STAINED-GLASS PIGMENTS.

_Flesh colour._--Take an ounce of red lead, two ounces of red enamel

(Venetian glass enamel, from alum and copperas calcined together), grind

them to fine powder, and work this up with spirits (alcohol) upon a hard

stone. When slightly baked, this produces a fine flesh colour.

_Black colour._--Take 14-1/2 ounces of smithy scales of iron, mix them

with two ounces of white glass (crystal), an ounce of antimony, and half

an ounce of manganese; pound and grind these ingredients together with

strong vinegar. A brilliant black may also be obtained by a mixture of

cobalt blue with the oxides of manganese and iron. Another black is made

from three parts of crystal glass, two parts of oxide of copper, and one

of (glass of) antimony worked up together, as above.

_Brown colour._--An ounce of white glass or enamel, half an ounce of

good manganese; ground together.

_Red, rose, and brown colours_, are made from peroxide of iron, prepared

by nitric acid. The flux consists of borax, sand, and minium in small

quantity.

_Red colour_, may be likewise obtained from one ounce of red chalk

pounded, mixed with two ounces of white hard enamel, and a little

peroxide of copper.

_A red_, may also be composed of rust of iron, glass of antimony, yellow

glass of lead, such as is used by potters (or litharge), each in equal

quantity; to which a little sulphuret of silver is added. This

composition, well ground, produces a very fine red colour on glass. When

protoxide of copper is used to stain glass, it assumes a bright red or

green colour, according as the glass is more or less heated in the

furnace, the former corresponding to the orange protoxide, the latter

having the copper in the state of peroxide.

_Bistres and brown reds_, may be obtained by mixtures of manganese,

orange oxide of copper, and the oxide of iron called umber, in different

proportions. They must be previously fused with vitreous solvents.

_Green colour._--Two ounces of brass calcined into an oxide, two ounces

of minium, and eight ounces of white sand; reduce them to a fine powder,

which is to be enclosed in a well luted crucible, and heated strongly in

an air-furnace for an hour. When the mixture is cold, grind it in a

brass mortar. Green may, however, be advantageously produced by a yellow

on one side, and a blue on the other. Oxide of chrome has been also

employed to stain glass green.

_A fine yellow colour._--Take fine silver laminated thin, dissolve in

nitric acid, dilute with abundance of water, and precipitate with

solution of sea salt. Mix this chloride of silver, in a dry powder, with

three times its weight of pipe-clay well burnt and pounded. The back of

the glass pane is to be painted with this powder; for when painted on

the face, it is apt to run into the other colours.

_Another yellow_ can be made by mixing sulphuret of silver with glass of

antimony, and yellow ochre previously calcined to a red-brown tint. Work

all these powders together, and paint on the back of the glass. Or

silver _laminæ_ melted with sulphur, and glass of antimony, thrown into

cold water, and afterwards ground to powder, afford a yellow.

_A pale yellow_ may be made with the powder resulting from brass,

sulphur, and glass of antimony, calcined together in a crucible, till

they cease to smoke; and then mixed with a little burnt yellow ochre.

_The fine yellow_ of M. Merand, is prepared from chloride of silver,

oxide of zinc, white-clay, and rust of iron. This mixture, simply

ground, is applied on the glass.

_Orange colour._--Take 1 part of silver powder, as precipitated from the

nitrate of that metal by plates of copper, and washed; mix it with 1

part of red ochre and 1 of yellow, by careful trituration; grind into a

thin pap with oil of turpentine or lavender, and apply this with a

brush, dry, and burn in.

In the Philosophical Magazine, of December, 1836, the anonymous author

of an ingenious essay, “On the Art of Glass-painting,” says, that if a

large proportion of ochre has been employed with the silver, the stain

is yellow; if a small proportion, it is orange-coloured; and by repeated

exposure to the fire, without any additional colouring-matter, the

orange may be converted into red; but this conversion requires a nice

management of the heat. Artists often make use of panes coloured

throughout their substance in the glass-house pots, because the perfect

transparency of such glass gives a brilliancy of effect, which enamel

painting, always more or less opaque, cannot rival. It was to a glass of

this kind that the old glass-painters owed their splendid red. This is,

in fact, the only point in which the modern and antient processes

differ; and this is the only part of the art which was ever really lost.

Instead of blowing plates of solid red, the old glass-makers (like those

of Bohemia, for some time back,) used to _flash_ a thin layer of

brilliant red over a substratum of colourless glass; by gathering a lump

of the latter upon the end of their iron rod in one pot, covering it

with a layer of the former in another pot, then blowing out the two

together into a globe or cylinder, to be opened into circular tables, or

into rectangular plates. The elegant art of tinging glass red by

protoxide of copper, and flashing it on common crown glass, has become

general within these few years.

That gold melted with flint glass stains it purple, was originally

discovered and practised, as a profitable secret, by Kunckel. Gold has

been recently used at Birmingham for giving a beautiful rose-colour to

scent bottles. The proportion of gold should be very small, and the heat

very great, to produce a good effect. The glass must contain either the

oxide of lead, bismuth, zinc, or antimony; for crown glass will take no

colour from gold. Glass combined with this metal, when removed from the

crucible is generally of a pale rose-colour; nay, sometimes is as

colourless as water, and does not assume its ruby colour till it has

been exposed to a low red heat, either under a muffle or at the lamp.

This operation must be nicely regulated; because a slight excess of fire

destroys the colour, leaving the glass of a dingy brown, but with a blue

(green?) transparency, like that of gold leaf. It is metallic gold which

gives the colour; and, indeed, the oxide is too easily reduced, not to

be converted into the metal by the intense heat which is necessarily

required.

Upon the kindred art of painting in enamel, Mr. A. Essex has published

an interesting paper in the same journal, for June, 1837, in which he

says that the antient ruby glass, on being exposed to the heat of a

glass-kiln, preserves its colour unimpaired, while the modern suffers

considerable injury, and in some cases becomes almost black. Hence the

latter cannot be painted upon, as the heat required to fix the fresh

colour would destroy the beauty of the original basis. To obviate this

difficulty, the artist paints upon a piece of plain glass the tints and

shadows necessary for blending the rich ruby glow with the other parts

of his picture, leaving those parts untouched where he wishes the ruby

to appear in undiminished brilliancy, and fixes the ruby glass in the

picture behind the painted piece, so that in such parts, the window is

double-glazed. Mr. Essex employs, as did the late Mr. Muss, chrome oxide

alone for greens; and he rejects the use of iron and manganese in his

enamel colours.

Coloured transparent glass is applied as enamel in silver and gold

_bijouterie_, previously _bright-cut_ in the metal with the graver or

the rose-engine. The cuts, reflecting the rays of light from their

numerous surfaces, exhibit through the glass, richly stained with gold,

silver, copper, cobalt, &c., a gorgeous play of prismatic colours,

varied with every change of aspect. When the enamel is to be painted on,

it should be made opalescent by oxide of arsenic, in order to produce

the most agreeable effect.

The artist in enamel has obtained from modern chemistry, preparations of

the metals platinum, uranium, and chromium, which furnish four of the

richest and most useful colours of his palette. Oxide of platinum

produces a substantive rich brown, formerly unknown in enamel painting;

a beautiful transparent tint, which no intensity or repetition of firing

can injure. Colours proper for enamel painting, he says, are not to be

purchased; those sold for the purpose, are adapted only for painting

upon china. The constituents of the green enamel used by his brother,

Mr. W. Essex, are, silica, borax, oxide of lead, and oxide of chrome.

Mr. Essex’s enamelling furnace is a cubic space of about 12 inches, and

contains a fire-clay muffle, without either bottom or back, which is

surrounded with coke, except in front. The entire draught of air which

supplies the furnace, passes through the muffle; the plates and

paintings being placed on a thin slab, made of tempered fire-clay,

technically termed _planche_, which rests on the bed of coke-fuel. As

the greatest heat is at the back of the muffle, the picture must be

turned round while in the fire, by means of a pair of spring tongs. The

above furnace serves for objects up to five inches in diameter; but for

larger works a different furnace is required, for the description of

which I must refer to the original paper.

Relatively to the receipts for enamel colours, and for staining and

gilding on glass, for which twenty guineas were voted by the Society for

the Encouragement of Arts, in the session of 1817, to Mr. R. Wynn, Mr.

A. Essex says, in p. 446. of his essay--“the unfortunate artist who

shall attempt to make colours for the purpose of painting in enamel from

these receipts, will assuredly find, to his disappointment, that they

are utterly useless.” In page 449. he institutes a comparison between

Mr. Wynn’s complex _farrago_ for green, as published in the Transactions

of the Society, with the simple receipt of his brother, as given above.

It is a remarkable circumstance, that not one of our enamel artists,

during a period of twenty years, should have denounced the fallacy of

these receipts, and the folly of sanctioning imposture by a public

reward. Should Mr. Essex’s animadversions be just, the well-intentioned

Society in the Adelphi may, from the negligence of its committee, come

to merit the _sobriquet_, “For the Discouragement of Arts.”

