To dye with archil, the quantity of this_A Dictionary of Arts, Manufactures and Mines containing a clear exposition of their principles and practice

according to the quantity of wool or stuff to be dyed, and according to

the shade to which they are to be brought, is to be diffused in a bath

of water as soon as it begins to grow warm. The bath is then heated till

it be ready to boil, and the wool or stuff is passed through it without

any other preparation, except keeping that longest in, which is to have

the deepest shade. A fine gridelin, bordering upon violet, is thereby

obtained; but this colour has no permanence. Hence archil is rarely

employed with any other view than to modify, heighten, and give lustre

to the other colours. Hellot says, that having employed archil on wool

boiled with tartar and alum, the colour resisted the air no more than

what had received no preparation. But he obtained from herb archil

(_l’orseille d’herbe_) a much more durable colour, by putting in the

bath some solution of tin. The archil thereby loses its natural colour,

and assumes one approaching more or less to scarlet, according to the

quantity of solution of tin employed. This process must be executed in

nearly the same manner as that of scarlet, except that the dyeing may be

performed in a single bath.

Archil is frequently had recourse to for varying the different shades

and giving them lustre; hence it is used for violets, lilacs, mallows,

and rosemary flowers. To obtain a deeper tone, as for the deep _soupes

au vin_, sometimes a little alkali or milk of lime is mixed with it. The

suites of this browning may also afford agates, rosemary flowers, and

other delicate colours, which cannot be obtained so beautiful by other

processes. Alum cannot be substituted for this purpose; it not only does

not give this lustre, but it degrades the deep colours.

The herb-archil is preferable to the archil of Auvergne, from the

greater bloom which it communicates to the colours, and from the larger

quantity of colouring matter. It has, besides, the advantage of bearing

ebullition. The latter, moreover, does not answer with alum, which

destroys the colour; but the herb archil has the inconvenience of dyeing

in an irregular manner, unless attention be given to pass the cloth

through hot water as soon as it comes out of the dye.

Archil alone is not used for dyeing silk, unless for lilacs; but silk is

frequently passed through a bath of archil, either before dyeing it in

other baths or after it has been dyed, in order to modify different

colours, or to give them lustre. Examples of this will be given in

treating of the compound colours. It is sufficient here to point out how

white silks are passed through the archil bath. The same process is

performed with a bath more or less charged with this colour, for silks

already dyed.

Archil, in a quantity proportioned to the colour desired, is to be

boiled in a copper. The clear liquid is to be run off quite hot from the

archil bath, leaving the sediment at the bottom, into a tub of proper

size, in which the silks, newly scoured with soap, are to be turned

round on the skein-sticks with much exactness, till they have attained

the wished-for shade. After this they must receive one beetling at the

river.

Archil is in general a very useful ingredient in dyeing; but as it is

rich in colour, and communicates an alluring bloom, dyers are often

tempted to abuse it, and to exceed the proportions that can add to the

beauty without at the same time injuring in a dangerous manner the

permanence of the colours. Nevertheless, the colour obtained when

solution of tin is employed, is less fugitive than without this

addition: it is red, approaching to scarlet. Tin appears to be the only

ingredient which can increase its durability. The solution of tin may be

employed, not only in the dyeing bath, but for the preparation of the

silk. In this case, by mixing the archil with other colouring

substances, dyes may be obtained which have lustre with sufficient

durability.

We have spoken of the colour of the archil as if it were natural to it;

but it is, really, due to an alkaline combination. The acids make it

pass to red, either by saturating the alkali, or by substituting

themselves for the alkali.

The lichen which produces archil is subjected to another preparation, to

make turnsole (litmus). This article is made in Holland. The lichen

comes from the Canary Islands, and also from Sweden. It is reduced to a

fine powder by means of a mill, and a certain proportion of potash is

mixed with it. The mixture is watered with urine, and allowed to suffer

a species of fermentation. When this has arrived at a certain degree,

carbonate of lime in powder is added, to give consistence and weight to

the paste, which is afterwards reduced into small parallelopipeds that

are carefully dried.

The latest researches on the lichens, as objects of manufacture, are

those of Westring of Stockholm. He examined 150 species, among which he

found several which might be rendered useful. He recommends that the

colouring matter should be extracted in the places where they grow,

which would save a vast expense in curing, package, carriage, and waste.

He styles the colouring substance itself cutbear, persio, or turnsole;

and distributes the lichens as follows:--1st. Those which left to

themselves, exposed to moderate heat and moisture, may be fixed without

a mordant upon wool or silk; such are the L. _cinereus_, _æmatonta_,

_ventosus_, _corallinus_, _westringii_, _saxatilis_, _conspassus_,

_barbatus_, _plicatus_, _vulpinus_, &c.

2. Those which develop a colouring matter fixable likewise without

mordant, but which require boiling and a complicated preparation; such

are the lichens _subcarneus_, _dillenii_, _farinaceus_, _jubatus_,

_furfuraceus_, _pulmonareus_, _cornigatus_, _cocciferus_, _digitatus_,

_ancialis_, _aduncus_, &c. Saltpetre or sea-salt are requisite to

improve the lustre and fastness of the dye given by this group to silk.

3. Those which require a peculiar process to develop their colour; such

as those which become purple through the agency of stale urine or

ammonia. Westring employed the following mode of testing:--He put three

or four drachms of the dried and powdered lichen into a flask; moistened

it with three or four measures of cold spring water; put the stuff to be

dyed into the mixture, and left the flask in a cool place. Sometimes he

added a little salt, saltpetre, quicklime, or sulphate of copper. If no

colour appeared, he then moistened the lichen with water containing one

twentieth of sal ammoniac, and one tenth of quicklime, and set the

mixture aside in a cool place from eight to fourteen days. There

appeared in most cases a reddish or violet coloured tint. Thus the

_lichen cinereus_ dyed silk a deep carmelite, and wool a light

carmelite; the _l. physodes_ gave a yellowish-gray; the _pustulatus_, a

rose red; _sanguinarius_, gray; _tartareus_, found on the rocks of

Norway, Scotland, and England, dyes a crimson-red. In Jutland, cutbear

is made from it, by grinding the dry lichen, sifting it, then setting it

to ferment in a close vessel with ammonia. The lichen must be of the

third year’s growth to yield an abundant dye; and that which grows near

the sea is the best. It loses half its weight by drying. A single person

may gather from twenty to thirty pounds a day in situations where it

abounds. No less than 2,239,685 pounds were manufactured at

Christiansand, Flekkefiort, and Fakrsund, in Norway, in the course of

the six years prior to 1812. Since more solid dyes of the same shade

have been invented, the archil has gone much into disuse. Federigo, of

Florence, who revived its use at the beginning of the fourteenth

century, made such an immense fortune by its preparation, that his

family became one of the grandees of that city, under the name of

Oricellarii, or Rucellarii. For more than a century Italy possessed the

exclusive art of making archil, obtaining the lichens from the islands

of the Mediterranean. According to an official report of 1831, Teneriffe

furnished annually 500 quintals (cwts.) of lichen; the Canary Isles,

400; Fuerta Santura, 300; Lancerot, 300; Gomera, 300; isle of Ferro,

800. This business belonged to the crown, and brought it a revenue of

1500 piastres. The farmers paid from 15 to 20 reals for the right to

gather each quintal. At that time the quintal fetched in the London

market 4_l._ sterling.

Archil is perhaps too much used in some cloth factories of England, to

the discredit of our dyes. It is said, that by its aid one third of the

indigo may be saved in the blue vat; but the colour is so much the more

perishable. The fine soft tint induced upon much of the black cloth by

means of archil is also deceptive. One half-pound of cutbear will dye

one pound of woollen cloth. A crimson red is obtained by adding to the

decoction of archil a little salt of tin (muriate), and passing the

cloth through the bath, after it has been prepared by a mordant of tin

and tartar. It must be afterwards passed through hot water.

ARDENT SPIRIT. Alcohol of moderate strength.

AREOMETER OF BAUMÉ. This scale is much used by the French authors.

Specific Gravity Numbers corresponding with Baumé’s Areometric Degrees.

