlines of the pattern. For

this purpose he adapts to _c_, perpendicularly to the plane of the

parallelogram, a small style terminated by a point C´, and he fixes the

pattern upon a vertical tablet E, parallel to the plane of the stuff and

the parallelogram, and distant from it only by the length of the style

_c_ C´´; this tablet is carried by the iron rod _c´_, which is secured

to a cast iron foot E´, serving also for other purposes, as we shall

presently see. The frame loaded with its beams and its cloth forms a

pretty heavy mass, and as it must not swerve from its plane, it needs to

be lightened in order that the operative may cause the point of the

pantograph to pass along the tablet without straining or uncertainty in

its movements. M. Heilmann has accomplished these objects in the

following way. A cord _e_ attached to the side _b c_ of the pantograph

passes over a return pulley, and carries at its extremity, a weight

which may be graduated at pleasure; this weight equipoises the

pantograph, and tends slightly to raise the frame. The lower side of the

frame carries two rods H and H, each attached by two arms _h h_, a

little bent to the left; both of these are engaged in the grooves of a

pulley. Through this mechanism a pressure can be exercised upon the

frame from below upwards, which may be regulated at pleasure, and

without preventing the frame from moving in all directions, it hinders

it from deviating from the primitive plane to which the pantograph was

adjusted. The length of the rods H ought to be equal to the amount of

the lateral movement of the frame. Two guides _i i_ carried by two legs

of cast iron, present vertical slits in which the lower part of the

frame F´ is engaged.

_Disposition of the carriages._--The two carriages, which are similar,

are placed the one to the right, and the other to the left of the frame.

The carriage itself is composed merely of a long hollow cylinder of cast

iron L, carrying at either end a system of two grooved castors or

pulleys L´, which roll upon the horizontal rails K; the pulleys are

mounted upon a forked piece _l´_, with two ends to receive the axes of

the pulleys, and the piece _l´_ is itself bolted to a projecting ear _l_

cast upon the cylinder.

This assemblage constitutes properly speaking the carriage, resting in a

perfectly stable equilibrium upon the rails K, upon which it may be most

easily moved backwards and forwards, carrying its train of needles to be

passed or drawn through the cloth.

M. Heilmann has contrived a mechanism by which the operative without

budging from his place may conduct the carriages, and regulate as he

pleases the extent of their course, as well as the rapidity of their

movements. By turning the axes M´´ in the one direction or the other,

the carriage may be made to approach to, or recede from the web.

When one of the carriages has advanced to prick the needles into the

stuff, the other is there to receive them; it lays hold of them with its

pincers, pulls them through, performs its course by withdrawing to

stretch the thread, and close the stitch, then it goes back with the

needles to make its pricks in return. During these movements the first

carriage remains at its post waiting the return of the second. Thus the

two chariots make in succession an advance and a return, but they never

move together.

To effect these movements M. Heilmann has attached to the piece O´ made

fast to the two uprights A C and A D of the frame, a bent lever _n o n´

n´´_ movable round the point _o_; the bend _n´_ carries a toothed wheel

O´, and the extremity _n´´_ a toothed wheel O´´; the four wheels M M´ O´

and O´´ have the same number of teeth and the same diameter; the two

wheels O´ and O´´ are fixed in reference to each other, so that it is

sufficient to turn the handle N to make the wheel O´´ revolve, and

consequently the wheel O´; when the lever _n o_ is vertical, the wheel

O´ touches neither the wheel M nor the wheel M´; but if it be inclined

to the one side or the other, it brings the wheel O´ alternately into

geer with the wheel M or the wheel M´. As the operative has his two

hands occupied, the one with the pantograph and the other with the

handle of impulsion, he has merely his feet for acting upon the lever _n

o_, and as he has many other things to do, M. Heilmann has adapted

before him a system of two pedals, by which he executes with his feet a

series of operations no less delicate than those which he executes with

his hands.

The pedals P are moveable round the axis _p_, and carry cords _p´_ wound

in an opposite direction upon the pulleys P´; these pulleys are fixed

upon a moveable shaft P´´, supported upon one side by the prop E´, and

on the other in a piece K´ attached to the two great uprights of the

frame. In depressing the pedal P (now raised in the figure), the upper

part of the shaft P´´ will turn from the left to the right, and the

lever _n o_ will become inclined so as to carry the wheel O´ upon the

wheel M´, but at the same time the pedal which is now depressed will be

raised, because its cord will be forced to wind itself upon its pulley,

as much as the other cord has unwound itself; and thus the apparatus

will be ready to act in the opposite direction, when wanted.

_Disposition of the pincers._--The shaft L´ carries, at regular

intervals of a semi-diameter, the appendages _q q_ cast upon it, upon

which are fixed, by two bolts, the curved branches Q destined to bear

the whole mechanism of the pincers. When the pincers are opened by their

appropriate leverage, and the half of the needle, which is pointed at

each end, with the eye in the middle, enters the opening of its plate,

it gets lodged in an angular groove, which is less deep than the needle

is thick, so that when the pincers are closed, the upper jaw presses it

into the groove. In this way the needle is firmly held, although touched

in only three points of its circumference.

Suppose, now, that all the pincers are mounted and adjusted at their

proper distances upon their prismatic bar, forming the upper range of

the right carriage. For opening all the pincers there is a long plate of

iron, U, capable of turning upon its axis, and which extends from the

one end of the carriage to the other. This axis is carried by a kind of

forks which are bolted to the extremity of the branches Q. By turning

that axis the workman can open the pincers at pleasure, and they are

again closed by springs. This movement is performed by his feet acting

upon the pedals.

The threads get stretched in proportion as the carriage is run out, but

as this tension has no elastic play, inconveniences might ensue which

are prevented by adapting to the carriage a mechanism by means of which

all the threads are pressed at the same time by a weight susceptible of

graduation. A little beneath the prismatic bar, which carries the

pincers, we see in the figure, a shaft Y, going from one end of the

carriage to the other, and even a little beyond it; this shaft is

carried by pieces _y_ which are fixed to the arms Q, and in which it can

turn. At its left end it carries two small bars _y´_ and _w´_, and at

its right a single bar _y´_, and a counterweight (not visible in this

view); the ends of the two bars _y´_ are joined by an iron wire somewhat

stout and perfectly straight. When the carriage approaches the web, and

before the iron wire can touch it, the little bar _w_ presses against a

pin _w´_, which rests upon it, and tends to raise it more and more. In

what has preceded we have kept in view only the upper range of pincers

and needles, but there is an inferior range quite similar, as the figure

shows, at the lower ends of the arms Q. In conclusion, it should be

stated, that the operative does not follow slidingly with the pantograph

the trace of the design which is upon the tablet or the picture, but he

must stop the point of the style upon the point of the pattern into

which the needle should enter, then remove it, and put it down again

upon the point by which the needle ought to re-enter in coming from the

other side of the piece, and so on in succession. To facilitate this

kind of reading off, the pattern upon the tablet is composed of right

lines terminated by the points for the entrance and return of the

needle, so that the operative (usually a child) has continually under

her eyes the series of broken lines which must be followed by the

pantograph; if she happens to quit this path an instant, without having

left a mark of the point at which she had arrived, she is under the

necessity of looking at the piece to see what has been already

embroidered, and to find by this comparison the point at which she must

resume her work, so as not to leave a blank, or to repeat the same

stitch.