STAMPING OF METALS. The following ingenious machine for manufacturing

metal spoons, forks, and other articles, was made the subject of a

patent by Jonathan Hayne, of Clerkenwell, in May, 1833. He employs a

stamping-machine with dies, in which the hammer is raised to a height

between guides, and is let fall by a trigger. He prefers fixing the

protuberant or relief portion of the die to the stationary block or bed

of the stamping-machine, and the counterpart or intaglio to the falling

hammer or ram.

The peculiar feature of improvement in this manufacture consists in

producing the spoon, ladle, or fork perfect at one blow in the

stamping-machine, and requiring no further manipulation of shaping, but

simply trimming off the barb or fin, and polishing the surface, to

render the article perfect and finished.

Heretofore, in employing a stamping-machine, or fly-press, for

manufacturing spoons, ladles, and forks, it has been the practice to

give the impressions to the handles, and to the bowls or prongs, by

distinct operations of different dies, and after having so partially

produced the pattern upon the article, the handles had to be bent and

formed by the operations of filing and hammering.

By his improved form of dies, which, having curved surfaces and bevelled

edges, allow of no parts of the faces of the die and counter-die to come

into contact, he is enabled to produce considerable elevations of

pattern and form, and to bring up the article perfect at one blow, with

only a slight barb or fin upon its edge.

[Illustration: 1042 1043 1044]

In the accompanying drawings, _fig._ 1042. is the lower or bed die for

producing a spoon, seen edgewise; _fig._ 1043. is the face of the upper

or counter-die, corresponding; _fig._ 1044. is a section, taken through

the middle of the pair of dies, showing the space in which the metal is

pressed to form the spoon.

To manufacture spoons, ladles, or forks according to his improved

process, he first forges out the ingot into flat pieces, of the shape

and dimensions of the die of the intended article; and if a spoon or

ladle is to be made, gives a slight degree of concavity to the bowl

part; but, if necessary, bends the back, in order that it may lie more

steadily, and bend more accurately, upon the lower die; if a fork, he

cuts or otherwise removes portions of the metal at those parts which

will intervene between the prongs; and, having thus produced the rude

embryo of the intended article, scrapes its entire surface clean and

free from oxidation-scale or fire-strain, when it is ready to be

introduced into the stamping-machine.

[Illustration: 1045 1046]

He now fixes the lower die in the bed of the stamping-machine, shown at

_a_, _a_, in the elevations _figs._ 1045. and 1046., and fixes, in the

hammer _b_, the upper or counter-die _c_, accurately adjusting them

both, so that they may correspond exactly when brought together. He then

places the rudely-formed article above described upon the lower die, and

having drawn up the hammer to a sufficient elevation by a windlass and

rope, or other ordinary means, lets go the trigger, and allows the

hammer with the counter-die to fall upon the under die, on which the

article is placed; when, by the blow thus given to the metal, the true

and perfect figure and pattern of the spoon, ladle, or fork is produced,

and which, as before said, will only require the removal of the slight

edging of barb or fin, with polishing, to finish it.

On striking the blow, in the operation of stamping the article, the

hammer will recoil and fly up some distance, and if allowed to fall

again with reiterated blows, would injure both the article and the dies;

therefore, to avoid this inconvenience, he causes the hammer on

recoiling to be caught by a pair of palls locking into racks on the face

of the standards, seen in _figs._ 1045. and 1046. In _fig._ 1045. the

hammer _b_, of the stamping-machine, is seen raised and suspended by a

rope attached to a pair of jointed hooks or holders _d_, _d_, the lower

ends of which pass into eyes _e_, _e_, extending from the top of the

hammer. When the lever or trigger _t_ is drawn forward, as in _fig._

1046., the two inclined planes _g_, _g_, on the axle _h_, press the two

legs of the holders _d_, _d_, inward, and cause their hooks or lower

ends to be withdrawn from the eyes _e_, _e_, when the hammer instantly

falls, and brings the dies together: such is the ordinary construction

of the stamping-machine.

On the hammer falling from a considerable elevation, the violence of the

blow causes it to recoil and bound upwards, as before mentioned; it

therefore becomes necessary to catch the hammer when it has rebounded,

in order to prevent the dies coming again together; this is done by the

following mechanism:--

Two latch levers _i_, _i_, are connected by joints to the upper part of

the hammer, and two pall levers _k_, _k_, turning upon pins, are mounted

in the bridge _l_, affixed to the hammer. Two springs _m_, _m_, act

against the lower arms of these levers, and press them outwards, for the

purpose of throwing the palls at the lower ends of the levers into the

teeth of the ratchet racks _n_, _n_, fixed on the sides of the upright

standards.

Previously to raising the hammer, the upper ends of the pall levers _k_,

are drawn back, and the latches _i_, being brought down upon them, as in

_fig._ 1045., the levers _k_ are confined, and their palls prevented

from striking into the side racks; but as the hammer falls, the ends of

the latches _i_ strike upon the fingers _o_, _o_, fixed to the side

standards, and liberate the palls, the lower ends of which, when the

hammer rebounds, after stamping, catch into the teeth of the racks, as

in _fig._ 1046., and thereby prevent the hammer from again descending.

STARCH; (_Amidon_, _Fecule_, Fr.; _Stärke_, Germ.); is a white

pulverulent substance, composed of microscopic spheroids, which are bags

containing the amylaceous matter. It exists in a great many different

plants, and varies merely in the form and size of its microscopic

particles; as found in some plants, it consists of spherical particles

1/1000 of an inch in diameter; and in others, of ovoid particles, of

1/300 or 1/400 of an inch. It occurs, 1. in the seeds of all the

acotyledinous plants, among which are the several species of corns, and

those of other _gramineæ_; 2. in the round perennial tap roots, which

shoot up an annual stem; in the tuberose roots, such as potatos, the

_Convolvulus batatas_ and _edulis_, the _Helianthus tuberosus_, the

_Jatropha manihot_, &c., which contain a great quantity of it; 3. in the

stems of several monocotyledinous plants, especially of the palm tribe,

whence sago comes; but it is very rarely found in the stems and branches

of the dicotyledinous plants; 4. it occurs in many species of lichen.

Three kinds of starch have been distinguished by chemists; that of

wheat, that called _inuline_, and lichen starch. These three agree in

being insoluble in cold water, alcohol, ether, and oils, and in being

converted into sugar by either dilute sulphuric acid or diastase. The

main difference between them consists in their habitudes with water and

iodine. The first forms with hot water a mucilaginous solution, which

constitutes, when cold, the paste of the laundress, and is tinged blue

by iodine; the second forms a granular precipitate, when its solution in

boiling-hot water is suffered to cool, which is tinged yellow by iodine;

the third affords, by cooling the concentrated solution, a gelatinous

mass, with a clear liquor floating over it, that contains little starch.

Its jelly becomes brown-gray with iodine.

1. _Ordinary starch._--This may be extracted from the following

grains:--wheat, rye, barley, oats, buckwheat, rice, maize, millet,

spelt; from the siliquose seeds, as peas, beans, lentiles, &c.; from

tuberous and tap roots, as those of the potato, the orchis, manioc;

arrowroot, batata, &c. Different kinds of corn yield very variable

quantities of starch. Wheat differs in this respect, according to the

varieties of the plant, as well as the soil, manure, season, and

climate. See BREAD.

Wheat partly damaged by long keeping in granaries, may be employed for

the manufacture of starch, as this constituent suffers less injury than

the gluten; and it may be used either in the ground or unground state.

1. _With unground wheat._--The wheat being sifted clean, is to be put

into cisterns, covered with soft water, and left to steep till it

becomes swollen and so soft as to be easily crushed between the fingers.

It is now to be taken out, and immersed in clear water of a temperature

equal to that of malting-barley, whence it is to be transferred into

bags, which are placed in a wooden chest containing some water, and

exposed to strong pressure. The water rendered milky by the starch being

drawn off by a tap, fresh water is poured in, and the pressure is

repeated. Instead of putting the swollen grain into bags, some prefer to

grind it under vertical edge-stones, or between a pair of horizontal

rollers, and then to lay it in a cistern, and separate the starchy

liquor by elutriation with successive quantities of water well stirred

up with it. The residuary matter in the sacks or cisterns contains much

vegetable albumen and gluten, along with the husks; when exposed to

fermentation, it affords a small quantity of starch of rather inferior

quality.