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

| Liquids denser than Water. | Less dense than Water. |

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

| | Spe- | | Spe- | | Spe- | | Spe- | | Spe- |

| De- |cific | De- |cific | De- |cific | De- |cific | De- |cific |

| | ty. | | ty. | | ty. | | ty. | | ty. |

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

| 0 |1·0000| 26 |1·2063| 52 |1·5200| 10 |1·0000| 36 |0·8488|

| 1 |1·0066| 27 |1·2160| 53 |1·5353| 11 |0·9932| 37 |0·8439|

| 2 |1·0133| 28 |1·2258| 54 |1·5510| 12 |0·9865| 38 |0·8391|

| 3 |1·0201| 29 |1·2358| 55 |1·5671| 13 |0·9799| 39 |0·8313|

| 4 |1·0270| 30 |1·2459| 56 |1·5833| 14 |0·9733| 40 |0·8295|

| 5 |1·0340| 31 |1·2562| 57 |1·6000| 15 |0·9669| 41 |0·8249|

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

| 6 |1·0411| 32 |1·2667| 58 |1·6170| 16 |0·9605| 42 |0·8202|

| 7 |1·0483| 33 |1·2773| 59 |1·6344| 17 |0·9542| 43 |0·8156|

| 8 |1·0556| 34 |1·2881| 60 |1·6522| 18 |0·9480| 44 |0·8111|

| 9 |1·0630| 35 |1·2992| 61 |1·6705| 19 |0·9420| 45 |0·8066|

| 10 |1·0704| 36 |1·3103| 62 |1·6889| 20 |0·9359| 46 |0·8022|

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

| 11 |1·0780| 37 |1·3217| 63 |1·7079| 21 |0·9300| 47 |0·7978|

| 12 |1·0857| 38 |1·3333| 64 |1·7273| 22 |0·9241| 48 |0·7935|

| 13 |1·0935| 39 |1·3451| 65 |1·7471| 23 |0·9183| 49 |0·7892|

| 14 |1·1014| 40 |1·3571| 66 |1·7674| 24 |0·9125| 50 |0·7849|

| 15 |1·1095| 41 |1·3694| 67 |1·7882| 25 |0·9068| 51 |0·7807|

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

| 16 |1·1176| 42 |1·3818| 68 |1·8095| 26 |0·9012| 52 |0·7766|

| 17 |1·1259| 43 |1·3945| 69 |1·8313| 27 |0·8957| 53 |0·7725|

| 18 |1·1343| 44 |1·4074| 70 |1·8537| 28 |0·8902| 54 |0·7684|

| 19 |1·1428| 45 |1·4206| 71 |1·8765| 29 |0·8848| 55 |0·7643|

| 20 |1·1515| 46 |1·4339| 72 |1·9000| 30 |0·8795| 56 |0·7604|

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

| 21 |1·1603| 47 |1·4476| 73 |1·9241| 31 |0·8742| 57 |0·7656|

| 22 |1·1692| 48 |1·4615| 74 |1·9487| 32 |0·8690| 58 |0·7526|

| 23 |1·1783| 49 |1·4758| 75 |1·9740| 33 |0·8639| 59 |0·7487|

| 24 |1·1875| 50 |1·4902| 76 |2·0000| 34 |0·8588| 60 |0·7449|

| 25 |1·1968| 51 |1·4951| | | 35 |0·8538| 61 |0·7411|

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

ARGILLACEOUS EARTH. The earth of clay, called in chemistry alumina,

because it is obtained in greatest purity from alum.

ARGOL. Crude _tartar_; which see.

ARMS. Weapons of war. See FIRE-ARMS for an account of this manufacture.

ARRACK. A kind of intoxicating beverage made in India, by distilling the

fermented juice of the cocoa-nut, the palmyra tree, and rice in the

husk.

ARROW ROOT. The root of the _maranta arundinacea_, a plant which grows

in the West Indies, furnishes, by pounding in mortars and elutriation

through sieves, a peculiar species of starch, commonly but improperly

called arrow root. It is reckoned more nourishing than the starch of

wheat or potatoes, and is generally also freer from peculiar taste or

flavour. The fresh root consists, according to Benzon, of 0·07 of

volatile oil; 26 of starch (23 of which are obtained in the form of

powder, while the other 3 must be extracted from the parenchyma in a

paste by boiling water); 1·58 of vegetable albumen; 0·6 of a gummy

extract; 0·25 of chloride of calcium; 6 of insoluble fibrine; and 65·6

of water.

The import duty upon arrow root from our own colonies, is 1_s._ per

cwt.; from foreign parts, 2_d._ per lib. In 1835, 987,966 lbs. were

imported, of which only 6267 were exported; leaving 895,406 for home

consumption. The total revenue derived that year from arrow root, was

518_l._ See STARCH.

ARSENIC. This metal occurs native, in the state of oxide, and also

combined with sulphur under the improper name of _yellow_ and _red

arsenic_, or orpiment and realgar. Arsenic is associated with a great

many metallic ores; but it is chiefly extracted from those of cobalt, by

roasting, in which case the white oxide of arsenic, or, more correctly,

the arsenious acid is obtained. This acid is introduced occasionally in

small quantities into the materials of flint glass, either before their

fusion, or in the melting pot. It serves to peroxidize the iron oxide in

the sand, and thereby to purify the body of the glass; but an excess of

it makes the glass milky.

_Scheele’s green_ is a combination of this arsenious acid with oxide of

copper, or an arsenite of copper, and is described under this metal.

_Arseniate of potash_ is prepared, in the small way, by exposing to a

moderate heat in a crucible, a mixture of equal parts of white arsenic

and nitre in powder. After fusion, the crucible is to be cooled; the

contents being dissolved in hot water, and the solution filtered, will

afford regular crystals on cooling. According to M. Berzelius, they are

composed of arsenic acid, 63·87; potash, 26·16; and water, 9·97. It is

an acidulous salt, and is hence usually called the binarseniate, to

denote that its composition is 2 atoms of arsenic acid, and 1 of potash.

This article is prepared upon the great scale, in Saxony, by melting

nitre and arsenious acid together in a cylinder of cast-iron. A neutral

arseniate also is readily formed, by saturating the excess of acid in

the above salt with potash; it does not crystallize. The acid arseniate

is occasionally used in calico printing, for preventing certain points

of the cotton cloth from taking on the mordant; with which view it is

mixed up with gum water and pipe clay into a paste, which is applied to

such places with a block.

The extraction of arsenic from the cobalt ores, is performed at

Altenberg and Reichenstein, in Silesia, with an apparatus, excellently

contrived to protect the health of the smelters from the vapours of this

most noxious metallic sublimate.

[Illustration: 20]

[Illustration: 23]

_Figs._ 20. to 23. represent the arsenical furnaces at Altenberg. _Fig._

20. is a vertical section of the poison tower; _fig._ 21., a

longitudinal section of the subliming furnace A, with the adjoining

vault B, and the poison tower in part at _n_; _fig._ 22., the transverse

section of the furnace A, of _fig._ 21.; _fig._ 23., ground plan of the

furnace A, where the left half shows the part above, and the right the

part below the muffle or oblong retort; B´ is the upper view, B´´ the

ground plan of the vault B, of _fig._ 21.; _m_, _n_, the base of the

poison tower. In the several figures the same letters denote the same

objects: _a_ is the muffle; _b_ is its mouth for turning over the

arsenical schlich, or ground ore; _c c c_, fire draughts or flues; _d_,

an aperture for charging the muffle with fresh schlich; _e_, the smoke

chimney; _f_, two channels or flues for the ascent of the arsenious

fumes, which proceed to other two flues _g_, and then terminate both in

_h_, which conducts the fumes into the vault B. They issue by the door

_i_, into the conduit _k_, thence by _l_ into the spaces _m_, _n_, _o_,

_p_, _q_, _r_, of the tower. The incondensable gases escape by the

chimney, _s_. The cover _t_, is removed after completion of the

process, in order to push down the precipitate into the lower

compartments.

[Illustration: 22 21]

The arsenious schlichs, to the amount of 9 or 10 cwt. for one operation

(1 _roast-post_, or roasting round), are spread 2 or 3 inches thick upon

the bottom of the muffle, heated with a brisk fire to redness, then with

a gentler heat, in order to oxidize completely, before subliming, the

arsenical ore. With this view the air must have free entrance, and the

front aperture of the muffle must be left quite open. After 11 or 12

hours, the calcined materials are raked out by the mouth of the muffle,

and fresh ones are introduced by the openings indicated above, which are

closed during the sublimation.

The arsenious acid found in these passages, is not marketable till it be

re-sublimed in large iron pots, surmounted with a series of sheet iron

drums or cast-iron cylinders, upon the sides of which the arsenic is

condensed in its compact glassy form. The top cylinder is furnished with

a pipe, which terminates in a condensing chamber.

[Illustration: 24]

_Figs._ 24, 25. represent the arsenic refining furnaces at Reichenstein.

_Fig._ 24. shows at A, a vertical section of the furnace, the kettle,

and the surmounting drums or cylinders; over B it is seen in elevation;

_fig._ 25. is a ground plan of the four fireplaces. _a_ is the grate;

_b_, the ash pit; _c_, the openings for firing; _d_, the fire-place;

_e_, iron pots or kettles which are charged with the arsenious powder;

_f_, the fire flues proceeding to the common chimney _g_; _h_, iron

cylinders; _i_, caps; _k_, pipes leading to the poison vent _l_; _m_,

openings in the pipes for introducing the probing wires.

[Illustration: 25]

The conduct of the process is as follows:--The pot is filled nearly to

its brim with 3-1/2 cwt. of the arsenic meal, the cylinders are fitted

on by means of their handles, and luted together with a mixture of loam,

blood, and hair; then is applied first a gentle, and after half an hour,

a strong fire, whereby the arsenic is raised partly in the form of a

white dust, and partly in crystals; which, by the continuance of the

heat, fuse together into a homogeneous mass. If the fire be too feeble,

only a sublimate is obtained; but, if too violent, much of the arsenic

is volatilized into the pipes. The workmen judge by the heat of the

cylinders whether the operation be going on well or not. After 12 hours

the furnace is allowed to cool, provided the probe wires show that the

sublimation is over. The cylinders are then lifted off, and the

arsenious glass is detached from their inner surface. According to the

quality of the poison-flour, it yields from 3/4 to 7/8 of its weight of

the glass or enamel. Should any dark particles of metallic arsenic be

intermixed with the glass, a fresh sublimation must be had recourse to.