_Explanation of figure:_

A, lower cross bars, which unite the legs of the two ends of the frame.

_a_, the six feet of the front end of the frame.

_a´_, the six feet of the posterior end of the frame.

_a´´_, curved pieces which unite the cross bars A´´ to the uprights.

B´´, handle of the pantograph.

_b b´ b´´_, three of the angles of the pantograph.

_c_, point of the side _b b´´_ on which the point is fixed.

C´´, point of the pantograph.

D´´, cross bar in form of a gutter, which unites the upper parts of the

frame.

_d_, fixed point, round which the pantograph turns.

E, tablet upon which the pattern to be embroidered is put.

E´, support of that tablet.

_e_, cord attached at one end to the side _b c_ of the pantograph

passing over a guide pulley, and carrying a weight at the other end.

_e´_, iron rod by which the tablet E is joined to its support E´.

F F, uprights of the cloth-carrying frame.

F´ F´, horizontal sides of the same frame.

G, four roll beams.

G´´, the piece of cloth.

_g´´_, the strings, which serve to stretch the cloth laterally.

EMERALD. (_Emeraude_, Fr.; _Smaragd_, Germ.) Is a precious stone of a

beautiful green colour; valued next to diamond, and in the same rank as

oriental ruby and sapphire. It occurs in prisms with a regular hexagonal

base; sp. grav. 2·7; scratches quartz with difficulty; is scratched by

topaz; fusible at the blowpipe into a frothy bead; the precipitate

afforded by ammonia, from its solution, is soluble, in a great measure,

in carbonate of ammonia. Its analysis is given very variously by

different chemists. It contains about 14 per cent. of glucina, which is

its characteristic constituent; along with 68 of silica, 16 of alumina,

a very little lime and iron. The beautiful emerald of Peru is found in a

clay schist mixed with some calcareous matter. A stone of 4 grains

weight is said to be worth from 4_l._ to 5_l._; one of 8 grains, 10_l._;

one of 15 grains, being fine, is worth 60_l._; one of 24 grains fetched,

at the sale of M. de Drée’s cabinet, 2400 francs, or nearly 100_l._

The beryl is analogous in composition to the emerald, and is employed

(when of the common opaque kind, found near Limoges,) by chemists, for

procuring the earth glucina.

EMERY. This mineral was long regarded as an ore of iron; and was called

by Haüy _fer oxidé quartzifère_. It is very abundant in the island of

Naxos, at cape _Emeri_, whence it is imported in large quantities. It

occurs also in the islands of Jersey and Guernsey, at Almaden, in

Poland, Saxony, Sweden, Persia, &c. Its colour varies from red brown to

dark brown; its specific gravity is about 4·000; it is so hard as to

scratch quartz and many precious stones. By Mr. Tennant’s analysis, it

consists of alumina, 80; silica, 3; iron, 4. Another inferior kind

yielded 32 of iron, and only 50 of alumina.

The alumina of emery is believed to be aggregated to the same degree of

hardness as in corundum or adamantine spar; which is one of the hardest

minerals known. Emery is extensively employed for grinding metals,

glass, &c.; for which purpose it is reduced to powders of different

degrees of fineness by grinding and elutriation. When so treated, it is

sold under the name of flour of emery, or washed emery.

EMPYREUMA, means the offensive smell produced by fire applied to organic

matters, chiefly vegetable, in close vessels. Thus, empyreumatic vinegar

is obtained by distilling wood at a red heat, and empyreumatic oil from

many animal substances in the same way.

ENAMELS, (_Emaux_, Fr.; _Schmelzglas_, Germ.) are varieties of glass,

generally opaque and coloured, always formed by the combination of

different metallic oxides, to which certain fixed fusible salts are

added, such as the borates, fluates, and phosphates.

The simplest enamel, and the one which serves as a basis to most of the

others, is obtained by calcining first of all a mixture of lead and tin,

in proportions varying from 15 to 50 parts of tin for 100 of lead. The

middle term appears to be the most suitable for the greater number of

enamels; and this alloy has such an affinity for oxygen, that it may be

calcined with the greatest ease in a flat cast-iron pot, and at a

temperature not above a cherry red, provided the dose of tin is not too

great. The oxide is drawn off to the sides of the melted metal according

as it is generated, new pieces of the alloy being thrown in from time to

time, till enough of the powder be obtained. Great care ought to be

taken that no metallic particles be left in the oxide, and that the

calcining heat be as low as is barely sufficient; for a strong fire

frits the powder, and obstructs its subsequent comminution. The powder

when cold is ground in a proper mill, levigated with water, and

elutriated, as will be described under _Red lead_. In this state of

fineness and purity, it is called _calcine_, or flux, and it is mixed

with siliceous sand and some alkaline matter or sea-salt. The most

ordinary proportions are, 4 of sand, 1 of sea-salt, and 4 of calcine.

Chaptal states, that he has obtained a very fine product from 100 parts

of calcine, made by calcining equal parts of lead and tin, 100 parts of

ground flint, and 200 parts of pure subcarbonate of potash. In either

case, the mixture is put into a crucible, or laid simply on a stratum of

sand, quicklime spontaneously slacked, or wood-ashes, placed under a

pottery or porcelain kiln. This mass undergoes a semi-vitrification; or

even a complete fusion on its surface. It is this kind of frit which

serves as a radical to almost every enamel; and by varying the

proportions of the ingredient, more fusible, more opaque, or whiter

enamels are obtained. The first of these qualities depends on the

quantity of sand or flux, and the other two on that of the tin.

The sea-salt employed as a flux may be replaced either by salt of

tartar, by pure potash, or by soda; but each of these fluxes gives

peculiar qualities to the enamel.

Most authors who have written on the preparation of enamels, insist a

great deal on the necessity of selecting carefully the particular sand

that should enter into the composition of the frit, and they even affirm

that the purest is not the most suitable. Clouet states, in the 34th

volume of the _Annales de Chimie_, that the sand ought to contain at

least 1 part of talc for 3 of siliceous matter, otherwise the enamel

obtained is never very glassy, and that some wrinkled spots from

imperfect fusion are seen on its surface; and yet we find prescribed in

some old treatises, to make use of ground flints, fritted by means of

salt of tartar or some other flux. It would thence appear that the

presence of talc is of no use towards the fusibility of the silica, and

that its absence may be supplied by increasing the dose of the flux. In

all cases, however, we ought to beware of metallic oxides in the sand,

particularly those of iron and manganese, which most frequently occur,

and always injure the whiteness of the frit.

The ancients carried the art of enamelling to a very high perfection,

and we occasionally find beautiful specimens of their work, of which we

know neither the composition, nor the manner of applying it. Then, as at

present, each artist made a mystery of the means that succeeded best

with him, and thus a multitude of curious processes have been buried

with their authors. Another cause contributes powerfully to this sort of

declension in the arts. Among the vast number of recipes which have been

published for the formation of enamels, there are several in which

substances are mentioned that can no longer be procured, whether owing

to a change of denomination, or because the substances cannot now be

found in commerce, or because they are not of the same nature as of old.