The above milky liquor, obtained by expression or elutriation, is run

into large cisterns, where it deposits its starch in layers successively

less and less dense; the uppermost containing a considerable proportion

of gluten. The supernatant liquor being drawn off, and fresh water

poured on it, the whole must be well stirred up, allowed again to

settle, and the surface-liquor again withdrawn. This washing should be

repeated as long as the water takes any perceptible colour. As the first

turbid liquor contains a mixture of gluten, sugar, gum, albumen, &c., it

ferments readily, and produces a certain portion of vinegar, which helps

to dissolve out the rest of the mingled gluten, and thus to bleach the

starch. It is, in fact, by the action of this fermented or soured water,

and repeated washing, that it is purified. After the last deposition and

decantation, there appears on the surface of the starch a thin layer of

a slimy mixture of gluten and albumen, which, being scraped off, serves

for feeding pigs or oxen; underneath will be found a starch of good

quality. The layers of different sorts are then taken up with a wooden

shovel, transferred into separate cisterns, where they are agitated with

water, and passed through fine sieves. After this pap is once more well

settled, the clear water is drawn off, the starchy mass is taken out,

and laid on linen cloths in wicker baskets, to drain and become

partially dry. When sufficiently firm, it is cut into pieces, which are

spread upon other cloths, and thoroughly desiccated in a proper

drying-room, which in winter is heated by stoves. The upper surface of

the starch is generally scraped, to remove any dusty matter, and the

resulting powder is sold in that state. Wheat yields, upon an average,

only from 35 to 40 per cent. of good starch. It should afford more by

skilful management.

2. In this country, wheat crushed between iron rollers is laid to steep

in as much water as will wet it thoroughly; in four or five days the

mixture ferments, soon afterwards settles, and is ready to be washed out

with a quantity of water into the proper fermenting vats. The common

time allowed for the steep, is from 14 to 20 days. The next process

consists in removing the stuff from the vats into a stout round basket

set across a back below a pump. One or two men keep going round the

basket, stirring up the stuff with strong wooden shovels, while another

keeps pumping water, till all the _farina_ is completely washed from the

bran. Whenever the subjacent back is filled, the liquor is taken out and

strained through hair sieves into square frames or cisterns, where it is

allowed to settle for 24 hours; after which the water is run off from

the deposited starch by plug taps at different levels in the side. The

thin stuff, called _slimes_, upon the surface of the starch, is removed

by a tray of a peculiar form. Fresh water is now introduced, and the

whole being well mixed by proper agitation, is then poured upon fine

silk sieves. What passes through is allowed to settle for 24 hours; the

liquor being withdrawn, and then the slimes, as before, more water is

again poured in, with agitation, when the mixture is again thrown upon

the silk sieve. The milky liquor is now suffered to rest for several

days, 4 or 5, till the starch becomes settled pretty firmly at the

bottom of the square cistern. If the starch is to have the blue tint,

called Poland, fine smalt must be mixed in the liquor of the last sieve,

in the proportion of 2 or 3 lbs. to the cwt. A considerable portion of

these slimes may, by good management, be worked up into starch by

elutriation and straining.

The starch is now fit for _boxing_, by shovelling the cleaned deposit

into wooden chests, about 4 feet long, 12 inches broad, and 6 inches

deep, perforated throughout, and lined with thin canvas. When it is

drained and dried into a compact mass, it is turned out by inverting the

chests upon a clean table, where it is broken into pieces 4 or 5 inches

square, by laying a ruler underneath the cake, and giving its surface a

cut with a knife, after which the slightest pressure with the hand will

make the fracture. These pieces are set upon half-burned bricks, which

by their porous capillarity imbibe the moisture of the starch, so that

its under surface may not become hard and horny. When sufficiently dried

upon the bricks, it is put into a stove (which resembles that of a sugar

refinery), and left there till tolerably dry. It is now removed to a

table, when all the sides are carefully scraped with a knife; it is next

packed up in the papers in which it is sold; these packages are returned

into the stove, and subjected to a gentle heat during some days; a point

which requires to be skilfully regulated.

Mr. Samuel Hall obtained a patent for bleaching starch by chloride of

lime in 1821. Chlorine water would probably be preferable, and might

prove useful in operating upon damaged wheat.

The sour water of the starch manufacture contains, according to

Vauquelin, acetic acid, acetate of ammonia, alcohol, phosphate of lime,

and gluten.

During the drying, starch splits into small prismatic columns, of

considerable regularity. When kept dry, it remains unaltered for a very

long period. When it is heated to a certain degree in water, the

envelopes of its spheroidal particles burst, and the _farina_ forms a

mucilaginous emulsion, magma, or paste. When this apparent solution is

evaporated to dryness, a brittle horny-looking substance is obtained,

quite different in aspect from starch, but similar in chemical

habitudes. When the moist paste is exposed for 2 or 3 months to the air

in summer, the starch is converted into sugar to the amount of one-third

or one-half of its weight, into gum, and gelatinous starch called

_amidine_ by De Saussure, with occasionally a resinous matter. This

curious change goes on even in close vessels.

_Starch from potatos._--From the following table of analyses, it appears

that potatos contain from 24 to 30 per cent. of dry substance:--

+-------------------+-------+-----------+--------+-----------+------+

| | | Fibrous | Veg. |Gum, Sugar,| |

| |Starch.|parenchyma.|Albumen.|and Salts. |Water.|

+-------------------+-------+-----------+--------+-----------+------+

|Red potato | 15·0 | 7·0 | 1·4 | 9·2 | 75·0 |

|Germinating potatos| 15·2 | 6·8 | 1·3 | 3·7 | 73·0 |

|Kidney potatos | 9·1 | 8·8 | 0·8 | --- | 81·3 |

|Large red potatos | 12·9 | 6·0 | 0·7 | --- | 78·0 |

|Sweet potatos | 15·1 | 8·2 | 0·8 | --- | 74·3 |

|Peruvian potatos | 15·0 | 5·2 | 1·9 | 1·9 | 76·0 |

|English potatos | 12·9 | 6·8 | 1·1 | 1·7 | 77·5 |

|Parisian potatos | 13·3 | 6·8 | 0·9 | 4·8 | 73·1 |

+-------------------+-------+-----------+--------+-----------+------+

[Illustration: 1047 1048]

_Manufacture of potato starch._--The potatos are first washed in a

cylindrical cage formed of wooden spars, made to revolve upon a

horizontal axis, in a trough filled with water to the level of the axis.

They are then reduced to a pulp by a rasping machine, similar to that

represented in _figs._ 1047, 1048., where _a_ is a wooden drum covered

with sheet-iron, roughened outside with numerous prominences, made by

punching out holes from the opposite side. It is turned by a winch fixed

upon each end of the shaft. The drum is enclosed in a square wooden box,

to prevent the potato-mash from being scattered about. The hopper _b_ is

attached to the upper frame, has its bottom concentric with the

rasp-drum, and nearly in contact with it. The pulp chest _c_ is made to

slide out, so as when full to be readily replaced by another. The two

slanting boards _d_, _d_, conduct the pulp into it. A moderate stream of

water should be made to play into the hopper upon the potatos, to

prevent the surface of the rasp from getting foul with fibrous matter.

Two men, with one for a relay, will rasp, with such a machine, from

2-1/2 to 3 tons of potatos in 12 hours.

The potato pulp must be now elutriated upon a fine wire or hair sieve,

which is set upon a frame in the mouth of a large vat, while water is

made to flow upon it from a spout with many jets. The pulp meanwhile

must be stirred and kneaded by the hand, or by a mechanical

brush-agitator, till almost nothing but fibrous particles are left upon

the sieve. These, however, generally retain about 5 per cent. of starch,

which cannot be separated in this way. This parenchyma should therefore

be subjected to a separate rasping upon another cylinder. The water

turbid with starch is allowed to settle for some time in a back; the

supernatant liquor is then run by a cock into a second back, and after

some time into a third, whereby the whole starch will be precipitated.

The finest powder collects in the last vessel. The starch thus obtained,

containing 33 per cent. of water, may be used either in the moist state,

under the name of _green fecula_, for various purposes, as for the

preparation of dextrine, and starch syrup; or it may be preserved under

a thin layer of water, which must be renewed from time to time, to

prevent fermentation; or lastly, it may be taken out and dried.

In trials made with St. Etienne’s rasp and starch machinery, in Paris,

which was driven by two horses, nearly 18 cwt. of potatos were put

through all the requisite operations in one hour, including the pumping

of the water. The product in starch amounted to from 17 to 18 per cent.

of the potatos. The quicker the process of potato-starch making, the

better is its quality.

_Starch from certain foreign plants._--1. From the pith of the _sago

palm_. See SAGO.

2. From the roots of the _Maranta arundinacea_, of Jamaica, the Bahamas,

and other West India islands, the powder called arrow-root is obtained,

by a process analogous to that for making potato starch.

3. From the root of the _Manioc_, which also grows in the West Indies,

as well as in Africa, the _cassava_ is procured, by a similar process.

The juice of this plant is poisonous, from which the wholesome starch is

deposited. When dried with stirring upon hot iron plates, it

agglomerates into small lumps, called _tapioca_; being a gummy fecula.

The characters of the different varieties of starch can be learnt only

from microscopic observation; by which means also their sophistication

or admixture may be readily ascertained.

Starch, from whatever source obtained, is a white soft powder, which

feels crispy, like flowers of sulphur, when pressed between the fingers;

it is destitute of taste and smell, unchangeable in the atmosphere, and

has a specific gravity of 1·53. I have already described the particles

as spheroids enclosed in a membrane. The potato contains some of the

largest, and the millet the smallest. Potato starch consists of

truncated ovoids, varying in size from 1/300 to 1/3000 of an inch;

arrow-root, of ovoids varying in size from 1/800 to 1/2000 of an inch;

flower starch, of insulated globules about 1/1000 of an inch; cassava,

of similar globules assembled in groups. These measurements I have made

with a good achromatic microscope, and a divided glass-slip micrometer

of Tully.