The following is the product in cwts. of arsenious acid, at Altenberg

and Reichenstein, in Silesia, in the years

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

| |1825.|1826.|1827.|1828.|1829.|1830.|1831.|1832.|

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

|glassy state | 2632| 1703| 2686| 1900| 2070| 2961| 3337| 2730|

|in powder | - | 27| 33| 31| 30| 44| 69| 38|

|glass | 112| 11| 56| - | 86| 313| 60| 219|

|glass | 3| - | - | - | 28| | | |

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

ARTESIAN WELLS. Under this name is designated a cylindrical perforation,

bored vertically down through one or more of the geological strata of

the earth, till it passes into a porous gravel bed containing water,

placed under such incumbent pressure as to make it mount up through the

perforation, either to the surface or to a height convenient for the

operation of a pump. In the first case, these wells are called spouting

or overflowing. This property is not directly proportional to the depth,

as might at first sight be supposed, but to the subjacent pressure upon

the water. We do not know exactly the period at which the borer or sound

was applied to the investigation of subterranean fountains, but we

believe the first overflowing wells were made in the ancient French

province of Artois, whence the name of Artesian. These wells, of such

importance to agriculture and manufactures, and which cost nothing to

keep them in condition, have been in use, undoubtedly, for several

centuries in the northern departments of France, and the north of Italy;

but it is not more than 50 or 60 years since they became known in

England and Germany. There are now a great many such wells in London and

its neighbourhood, perforated through the immensely thick bed of the

London clay, and even through some portions of the subjacent chalk. The

boring of such wells has given much insight into the geological

structure of many districts.

The formation of artesian wells depends on two things, essentially

distinct from each other: 1. On an acquaintance with the physical

constitution, or nature, of the mineral structure of each particular

country; and, 2. On the skilful direction of the processes by which we

can reach the water level, and of those by which we can promote its

ascent in the tube. We shall first treat of the best method of making

the well, and then offer some general remarks on the other subjects.

The operations employed for penetrating the soil are entirely similar to

those daily practised by the miner, in boring to find metallic veins;

but the well excavator must resort to peculiar expedients to prevent the

purer water, which comes from deep strata, mingling with the cruder

waters of the alluvial beds near the surface of the ground, as also to

prevent the small perforation getting eventually filled with rubbish.

The cause of overflowing wells has been ascribed to a variety of

circumstances. But, as it is now generally admitted that the numerous

springs which issue from the ground proceed from the infiltration of the

waters progressively condensed in rain, dew, snow, &c. upon the surface

of our globe, the theory of these interior streamlets becomes by no

means intricate; being analogous to that of syphons and water jets, as

expounded in the treatises of physics. The waters are diffused, after

condensation, upon the surface of the soil, and percolate downwards,

through the various pores and fissures of the geological strata, to be

again united subterraneously in veins, rills, streamlets, or expanded

films, of greater or less magnitude, or regularity. The beds traversed

by numerous disjunctions will give occasion to numerous interior

currents in all directions, which cannot be recovered, and brought to

the day; but when the ground is composed of strata of sand, or gravel

very permeable to water, separated by other strata nearly impervious to

it, reservoirs are formed to our hand, from which an abundant supply of

water may be spontaneously raised. In this case, as soon as the upper

stratum is perforated, the waters may rise, in consequence of the

hydrostatic pressure upon the lower strata, and even overflow the

surface in a constant stream, provided the level from which they proceed

be proportionally higher.

The sheets of water occur principally at the separation of two

contiguous formations; and, if the succession of the geological strata

be considered, this distribution of the water will be seen to be its

necessary consequence. In fact, the lower beds are frequently composed

of compact sandstone or limestone, and the upper beds of clay. In level

countries, the formations being almost always in horizontal-beds, the

waters which feed the artesian wells must come from districts somewhat

remote, where the strata are more elevated, as towards the secondary and

transition rocks. The copious streams condensed upon the sides of these

colder lands may be therefore regarded as the proper reservoirs of our

wells.

[Illustration: 26]

_Fig._ 26. represents the manner in which the condensed water of the

heavens distributes itself under the surface of our globe. Here we have

a geological section, showing the succession of the several formations,

and the sheets or laminæ of water that exist at their boundaries, as

well as in their sandy beds. The figure shows also very plainly that the

height to which the water reascends in the bore of a well depends upon

the height of the reservoir which supplies the sheet of water to which

the well is perforated. Thus the well A, having gone down to the aqueous

expanse A A, whose waters of supply are derived from the percolation M,

will afford rising waters, which will come to the surface; whilst in the

well B, supplied by the sheet P, the waters will spout above the

surface, and in the well C they will remain short of it. The same figure

shows that these wells often traverse sheets of water, which rise to

different heights. Thus, in the well C there are five columns of

ascending waters, which rise to heights proportional to the points

whence they take their origin. Several of these will be spouting or

overflowing, but some will remain beneath the surface.

[Illustration: 27]

The situation of the intended well being determined upon, a circular

hole is generally dug in the ground, about 6 or 8 feet deep, and 5 or 6

feet wide. In the centre of this hole the boring is carried on by two

workmen below, assisted by a labourer above, as shown in _fig._ 27.

[Illustration: 28 29]

The handle (_fig._ 28.) having a female screw in the bottom of its iron

shank, with a wooden bar or rail passing through the socket of the

shank, and a ring at top, is the general agent to which all the boring

implements are to be attached. A chisel (_fig._ 29.) is first employed,

and connected to this handle by its screw at top. If the ground is

tolerably soft, the weight of the two workmen bearing upon the cross

bar, and occasionally forcing it round, will soon cause the chisel to

penetrate; but if the ground is hard or strong, the workmen strike the

chisel down with repeated blows, so as to peck their way, often changing

their situation by walking round, which breaks the stones, or other hard

substances, that may happen to obstruct its progress.

The labour is very considerably reduced, by means of an elastic wooden

pole, placed horizontally over the well, from which a chain is brought

down, and attached to the ring of the handle. This pole is usually made

fast at one end, as a fulcrum, by being set into a heap of heavy loose

stones; at the other end the labourer above gives it a slight up and

down vibrating motion, corresponding to the beating motion of the

workmen below, by which means the elasticity of the pole in rising lifts

the handle and pecker, and thereby very considerably diminishes the

labour of the workmen. See _fig._ 27.

[Illustration: 30 31 32]

When the hole has been thus opened by a chisel, as far as its strength

would permit, the chisel is withdrawn, and a sort of cylindrical auger

(_fig._ 30.) attached to the handle (_fig._ 28.), for the purpose of

drawing up the dirt or broken stones which have been disturbed by the

chisel. A section of this auger is shown in _fig._ 31., by which the

internal valve will be seen. The auger being introduced into the hole,

and turned round by the workman, the dirt or broken stones will pass

through the aperture at bottom (shown at _fig._ 32.), and fill the

cylinder, which is then drawn up, and discharged at the top of the

auger, the valve preventing its escape at bottom.

[Illustration: 33 34 35 36 37]

In order to penetrate deeper into the ground, an iron rod, as _a_,

_fig._ 33., is now to be attached to the chisel, _fig._ 29., by screwing

on to its upper end, and the rod is also fastened to the handle, _fig._

28., by screwing into its socket. The chisel having thus become

lengthened, by the addition of the rod, it is again introduced into the

hole; and the operation of pecking or forcing it down, is carried on by

the workmen as before. When the ground has been thus perforated, as far

as the chisel and its rod will reach, they must be withdrawn, in order

again to introduce the auger, _fig._ 30., to collect and bring up the

rubbish; which is done by attaching it to the iron rod, in place of the

chisel. Thus as the hole becomes deepened, other lengths of iron rods

are added, by connecting them together, as _a b_ are in _fig._ 34. The

necessity of frequently withdrawing the rods from the holes, in order to

collect the mud, stones, or rubbish, and the great friction produced by

the rubbing of the tools against its sides, as well as the lengths of

rods augmenting in the progress of the operation, sometimes to the

extent of several hundred feet, render it extremely inconvenient, if not

impossible, to raise them by hand. A tripedal standard is, therefore,

generally constructed by three scaffolding poles tied together, over the

hole, as shown _fig._ 27., from the centre of which a wheel and axle, or

a pair of pully blocks is suspended, for the purpose of hauling up the

rods, and from which hangs the fork, _fig._ 35. This fork is to be

brought down under the shoulder, near the top of each rod, and made fast

to it by passing a pin through two little holes in the claws. The rods

are thus drawn up, about seven feet at a time, which is the usual

distance between each joint, and at every haul a fork, _fig._ 36., is

laid horizontally over the hole, with the shoulders of the lower rod

resting between its claws, by which means the rods are prevented from

sinking down into the hole again, while the upper length is unscrewed

and removed. In attaching and detaching these lengths of rod, a wrench,

_fig._ 37., is employed, by which they are turned round, and the screws

forced up to their firm bearing.