Hence, in many cases, we find it impossible to obtain satisfactory

results. What we have now said renders it desirable that the operations

should be resumed anew, or upon new bases, and availing ourselves of all

the known chemical facts, we should employ in the production of enamels,

raw materials of the purest kind.

The Venetians are still in possession of the best enamel processes, and

they supply the French and other nations with the best kinds of enamel,

of every coloured shade.

Enamels are distinguished into transparent and opaque; in the former all

the elements have experienced an equal degree of liquefaction, and are

thus run into crystal glass, whilst in the others, some of their

elements have resisted the action of heat more, so that their particles

retain sufficient aggregation to prevent the transmission of light. This

effect is produced, particularly by the oxide of tin, as we shall

perceive in treating of white enamel.

The frits for enamels that are to be applied to metallic surfaces

require greater fusibility, and should therefore contain more flux; and

the sand used for these should be calcined beforehand with one-fourth

its weight of sea-salt; sometimes, indeed, metallic fluxes are added, as

minium or litharge. For some metallic colours, the oxides of lead are

very injurious, and in this case recourse must be had to other fluxes.

Clouet states that he has derived advantage from the following mixtures,

as bases for purples, blues, and some other delicate colours:--

Three parts of siliceous sand, one of chalk, and three of calcined

borax; or, three of glass (of broken crystal goblets), one of calcined

borax, one-fourth of a part of nitre, and one part of well washed

diaphoretic antimony. These compositions afford a very white enamel,

which accords perfectly well with blue.

It is obvious that the composition of this primary matter may be greatly

varied; but we should never lose sight of the essential quality of a

good enamel; which is, to acquire, at a moderate heat, sufficient

fluidity, to take a shining surface, without running too thin. It is not

complete fusion which is wanted; but a pasty state, of such a degree as

may give it, after cooling, the aspect of having suffered complete

liquefaction.

_Dead-white Enamel._--This requires greater nicety in the choice of its

materials than any other enamel, as it must be free from every species

of tint, and be perfectly white; hence the frit employed in this case

should be itself composed of perfectly pure ingredients. But a frit

should not be rejected hastily because it may be somewhat discoloured,

since this may depend on two causes; either on some metallic oxides, or

on fuliginous particles proceeding from vegetable or animal substances.

Now the latter impurities may be easily removed by means of a small

quantity of peroxide of manganese, which has the property of readily

parting with a portion of its oxygen, and of thus facilitating the

combustion, that is to say, the destruction of the colouring

carbonaceous matter. Manganese indeed possesses a colouring power itself

on glass, but only in its highest state of oxidizement, and when reduced

to the lower state, as is done by incombustible matters, it no longer

communicates colour to the enamel combinations. Hence the proportion of

manganese should never exceed what is just; for the surplus would cause

colour. Sometimes, indeed, it becomes necessary to give a little

manganese-colour, in order to obtain a more agreeable shade of white; as

a little azure blue is added to linens, to brighten or counteract the

dulness of their yellow tint.

A white enamel may be conveniently prepared also with a _calcine_

composed of two parts of tin and one of lead calcined together; of this

combined oxide, one part is melted with two parts of fine crystal and a

very little manganese, all previously ground together. When the fusion

is complete, the vitreous matter is to be poured into clear water, and

the frit is then dried, and melted anew. The pouring into water and

fusion are sometimes repeated 4 times, in order to secure a very uniform

combination. The crucible must be carefully screened from smoke and

flame. The smallest portions of oxide of iron or copper admitted into

this enamel will destroy its value.

Some practitioners recommend the use of washed diaphoretic antimony

(antimoniate of potash, from metallic antimony and nitre deflagrated

together) for white enamel; but this product cannot be added to any

preparation of lead or other metallic oxides; for it would tend rather

to tarnish the colour than to clear it up; and it can be used therefore

only with ordinary glass, or with saline fluxes. For three parts of

white glass (without lead) one part of washed diaphoretic antimony is to

be taken; the substances are well ground together, and fused in the

common way.

_Blue Enamel._--This fine colour is almost always obtained from the

oxide of cobalt or some of its combinations, and it produces it with

such intensity that only a very little can be used, lest the shade

should pass into black. The cobalt blue is so rich and lively that it

predominates in some measure over every other colour, and masks many so

that they can hardly be perceived; it is also most easily obtained. To

bring it out, however, in all its beauty, the other colours must be

removed as much as possible, and the cobalt itself should be tolerably

pure. This metal is associated in the best known ores with a

considerable number of foreign substances, as iron, arsenic, copper,

nickel, and sulphur, and it is difficult to separate them completely;

but for enamel blues, the oxide of cobalt does not require to be

perfectly free from all foreign metals; the iron, nickel, and copper

being most prejudicial, should be carefully eliminated. This object may

be most easily attained by dissolving the ore in nitric acid,

evaporating the solution to a syrupy consistence, to expel the excess of

acid, and separate a portion of arsenic. It is now diluted with water,

and solution of carbonate of soda is dropped slowly into it with brisk

agitation, till the precipitate, which is at first of a whitish gray,

begins to turn of a rose-red. Whenever this colour appears, the whole

must be thrown on a filter, and the liquid which passes through must be

treated with more of the carbonate of soda, in order to obtain the

arseniate of cobalt, which is nearly pure. Since arsenic acid and its

derivatives are not capable of communicating colour themselves, and as

they moreover are volatile, they cannot impair the beauty of the blue,

and hence this preparation affords it in great perfection.

Metallic fluxes are not the most suitable for this colour; because they

always communicate a tint of greater or less force, which never fails to

injure the purity of the blue. Nitre is a useful addition, as it keeps

the oxide at the maximum of oxidation, in which state it produces the

richest colour.

_Yellow Enamel._--There are many processes for making this colour in

enamel; but it is somewhat difficult to fix, and it is rarely obtained

of an uniform and fine tint. It may be produced directly with some

preparations of silver, as the phosphate or sulphate; but this method

does not always succeed, for too strong a heat or powerful fluxes

readily destroy it, and nitre is particularly prejudicial. This

uncertainty of success with the salts of silver causes them to be seldom

employed; and oxides of lead and antimony are therefore preferred, which

afford a fine yellow when combined with some oxides that are refractory

enough to prevent their complete vitrification. One part of white oxide

of antimony may be taken with from one to three parts of white lead, one

of alum, and one of sal-ammoniac. Each of these substances is to be

pulverized, and then all are to be exactly mixed, and exposed to a heat

adequate to decompose the sal-ammoniac. This operation is judged to be

finished when the yellow colour is well brought out. There is produced

here a combination quite analogous to that known under the name of

Naples yellow.

Other shades of yellow may be procured either with the oxide of lead

alone, or by adding to it a little red oxide of iron; the tints varying

with the proportion of the latter.