For the saccharine changes which starch undergoes by the action of

_diastase_, see FERMENTATION.

_Lichenine_, a species of starch obtained from Iceland moss (_Cetraria

islandica_), as well as _inuline_, from elecampane (_Inula Helenium_),

are rather objects of chemical curiosity, than of manufactures.

There is a kind of starch made in order to be converted into gum for the

calico-printer. This conversion having been first made upon the great

scale in this country, has occasioned the product to be called British

gum. The following is the process pursued in a large and well conducted

establishment near Manchester. A range of four wooden cisterns, each

about 7 or 8 feet square, and 4 feet deep, is provided. Into each of

them 2000 gallons of water being introduced, 12-1/2 loads of flour are

stirred in. This mixture is set to ferment upon old leaven left at the

bottom of the backs, during 2 or 3 days. The contents are then stirred

up, and pumped off into 3 stone cisterns, 7 feet square and 4 feet deep;

as much water being added, with agitation, as will fill the cisterns to

the brim. In the course of 24 hours the starch forms a firm deposit at

the bottom; and the water is then syphoned off. The gluten is next

scraped from the surface, and the starch is transferred into wooden

boxes pierced with holes, which may be lined with coarse cloth, or not,

at the pleasure of the operator.

The starch, cut into cubical masses, is put into iron trays, and set to

dry in a large apartment, two stories high, heated by a horizontal

cylinder of cast-iron traversed by the flame of a furnace. The drying

occupies two days. It is now ready for conversion into gum, for which

purpose it is put into oblong trays of sheet iron, and heated to the

temperature of 300° F. in a cast-iron oven, which holds four of these

trays. Here it concretes into irregular semi-transparent yellow-brown

lumps, which are ground into fine flour between mill-stones, and in

this state brought to the market. In this roasted starch, the vesicles

being burst, their contents become soluble in cold water. British gum is

not convertible into sugar, as starch is, by the action of dilute

sulphuric acid; nor into mucic acid, by nitric acid; but into the

oxalic; and it is tinged purple-red by iodine. It is composed, in 100

parts, of 35·7 carbon, 6·2 hydrogen, and 58·1 oxygen; while starch is

composed of, 43·5 carbon, 6·8 hydrogen, and 49·7 oxygen.

To prove whether starch be quite free from gluten, or whether it be

mixed with any wheat flour, diffuse 12 grains of it through six ounces

of water, heat the mixture to boiling, stirring it meanwhile with a

glass slip. If the starch be pure, no froth will be seen upon the

surface of the pasty fluid; or if any be produced during the stirring,

it will immediately subside after it; but if the smallest portion of

gluten be present, much froth will be permanently formed, which may be

raised by stirring into the appearance of soap-suds.

[Illustration: 1049 1050]

STARCHING AND STEAM-DRYING APPARATUS. The system of hollow cylinders,

for drying goods in the processes of bleaching or calico-printing, is

represented in _fig._ 1049. in a longitudinal section, and in _fig._

1050. in a top view; but the cylinders are supposed to be broken off in

the middle, as it was needless to repeat the parts at the other end,

which are sufficiently shown in the section.

A is the box containing the paste, when the goods are to be starched or

stiffened: _a_, a winch, when it is desired to turn the machine by

hand, though it is always moved by power in considerable factories; _b_,

is the driving pinion; _d_, _d´_, two brass rollers with iron shafts,

the undermost of which is moved by the wheel _c_, in geer with the

pinion _b_. The uppermost roller _d´_, is turned by the friction with

the former, _d_, being pressed upon it by the weighted lever _h_; _e_ is

the trough filled with the paste, which rests upon the bars _f_, and may

be placed higher or lower by means of the adjusting screws _g_,

according as the roller _d_ is to be plunged more or less deeply. A

brass roller _i_ serves to force down the cloth into the paste.

B, is the drying part of the machine: _k_, _k_, its iron framing; _l_,

_l_, &c., five drums, or hollow copper cylinders, heated with steam:

_m_, _m_, _m_, &c., small copper drums, in pairs, turning freely on

shafts under the former, for stretching the goods, and airing them,

during their passage through the machine: _n_, _n_, is the main

steam-pipe, from which branch off small copper tubes, _o_, _o_, &c.,

which conduct the steam through stuffing-boxes into the cavity of the

drying-drums. There are similar tubes upon the other ends of the drums,

for discharging the condensed water through similar stuffing-boxes: _q_,

_q_, are valves, opening internally, for admitting the air whenever the

steam is taken _off_, or becomes feeble, to prevent the drums from being

crushed by the unbalanced pressure of the atmosphere upon their external

surfaces.

C, is the cloth-beam, from which the starching roller draws forward the

goods; _d_, _d_, are two rollers, of which the lower is provided with a

band-pulley or rigger, driven by a similar pulley fixed upon the shaft

of the starching roller _d_. These two rollers pull the goods through

the drying machine, and then let them fall either upon a table or the

floor.

STEAM, is the vapour of hot water; the discussion of which belongs to

chemistry, physics, and engineering. Certain practical applications of

the subject will be found in the article EVAPORATION.

STEARIC ACID, improperly called STEARINE (_Talgsaüre_, Germ.), is the

solid constituent of fatty substances, as of tallow and olive oil,

converted into a crystalline mass by saponification with alkaline

matter, and abstraction of the alkali by an acid. By this process, fats

are convertible into three acids, called Stearic, Margaric, and Oleic;

the first two being solid, and the last liquid. The stearine, of which

_factitious wax_ candles are made, consists of the stearic and margaric

acids combined. These can be separated from each other only by the

agency of alcohol, which holds the margaric acid in solution after it

has deposited the stearic in crystals. Pure stearic acid is prepared,

according to its discoverer, Chevreul, in the following way:--Make a

soap, by boiling a solution of potash and mutton-suet in the proper

equivalent proportions (see SOAP); dissolve one part of that soap in 6

parts of hot water, then add to the solution 40 or 50 parts of cold

water, and set the whole into a place whose temperature is about 52°

Fahrenheit. A substance falls to the bottom, possessed of pearly lustre,

consisting of the bi-stearate and bi-margarate of potash; which is to be

drained and washed upon a filter. The filtered liquor is to be

evaporated, and mixed with the small quantity of acid necessary to

saturate the alkali left free by the precipitation of the above

bi-salts. On adding water to it afterwards, the liquor affords a fresh

quantity of bi-stearate and bi-margarate. By repeating this operation

with precaution, we finally arrive at a point when the solution contains

no more of these solid acids, but only the oleic. The precipitated

bi-salts are to be washed and dissolved in hot alcohol, of specific

gravity 0·820, of which they require about 24 times their weight. During

the cooling of the solution, the bi-stearate falls down, while the

greater part of the bi-margarate, and the remainder of the oleate,

remain dissolved. By once more dissolving in alcohol, and crystallizing,

the bi-stearate will be obtained alone; as may be proved by decomposing

a little of it in water at a boiling heat, with muriatic acid, letting

it cool, washing the stearic acid obtained, and exposing it to heat,

when, if pure, it will not fuse in water under the 158th degree of

Fahrenheit’s scale. If it melts at a lower heat, it contains more or

less margaric acid. The purified bi-stearate being decomposed by boiling

in water along with any acid, as the muriatic, the disengaged stearic

acid is to be washed by melting in water, then cooled and dried.

Stearic acid, prepared by the above process, contains combined water,

from which it cannot be freed. It is insipid and inodorous. After being

melted by heat, it solidifies at the temperature of 158° Fahrenheit, and

affects the form of white brilliant needles grouped together. It is

insoluble in water, but dissolves in all proportions in boiling

anhydrous alcohol, and on cooling to 122°, crystallizes therefrom, in

pearly plates; but if the concentrated solution be quickly cooled to

112°, it forms a crystalline mass. A dilute solution affords the acid

crystallized in large white brilliant scales. It dissolves in its own

weight of boiling ether of 0·727, and crystallizes on cooling in

beautiful scales, of changing colours. It distils over _in vacuo_

without alteration; but if the retort contains a little atmospheric air,

a small portion of the acid is decomposed during the distillation; while

the greater part passes over unchanged, but slightly tinged brown, and

mixed with traces of empyreumatic oil. When heated in the open air, and

kindled, stearic acid burns like wax. It contains 3·4 per cent. of

water, from which it may be freed by combining it with oxide of lead.

When this anhydrous acid is subjected to ultimate analysis, it is found

to consist of--80 of carbon, 12·5 hydrogen, and 7·5 oxygen, in 100

parts. Stearic acid displaces, at a boiling heat in water, carbonic acid

from its combinations with the bases; but in operating upon an alkaline

carbonate, a portion of the stearic acid is dissolved in the liquor

before the carbonic acid is expelled. This decomposition is founded upon

the principle, that the stearic acid transforms the salt into a

bicarbonate, which is decomposed by the ebullition.