[Illustration: 38]

The boring is sometimes performed for the first sixty or a hundred feet,

by a chisel of 2-1/2 inches wide, and cleared out by a gouge of 2-1/4

diameter, and then the hole is widened by a tool, such as is shown at

_fig._ 38. This is merely a chisel, as _fig._ 29., four inches wide, but

with a guide, _a_, put on at its lower part, for the purpose of keeping

it in a perpendicular direction; the lower part is not intended to peck,

but to pass down the hole previously made, while the sides of the chisel

operate in enlarging the hole to four inches. The process, however, is

generally performed at one operation, by a chisel of four inches wide,

as _fig._ 29., and a gouge of three inches and three quarters, as _fig._

30.

It is obvious, that placing and displacing the lengths of rod, which is

done every time that the auger is required to be introduced or

withdrawn, must, of itself, be extremely troublesome, independent of the

labour of boring, but yet the operation proceeds, when no unpropitious

circumstances attend it, with a facility almost incredible. Sometimes,

however, rocks intercept the way, which require great labour to

penetrate; but this is always effected by pecking, which slowly

pulverises the stone. The most unpleasant circumstance attendant upon

this business is the occasional breaking of a rod into the hole, which

sometimes creates a delay of many days, and an incalculable labour in

drawing up the lower portion.

When the water is obtained in such quantities and of such quality as may

be required, the hole is dressed or finished by passing down it a

diamond chisel, funnel mouthed, with a triangular bit in its centre;

this makes the sides smooth previous to putting in the pipe. This chisel

is attached to rods, and to the handle, as before described; and, in its

descent, the workmen continually walk round, by which the hole is made

smooth and cylindrical. In the progress of the boring, frequent veins of

water are passed through; but, as these are small streams, and perhaps

impregnated with mineral substances, the operation is carried on until

an aperture is made into a main spring, which will flow up to the

surface of the earth. This must, of course, depend upon the level of its

source, which, if in a neighbouring hill, will frequently cause the

water to rise up, and produce a continued fountain. But if the altitude

of the distant spring happens to be below the level of the surface of

the ground where the boring is effected, it sometimes happens that a

well of considerable capacity is obliged to be dug down to that level,

in order to form a reservoir, into which the water may flow, and whence

it must be raised by a pump; while, in the former instance, a perpetual

fountain may be obtained. Hence, it will always be a matter of doubt, in

level countries, whether water can be procured, which would flow near to

or over the surface; if this cannot be effected, the process of boring

will be of little or no advantage, except as an experiment to ascertain

the fact.

In order to keep the strata pure, and uncontaminated with mineral

springs, the hole is cased, for a considerable depth, with a metallic

pipe, about a quarter of an inch smaller than the bore. This is

generally made of tin (though sometimes of copper or lead) in convenient

lengths; and, as each length is let down, it is held by a shoulder

resting in a fork, while another length is soldered to it; by which

means a continuous pipe is carried through the bore, as far as may be

found necessary, to exclude land springs, and to prevent loose earth or

sand from falling in, and choking the aperture.

Mr. John Good, of Tottenham, who had been extensively employed in boring

the earth for water, obtained a patent, in Aug. 1823, for certain

improved implements contrived by him to facilitate his useful labours; a

description of which cannot fail to be interesting.

[Illustration: 39 40 41 42]

The figures annexed exhibit these ingenious tools; _fig._ 39. is an

auger, to be connected by the screw-head to the length of rods by which

the boring is carried on. This auger is for boring in soft clay or sand;

it is cylindrical, and has a slit or opening from end to end, and a bit,

or cutting-piece at bottom. When the earth is loose or wet, an auger of

the same form is to be employed, but the slit or opening reduced in

width, or even without a slit or opening. A similar auger is used for

cutting through chalk; but the point or bit at bottom should then

project lower, and, for that purpose, some of these cylindrical augers

are made with moveable bits, to be attached by screws, which is

extremely desirable in grinding them to cutting edges. _Fig._ 40. is a

hollow conical auger, for boring loose sandy soils; it has a spiral

cutting edge coiled round it, which, as it turns, causes the loose soil

to ascend up the inclined plane, and deposit itself in the hollow

within. _Fig._ 41. is a hollow cylinder or tube, shown in section, with

a foot-valve, and a bucket to be raised by a rod and cord attached at

the top; this is a pumping tool, for the purpose of getting up water and

sand that would not rise by the auger. When this cylinder is lowered to

the bottom of the bore, the bucket is lifted up by the rod and cord, and

descends again by its own gravity, having a valve in the bucket, opening

upwards, like other lift pumps; which, at every stroke, raises a

quantity of water and sand in the cylinder equal to the stroke; the

ascent and descent of the bucket being limited by a guide-piece at the

top of the cylinder, and two small knobs upon the rod, which stop

against the cross-guide. _Fig._ 42. is a tool for getting up broken

rods. It consists of a small cylindrical piece at bottom, which the

broken rod slips through when it is lowered, and a small catch with a

knife-edge, acted upon by a back-spring. In rising, the tool takes hold

of the broken rod, and thereby enables the workmen at top to draw it up.

Another tool for the same purpose, is shown at _fig._ 43., which is like

a pair of tongs; it is intended to be slidden down the bore, and for the

broken rod to pass between the two catches, which, pressed by

back-springs, will, when drawn up, take fast hold of the broken rod.

[Illustration: 43 44 45 46]

_Fig._ 44. is a tool for widening the hole, to be connected, like all

the others, to the end of the length of rods passed down the bore; this

tool has two cutting-pieces extending on the sides at bottom, by which,

as the tool is turned round in the bore, the earth is peeled away.

_Fig._ 45. is a chisel, or punch, with a projecting piece to be used for

penetrating through stone; this chisel is, by rising and falling, made

to peck the stone, and pulverize it; the small middle part breaking it

away first, and afterwards the broad part coming into action. _Fig._ 46.

is another chisel, or punching tool, twisted on its cutting edge, which

breaks away a greater portion of the stone as it beats against it.

[Illustration: 47 48 49]

The manner of forcing down lengths of cast-iron pipe, after the bore is

formed, is shown at _fig._ 47.; the pipe is seen below in the socket, at

the end of which a block is inserted; and from this block a rod extends

upwards, upon which a weight at top slides. To this weight cords are

shown to be attached, reaching to the top of the bore; where the workmen

alternately raise the weight and let it fall, which, by striking upon

the block in its middle, beats down the pipe by a succession of strokes;

and when one length of pipe has, by these means, been forced down,

another length is introduced into the socket of the former. Another

tool for the same purpose is shown at _fig._ 48., which is formed like

an acorn; the raised part of the acorn strikes against the edge of the

pipe, and by that means, it is forced down the bore. When it happens

that an auger breaks in the hole, a tool similar to that shown at _fig._

49. is introduced; on one side of this tool a curved piece is attached,

for the purpose of a guide, to conduct it past the cylindrical auger;

and at the end of the other side is a hook, which, taking hold of the

bottom edge of the auger, enables it to be drawn up.

[Illustration: 50 51 52]

Wrought iron, copper, tin, and lead pipes, are occasionally used for

lining the bore; and as these are subject to bends and bruises, it is

necessary to introduce tools for the purpose of straightening their

sides. One of these tools is shown at _fig._ 50., which is a bow, and is

to be passed down the inside of the pipe, in order to press out any

dents. Another tool, for the same purpose, is shown at _fig._ 51., which

is a double bow, and may be turned round in the pipe for the purpose of

straightening it all the way down; at _fig._ 52., is a pair of clams,

for turning the pipe round in the hole while driving.

[Illustration: 53 54]

When loose stones lie at the bottom of the hole, which are too large to

be brought up by the cylindrical auger, and cannot be conveniently

broken, then it is proposed to introduce a triangular claw, as _fig._

53., the internal notches of which take hold of the stone, and as the

tool rises, bring it up. For raising broken rods, a tool like _fig._ 54.

is sometimes employed, which has an angular claw that slips under the

shoulder of the rod, and holds it fast while drawing up.

[Illustration: 55 56]

In raising pipes, it is necessary to introduce a tool into the inside of

the pipe, by which it will be held fast. _Fig._ 55. is a pine-apple tool

for this purpose; its surface is cut like a rasp, which passes easily

down into the pipe, but catches as it is drawn up; and by that means

brings the pipe with it. _Fig._ 56. is a spear for the same purpose,

which easily enters the pipe by springing; at the ends of its prongs

there are forks which stick into the metal as it is drawn up, and

thereby raise it.

These are the new implements, for which the patent was granted. In the

process of boring, there does not appear to be any thing new proposed;

but that these several tools are to be employed for boring, packing, and

otherwise penetrating, raising the earth, and extracting broken or

injured tools. There are also suggestions for employing long buckets,

with valves opening upward in their bottoms, for the purpose of drawing

water from these wells when the water will not flow over the surface;

also lift pumps, with a succession of buckets for the same purpose. But

as these suggestions possess little if any novelty, it cannot be

intended to claim them as parts of the patent.

ASPHALTUM. Native bitumen, so called from the lake Asphaltites.

ASSAY and ASSAYING. (_Coupellation_, Fr.; _Abtreiben auf der capelle_,

Germ.) This is the process by which the quality of gold and silver

bullion, coin, plate, or trinkets is ascertained with precision, or by

which the quantity of either or both these precious metals is determined

in any given alloy. It is, therefore, a case of chemical analysis, in

which peculiar methods are employed to attain the object in view with

accuracy and dispatch. Assaying has been also extended of late years, to

determine the quantity of palladium and platina in certain bullion and

gold dust brought from Brazil.