Clouet says, in his memoir on enamels, that a fine yellow is obtained

with pure oxide of silver, and that it is merely necessary to spread a

thin coat of it on the spot to be coloured. The piece is then exposed to

a moderate heat, and withdrawn as soon as this has reached the proper

point. The thin film of metallic silver revived on the surface being

removed, the place under it will be found tinged of a fine yellow, of

hardly any thickness. As the pellicle of silver has to be removed which

covers the colour, it is requisite to avoid fixing this film with

fluxes; and it ought therefore to be applied after the fusion of the

rest. The yellows require in general little flux, and they answer better

with one of a metallic nature.

_Green Enamel._--It is known that a green colour may be produced by a

mixture of yellow and blue; but recourse is seldom had to this practice

for enamels, as they can be obtained almost always directly with the

oxide of copper; or still better with the oxide of chrome, which has the

advantage of resisting a strong heat.

Chemists describe two oxides of copper, the protoxide, of an orange red

colour, which communicates its colour to enamels, but it is difficult to

fix; the deutoxide is blue in the state of hydrate, but blackish-brown

when dry, and it colours green all the vitreous combinations into which

it enters. This oxide requires, at most, one or two proportions of flux,

either saline or metallic, to enter into complete fusion; but a much

smaller dose is commonly taken, and a little oxide of iron is

introduced. To four pounds of frit, for instance, two ounces of oxide of

copper and 48 grains of red oxide of iron are used; and the ordinary

measures are pursued for making very homogeneous enamel.

The green produced by the oxide of chrome is much more solid; it is not

affected by a powerful fire, but it is not always of a fine shade. It

generally inclines too much to the dead-leaf yellow, which depends on

the degree of oxygenation of the chrome.

_Red Enamel._--We have just stated, that protoxide of copper afforded a

fine colour when it could be fixed, a result difficult to obtain on

account of the fugitive nature of this oxide; slight variations of

temperature enabling it to absorb more oxygen. The proper point of

fusion must be seized, for taking it from the fire whenever the desired

colour is brought out. Indeed, when a high temperature has produced

peroxidizement, this may be corrected by adding some combustible matter,

as charcoal, tallow, tartar, &c. The copper then returns to its minimum

of oxidizement, and the red colour which had vanished, reappears. It is

possible, in this way, and by pushing the heat a little, to accomplish

the complete reduction of a part of the oxide; and the particles of

metallic copper thereby disseminated in a reddish ground, give this

enamel the aspect of the stone called _avanturine_. The surest and

easiest method of procuring protoxide of copper is to boil a solution of

equal parts of sugar, and sulphate or rather acetate of copper, in four

parts of water. The sugar takes possession of a portion of the oxygen of

the cupreous oxide, and reduces it to the protoxide; when it may be

precipitated in the form of a granular powder of a brilliant red. After

about two hours of moderate ebullition, the liquid is set aside to

settle, decanted off the precipitate, which is washed and dried.

This pure oxide, properly employed by itself, furnishes a red which vies

with the finest carmine, and by its means every tint may be obtained

from red to orange, by adding a greater or smaller quantity of peroxide

of iron.

The preparations of gold, and particularly the oxide and purple of

Cassius, are likewise employed, with advantage, to colour enamel red,

and this composition resists a powerful fire tolerably well. For some

time back, solutions of gold, silver, and platinum have been used with

success instead of their oxides; and, in this way, a more intimate

mixture may be procured, and, consequently, more homogeneous tints.

_Black Enamel._--Black enamels are made with peroxide of manganese or

protoxide of iron; to which more depth of colour is given with a little

cobalt. Clay alone, melted with about a third of its weight of protoxide

of iron, gives, according to Clouet, a fine black enamel.

_Violet Enamel._--The peroxide of manganese in small quantity by itself

furnishes, with saline or alkaline fluxes, an enamel of a very fine

violet hue; and variations of shade are easily had by modifying the

proportions of the elements of the coloured frit. The great point is to

maintain the manganese in a state of peroxidation, and consequently to

beware of placing the enamel in contact with any substance attractive of

oxygen.

Such are the principal coloured enamels hitherto obtained by means of

metallic oxides; but since the number of these oxides is increasing

every day, it is to be wished that new trials be made with such as have

not yet been employed. From such researches some interesting results

would unquestionably be derived.

_Of painting on Enamel._--Enamelling is only done on gold and copper;

for silver swells up, and causes blisters and holes in the coat of

enamel. All enamel paintings are, in fact, done on copper or gold.

The goldsmith prepares the plate that is to be painted upon. The gold

should be 22 carats fine: if purer, it would not be sufficiently stiff;

if coarser, it would be subject to melt; and its alloy should be half

white and half red, that is, half silver and half copper; whereby the

enamel with which it is covered will be less disposed to turn green,

than if the alloy were entirely copper.

The workman must reserve for the edge of the plate a small fillet, which

he calls the _border_. This ledge serves to retain the enamel, and

hinders it from falling off when applied and pressed on with a spatula.

When the plate is not to be counter-enamelled, it should be charged with

less enamel, as, when exposed to heat, the enamel draws up the gold to

itself, and makes the piece convex. When the enamel is not to cover the

whole plate, it becomes necessary to prepare a lodgement for it. With

this view, all the outlines of the figure are traced on the plate with a

black-lead pencil, after which recourse is had to the graver.

The whole space enclosed by the outlines must be hollowed out in

_bas-relief_, of a depth equal to the height of the fillet, had the

plate been entirely enamelled. This sinking of the surface must be done

with a flat graver as equally as possible; for if there be an eminence,

the enamel would be weaker at that point, and the green would appear.

Some artists hatch the bottom of the hollow with close lines, which

cross each other in all directions; and others make lines or scratches

with the end of a file broken off square. The hatchings or scratches lay

hold of the enamel, which might otherwise separate from the plate. After

this operation, the plate is cleansed by boiling it in an alkaline ley,

and it is washed first with a little weak vinegar, and then with clear

water.

The plate thus prepared is to be covered with a coat of white enamel,

which is done by bruising a piece of enamel in an agate or porcelain

mortar to a coarse powder like sand, washing it well with water, and

applying it in the hollow part in its moist state. The plate may

meanwhile be held in an ordinary forceps. The enamel powder is spread

with a spatula. For condensing the enamel powder, the edges of the plate

are struck upon with this spatula.

[Illustration: 375]

Whenever the piece is dry, it is placed on a slip of sheet iron

perforated with several small holes, see _fig._ 375., which is laid on

hot cinders; and it is left there until it ceases to steam. It must be

kept hot till it goes to the fire; for were it allowed to cool it would

become necessary to heat it again very gradually at the mouth of the

furnace of fusion, to prevent the enamel from decrepitating and flying

off.

[Illustration: 376 377]

Before describing the manner of exposing the piece to the fire, we must

explain the construction of the furnace. It is square, and is shewn in

front elevation in _fig._ 376. It consists of two pieces, the lower part

A, or the body of the furnace, and the upper part B, or the capital,

which is laid on the lower part as is shewn in _fig._ 377., where these

two parts are separately represented. The furnace is made of good

fire-clay, moderately baked, and resembles very closely the assay or

cupellation furnace. Its inside dimensions are 9 inches in width; 13

inches in height in the body, and 9 in the capital. Its general

thickness is 2 inches.