Stearic acid put into a strong watery infusion of litmus, has no action

upon it in the cold; but when hot, the acid combines with the alkali of

the litmus, and changes its blue colour to red; so that it has

sufficient energy to abstract from the concentrated tincture all the

alkali required for its neutralization. If we dissolve bi-stearate of

potash in weak alcohol, and pour litmus water, drop by drop, into the

solution, this will become red, because the litmus will give up its

alkali to a portion of the bi-stearate, and will convert it into neutral

stearate. If we now add cold water, the reddened mixture will resume its

blue tint, and will deposit bi-stearate of potash in small spangles. In

order that the alcoholic solution of the bi-stearate may redden the

litmus, the alcohol should not be very strong.

From the composition of stearate of potash, the atomic weight of the

acid appears to be 106·6; hydrogen being 1; for 18 : 48 × 2 ∷ 100 :

533·3 = 5 atoms of acid.

From the stearate of soda, it appears to be 104; and from that of lime,

102. The stearate of lead, by Chevreul, gives 109 for the atomic weight

of the acid.

The margaric and oleic acids seem to have the same neutralizing power,

and the same atomic weight.

The preceding numbers will serve to regulate the manufacture of stearic

acid for the purpose of making candles. Potash and soda were first

prescribed for saponifying fat, as may be seen in M. Gay Lussac’s

patent, under the article CANDLE; and were it not for the cost of these

articles, they are undoubtedly preferable to all others in a chemical

point of view. Of late years lime has been had recourse to, with perfect

success, and has become subservient to a great improvement in

candle-making. The stearine block now made by many London houses, though

containing not more than 2 or 3 per cent. of wax, is hardly to be

distinguished from the purified produce of the bee. The first process is

to boil the fat with quicklime and water in a large tub, by means of

perforated steam pipes distributed over its bottom. From the above

statements we see that about 11 parts of dry lime are fully equivalent

to 100 of stearine and oleine mixed: but as the lime is in the state of

hydrate, 14 parts of it will be required when it is perfectly pure; in

the ordinary state, however, as made from average good limestone, 16

parts may be allowed. After a vigorous ebullition of 3 or 4 hours, the

combination is pretty complete. The stearate being allowed to cool to

such a degree as to allow of its being handled, becomes a concrete mass,

which must be dug out with a spade, and transferred into a contiguous

tub, in order to be decomposed with the equivalent quantity of sulphuric

acid diluted with water, and also heated with steam. Four parts of

concentrated acid will be sufficient to neutralize three parts of slaked

lime. The saponified fat now liberated from the lime, which is thrown

down to the bottom of the tub in the state of sulphate, is skimmed off

the surface of the watery menstruum into a third contiguous tub, where

it is washed with water and steam.

The washed mixture of stearic, margaric, and oleic acids, is next cooled

in tin pans; then shaved by large knives, fixed on the face of a

fly-wheel, called a tallow cutter, preparatory to its being subjected in

canvas or caya bags to the action of a powerful hydraulic press. Here a

large portion of the oleic acid is expelled, carrying with it a little

of the margaric. The pressed cakes are now subjected to the action of

water and steam once more, after which the supernatant stearic acid is

run off, and cooled in moulds. The cakes are then ground by a rotatory

rasping-machine to a sort of mealy powder, which is put into canvas

bags, and subjected to the joint action of steam and pressure in a

horizontal hydraulic press of a peculiar construction, somewhat similar

to that which has been long used in London for pressing spermaceti. The

cakes of stearic acid thus freed completely from the margaric and oleic

acids, are subjected to a final cleansing in a tub with steam, and then

melted into hemispherical masses called blocks. When these blocks are

broken, they display a highly crystalline texture, which would render

them unfit for making candles. This texture is therefore broken down or

comminuted by fusing the stearine in a plated copper pan, along with one

thousandth part of pulverized arsenious acid, after which it is ready to

be cast into candles in appropriate moulds. See CANDLE.

[Illustration: 1051 _Scale 3-20ths of an inch to the foot._]

[Illustration: 1052 1053]

STEARINE COLD PRESS. The cold hydraulic press, as mounted by Messrs.

Maudslay and Field, for squeezing out the oleic acid from saponified

fat, or the oleine from coco-nut lard, is represented in plan in _fig._

1051.; in side view of pump in _fig._ 1052.; and in elevation, _fig._

1053.; where the same letters refer to like objects.

A, A, are two hydraulic presses; B the frame; C, the cylinder; D, the

piston or ram; E, the follower; F, the recess in the bottom to receive

the oil; G, twilled woollen bags with the material to be pressed, having

a thin plate of wrought iron between each; H, apertures for the

discharge of the oil; I, cistern in which the pumps are fixed; K,

framing for machinery to work in; L, two pumps, large and small, to

inject the water into the cylinders; M, a frame containing three double

branches; N, three branches, each having two stops or plugs, by which

the action of one of the pumps may be intercepted from, or communicated

to, one or both of the presses; the large pump is worked at the

beginning of the operation, and the small one towards the end; by these

branches, one or both presses may be discharged when the operation is

finished; O, two pipes from the pumps to the branches; P, pipe to return

the water from the cylinders to the cisterns; Q, pipes leading from the

pumps through the branches to the cylinders; R, conical drum, fixed upon

the main shaft Y, driven by the steam-engine of the factory; S, a like

conical drum to work the pumps; T, a narrow leather strap to communicate

the motion from R to S; U, a long screw bearing a nut, which works along

the whole length of the drum; V, the fork or guide for moving the strap

T; W, W, two hanging bearings to carry the drum S; X, a pulley on the

spindle of the drum S; Y, the main shaft; Z, fly-wheel with groove on

the edge, driven by the pulley X; on the axis of S, is a double crank,

which works the two pumps L. _a_, is a pulley on the end of the long

screw U; an endless cord passes twice round this pulley, and under a

pulley fixed in the weight _b_; by laying hold of both sides of his

cord, and raising or lowering it, the forked guide V, and the leather

strap T, are moved backwards or forwards, by means of the nut fixed in

the guide, so as to accelerate or retard at pleasure the speed of the

working of the pumps; _c_, is a piece of iron, with a long slit, in

which a pin, attached to the fork V, travels, to keep it in the vertical

position.

STEATITE (_Soapstone_; _Craie de Briançon_, Fr.; _Speckstein_, Germ.);

is a mineral of the magnesian family. It has a grayish-white or

greenish-white colour, often marked with dendritic delineations, and

occurs massive, as also in various supposititious crystalline forms; it

has a dull or fatty lustre; a coarse splintery fracture, with

translucent edges; a shining streak; it writes feebly; is soft, and

easily cut with a knife; but somewhat tough; does not adhere to the

tongue; feels very greasy; infusible before the blowpipe; specific

gravity from 2·6 to 2·8. It consists of--silica, 44; magnesia, 44;

alumina, 2; iron, 7·3; manganese, 1·5; chrome, 2; with a trace of lime.

It is found frequently in small contemporaneous veins that traverse

serpentine in all directions, as at Portsoy, in Shetland, in the

limestone of Icolmkiln, in the serpentine of Cornwall, in Anglesey, in

Saxony, Bavaria (at Bayruth), Hungary, &c. It is used in the manufacture

of porcelain. It makes the biscuit semi-transparent, but rather brittle,

and apt to crack with slight changes of heat. It is employed for

polishing serpentine, marble, gypseous alabaster, and mirror glass; as

the basis of cosmetic powders; as an ingredient in anti-attrition

pastes; it is dusted in powder upon the inside of boots, to make the

feet glide easily into them; when rubbed upon grease-spots in silk and

woollen clothes, it removes the stains by absorption; it enters into the

composition of certain crayons, and is used itself for making traces

upon glass, silk, &c. The spotted steatite, cut into cameos and

calcined, assumes an onyx aspect. Soft steatite forms excellent stoppers

for the chemical apparatus used in distilling or subliming corrosive

vapours. Lamellar steatite is TALC.

STEEL (_Acier_, Fr.; _Stahl_, Germ.); as a carburet of iron, has already

been considered under that metal. I shall treat in this article more

particularly of its manufacture and technical relations.

1. _Steel of cementation, bar or blistered steel._--With the exception

of the Ulverstone charcoal iron, no bars are manufactured in Great

Britain capable of conversion into steel at all approaching in quality

to that made from the Madras, Swedish, and Russian irons, so largely

imported for that purpose. The first rank is assigned to the Swedish

iron stamped with a circle enclosing the letter L (hence called hoop L);

which fetches the high price of 36_l._ 10_s._ per ton, while excellent

English coke-iron may be had for one-fifth of the price. The other

Swedish irons are sold at a much lower rate, though said to be

manufactured in the same way; and therefore the superiority of the

Dannemora iron must be owing to some peculiarity in the ore from which

it is smelted. The steel recently made in the Indian steel-works at

Chelsea, from Mr. Heath’s Madras iron, rivals that from the hoop L.