The art of assaying gold and silver _by the cupel_, is founded upon the

feeble affinity which these metals have for oxygen, in comparison with

copper, tin, and the other cheaper metals; and on the tendency which the

latter metals have to oxidize rapidly in contact with lead at a high

temperature, and sink with it into any porous earthy vessel in a thin

glassy or vitriform state. The porous vessel may be made either of

wood-ashes, freed from their soluble matter by washing with water; or,

preferably, of burned bones reduced to a fine powder.

The lead added to the silver or gold to be assayed, serves chiefly to

dissolve the oxidized copper, whence it appears that the quantity of

lead requisite for silver assays, ought to be directly proportional to

the quantity which the silver and copper would separately require. It

has been found by experiment, that 16 parts of lead are quite sufficient

to pass 1 of copper through the cupel; and that 3/10 of lead presents

the most suitable proportion for passing one of silver. From these

principles, however, if we should always regard the dose of lead to be

employed for any alloy as being equal to (16 × C) + (3/30 × S) we should

certainly commit an error. The phenomena of cupellation is of a more

complex nature. Long practice and delicate trials alone can guide to the

proper quantity of lead to be employed for every various state of the

alloy. The following Table contains the results of M. D’Arcet’s

elaborate experiments upon this subject:--

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

| Alloy. |Lead for|Ratio of the |

+-------+-------+ 1 of |Copper to the|

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

| 1000 | 0 | 3/10| 0 |

| 950 | 50 | 3 | 1 : 60 |

| 900 | 100 | 7 | 1 : 70 |

| 800 | 200 | 10 | 1 : 50 |

| 700 | 300 | 12 | 1 : 40 |

| 600 | 400 | 14 | 1 : 35 |

| 500 | 500 |16 or 17| 1 : 32 |

| 400 | 600 |16 -- 17| 1 : 26·7 |

| 300 | 700 |16 -- 17| 1 : 22·9 |

| 200 | 800 |16 -- 17| 1 : 20 |

| 100 | 900 |16 -- 17| 1 : 17·8 |

| 0 | 1000 |16 -- 17| 1 : 16 |

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

Bismuth may be used as a substitute for lead in cupellation; two parts

of it being nearly equivalent to three of lead. But its higher prices

will prevent its general introduction among assay masters.

We begin this assay process by weighing, in a delicate balance, a

certain weight of the metallic alloy; a gramme (= 15·444 gr.) is usually

taken in France, and 12 grains in this country. This weight is wrapped

up in a slip of lead foil or paper, should it consist of several

fragments. This small parcel, thus enveloped, is then laid in a watch

glass or a capsule of copper, and there is added to it the proportion of

lead suited to the quality of alloy to be assayed; there being less

lead, the finer the silver is presumed to be. Those who are much in the

habit of cupellation can make good guesses in this way; though it is

still guess work, and often leads to considerable error, for if too much

lead be used for the proportion of baser metal present, a portion of the

silver is wasted; but if too little, then the whole of the copper, &c.

is not carried off, and the button of fine silver remains more or less

impure. The most expert and experienced assayer by the cupel, produces

merely a series of approximate conjectural results, which fall short of

chemical demonstration and certainty in every instance. The lead must

be, in all cases, entirely free from silver, being such as has been

revived from pure litharge; otherwise errors of the most serious kind

would be occasioned in the assays.

The best cupels weigh 12-1/2 grammes, or 193 grains. The cupels allow

the fused oxides to flow through them as through a fine sieve, but are

impermeable to the particles of metals; and thus the former pass readily

down into their substance while the latter remain upon their surface; a

phenomenon owing to the circumstance of the glassy oxides moistening, as

it were, the bone-ash powder, whereas the metals can contract no

adherence with it. Hence also the liquid metals preserve a hemispherical

shape in the cupels, as quicksilver does in a cup of glass, while the

fused oxide spreads over, and penetrates their substance, like water. A

cupel may be regarded, in some measure, as a filter permeable only to

certain liquids.

If we put into a cupel, therefore, two metals, of which the one is

unalterable in the air, the other susceptible of oxidizement, and of

producing a very fusible oxide, it is obvious that, by exposing both to

a proper degree of heat, we shall succeed in separating them. We should

also succeed, though the oxide were infusible, by placing it in contact

with another one, which may render it fusible. In both cases, however,

the metal from which we wish to part the oxides must not be volatile; it

should also melt, and form a button at the heat of cupellation; for

otherwise it would continue disseminated, attached to the portion of

oxide spread over the cupel, and incapable of being collected.

The furnace and implements used for assaying in the Royal Mint and the

Goldsmiths’ Hall, in the city of London, are the following:--

[Illustration: 58 59]

A A A A, _fig._ 58., is a front elevation of an assay furnace; _a a_, a

view of one of the two iron rollers on which the furnace rests, and by

means of which it is moved forward or backward; _b_, the ash-pit; _c c_

are the ash-pit dampers, which are moved in a horizontal direction

towards each other for regulating the draught of the furnace; _d_, the

door, or opening, by which the cupels and assays are introduced into the

muffle; _e_, a moveable funnel or chimney by which the draught of the

furnace is increased. B B B B, _fig._ 59., is a perpendicular section

of _fig._ 58.; _a a_, end view of the rollers; _b_ the ash-pit; _c_ one

of the ash-pit dampers; _d_ the grate, over which is the plate upon

which the muffle rests, and which is covered with loam nearly one inch

thick; _f_ the muffle in section representing the situation of the

cupels; _g_ the mouth-plate, and upon it are laid pieces of charcoal,

which during the process are ignited, and heat the air that is allowed

to pass over the cupels, as will be more fully explained in the sequel;

_h_ the interior of the furnace, exhibiting the fuel.

The total height of the furnace is 2 feet 6-1/2 inches; from the bottom

to the grate, 6 inches; the grate, muffle, plate, and bed of loam, with

which it is covered, 3 inches; from the upper surface of the grate to

the commencement of the funnel _e_, _fig._ 58., 21-1/2 inches; the

funnel _e_, 6 inches. The square of the furnace which receives the

muffle and fuel is 11-3/4 inches by 15 inches. The external sides of the

furnace are made of plates of wrought iron, and are lined with a 2-inch

fire-brick.

[Illustration: 60]

C C C C, _fig._ 60., is a horizontal section of the furnace over the

grate, showing the width of the mouth-piece, or plate of wrought iron,

which is 6 inches, and the opening which receives the muffle-plate.

[Illustration: 61]

_Fig._ 61. represents the muffle or pot, which is 12 inches long, 6

inches broad inside; in the clear 6-3/4: in height 4-1/2 inside measure,

and nearly 5-1/2 in the clear.

[Illustration: 62]

_Fig._ 62., the muffle-plate, which is of the same size as the bottom of

the muffle.

[Illustration: 63]

_Fig._ 63. is a representation of the sliding-door of the mouth-plate,

as shewn at _d_, in _fig._ 58.

[Illustration: 64]

_Fig._ 64., a front view of the mouth-plate or piece, _d_, _fig._ 58.

[Illustration: 65]

_Fig._ 65., a representation of the mode of making, or shutting up with

pieces of charcoal, the mouth of the furnace.

_Fig._ 66., the teaser for cleaning the grate.

[Illustration: 66 67 68]

_Fig._ 67., a larger teaser, which is introduced at the top of the

furnace, for keeping a complete supply of charcoal around the muffle.

_Fig._ 68., the tongs used for charging the assays into the cups.

[Illustration: 69]

_Fig._ 69. represents a board of wood used as a register, and is divided

into 45 equal compartments, upon which the assays are placed previously

to their being introduced into the furnace. When the operation is

performed, the cupels are placed in the furnace in situations

corresponding to these assays on the board. By these means all confusion

is avoided, and without this regularity it would be impossible to

preserve the accuracy which the delicate operations of the assayer

require.

[Illustration: 70 71 72]

I shall now proceed to a description of a small assay furnace, invented

by Messrs. Anfrye and d’Arcet, of Paris. They term it, _Le Petit

Fourneau à Coupelle_. _Fig._ 70. represents this furnace, and it is

composed of a chimney or pipe of wrought iron _a_, and of the furnace B.

It is 17-1/2 inches high, and 7-1/4 inches wide. The furnace is formed

of three pieces; of a dome A; the body of the furnace B; and the ash-pit

C, which is used as the base of the furnace, _fig._ 70. and 71. The

principal piece, or body of the furnace, B, has the form of a hollow

tower, or of a hollow cylinder, flattened equally at the two opposite

sides parallel to the axis, in such a manner that the horizontal section

is elliptical. The foot which supports it is a hollow truncated cone,

flattened in like manner upon the two opposite sides, and having

consequently for its basis two ellipses of different diameters; the

smallest ought to be equal to that of the furnace, so that the bottom of

the latter may exactly fit it. The dome, which forms an arch above the

furnace, has also its base elliptical, whilst that of the superior

orifice by which the smoke goes out preserves the cylindrical form. The

tube of wrought iron is 18 inches long and 2-1/2 inches diameter, having

one of its ends a little enlarged, and slightly conical, that it may be

exactly fitted or jointed upon the upper part of the furnace dome _d_,

_fig._ 70. At the union of the conical and cylindrical parts of the

tube, there is placed a small gallery of iron, _e_, _fig._ 70, 71. See

also a plan of it, _fig._ 72. This gallery is both ingenious and useful.