The capital has an aperture or door C, _fig._ 376., which is closed by a

fire-brick stopper _m_, when the fire is to be made active. By this door

fuel is supplied.

The body of the furnace has likewise a door D, which reaches down to the

projecting shelf E, called the bib (_mentonnière_), whose prominence is

seen at E, _fig._ 376. This shelf is supported and secured by the two

brackets F, F; the whole being earthenware. The height of the door D, is

abridged by a peculiar fire-brick G, which not only covers the whole

projection of the shelf E, but enters within the opening of the door D,

filling its breadth, and advancing into the same plane with the inner

surface of the furnace. This plate is called the hearth; its purpose

will appear presently; it may be taken out and replaced at pleasure, by

laying hold of the handle in its front.

Below the shelf E, a square hole, H, is seen, which serves for admitting

air, and for extracting the ashes. Similar holes are left upon each side

of the furnace, as is shown in the ground plan of the base, _fig._ 377.,

at H H H.

[Illustration: 378 379 380]

On a level with the shelf, in the interior of the furnace, a thin

fire-tile I rests, perforated with numerous small holes. This is the

grate represented in a ground view in _fig._ 375. _Fig._ 378, 379, 380.

represent, under different aspects, the muffle. _Fig._ 377. shows the

elevation of its further end; _fig._ 379. its sides; and _fig._ 380. its

front part. At J, _fig._ 377. the muffle is seen in its place in the

furnace, resting on two bars of iron, or, still better, on ledges of

fire-clay, supported on brackets attached to the lateral sides of the

furnace. The muffle is made of earthenware, and as thin as possible. The

fuel consists of dry beech-wood, or oaken branches, about an inch in

diameter, cut to the length of 9 inches, in order to be laid in

horizontal strata within the furnace, one row only being placed above

the muffle. When the muffle has attained to a white-red heat, the sheet

iron tray, bearing its enamel plate, is to be introduced with a pair of

pincers into the front of the muffle, and gradually advanced towards its

further end. The mouth of the muffle is to be then closed with two

pieces of charcoal only, between which the artist may see the progress

of the operation. Whenever the enamel begins to flow, the tray must be

turned round on its base to ensure equality of temperature; and as soon

as the whole surface is melted, the tray must be withdrawn with its

plate, but slowly, lest the vitreous matter be cracked by sudden

refrigeration.

The enamel plate, when cold, is to be washed in very dilute nitric acid,

and afterwards in cold water, and a second coat of granular enamel paste

is to be applied, with the requisite precautions. This, being passed

through the fire, is to be treated in the same way a third time, when

the process will be found complete. Should any chinks happen to the

enamel coat, they must be widened with a graver, and the space being

filled with ground enamel, is to be repaired in the muffle. The plate,

covered with a pure white enamel, requires always to be polished and

smoothed with sandstone and water, particularly if the article have a

plane surface; and it is then finally glazed at the fire.

The painting operation now follows. The artist prepares his enamel

colours by pounding them in an agate mortar, with a pestle of agate, and

grinding them on an agate slab, with oil of lavender, rendered viscid by

exposure to the sun in a shallow vessel, loosely covered with gauze or

glass. The grinding of two drachms of enamel pigment into an impalpable

powder, will occupy a labourer a whole day. The painter should have

alongside of him a stove in which a moderate fire is kept up, for drying

his work whenever the figures are finished. It is then passed through

the muffle.

_Enamelling at the Lamp._--The art of the lamp enameller is one of the

most agreeable and amusing that we know. There is hardly a subject in

enamel which may not be executed by the lamp-flame in very little time,

and more or less perfectly, according to the dexterity of the artist,

and his acquaintance with the principles of modelling.

In working at the lamp, tubes and rods of glass and enamel must be

provided, of all sizes and colours.

[Illustration: 373]

The enamelling table is represented in _fig._ 373., round which several

workmen, with their lamps, may be placed, while the large double bellows

D below is set a-blowing by a treadle moved with the foot. The flame of

the lamp, when thus impelled by a powerful jet of air, acquires

surprising intensity. The bent nozzles or tubes A A A A, are made of

glass, and are drawn to points modified to the purpose of the enameller.

[Illustration: 374]

_Fig._ 374. shows, in perspective, the lamp A of the enameller standing

in its cistern B; the blowpipe C is seen projecting its flame obliquely

upwards. The blowpipe is adjustable in an elastic cork D, which fills up

exactly the hole of the table into which it enters. When only one person

is to work at a table provided with several lamps, he sits down at the

same side with the pedal of the bellows; he takes out the other

blowpipes, and plugs the holes in the table with solid corks.

The lamp is made of copper or tin-plate, the wick of cotton threads, and

either tallow or oil may be used. Between the lamp and the workman a

small board or sheet of white iron B, called the screen, is interposed

to protect his eyes from the glare of light. The screen is fastened to

the table by a wooden stem, and it throws its shadow on his face.

The enamelling workshop ought to admit little or no daylight, otherwise

the artist, not perceiving his flame distinctly, would be apt to commit

mistakes.

It is impossible to describe all the manipulations of this ingenious

art, over which taste and dexterity so entirely preside. But we may give

an example. Suppose the enameller wishes to make a swan. He takes a tube

of white enamel, seals one of its ends hermetically at his lamp, and

while the matter is sufficiently hot, he blows on it a minikin flask,

resembling the body of the bird; he draws out, and gracefully bends the

neck; he shapes the head, the beak, and the tail; then, with slender

enamel rods of a proper colour, he makes the eyes; he next opens up the

beak with pointed scissors; he forms the wings and the legs; finally

attaching the toes, the bird stands complete.

The enameller also makes artificial eyes for human beings, imitating so

perfectly the colours of the sound eye of any individual, as to render

it difficult to discover that he has a blind and a seeing one.

It is difficult to make large articles at the blowpipe; those which

surpass 5 or 6 inches become nearly unmanageable by the most expert

workmen.

EPSOM SALTS. Sulphate of Magnesia.

EQUIVALENTS, CHEMICAL. (_Stöchiometrie_, Germ.) This expression was

first employed by Dr. Wollaston, to denote the primary proportions in

which the various chemical bodies reciprocally combine; the numbers

representing these proportions being referred to one standard substance

of general interest, such as oxygen or hydrogen reckoned unity, or

1,000. Dr. Dalton, who is the true author of the grand discovery of

definite, and multiple chemical ratios, calls these equivalent numbers

_atomic weights_, when reduced to their lowest terms, either hydrogen or

oxygen being the radix of the scale. Though it belongs to a chemical

work, to discuss the principles and develope the applications of the

Atomic Theory, I shall be careful, upon all proper occasions, to point

out the vast advantages which the chemical manufacturer may derive from

it, and to show how much he may economize and improve his actual

processes by its means. See ELEMENT.

ESSENCES, are either ethereous oils, in which all the fragrance of

vegetable products reside; or the same combined and diluted with

alcohol. See OILS, ETHEREOUS.