[Illustration: 1054 1055]

The Sheffield furnace for making bar or blistered steel, called the

furnace of cementation, is represented in _fig._ 1054. in a cross

section, and in _fig._ 1055. in a ground plan. The hearth of this oblong

quadrangular furnace, is divided by a grate into two parts, upon each

side of which there is a chest _a_, called a _trough_, made of

fire-clay, or fire-tiles. The breadth of the grate varies according to

the quality of the fuel. _b_, _b_, are air-holes; _c_, _c_, flues

leading to the chimney _d_, _d_. To aid the draught of the smoke and the

flame, an opening _e_, is made in the middle of the flat arch of the

furnace. In one of its shorter sides (ends), there are orifices _f_,

_f_, through which the long bars of iron may be put in and taken out;

_g_, is the door by which the steel-maker enters, in filling or emptying

the trough; _h_, is a proof hole, at which small samples of the steel,

in the act of its conversion, may be drawn out. The furnace is built

under a conical hood or chimney, from 30 to 50 feet high, for aiding the

draught, and carrying off the smoke.

The two chests are built of fire-stone grit. They are 8, 10, or even 15

feet long, and from 26 to 36 inches in width and depth; the lower and

smaller they are, the more uniform will the quality of the steel be. A

great breadth and height of trough are incompatible with equability of

the cementing temperature. The sides are a few inches thick. The space

between them is at least a foot wide. They should never rest directly

upon the sole of the furnace, but must have their bottom freely played

upon by the flame, as well as the sides and top. The degree of heat is

regulated by openings in the arch, or upon the long sides of the

furnace, which lead to the chimney; as also by the greater or less

quantity of air admitted below the grate, as in glass-house furnaces.

The _cement_ consists of ground charcoal (sometimes of soot), mixed with

one-tenth of ashes, and some common salt; the charcoal of hard wood

being preferred. Ground coke is inadmissible, on account of the sulphur,

silica, and clay which it generally contains. Possibly the salt serves

to vitrify the particles of silica in the charcoal, and thus to prevent

their entering into combination with the steel. As for the ashes, it is

difficult to discover their use. The best steel may be made without

their presence. The bottom of the trough being covered with two inches

of the powder of cementation, the bars are laid along in it, upon their

narrow edge, the side bar being one inch from the trough, and the rest

being from 1/2 to 3/4 of an inch apart. Above this first layer of iron

bars, fully half an inch depth of the powder is spread, then a new

series of bars is stratified, and so on till the trough is filled within

six inches of the top. This space is partially filled with old cement

powder, and is covered with refractory damp sand. Sometimes the trough

is filled to the surface with the old cement, and then closely covered

with fire-tiles. The bars should never be allowed to touch each other,

or the trough. The fire must be carefully urged from 2 to 4 days, till

it acquires the temperature of 100° Wedgewood; which must be steadily

maintained during the 4, 6, 8, or 10 days requisite for the cementation;

a period dependent on the size of the furnace, and which is determined

by the examination of the proof pieces, taken out from time to time.

In the front or remote end of the furnace, _fig._ 1054., a door is left

in the outer building, corresponding to a similar one in the end of the

interior vault, through which the workman enters for charging the

furnace with charcoal and iron bars, as also for taking out the steel

after the conversion. Small openings are likewise made in the ends of

the chests, through which the extremities of a few bars are left

projecting, so that they may be pulled out and examined, through small

doors opposite to them in the exterior walls. These _tap_ holes, as they

are called, should be placed near the centre of the end stones of the

chests, that the bars may indicate the average state of the process. The

joinings of the fire-stones are secured with a finely ground Stourbridge

clay.

The interval between the two chests (in furnaces containing two, for

many have only one,) being covered with an iron platform, the workman

stands on it, and sifts a layer of charcoal on the bottom of the chests

evenly, about half an inch thick; he then lays a row of bars, cut to the

proper length, over the charcoal, about an inch from each other; he next

sifts on a second stratum of charcoal-dust, which, as it must serve for

the bars above, as well as below, is made an inch thick; thus, he

continues to stratify, till the chest be filled within two inches of the

top; and he covers the whole with the earthy detritus found at the

bottom of grindstone troughs, or any convenient fire-loam. It is obvious

that the second series of bars should correspond vertically with the

interstices between the first series, and so in succession. The

trial-rods are left longer than the others, and their projecting ends

are encrusted with fire-clay, or imbedded in sand. The iron platform

being removed, and all the openings into the vault closed, the fire is

lighted, and very gradually increased, to avoid every risk of cracking

the gritstone by too sudden a change of temperature; and the ignition

being finally raised to about 100° Wedgewood, but not higher, for fear

of melting the metal, must be maintained at a uniform pitch, till the

iron have absorbed the desired quantity of carbon, and have been

converted as highly as the manufacturer intends for his peculiar object.

From six to eight days may be reckoned a sufficient period for the

production of steel of moderate hardness, and fit for tilting into shear

steel. A softer steel, for saws and springs, takes a shorter period; and

a harder steel, for fabricating chisels used in cutting iron, will need

longer exposure to the ignited charcoal. But, for a few purposes, such

as the bits for boring cast iron, the bars are exposed to two or three

successive processes of cementation, and are hence said to be twice or

thrice converted into steels. The higher the heat of the furnace, the

quicker is the process of conversion.

The furnace being suffered to cool, the workman enters it again, and

hands out the steel bars, which being covered with blisters, from the

formation and bursting of vesicles on the surface filled with gaseous

carbon, is called _blistered steel_. This steel is very irregular in its

interior texture, has a white colour, like frosted silver, and displays

crystalline angles and facettes, which are larger the further the

cementation has been urged, or the greater the dose of carbon. The

central particles are always smaller than those near the surface of the

bar.

In such a furnace as the above, twelve tons of bar iron may be converted

at a charge. But other furnaces are constructed with one chest, which

receives six or eight tons at a time; the small furnaces, however,

consume more fuel in proportion than the larger.

The absorption and action of the carbonaceous matter, to the amount of

about a half per cent., occasions fissures and cavities in the substance

of the blistered bars, which render the steel unfit for any useful

purpose in tool-making, till it be condensed and rendered uniform by the

operation of _tilting_, under a powerful hammer driven by machinery. See

IRON.[59]

[59] For minute details of the parts, see the excellent article

TILTING-HAMMER, in _Rees’s Cyclopædia_.

The heads of the tilt-hammers for steel weigh from one and a half to two

hundred pounds. Those in the neighbourhood of Sheffield are much simpler

than the one referred to in the note. They are worked by a small

water-wheel, on whose axis is another wheel, bearing a great number of

cams or wipers on its circumference, which strike the tail of the hammer

in rapid succession, raise its head, and then let it fall smartly on the

hot metal rod, dexterously presented on its several parts to the anvil

beneath it, by the workman. The machinery is adapted to produce from 300

to 400 blows per minute; which on this plan requires an undue and

wasteful velocity of the float-boards. Were an intermediate toothed

wheel substituted between the water-wheel and the wiper-wheel, so that

while the former made one turn, the latter might make three, a much

smaller force of water would do the work. The anvils of the tilt-hammer

are placed nearly on a level with the floor of the mill-house; and the

workman sits in a fosse, dug on purpose, in a direction perpendicular to

the line of the helve, on a board suspended from the roof of the

building by a couple of iron rods. On this swinging seat, he can advance

or retire with the least impulse of his feet, pushing forward the steel

bar, or drawing it back with equal rapidity and convenience.

At a small distance from each tilt, stands the forge-hearth, for heating

the steel. The bellows for blowing the fire are placed above-head, and

are worked by a small crank fixed on the end of the axis of the wheel,

the air being conveyed by a copper pipe down to the nozzle. Each workman

at the tilt has two boys in attendance, to serve him with hot rods, and

to take them away after they are hammered. In small rods, the bright

ignition originally given at the forge soon declines to darkness; but

the rapid impulsions of the tilt revive the redness again in all the

points near the hammer; so that the rod, skilfully handled by the

workman, progressively ignites where it advances to the strokes.

Personal inspection alone can communicate an adequate idea of the

precision and celerity with which a rude steel rod is stretched and

fashioned into an even, smooth, and sharp-edged prism, under the

operation of the tilt-hammer. The heat may be clearly referred to the

prodigious friction among the particles of so cohesive a metal, when

they are made to slide so rapidly over each other in every direction

during the elongation and squaring of the rod.