Upon it are placed the cupels, which are thus annealed during the

ordinary work of the furnace, that they may be introduced into the

muffle, when it is brought into its proper degree of heat. A little

above this gallery is a door _f_, by which, if thought proper, the

charcoal could be introduced into the furnace; above that there is

placed at _g_ a throttle valve, which is used for regulating the draught

of the furnace at pleasure. Messrs. Anfrye and d’Arcet say, that, to

give the furnace the necessary degree of heat so as to work the assays

of gold, the tube must be about 18 inches above the gallery, for

annealing or heating the cupels. The circular opening _h_, in the dome,

_fig._ 70., and as seen in the section, _fig._ 71., is used to introduce

the charcoal into the furnace: it is also used to inspect the interior

of the furnace, and to arrange the charcoal round the muffle. This

opening is kept shut during the working of the furnace, with the

mouth-piece, of which the face is seen at _n_, _fig._ 71.

The section of the furnace, _fig._ 71., presents several openings, the

principal of which is that of the muffle; it is placed at _i_; it is

shut with the semicircular door _m_, _fig._ 70., and seen in the section

_m_, _fig._ 71. In front of this opening, is the table or shelf, upon

which the door of the muffle is made to advance or recede; the letter

_q_, _fig._ 71., shows the face, side, and cross section of the shelf,

which makes part of the furnace. Immediately under the shelf, is a

horizontal slit, _l_, which is pierced at the level of the upper part of

the grate, and used for the introduction of a slender rod of iron, that

the grate may be easily kept clean. This opening is shut at pleasure, by

the wedge represented at _k_, _fig._ 70. and 71.

Upon the back of the furnace is a horizontal slit _p_, _fig._ 71, which

supports the fire-brick, _s_, and upon which the end of the muffle, if

necessary, may rest; _u_, _fig._ 71., is the opening in the furnace

where the muffle is placed.

[Illustration: 73]

The plan of the grate of the furnace is an ellipse: _fig._ 73. is a

horizontal view of it. The dimensions of that ellipsis determine the

general form of the furnace, and thickness of the grate. To give

strength and solidity to the grate, it is encircled by a bar or hoop of

iron. There is a groove in which the hoop of iron is fixed. The holes of

the grate are truncated cones, having the greater base below, that the

ashes may more easily fall into the ash-pit. The letter _v_, _fig._ 71.,

shows the form of these holes. The grate is supported by a small bank or

shelf, making part of the furnace, as seen at _a_, _fig._ 71.

The ash-pit, C, has an opening _y_ in front, _fig._ 71.; and is shut

when necessary by the mouth-piece _r_, _fig._ 70. and 71.

To give strength and solidity to the furnace, it is bound with hoops of

iron, at _b_, _b_, _b_, _b_, _fig._ 70.

[Illustration: 74 75 76]

_Figs._ 74. 75. 76. are views of the muffle.

_Fig._ 77. is a view of a crucible for annealing gold.

[Illustration: 77 78 79 80]

_Figs._ 78. 79. 80. are cupels of various sizes, to be used in the

furnace. They are the same as those used by assayers in their ordinary

furnaces.

[Illustration: 81 82]

_Figs._ 81. and 82. are views of the hand-shovels, used for filling the

furnace with charcoal; they should be made of such size and form as to

fit the opening _h_, in _figs._ 70. and 71.

The smaller pincers or tongs, by which the assays are charged into the

cupels, and by which the latter are withdrawn from the furnace, as well

as the teaser for cleaning the grate of the furnace, are similar to

those used in the British Mint.

In the furnace of the Mint above described, the number of assays that

can be made at one time, is 45. The same number of cupels are put into

the muffle. The furnace is then filled with charcoal to the top, and

upon this are laid a few pieces already ignited. In the course of three

hours, a little more or less, according to circumstances, the whole is

ignited; during which period, the muffle, which is made of fire-clay, is

gradually heated to redness, and is prevented from cracking; which a

less regular or more sudden increase of temperature would not fail to

do: the cupels, also, become properly annealed. All moisture being

dispelled, they are in a fit state to receive the piece of silver or

gold to be assayed.

The greater care that is exercised in this operation, the less liable is

the assayer to accidents from the breaking of the muffle; which it is

both expensive and troublesome to fit properly into the furnace.

The cupels used in the assay process, are made of the ashes of burnt

bones (phosphate of lime). In the Royal Mint, the cores of ox-horn are

selected for this purpose; and the ashes produced are about four times

the expense of the bone-ash, used in the process of cupellation upon the

large scale. So much depends upon the accuracy of an assay of gold or

silver, where a mass of 15lbs. troy in the first, and 60lbs. troy in the

second instance, is determined by the analysis of a portion not

exceeding 20 troy grains, that every precaution which the longest

experience has suggested, is used to obtain an accurate result. Hence

the attention paid to the selection of the most proper materials for

making the cupels.

The cupels are formed in a circular mould made of cast steel, very

nicely turned, by which means they are easily freed from the mould when

struck. The bone-ash is used moistened with a quantity of water,

sufficient to make the particles adhere firmly together. The circular

mould is filled, and pressed level with its surface; after which, a

pestle or rammer, having its end nicely turned, of a globular or convex

shape, and of a size equal to the degree of concavity wished to be made

in the cupel for the reception of the assay, is placed upon the ashes in

the mould, and struck with a hammer until the cupel is properly formed.

These cupels are allowed to dry in the air for some time before they are

used. If the weather is fine, a fortnight will be sufficient.

An assay may prove defective for several reasons. Sometimes the button

or bead sends forth crystalline vegetations on its surface with such

force, as to make one suppose a portion of the silver may be thrown out

of the cupel. When the surface of the bead is dull and flat, the assay

is considered to have been too hot, and it indicates a loss of silver in

fumes. When the tint of the bead is not uniform, when its inferior

surface is bubbly, when yellow scales of oxide of lead remain on the

bottom of the cupel, and the bead adheres strongly to it, by these signs

it is judged that the assay has been too cold, and that the silver

retains some lead.

Lastly, the assay is thought to be good if the bead is of a round form,

if its upper surface is brilliant, if its lower surface is granular and

of a dead white, and if it separates readily from the cupel.

After the lead is put into the cupel, it gets immediately covered with a

coat of oxide, which resists the admission of the silver to be assayed

into the melted metal; so that the alloy cannot form. When a bit of

silver is laid on a lead bath in this predicament, we see it swim about

for a long time without dissolving. In order to avoid this result, the

silver is wrapped up in a bit of paper; and the carburetted hydrogen

generated by its combustion, reduces the film of the lead oxide, gives

the bath immediately a bright metallic lustre, and enables the two

metals readily to combine.

As the heat rises, the oxide of lead flows round about over the surface,

till it is absorbed by the cupel. When the lead is wasted to a certain

degree, a very thin film of it only remains on the silver, which causes

the iridescent appearance, like the colours of soap-bubbles; a

phenomenon, called by the old chemists, fulguration.

When the cupel cools in the progress of the assay, the oxygenation of

the lead ceases; and, instead of a very liquid vitreous oxide, an

imperfectly melted oxide is formed, which the cupel cannot absorb. To

correct a cold assay, the temperature of the furnace ought to be raised,

and pieces of paper ought to be put into the cupel, till the oxide of

lead which adheres to it, be reduced. On keeping up the heat, the assay

will resume its ordinary train.

Pure silver almost always vegetates. Some traces of copper destroy this

property, which is obviously due to the oxygen which the silver can

absorb while it is in fusion, and which is disengaged the moment it

solidifies. An excess of lead, by removing all the copper at an early

stage, tends to cause the vegetation.

The brightening is caused by the heat evolved, when the button passes

from the liquid to the solid state. Many other substances present the

same phenomenon.

In the above operation it is necessary to employ lead which is very

pure, or at least free from silver. That kind is called _poor lead_.

It has been observed at all times, that the oxide of lead carries off

with it, into the cupel, a little silver in the state of an oxide. This

effect becomes less, or even disappears, when there is some copper

remaining; and the more copper, the less chance there is of any silver

being lost. The loss of silver increases, on the other hand, with the

dose of lead. Hence the reason why it is so important to proportion the

lead with a precision which, at first sight, would appear to be

superfluous. Hence, also, the reason of the attempts which have, of late

years, been made to change the whole system of silver assays, and to

have recourse to a method exempt from the above causes of error.

M. d’Arcet, charged by the Commission of the Mint in Paris, to examine

into the justice of the reclamations made by the French silversmiths

against the public assays, ascertained that they were well founded; and

that the results of cupellation gave for the alloys between 897 and 903

thousandths (the limits of their standard coin) an inferior standard, by

from 4 to 5 thousandth parts, from the standard or title which should

result from the absolute or actual alloy.