ESSENCE D’ORIENT, the name of a pearly looking matter procured from the

blay or bleak, a fish of the genus _cyprinus_. This substance, which is

found principally at the base of the scales, is used in the manufacture

of artificial pearls. A large quantity of the scales being scraped into

water in a tub, are there rubbed between the hands to separate the

shining stuff, which subsides on repose. The first water being decanted,

more is added with agitation till the essence is thoroughly washed from

all impurities; when the whole is thrown upon a sieve; the substance

passes through, but the scales are retained. The water being decanted

off, the essence is procured in a viscid state, of a bluish white

colour, and a pearly aspect. The intestines of the same fish are also

covered with this beautiful glistening matter. Several other fish yield

it, but in smaller proportion. When well prepared, it presents exactly

the appearance and reflections of the real pearls, or the finest mother

of pearl; properties which are probably owing to the interposition of

some portions of this same substance, between the laminæ of these shelly

concretions. Its chemical nature has not been investigated; it putrefies

readily when kept moist, an accident which may however be counteracted

by water of ammonia. See PEARLS.

ETCHING _Varnish_. (_Aetzgrund-Deckfirniss_, Germ.) Though the practice

of this elegant art does not come within the scope of our Dictionary,

the preparation of the varnishes, and of the biting menstrua which it

employs, legitimately does.

The varnish of Mr. Lawrence, an English artist resident in Paris, is

made as follows: Take of virgin wax and asphaltum, each two ounces, of

black pitch and burgundy-pitch each half an ounce. Melt the wax and

pitch in a new earthenware glazed pot, and add to them, by degrees, the

asphaltum, finely powdered. Let the whole boil till such time as that,

taking a drop upon a plate, it will break when it is cold, on bending it

double two or three times betwixt the fingers. The varnish, being then

enough boiled, must be taken off the fire, and after it cools a little,

must be poured into warm water that it may work the more easily with the

hands, so as to be formed into balls, which must be kneaded, and put

into a piece of taffety for use.

Care must be taken, first, that the fire be not too violent, for fear of

burning the ingredients, a slight simmering being sufficient; secondly,

that whilst the asphaltum is putting in, and even after it is mixed with

the ingredients, they should be stirred continually with the spatula;

and, thirdly, that the water into which this composition is thrown

should be nearly of the same degree of warmth with it, in order to

prevent a kind of cracking that happens when the water is too cold.

The varnish ought always to be made harder in summer than in winter, and

it will become so if it be suffered to boil longer, or if a greater

proportion of the asphaltum or brown rosin be used. The experiment

above mentioned, of the drop suffered to cool, will determine the degree

of hardness or softness that may be suitable to the season when it is

used.

Preparation of the hard varnish used by Callot, commonly called the

Florence Varnish:--Take four ounces of fat oil very clear, and made of

good linseed oil, like that used by painters; heat it in a clean pot of

glazed earthenware, and afterwards put to it four ounces of mastick well

powdered, and stir the mixture briskly till the whole be well melted,

then pass the mass through a piece of fine linen into a glass bottle

with a long neck, that can be stopped very securely; and keep it for the

use that will be explained below.

Method of applying the soft varnish to the plate, and of blackening

it.--The plate being well polished and burnished, as also cleansed from

all greasiness by chalk or Spanish white, fix a hand-vice on the edge of

the plate where no work is intended to be, to serve as a handle for

managing it when warm; then put it upon a chafing dish, in which there

is a moderate fire, and cover the whole plate equally with a thin coat

of the varnish; and whilst the plate is warm, and the varnish upon it in

a fluid state, beat every part of the varnish gently with a small ball

or dauber made of cotton tied up in taffety, which operation smooths and

distributes the varnish equally over the plate.

When the plate is thus uniformly and thinly covered with the varnish, it

must be blackened by a piece of flambeau, or of a large candle which

affords a copious smoke; sometimes two or even four such candles are

used together for the sake of dispatch, that the varnish may not grow

cold, which if it does during the operation, the plate must be heated

again, that it may be in a melted state when that operation is

performed; but great care must be taken not to burn it, which when it

happens may be easily perceived by the varnish appearing burnt and

losing its gloss.

The menstruum used and recommended by Turrell, an eminent London artist,

for etching upon steel, was prepared as follows:--

Take Pyrolignous acid 4 parts by measure,

Alcohol 1 part, mix, and add

Nitric acid 1 part.

This mixed liquor is to be applied from 1-1/2 to 15 minutes, according

to the depth desired. The nitric acid was employed of the strength of

1·28--the double aquafortis of the shops.

The _eau forte_ or menstruum for copper, used by Callot, as also by

Piranesi, with a slight modification, is prepared, with

8 parts of strong French vinegar,

4 parts of verdigris,

4 ditto sea salt,

4 ditto sal ammoniac,

1 ditto alum,

16 ditto water.

The solid substances are to be well ground, dissolved in the vinegar,

and diluted with the water; the mixture is now to be boiled for a

moment, and then set aside to cool. This menstruum is applied to the

washed, dried, and varnished plate, after it has suffered the ordinary

action of aquafortis, in order to deepen and finish the delicate

touches. It is at present called the _eau forte à passer_.

ETHER, is the name of a class of very light, volatile, inflammable, and

fragrant spirituous liquids, obtained by distilling in a glass retort, a

mixture of alcohol with almost any strong acid. Every acid modifies the

result, in a certain degree, whence several varieties of ether are

produced. The only one of commercial importance is sulphuric ether,

which was first made known under the name of _sweet oil of vitriol_, in

1540, by the receipt of Walterus Cordus. Froberus, 190 years after that

date, directed the attention of chemists afresh to this substance, under

the new denomination of _ether_.

There are two methods of preparing it; by the first, the whole quantity

of acid and alcohol are mixed at once, and directly subjected to

distillation; by the second, the alcohol is admitted, in a slender

streamlet, into a body of acid previously mixed with a little alcohol,

and heated to 220° Fahr.

1. Mix equal weights of alcohol at spec. grav. 0·830, and sulphuric acid

at 1·842, by introducing the former into a large tubulated retort,

giving it a whirling motion, so that the alcohol may revolve round a

central conical cavity. Into this species of whirlpool the acid is to be

slowly poured. The mixture, which becomes warm, is to be forthwith

distilled by attaching a spacious receiver to the retort, and applying

the heat of a sand-bath. The formation of ether takes place only at a

certain temperature. If the contents of the retort be allowed to cool,

and be then slowly heated in a water bath, alcohol alone will come over

for some time without ether, till the mixture acquires the proper

degree of heat. The first receiver should be a globe, with a tube

proceeding from its bottom, into a second receiver, of a cylindric

shape, surrounded with ice-cold water. The joints must be well secured

by lutes, after the expanded air has been allowed to escape. The liquid

in the retort should be kept in a steady state of bullition. The ether,

as long as it is produced, condenses in the balloon and neck of the

receiver in striæ; when these disappear the process is completed. The

retort must now be removed from the sand; otherwise it would become

filled with white fumes containing sulphurous acid, and denser striæ

would flow over, which would contaminate the light product with a liquid

called sweet oil of wine.

The theory of etherification demonstrates that when strong sulphuric

acid is mixed with alcohol, there is formed, on the one hand, a more

aqueous sulphuric acid, and, on the other, sulphovinic acid. When this

mixture is made to boil, the sulphovinic acid is decomposed, its

dihydrate of carbon combines with the alcohol, and constitutes ether;

while the proportion of sulphovinic acid progressively diminishes. Mr.