2. _Shear steel_ derives its name from the accidental circumstance of

the shears for dressing woollen cloth being usually forged from it. It

is made by binding into a bundle, with a slender steel rod, four

parallel bars of blistered steel, previously broken into lengths of

about 18 inches, including a fifth of double length, whose projecting

end may serve as a handle. This faggot, as it is called, is then heated

in the forge-hearth to a good welding heat, being sprinkled over with

sand to form a protecting film of iron slag, carried forthwith to the

tilt, and notched down on both sides to unite all the bars together, and

close up every internal flaw or fissure. The mass being again heated,

and the binding rings knocked off, is drawn out into a uniform rod of

the size required. Manufacturers of cutlery are in the habit of

purchasing the blistered bars at the conversion furnaces, and sending

them to tilt-mills to have them drawn out to the proper size, which is

done at regular prices to the trade; from 5 to 8 per cent. discount

being allowed on the rude bars for waste in the tilting. The metal is

rendered so compact by the welding and hammering, as to become

susceptible of a much finer polish than blistered steel can take; while

the uniformity of its body, tenacity, and malleability are at the same

time much increased; by which properties it becomes well adapted for

making table knives and powerful springs, such as those of gun-locks.

The steel is also softened down by this process, probably from the

expulsion of a portion of its carbon during the welding and subsequent

heats; and if these be frequently or awkwardly applied, it may pass back

into common iron.

3. _Cast steel_ is made by melting, in the best fire-clay crucibles,

blistered steel, broken down into small pieces of convenient size for

packing; and as some carbon is always dissipated in the fusion, a

somewhat highly converted steel is used for this purpose. The furnace is

a square prismatic cavity, lined with fire-bricks, 12 inches in each

side, and 24 deep, with a flue immediately under the cover, 3-1/2 inches

by 6, for conducting the smoke into an adjoining chimney of considerable

height. In some establishments a dozen such furnaces are constructed in

one or two ranges, their tops being on a level with the floor of the

laboratory, as in brass-foundries, for enabling the workmen more

conveniently to inspect, and lift out, the crucibles with tongs. The

ash-pits terminate in a subterraneous passage, which supplies the grate

with a current of cool air, and serves for emptying out the ashes. The

crucible, stands of course, on a sole-piece of baked fire-clay; and its

mouth is closed with a well-fitted lid. Sometimes a little bottle-glass,

or blast-furnace slag, is put into the crucible, above the steel pieces,

to form a vitreous coating, that may thoroughly exclude the air from

oxidizing the metal. The fuel employed in the cast-steel furnace is a

dense coke, brilliant and sonorous, broken into pieces about the size of

an egg, one good charge of which is sufficient. The tongs are furnished

at the fire end with a pair of concave jaws, for embracing the curvature

of the crucible, and lifting it out whenever the fusion is complete. The

lid is then removed, the slag or scoriæ cleared away, and the liquid

metal poured into cast-iron octagonal or rectangular moulds, during

which it throws out brilliant scintillations.

Cast-steel works much harder under the hammer than shear steel and will

not, in its usual state, bear much more than a cherry-red heat without

becoming brittle; nor can it bear the fatigue incident to the welding

operation. It may, however, be firmly welded to iron, through the

intervention of a thin film of vitreous boracic acid, at a moderate

degree of ignition. Cast steel, indeed, made from a less carburetted bar

steel, would be susceptible of welding and hammering at a higher

temperature; but it would require a very high heat for its preparation

in the crucible.

Iron may be very elegantly plated with cast steel, by pouring the liquid

metal from the crucible into a mould containing a bar of iron polished

on one face. In this circumstance the adhesion is so perfect as to admit

of the two metals being rolled out together; and in this way the chisels

of planes and other tools may be made, at a moderate rate and of

excellent quality, the cutting-edge being formed in the steel side. Such

instruments combine the toughness of iron with the hardness of steel.

For correcting the too high carbonization of steel, or equalizing the

too highly converted exterior of a bar with the softer steel of the

interior, the metal requires merely to be imbedded, at a cementing heat,

in oxide of iron or manganese; the oxygen of which soon abstracts the

injurious excess of carbon, so that the outer layers may be even

converted into soft iron, while the axis continues steely; because the

decarbonizing advances far more rapidly than the carbonizing.

[Illustration: 1056]

_Fig._ 1056. represents the mould for making crucibles for the

cast-steel works. M, M, is a solid block of wood, to support the

two-handled outside mould N, N. This being rammed full of the proper

clay dough or compost (see CRUCIBLE), the inner mould is to be then

pressed vertically into it, till it reaches the bottom P, being directed

and facilitated in its descent by the point _K_. A cord passes through

O, by which the inner mould is suspended over a pulley, and guided in

its motions.

When a plate of polished steel is exposed to a progressive heat, it

takes the following colours in succession: 1. a faint yellow; 2. a pale

straw-colour; 3. a full yellow; 4. a brown yellow; 5. a brown with

purple spots; 6. a purple; 7. a bright blue; 8. a full blue; 9. a dark

blue, verging on black; after which the approach to ignition supersedes

all these colours. If the steel plate has been previously hardened by

being dipped in cold water or mercury when red-hot, then those

successive shades indicate or correspond to successive degrees of

softening or tempering. Thus, No. 1. suits the hard temper of a lancet,

which requires the finest edge, but little strength of metal; No. 2. a

little softer, for razors and surgeons’ amputating instruments; No. 3.

somewhat more toughness, for penknives; No. 4. for cold chisels and

shears for cutting iron; No. 5. for axes and plane-irons; No. 6. for

table knives and cloth shears; No. 7. for swords and watch springs; No.

8. for small fine saws and daggers; No. 9. for large saws, whose teeth

need to be set with pliers, and sharpened with a file. After ignition,

if the steel be very slowly cooled, it becomes exceedingly soft, and fit

for the engraver’s purposes. Hardened steel may be tempered to the

desired pitch, by plunging it in metallic baths heated to the proper

thermometric degree, as follows: for No. 1. 430° Fahr.; No. 2. 450°; No.

3. 470°; No. 4. 490°; No. 5. 510°; No. 6. 530°; No. 7. 550°; No. 8.

560°; No. 9. 600°.

Small steel tools are most frequently tempered, after hardening, by

covering their surface with a thin coat of tallow, and heating them in

the flame of a candle till the tallow diffuses a faint smoke, and then

thrusting them into the cold tallow. Rinman long ago defined steel to be

any kind of iron which, when heated to redness, and then plunged in cold

water, becomes harder. But several kinds of cast iron are susceptible of

such hardening. Every malleable and flexible iron, however, which may be

hardened in that way, is a steel. Moreover, steel may be distinguished

from pure iron by its giving a dark-gray spot when a drop of dilute

nitric acid is let fall on its surface, while iron affords a green one.

Exposed to the air, steel rusts less rapidly than iron; and the more

highly carburetted, the more slowly does it rust, and the blacker is the

spot left by an acid.

After hardening, steel seems to be quite a different body; even its

granular texture becomes coarser or finer according to the degree of

heat to which it was raised; it grows so hard as to scratch glass, and

resist the keenest file, while it turns exceedingly brittle. When a

slowly cooled steel rod is forged and filed, it becomes capable of

affording agreeable and harmonious sounds by its vibrations; but

hard-tempered steel affords only dull deafened tones, like those emitted

by a cracked instrument.

The good quality of steel is shown by its being homogeneous; being

easily worked at the forge; by its hardening and tempering well; by its

resisting or overcoming forces; and by its elasticity. To ascertain the

first point, the surface should be ground and polished on the wheel;

when its lustre and texture will appear. The second test requires a

skilful workman to give it a heat suitable to its nature and state of

conversion. The size and colour of the grain are best shown by taking a

bar forged into a razor form; hardening and tempering it; and then

breaking off the thin edge in successive bits with a hammer and anvil.

If it had been fully ignited only at the end, then, after the hardening,

it will display, on fracture, a succession in the aspect of its grains

from that extremity to the other; as they are whiter and larger at the

former than the latter. The other qualities become manifest on filing

the steel; using it as a chisel for cutting iron; or bending it under a

heavy weight.

Much interest was excited a few years back by the experiments of Messrs.

Stodart and Faraday on the alloys of steel with silver, platinum,

rhodium, and iridium. Steel refuses to take up in fusion more than one

five-hundreth part of silver; but with this minute quantity of alloy, it

is said to bear a harder temper, without losing its tenacity. When pure

iron is substituted for steel, the alloys so formed are much less

subject to oxidation in damp air than before. With three _per cent._ of

iridium and osmium, an alloy was obtained which had the property of

tempering like steel, and of remaining clean and bright, in

circumstances when simple iron became covered with rust. “Upon the

whole,” says the editor of the Quarterly Journal of Science, giving a

report of these experiments in his 14th volume, p. 378, “though we

consider these researches upon the alloys of steel as very interesting,

we are not sanguine as to their important influence upon the improvement

of the manufacture of cutlery, and suspect that a bar of the best

ordinary steel, selected with precaution, and most carefully forged,

wrought, and tempered, _under the immediate inspection of the master_,

would afford cutting instruments as perfect and excellent as those

composed of wootz, or of the alloys.”

_Case-hardening_ of iron, is a process for converting a thin film of the

outer surface into steel, while the interior remains as before. Fine

keys are generally finished in this way. See CASE-HARDENING.