The mode of assay shows, in fact, that an ingot, experimentally composed

of 900 thousandths of fine silver, and 100 thousandths of copper,

appears, by cupellation, to be only, at the utmost, 896 or 897

thousandths; whereas fine silver, of 1000 thousandths, comes out nearly

of its real standard. Consequently a director of the Mint, who should

compound his alloy with fine silver, would be obliged to employ 903 or

904 thousandths, in order that, by the assay in the laboratory of the

Mint, it should appear to have the standard of 900 thousandths. These 3

or 4 thousandths would be lost to him, since they would be disguised by

the mode of assay, the definitive criterion of the quantity of silver,

of which the government keeps count from the coiner of the money.

From experiments subsequently made by M. d’Arcet, it appears that silver

assays always suffer a loss of the precious metal, which varies,

however, with the standard of the alloy. It is 1 thousandth for fine

silver,

4·3 thousandths for silver of 900 thousandths,

4·9 -- for -- of 800 --

4·2 -- for -- of 500 --

and diminishes thereafter, progressively, till the alloy contains only

100 thousandths of silver, at which point the loss is only 0·4.

Assays requested by the Commission of the Paris Mint, from the assayers

of the principal Royal Mints in Europe, to which the same alloys,

synthetically compounded, were sent, afforded the results inscribed in

the following table.

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

| | | Standards found for the |

| | Cities | Mathematical Alloys. |

|Names of the Assayers.|where they+---------+---------+---------+

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

|Assayer |Vienna |946·20 |898·40 |795·10 |

|A. R. Vervaëz, Ditto |Madrid |944·40 |893·70 |789·20 |

|in Spain |Ditto |944·40 |893·70 |788·60 |

|Assayer |Amsterdam |947·00 |895·00 |795·00 |

|Master |London |946·25 |896·25 |794·25 |

|Mr. Johnson, Assayer |Ditto |933·33 |883·50 |783·33 |

|Inspector of the Mint |Utrecht |945·00 |896·50 |799·00 |

|Assayer of the Mint |Naples |945·00 |891·00 |787·00 |

|Assayer of Trade |Ditto |945·00 |891·00 |787·00 |

|Assayer of the Mint |Hamburgh |946·13/72|897·41/72|798·44/72|

|Ditto |Altona |942·1/4 |894·00 |790 |

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

These results, as well as those in still greater numbers, obtained from

the ablest Parisian assayers, upon identical alloys of silver and

copper, prove that the mode of assay applied to them brings out the

standard too low; and further, that the quantity of silver masked or

disguised, is not uniform for these different eminent assay masters. An

alloy, for example, at the standard of 900 thousandths is judged at

the Mint of Paris to have a standard of 895·6

At that of Vienna -- 898·4

-- Madrid -- 893·7

-- Naples -- 891·0

The fact thus so clearly made out of a loss in the standard of silver

bullion and coin, merits the most serious attention; and it will appear

astonishing, perhaps, that a thing recurring every day, should have

remained for so long a time in the dark. In reality, however, the fact

is not new; as the very numerous and well-made experiments of Tillet

from 1760 to 1763, which are related in the memoirs of the Academy of

Sciences, show, in the silver assays, a loss still greater than that

which was experienced lately in the laboratory of the Commission of the

French Mint. But he thought that, as the error was common to the nations

in general, it was not worth while or prudent to introduce any

innovation.

A mode of assaying, to give, with certainty, the standard of silver

bullion, should be entirely independent of the variable circumstances of

temperature, and the unknown proportions of copper, so difficult to

regulate by the mere judgment of the senses. The process by the humid

way, recommended by me to the Royal Mint in 1829, and exhibited as to

its principles before the Right Honourable John Herries, then Master, in

1830, has all the precision and certainty we could wish. It is founded

on the well-known property which silver has, when dissolved in nitric

acid, to be precipitated in a chloride of silver quite insoluble, by a

solution of sea salt, or by muriatic acid; but, instead of determining

the weight of the chloride of silver, which would be somewhat uncertain

and rather tedious, on account of the difficulty of drying it, we take

the quantity of the solution of sea salt which has been necessary for

the precipitation of the silver. To put the process in execution, a

liquor is prepared, composed of water and sea salt in such proportions

that 1000 measures of this liquor may precipitate, completely, 12 grains

of silver, perfectly pure, or of the standard 1000, previously dissolved

in nitric acid. The liquor thus prepared, gives, immediately, the true

standard of any alloy whatever, of silver and copper, by the weight of

it which may be necessary to precipitate 12 grains of this alloy. If,

for example 905 measures have been required to precipitate the 12 grains

of alloy, its standard would be 905 thousandths.

The process by the humid way is, so to speak, independent of the

operator. The manipulations are so easy; and the term of the operation

is very distinctly announced by the absence of any sensible nebulosities

on the affusion of sea salt into the silver solution, while there

remains in it 1/2 thousandth of metal. The process is not tedious, and

in experienced hands it may rival the cupel in rapidity; it has the

advantage over the cupel of being more within the reach of ordinary

operators, and of not requiring a long apprenticeship. It is

particularly useful to such assayers as have only a few assays to make

daily, as it will cost them very little time and expense.

By agitating briskly during two minutes, or thereby, the liquid rendered

milky by the precipitation of the chloride of silver, it may be

sufficiently clarified to enable us to appreciate, after a few moments

of repose, the disturbance that can be produced in it by the addition of

1000 of a grain of silver. Filtration is more efficacious than

agitation, especially when it is employed afterwards; it may be

sometimes used; but agitation, which is much more prompt, is generally

sufficient. The presence of lead and copper, or any other metal, except

mercury, has no perceptible influence on the quantity of sea salt

necessary to precipitate the silver; that is to say, the same quantity

of silver, pure or alloyed, requires for its precipitation a constant

quantity of the solution of sea salt.

Supposing that we operate upon a gramme of pure silver, the solution of

sea salt ought to be such that 100 centimetres cube may precipitate

exactly the whole silver. The standard of an alloy is given by the

number of thousandths of solution of sea salt necessary to precipitate

the silver contained in a gramme of the alloy.

When any mercury is accidentally present, which is, however, a rare

occurrence, it is made obvious by the precipitated chloride remaining

white when exposed to daylight, whereas when there is no mercury

present, it becomes speedily first grey and then purple. Silver so

contaminated must be strongly ignited in fusion before being assayed,

and its loss of weight noted. In this case, a cupel assay must be had

recourse to.

_Preparation of the Normal Solution of Sea Salt, when it is measured by

Weight._--Supposing the sea salt pure as well as the water, we have only

to take these two bodies in the proportion of 0·5427 k. of salt to

99·4573 k. of water, to have 100 k. of solution, of which 100 grammes

will precipitate exactly one gramme of silver. But instead of pure salt,

which is to be procured with difficulty, and which besides may be

altered readily by absorbing the humidity of the air, a concentrated

solution of the sea salt of commerce is to be preferred, of which a

large quantity may be prepared at a time, to be kept in reserve for use,

as it is wanted. _Instruction de Gay Lussac._

_Preparation of the Normal Solution of Sea Salt, when measured by

Volume._--The measure by weight has the advantage of being independent

of temperature, of having the same degree of precision as the balance,

and of standing in need of no correction. The measure by volume has not

all these advantages; but, by giving it sufficient precision, it is more

rapid, and is quite sufficient for the numerous daily assays of the

mint. This normal solution is so made, that a volume equal to that of

100 grammes of water, or 100 centimetres cube, at a determinate

temperature, may precipitate exactly one gramme of silver. The solution

may be kept at a constant temperature, and in this case the assay stands

in want of no correction; or if its temperature be variable, the assay

must be corrected according to its influence. These two circumstances

make no change in the principle of the process, but they are

sufficiently important to occasion some modifications in the apparatus.

Experience has decided the preference in favour of applying a correction

to a variable temperature.

We readily obtain a volume of 100 cubic centimetres by means of a

_pipette_, _fig._ 83., so gauged that when filled with water up to the

mark _a_, _b_, and well dried at its point, it will run out, at a

continuous efflux, 100 grammes of water at the temperature of 15 C. (59

Fah.). We say purposely at one efflux, because after the cessation of

the jet, the pipette may still furnish two or three drops of liquid,

which must not be counted or reckoned upon. The weight of the volume of

the normal solution, taken in this manner with suitable precautions,

will be uniform from one extreme to another, upon two centimetres and a

half, at most, or to a quarter of a thousandth, and the difference from

the mean will be obviously twice less, or one half. Let us indicate the

most simple manner of taking a measure of the normal solution of sea

salt.

[Illustration: 83 84]

After having immersed the beak _c_ of the pipette in the solution, we

apply suction by the mouth, to the upper orifice, and thereby raise the

liquid to _d_ above the circular line _a b_. We next apply neatly the

forefinger of one hand to this orifice, remove the pipette from the

liquid, and seize it as represented in _fig._ 84. The mark _a b_ being

placed at the level of the eye, we make the surface of the solution

become exactly a tangent to the plane _a b_. At the instant it becomes a

tangent, we leave the beak _c_ of the pipette open, by taking away the

finger that had been applied to it, and without changing any thing else

in the position of the hands, we empty it into the bottle which should

receive the solution, taking care to remove it whenever the efflux has

run out.

If after filling the pipette by suction, any one should find a

difficulty in applying the forefinger fast enough to the upper orifice,

without letting the liquid run down below the mark _a b_, he should

remove the pipette from the solution with its top still closed with his

tongue, then apply the middle finger of one of his hands to the lower

orifice; after which he may withdraw his tongue, and apply the

forefinger of the other hand to the orifice previously wiped. This mode

of obtaining a measure of normal solution of sea salt is very simple,

and requires no complex apparatus; but we shall indicate another

manipulation still easier, and also more exact.