Hennell, of the Apothecaries’ Hall, first explained these phenomena, and

he was confirmed in his views by the interesting researches of Serullas.

The acid left in the retort is usually of a black colour, and may be

employed to convert into ether half as much alcohol again; an experiment

which may be repeated several times in succession.

The most profitable way of manufacturing ether has been pointed out by

Boullay. It consists in letting the alcohol drop in a slender stream

into the acid, previously heated to the etherifying temperature. If the

acid in this case were concentrated to 1·846, the reaction would be too

violent, and the ether would be transformed into bicarburetted hydrogen

(dihydrate of carbon.) It is therefore necessary to dilute the acid down

to the density of 1·780; but this dilution may be preferably effected

with alcohol instead of water, by mixing three parts of the strongest

acid with 2 of alcohol, specific gravity 0·830, and distilling off a

portion of the ether thereby generated; after which the stream of

alcohol is to be introduced into the tubulure of the retort through a

small glass tube plunged into the mixture; this tube being the

prolongation of a metallic syphon, whose shorter leg dips into a bottle

filled with the alcohol. The longer leg is furnished with a stop-cock,

for regulating at pleasure the alcoholic streamlet. The distilled

vapours should be transmitted through a worm of pure tin surrounded by

cold water, and the condensed fluid received in a glass bottle. The

quantity of alcohol which can be thus converted into ether by a given

weight of sulphuric acid, has not hitherto been accurately determined;

but it is at least double. In operating in this way, neither sulphurous

acid, nor sweet oil of wine is generated, while the residuary liquid in

the retort continues limpid and of a merely brownish yellow colour. No

sulphovinic acid is formed, and according to the experiments of Geiger,

the proportion of ether approaches to what theory shows to be the

maximum amount. In fact 57 parts of alcohol of 0·83 sp. grav. being

equivalent to 46·8 parts of anhydrous alcohol, yield according to

Geiger, 33-1/2 parts of ether; and by calculation, they should yield

37-1/4.

The ether of the first distillation is never pure, but always contains a

certain quantity of alcohol. The density of that product is usually

0·78, and if prepared by the first of the above methods, contains

besides alcohol, pretty frequently sulphurous acid, and sweet oil of

wine, impurities from which it must be freed. Being agitated with its

bulk of milk of lime, both the acid and the alcohol are removed at the

same time; and if it be then decanted and agitated, first with its bulk

of water, next decanted into a retort containing chloride of calcium in

coarse powder and distilled, one third of perfectly pure ether may be

drawn over. Gay Lussac recommends to agitate the ether, first with twice

its volume of water, to mix it, and leave it in contact with powdered

unslaked lime for 12 or 14 hours, and then to distil off one third of

pure ether. The remaining two thirds consist of ether containing a

little alcohol. If in preparing ether by Boullay’s method, the alcohol

be too rapidly introduced, much of this liquid will come over unchanged.

If in this state the ether be shaken with water, a notable quantity of

it will be absorbed, because weak alcohol dissolves it very copiously.

The above product should therefore be re-distilled, and the first half

that comes over may be considered as ether, and treated with water and

lime. The other half must be exposed afresh to the action of sulphuric

acid.

Pure ether possesses the following properties. It is limpid, of spec.

grav. 0·713, or 0·715 at 60°; has a peculiar penetrating strong smell; a

taste at first acrid, burning, sweetish, and finally cooling. It has

neither an acid nor alkaline reaction; is a non-conductor of

electricity, and refracts light strongly. It is very volatile, boiling

at 96° or 97° F., and produces by its evaporation a great degree of

cold. At the temperature of 62·4, the vapour of ether balances a column

of mercury 15 inches high, or half the weight of the atmosphere. When

ether is cooled to -24° F. it begins to crystallize in brilliant white

plates, and at -47° it becomes a white crystalline solid. When vapour of

ether is made to traverse a red hot porcelain tube, it deposits within

it one half per cent. of charcoal, and there are condensed in the

receiver one and two thirds per cent. of a brown oil, partly in

crystalline scales, and partly viscid. The crystalline portion is

soluble in alcohol, but the viscid only in ether. The remainder of the

decomposed ether consists of bi-carburetted hydrogen gas, tetrahydric

carburet, carbonic oxide gas, and one per cent. at most of gaseous

carbonic acid.

Ether takes fire readily, even at some distance from a flame, and it

should not therefore be poured from one vessel to another in the

neighbourhood of a lighted candle. It may be likewise set on fire by the

electric spark. It burns all away with a bright fuliginous flame. When

the vapour of ether is mixed with 10 times its volume of oxygen, it

burns with a violent explosion, absorbs 6 times its bulk of oxygen, and

produces 4 times its volume of carbonic acid gas.

Ether alters gradually with contact of air; absorbing oxygen, and

progressively changing into acetic acid and water. This conversion takes

place very rapidly when the ether is boiled in an open vessel, while the

acid enters into a new combination forming acetic ether. Ether should be

preserved in bottles perfectly full and well corked, and kept in a cool

place, otherwise it becomes sour, and is destroyed. It contains in this

state 15 per cent. of its bulk of azote, but no oxygen gas, as this has

combined with its elements. Ether is composed of oxygen 21·24; hydrogen

13·85; carbon 65·05. This composition may be represented by 1 prime

equivalent of water, and 4 primes of bi-carburetted hydrogen gas; in

other words, ether contains for 1 prime of water, once as much olefiant

gas as alcohol, and its prime equivalent is therefore 468·15 to oxygen

100. By my analysis, as published in the Phil. Trans. for 1822, ether is

composed of oxygen 27·10; hydrogen 13·3; and carbon 59·6 in 100 parts.

The density of my ether was 0·700. One volume of vapour of ether

consists of one volume of aqueous vapour and two volumes of olefiant gas

(bi-carburetted hydrogen,) while alcohol consists of two volumes of

each.

ETHER, ACETIC, is used to flavour silent corn spirits in making

imitation brandy. It may be prepared by mixing 20 parts of acetate of

lead, 10 parts of alcohol, and 11-1/2 of concentrated sulphuric acid; or

16 of the anhydrous acetate, 5 of the acid, and 4-1/2 of absolute

alcohol; distilling the mixture in a glass retort into a very cold

receiver, agitating along with weak potash lye the liquor which comes

over, decanting the supernatant ether, and rectifying it by

re-distillation over magnesia and ground charcoal.

Acetic ether is a colourless liquid of a fragrant smell and pungent

taste, of spec. grav. 0·866 at 45° F., boiling at 166° F, burning with a

yellowish flame, and disengaging fumes of acetic acid. It is soluble in

8 parts of water.

Acetic ether may be economically made with 3 parts of acetate of potash,

3 of very strong alcohol, and 2 of the strongest sulphuric acid,

distilled together. The first product must be re-distilled along with

one fifth of its weight of sulphuric acid; as much ether will be

obtained as there was alcohol employed.

ETHIOPS, is the absurd name given by the alchemists to certain black

metallic preparations. Martial ethiops was the black oxide of iron;

mineral ethiops, the black sulphuret of mercury; and ethiops _per se_,

the black oxide of mercury.