So great is the affinity of iron for carbon, that, in certain

circumstances, it will absorb it from carburetted hydrogen, or coal-gas,

and thus become converted into steel. On this principle, Mr. Macintosh

of Glasgow obtained a patent for making steel. His furnace consists of

one cylinder of bricks built concentrically within another. The bars of

iron are suspended in the innermost, from the top; a stream of purified

coal-gas circulates freely round them, entering below and escaping

slowly above, while the bars are maintained in a state of bright

ignition by a fire burning in the annular space between the cylinders.

The steel so produced is of excellent quality; but the process does not

seem to be so economical as the ordinary cementation with charcoal

powder.

_Damasking of steel_, is the art of giving to sabre blades a variety of

figures in the style of watering. See DAMASCUS BLADES.

Several explanations have been offered of the change in the constitution

of steel, which accompanies the tempering operation; but none of them

seems quite satisfactory. It seems to be probable that the ultimate

molecules are thrown by the sudden cooling into a constrained state, so

that their poles are not allowed to take the position of strongest

attraction and greatest proximity; and hence the mass becomes hard,

brittle, and somewhat less dense. An analogous condition may be justly

imputed to hastily cooled glass, which, like hardened steel, requires to

be annealed by a subsequent nicely graduated heat, under the influence

of which the particles assume the position of repose, and constitute a

denser, softer, and more tenacious body. The more sudden the cooling of

ignited steel, the more unnatural and constrained will be the

distribution of its particles, and also the more refractory, an effect

produced by plunging it into cold mercury. This excess of hardness is

removed in any required degree by judicious annealing or tempering. The

state of the carbon present in the steel may also be modified by the

rate of refrigeration, as Mr. Karsten and M. Bréant conceive happens

with cast iron and the damask metal. If the uniform distribution and

combination of the carbon through the mass, determine the peculiarity of

white cast iron, which is a hard and brittle substance, and if its

transition to the dark-gray and softer cast metal be effected by a

partial formation of plumbago during slow cooling, why may not something

similar be supposed to occur with steel, an analogous compound?

Mr. Oldham, printing engineer of the Bank of England, who has had great

experience in the treatment of steel for dies and mills, says that, for

hardening it, the fire should never be heated above the redness of

sealing-wax, and kept at that pitch for a sufficient time. On taking it

out, he hardens it by plunging it, not in water, but in olive oil, or

rather naphtha, previously heated to 200° F. It is kept immersed only

till the ebullition ceases, then instantly transferred into cold spring

water, and kept there till quite cold. By this treatment the tools come

out perfectly clean, and as hard as it is possible to make cast-steel,

while they are perfectly free from cracks, flaws, or twist. Large tools

are readily brought down in temper by being suspended in the red-hot

muffle till they show a straw-colour; but for small tools, he prefers

plunging them in the oil heated to 400 degrees; and leaves them in till

they become cold.

Mr. Oldham softens his steel dies by exposing them to ignition for the

requisite time, imbedded in a mixture of chalk and charcoal.

“The common mode of softening steel,” says Mr. Baynes, “is to put it

into an iron case, surrounded with a paste made of lime, cow’s gall, and

a little nitre and water; then to expose the case to a slow fire, which

is gradually increased to a considerable heat, and afterwards allowed to

go out, when the steel is found to be soft and ready for the

engraver.”[60]

[60] History of the Cotton Manufacture, p. 269. If that strange

farrago be employed by Mr. Locket of Manchester, for softening his

dies and mills, it deserves consideration. Should the nitre be used in

too great quantity to be all carbonated by the gall, its oxygen may

serve to consume some of the carbon of the steel, and thus bring it

nearer to iron. The recipe may be old, but it is a novelty to me.

_Indian steel, or wootz._--The wootz ore consists of the magnetic oxide

of iron, united with quartz, in proportions which do not seem to differ

much, being generally about 42 of quartz and 58 of magnetic oxide. Its

grains are of various size, down to a sandy texture. The natives prepare

it for smelting by pounding the ore, and winnowing away the stony

matrix, a task at which the Hindoo females are very dexterous. The

manner in which iron ore is smelted and converted into wootz or Indian

steel, by the natives at the present day, is probably the very same that

was practised by them at the time of the invasion of Alexander; and it

is a uniform process, from the Himalaya mountains to Cape Comorin. The

furnace or bloomery in which the ore is smelted, is from 4 to 5 feet

high; it is somewhat pear-shaped, being about 2 feet wide at bottom, and

one foot at top; it is built entirely of clay, so that a couple of men

can finish its erection in a few hours, and have it ready for use the

next day. There is an opening in front about a foot or more in height,

which is built up with clay at the commencement, and broken down at the

end, of each smelting operation. The bellows are usually made of a

goat’s skin, which has been stripped from the animal without ripping

open the part covering the belly. The apertures at the legs are tied up,

and a nozzle of bamboo is fastened in the opening formed by the neck.

The orifice of the tail is enlarged and distended by two slips of

bamboo. These are grasped in the hand, and kept close together in making

the stroke for the blast; in the returning stroke they are separated to

admit the air. By working a bellows of this kind with each hand, making

alternate strokes, a pretty uniform blast is produced. The bamboo

nozzles of the bellows are inserted into tubes of clay, which pass into

the furnace at the bottom corners of the temporary wall in front. The

furnace is filled with charcoal, and a lighted coal being introduced

before the nozzles, the mass in the interior is soon kindled. As soon as

this is accomplished, a small portion of the ore, previously moistened

with water, to prevent it from running through the charcoal, but without

any flux whatever, is laid on the top of the coals, and covered with

charcoal to fill up the furnace.

In this manner ore and fuel are supplied; and the bellows are urged for

3 or 4 hours, when the process is stopped; and the temporary wall in

front being broken down, the bloom is removed by a pair of tongs from

the bottom of the furnace. It is then beaten with a wooden mallet, to

separate as much of the scoriæ as possible from it, and, while still

red-hot, it is cut through the middle, but not separated, in order

merely to show the quality of the interior of the mass. In this state it

is sold to the blacksmiths, who make it into bar iron. The proportion of

such iron made by the natives from 100 parts of ore, is about 15 parts.

In converting the iron into steel, the natives cut it into pieces, to

enable it to pack better in the crucible, which is formed of refractory

clay, mixed with a large quantity of charred husk of rice. It is seldom

charged with more than a pound of iron, which is put in with a proper

weight of dried wood chopped small, and both are covered with one or two

green leaves; the proportions being in general 10 parts of iron to 1 of

wood and leaves. The mouth of the crucible is then stopped with a

handful of tempered clay, rammed in very closely, to exclude the air.

The wood preferred is the _Cassia auriculata_, and the leaf that of the

_Asclepias gigantea_, or the _Convolvulus laurifolius_. As soon as the

clay plugs of the crucibles are dry, from 20 to 24 of them are built up

in the form of an arch, in a small blast furnace; they are kept covered

with charcoal, and subjected to heat urged by a blast for about two

hours and a half, when the process is considered to be complete. The

crucibles being now taken out of the furnace and allowed to cool, are

broken, and the steel is found in the form of a cake, rounded by the

bottom of the crucible. When the fusion has been perfect, the top of the

cake is covered with striæ, radiating from the centre, and is free from

holes and rough projections; but if the fusion has been imperfect, the

surface of the cake has a honeycomb appearance, with projecting lumps of

malleable iron. On an average, four out of five cakes are more or less

defective. These imperfections have been tried to be corrected in London

by re-melting the cakes, and running them into ingots; but it is

obvious, that when the cakes consist partially of malleable iron and of

unreduced oxide, simple fusion cannot convert them into good steel. When

care is taken, however, to select only such cakes as are perfect, to

re-melt them thoroughly, and tilt them carefully into rods, an article

has been produced which possesses all the requisites of fine steel in an

eminent degree. In the Supplement to the Encyclopædia Britannica,

article _Cutlery_, the late Mr. Stodart, of the Strand, a very competent

judge, has declared “that for the purposes of fine cutlery, it is

infinitely superior to the best English cast steel.”

The natives prepare the cakes for being drawn into bars by annealing

them for several hours in a small charcoal furnace, actuated by bellows;

the current of air being made to play upon the cakes while turned over

before it; whereby a portion of the combined carbon is probably

dissipated, and the steel is softened; without which operation the cakes

would break in the attempt to draw them. They are drawn by a hammer of a

few pounds weight.

The natives weld two pieces of cast steel, by giving to each a sloping

face, jagged all over with a small chisel; then applying them with some

calcined borax between, and tying them together with a wire, they are

brought to a full red heat, and united by a few smart blows of a hammer.

The ordinary bar iron of Sweden and England, when converted by

cementation into steel, exhibits upon its surface numerous small warty

points, but few or no distinct vesicular eruptions; whereas the

Dannemora and the Ulverston steels present, all over the surface of the

bars, well raised blisters, upwards of three-eighths of an inch in

diameter horizontally, but somewhat flattened at top. Iron of an

inferior description, when highly converted in the cementing-chest,

becomes gray on the outer edges of the fracture; while that of Dannemora

acquires a silvery colour and lustre on the edges, with crystalline

facets within. The highly converted steel is used for tools that require

to be made very hard; the slightly converted, for softer and more

elastic articles, such as springs and sword blades.