In this new process the pipette is filled from the top like a bottle,

instead of being filled by suction, and it is moreover fixed. _Fig._ 85.

represents the apparatus. D and D´ are two sockets separated by a stop

cock R. The upper one, tapped interiorly, receives, by means of a cork

stopper L, the tube T, which admits the solution of sea salt. The lower

socket is cemented on to the _pipette_; it bears a small air-cock R´,

and a screw plug V, which regulates a minute opening intended to let the

air enter very slowly into the pipette. Below the stop-cock R´, a silver

tube N, of narrow diameter, soldered to the socket, leads the solution

into the _pipette_, by allowing the air, which it displaces, to escape

by the stop-cock R´. The screw plug, with the milled head V´, replaces

the ordinary screw by which the key of the stop-cock may be made to

press, with more or less force, upon its conical seat.

[Illustration: 85 86]

_Fig._ 86. represents, in a side view, the apparatus just described. We

here remark an air-cock R, and an opening _m_. At the extremity Q of the

same figure, the conical pipe T enters, with friction. It is by this

pipe that the air is sucked into the pipette, when it is to be filled

from its beak.

[Illustration: 87]

The _pipette_ is supported by two horizontal arms H K (_fig._ 87.)

moveable about a common axis A A, and capable of being drawn out or

shortened by the aid of two longitudinal slits. They are fixed steadily

by two screw nuts _e e´_, and their distance may be varied by means of

round bits of wood or cork interposed, or even by opposite screw nuts _o

o´_. The upper arm H is pierced with a hole, in which is fixed, by the

pressure of a wooden screw _v_, the socket of the _pipette_. The

corresponding hole of the lower arm is larger; and the beak of the

_pipette_ is supported in it by a cork stopper L. The apparatus is fixed

by its tail-piece P, by means of a screw to the corner of a wall, or any

other prop.

The manner of filling the pipette is very simple. We begin by applying

the fore-finger of the left hand to the lower aperture _c_; we then open

the two stop-cocks R and R´. Whenever the liquor approaches the neck of

the _pipette_, we must temper its influx, and when it has arrived at

some millimetres above the mark _a b_, we close the two stop-cocks, and

remove our forefinger. We have now nothing more to do than to regulate

the _pipette_; for which purpose the liquid must touch the line _a b_,

and must simply adhere externally to the beak of the _pipette_.

[Illustration: 88]

This last circumstance is easily adjusted. After taking away the finger

which closed the aperture _c_ of the _pipette_, we apply to this orifice

a moist sponge _m_, _fig._ 88., wrapped up in a linen rag, to absorb the

superfluous liquor as it drops out. This sponge is called the

handkerchief (_mouchoir_), by M. Gay Lussac. The _pipette_ is said to be

wiped when there is no liquor adhering to its point exteriorly.

For the convenience of operating, the handkerchief is fixed by friction

in a tube of tin plate, terminated by a cup, open at bottom to let the

droppings flow off into the cistern C, to which the tube is soldered. It

may be easily removed for the purpose of washing it; and, if necessary,

a little wedge of wood, _o_, can raise it towards the _pipette_.

To complete the adjustment of the _pipette_, the liquid must be made

merely to descend to the mark _a_, _b_. With this view, and whilst the

handkerchief is applied to the beak of the _pipette_, the air must be

allowed to enter very slowly by unscrewing the plug V, _fig._ 85.; and

at the moment of the contact the handkerchief must be removed, and the

bottle F, destined to receive the solution, must be placed below the

orifice of the _pipette_, _fig._ 88. As the motion must be made rapidly,

and without hesitation, the bottle is placed in a cylinder of tin-plate,

of a diameter somewhat greater, and forming one body with the cistern

and the handkerchief. The whole of this apparatus has for a basis a

plate of tinned iron, moveable between two wooden rulers R R, one of

which bears a groove, under which the edge of the plate slips. Its

traverses are fixed by two abutments _b b_, placed so that when it is

stopped by one of them, the beak of the _pipette_ corresponds to the

centre of the neck of the bottle, or is a tangent to the handkerchief.

This arrangement, very convenient for wiping the _pipette_ and emptying

it, gives the apparatus sufficient solidity, and allows of its being

taken away, and replaced without deranging any thing. It is obvious that

it is of advantage, when once the entry of the air into the _pipette_

has been regulated by the screw V, to leave it constantly open, because

the motion from the handkerchief to the bottle is performed with

sufficient rapidity to prevent a drop of the solution from collecting

and falling down.

[Illustration: 89]

_Temperature of the Solution._--After having described the manner of

measuring by volume the normal solution of the sea salt, we shall

indicate the most convenient means of taking the temperature. The

thermometer is placed in a tube of glass T, _fig._ 89., which the

solution traverses to arrive at the _pipette_. It is suspended in it by

a piece of cork, grooved on the four sides to afford passage to the

liquid. The scale is engraved upon the tube itself, and is repeated at

the opposite side, to fix the eye by the coincidence of this double

division at the level of the thermometric column. The tube is joined

below to another narrower one, through which it is attached by means of

a cork stopper B, in the socket of the stop-cock of the _pipette_. At

its upper part it is cemented into a brass socket, screw-tapped in the

inside, which is connected in its turn by a cock, with the extremity,

also tapped, of the tube above T, belonging to the reservoir of the

normal solution. The corks employed here as connecting links between the

parts of the apparatus, give them a certain flexibility, and allow of

their being dismounted and remounted in a very short time; but it is

indispensable to make them be traversed by a hollow tube of glass or

metal, which will hinder them from being crushed by the pressure they

are exposed to. If the precaution be taken to grease them with a little

suet and to fill their pores, they will suffer no leakage.

_Preservation of the Normal Solution of Sea Salt in metallic

Vessels._--M. Gay Lussac uses for this purpose a cylindrical vessel or

drum of copper, of a capacity of about 110 litres, having its inside

covered with a rosin and wax cement.

_Preparation of the Normal Solution of Sea Salt, measuring it by

Volume._--If the drum contains 110 litres, we should put only 105 into

it, in order that sufficient space may be left for agitating the liquor

without throwing it out. According to the principle that 100 centimetres

cube, or 1/10 of a litre of the solution should contain enough of sea

salt to precipitate a gramme of pure silver; and, admitting moreover,

13·516 for the prime equivalent of silver, and 7·335 for that of sea

salt, we shall find the quantity of pure salt that should be dissolved

in the 105 litres of water, and which corresponds to 105 × 10 = 1050

grammes of silver, to be by the following proportion:--

13·516 : 7·335 ∷ 1050 gramm. : x = 569·83 gr.

And as the solution of the sea salt of commerce, formerly mentioned,

contains approximately 250 grammes per kilogramme, we must take 2279·3

grammes of this solution to have 569·83 gram. of salt. The mixture being

perfectly made, the tubes and the _pipette_ must be several times washed

by running the solution through them, and putting it into the drum. The

standard of the solution must be determined after it has been well

agitated, supposing the temperature to remain uniform.

To arrive more conveniently at this result, we begin by preparing two

_decimes_ solutions; one of silver, and another of sea salt.

The decime solution of silver is obtained by dissolving 1 gramme of

silver in nitric acid, and diluting the solution with water till its

volume become a litre.

The decime solution of sea salt may be obtained by dissolving 0·543

grammes of pure sea salt in water, so that the solution shall occupy a

litre; but we shall prepare it even with the normal solution which we

wish to test, by mixing a measure of it with 9 measures of water; it

being understood that this solution is not rigorously equivalent to that

of silver, and that it will become so, only when the normal solution

employed for its preparation shall be finally of the true standard.

Lastly, we prepare beforehand several stoppered phials, in each of which

we dissolve 1 gramme of silver in 8 or 10 grammes of nitric acid. For

brevity’s sake we shall call these tests.

Now to investigate the standard of the normal solution, we must transfer

a _pipette_ of it into one of these test phials; and we must agitate the

liquors briskly to clarify them. After some instants of repose, we must

pour in 2 thousandths of the _decime_ solution of sea salt, which, we

suppose, will produce a precipitate. The normal liquor is consequently

too feeble; and we should expect this, since the sea salt employed was

not perfectly pure. We agitate and add 2 fresh thousandths, which will

also produce a precipitate. We continue thus by successive additions of

2 thousandths, till the last produces no precipitation. Suppose that we

have added 16 thousandths: the last two should not be reckoned, as they

produced no precipitate; the preceding two were necessary, but only in

part; that is to say, the useful thousandths added are above 12 and

below 14, or otherwise they are on an average equal to 13.

Thus, in the condition of the normal solution, we require 1013 parts of

it to precipitate one gramme of silver, while we should require only

1000. We shall find the quantity of concentrated solution of sea salt

that we should add, by noting that the quantity of solution of sea salt,

at first employed, viz. 2279·3 grammes, produced a standard of only 987

thousandths = 1000 - 13; and by using the following proportion:

A Dictionary of Arts, Manufactures and Mines containing a clear exposition of their principles and practice · 第 8 / 421 题

To dye with archil, the quantity of this substance deemed necessary,