EVAPORATION, (Eng. and Fr.; _Abdampfen_; _Abdunsten_, Germ.) is the

process by which any substance is converted into, and carried off in,

vapour. Though ice, camphor, and many other solids evaporate readily in

dry air, I shall consider, at present, merely the vaporization of water

by heat artificially applied.

The vapour of water is an elastic fluid, whose tension and density

depend upon the temperature of the water with which it is in contact.

Thus the vapour rising from water heated to 165° F. possesses an elastic

force capable of supporting a column of mercury 10·8 high; and its

density is such that 80 cubic feet of such vapour contain one pound

weight of water; whereas 32-1/2 cubic feet of steam of the density

corresponding to a temperature of 212° and a pressure of 30 inches of

mercury, weigh one pound. When the temperature of the water is given,

the elasticity and specific gravity of the vapour emitted by it, may be

found.

Since the vapour rises from the water only in virtue of the elasticity

due to its gaseous nature, it is obvious that no more can be produced,

unless what is already incumbent upon the liquid have its tension

abated, or be withdrawn by some means. Suppose the temperature of the

water to be midway between freezing and boiling, viz. 122° Fahr., as

also that of the air in contact with it, to be the same but replete with

moisture, so that its interstitial spaces are filled with vapour of

corresponding elasticity and specific gravity with that given off by the

water, it is certain that no fresh formation of vapour can take place in

these circumstances. But the moment a portion of vapour is allowed to

escape, or is drawn off by condensation to another vessel, an equivalent

portion of vapour will be immediately exhaled from the water.

The pressure of the air and of other vapours upon the surface of water

in an open vessel, does not prevent evaporation of the liquid; it merely

retards its progress. Experience shows that the space filled with an

elastic fluid, as air or other gaseous body, is capable of receiving as

much aqueous vapour as if it were vacuous, only the repletion of that

space with the vapour proceeds more slowly in the former predicament

than in the latter, but in both cases it arrives eventually at the same

pitch. Dr. Dalton has very ingeniously proved, that the particles of

aeriform bodies present no permanent obstacle to the introduction of a

gaseous atmosphere of another kind among them, but merely obstruct its

diffusion momentarily, as if by a species of friction. Hence, exhalation

at atmospheric temperatures is promoted by the mechanical diffusion of

the vapours through the air with ventilating fans or chimney draughts;

though under brisk ebullition, the force of the steam readily overcomes

that mechanical obstruction.

The quantities of water evaporated under different temperatures in like

times, are proportional to the elasticities of the steam corresponding

to these temperatures. A vessel of boiling water exposing a square foot

of surface to the fire, evaporates 725 grains in the minute; the

elasticity of the vapour is equivalent to 30 inches of mercury. To find

the quantity that would be evaporated from the same surface per minute

at a heat of 88° F. At this temperature the steam incumbent upon water

is capable of supporting 1·28 inch of mercury; whence the rule of

proportion is 30 : 1·28 ∷ 725 : 30·93; showing that about 31 grains of

water would be evaporated in the minute. If the air contains already

some aqueous vapour, as it commonly does, then the quantity of

evaporation will be proportional to the difference between the elastic

force of that vapour, and what rises from the water.

Suppose the air to be in the hygrometric state denoted by 0·38 of an

inch of mercury, then the above formula will become: 30 : 1·28 - 0·38 ∷

725 : 21·41; showing that not more than 21-1/2 grains would be

evaporated per minute under these circumstances.

The elastic tension of the atmospheric vapour is readily ascertained by

the old experiment of Le Roi, which consists in filling a glass cylinder

(a narrow tumbler for example) with cool spring water, and noting its

temperature at the instant it becomes so warm that dew ceases to be

deposited upon it. This temperature is that which corresponds to the

elastic tension of the atmospheric vapour. See VAPOUR, Table of.

Whenever the elasticity of the vapour, corresponding to the temperature

of the water, is greater than the atmospheric pressure, the evaporation

will take place not only from its surface, but from every point in its

interior; the liquid particles throughout the mass assuming the gaseous

form, as rapidly as they are actuated by the caloric, which subverts the

hydrostatic equilibrium among them, to constitute the phenomena of

ebullition. This turbulent vaporization takes place at any temperature,

even down to the freezing point, provided the pneumatic pressure be

removed from the liquid by the air pump, or any other means. Ebullition

always accelerates evaporation, as it serves to carry off the aqueous

particles not simply from the surface, but from the whole body of the

water.

The vapours, exhaled from a liquid at any temperature, contain more heat

than the fluid from which they spring; and they cease to form whenever

the supply of heat into the liquid is stopped. Any volume of water

requires for its conversion into vapour _five and a half times_ as much

heat as is sufficient to heat it from the freezing to the boiling

temperature. The heat, in the former case, seems to be absorbed, being

inappreciable by the thermometer; for steam is no hotter than the

boiling water from which it rises. It has been therefore called _latent

heat_; in contradistinction to that perceived by the touch and measured

by the thermometer, which is called _sensible heat_. The quantity of

heat absorbed by one volume of water in its conversion into steam, is

about 1000° Fahr.; it would be adequate to heat 1000 volumes of water,

one degree of the same scale; or to raise one volume of boiling water,

confined in a non-conducting vessel, to 1180°. Were the vessel charged

with water so heated, opened, it would be instantaneously emptied by

vaporization, since the whole caloric equivalent to its constitution as

steam, is present. When, upon the other hand, steam is condensed by

contact with cold substances, so much heat is set free as is capable of

heating five and a half times its weight of water, from 32° to 212° F.

If the supply of heat to a copper be uniform, five hours and a half will

be required to drive off its water in steam, provided one hour was taken

in heating the water, from the freezing to the boiling pitch, under the

atmospherical pressure.

Equal weights of vapour of any temperature contain equal quantities of

heat; for example, the vapour exhaled from one pound of water, at 77°

F., absorbs during its formation, and will give out in its condensation,

as much heat as the steam produced by one pound of water, at 212° F. The

first portion of vapour with a tension = 30 inches, occupies a space of

27·31 cubic feet; the second, with a tension of 0·92 inch, occupies a

space of 890 cubic feet.[29] Suppose that these 890 volumes were to be

compressed into 27·31 in a cylinder capable of confining the heat, the

temperature of the vapour would rise from 77° to 212°, in virtue of the

condensation, as air becomes so hot by compression in a syringe, as to

ignite _amadou_. The latent heat of steam at 212° F. is 1180° - 180 =

1000; that of vapour, at 77°, is 1180 - 45 = 1135°; so that, in fact,

the lower the temperature at which the vapour is exhaled, the greater is

its latent heat, as Joseph Black and James Watt long ago proved by

experiments upon distillation and the steam engine.

[29] One pound avoirdupois of water contains 27·72 cubic inches; one

cubic inch of water forms 1696 cubic inches of steam at 212° F.:

therefore one pound of water will form 27·31 cubic feet of such steam:

and 0·92 : 30 ∷ 27·31 : 890 cubic feet.

From the preceding researches it follows, that evaporation may be

effected upon two different plans:--