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,.^:

'■1^'^.:^\, ^:,

N THE CUSTODY Or THE

BOSTON PUBLIC LIBRARY.

CHEMICAL ESSAYS.

CHEMICAL ESSAYS.

B Y

R. WATSON,

D. D. F. R. S.

AND REGIUS PROFESSOR OF DIVINITY IK THE UNIVERSITY OF CAMBRIDGE.

VOL. in.

THIRD EDITION.

LONDON:

PRINTED BYJ. DAVIS

FOR T. EVANS, PATERNOSTER-ROW.

MDCCLXXXV,

ADAMS

CONTENTS,

ESSAY

I. Of Bitumens and Charcoal, Page i

IL Of the ^iantity of Water ev apo-- rated from, the Surf ace of the Earth In hot Weather, 5 1

III. Of Water dijfolved in Air, 75

IV. Of Cold produced during the Eva- poration of Water ^ and the Solu- tion of Salts, 1 1 9

V. Of the Degrees of Heat in which Water begins to part with its Air^ and in which it boils, 143

VL Of Water in a f olid State : of the Heat of Spring Water -, and of a probable Caufe of the Impregnation of Julphureous E'aiers, 171

YIL Of

CONTENTS.

ESSAY

Wl, Of Derhyjhire Lead Ore, 207

VI I L Of the /melting of Lead Ore, as fra^iifed in Derhyfhire, 25 1

IX. Of Silver extraEiedfrom Lead.i^o i

X. Of Red and White Lead, 337

A D V E R"

ADVERTISEMENT.

I Have every reafon to be fatisfied with the reception which has been given to my two former volumes of Chemical EfTays. My defign was to have publijfhed two others on the fame plan 3 but this is the laft for which I fhall ever prefume to intreat the indulgence of the public. I perceived, as I proceeded in the work, that two additional volumes would not contain half the materials which I had colle6ted ; and defpair- ing of ever finding leifure to arrange the whole, I have contented myfelf 2 with

( " )

With putting into this volurtie, what gave me the kail trouble in revifmg. For feveral months I have had great reafon to believe, that an attention to health ought to occupy that lei- fure, which I have hitherto beftowed on the fiudy of chemiftry. It is a fiiudy of fo bewitching a kind, that few perfons can cultivate it with moderation, or fail of feeling fymp- toivns of that diforder which Beccher in fpeaking of himfelf, defcribes in the following terms,* — cut nee Au- la Splendor J me ceeonomi^e ratio^ nee fama integritaSj nee Janitatis vigGVy quiequajn p'ce earhonibiiSy venenis, fti^ liginey follibusy et furnis valerepoteft^

* Phy. Subter. Pra.

ESSAY

E S S A Y

OF BITUMENS AND CHARCOAL.

'^I^HE analyfes of pitcoal and of A different woods, mentioned in the laft ElTay, may ferve as inflances of the produdrs obtainable by diftil- .lation from .Mruminous and vege- table fubilancestn general. They all of them yield water impregnated with an acid, and often alfo with a volatile alkaline fait, air, oils of dif- ferent colours, weights, and confift- ence^, and a black coaly refiduum. The bitumens generally taken notice

VOL. III. A of

( 2 )

of by writers on Natural Hiftory are, with refpedl to their confiflence, either as fluid as oil^ or as thick and tenacious as tar, or quite folid. The fluid bitumens are two, Naptha, and PetrcleumyOr rock-oil. Thefe are oils which differ from each other in co- lour and confifcence, and fome other properties 3 the naptha is pale, light, and very inflammable; the petroleum is yellow, brown, or blackifn, hea- vier and lefs inflammable than nap- tha : its difference from naptha is attributed to its containing a greater quantity of acid in its compofltion. Both thefe oils are found in many parts of the globe, either floating on fpring v/ater, or dripping from the crevices of rocks. Mineral fitch \s a bitumen which differs from petro- leum in being thicker, heavier,

and

( 3 )

and more glutinous ; it was formerly

-found in the environs of Babylon, and conftituted, according to Vitruvius, when mixed with lime, the cement which was ufed in building the walls

^of that city. At prefent it is met with in fcveral parts of Europe, and in America, where it drips from rocks, and is called by us Barhadoes tar: it has a very offenfive fmell,

. and great tenacity, and is called by the inhabitants of Auvergne, in

• France, where it exudes from the

^ earth, and flicks to the feet, devils dung. Tht ^pballum, or jewj-pitcby is a bitumen much refembling mine- ral pitchy it is thrown up in a? liquid form from the bottom of the lake where Sodom and Gomorrah flood, otherwife called the Deadfea^ or the

:lake JJphaltes^ from a Greek word A 1 denotin^y

( 4 )

denoting abitumen. This lake in the time of Efdras yielded Bitumen — re- memher what 1 did to Sodom and Gomor- rah^ whoje land lieth in clods offitch^. The bitumen floating upon the fur- face of the fait water, is condenfed by the heat of the fun into a folid form, and is gathered by the Arabs on the Ihore where it is thrown. It is faid to be the fame fubilance which the Egyptians ufed in embalming their mummies, and it was called by them mmnia jyiineruUs, f This bitumen has been found in many places of Afia and Europe, as v/ell as on the Ihores of the Dead Sea^ ail that we meet with in the ihops, is either an arti- ficial compofition, or an European afphaltum, the Eallern ones being fsldom brought into Europe, but

ufed

'^ Efd. B. 2. c. 2.

•| H^^il^lquiil's Vov. p. 285.

( 5 )

iiled by the natives either as pitch

for their fhios. or as an ing-redient in varnilhing, or dying wool.

There is a very curious experi- ment v/hich illuftrates the relation which thele four bitumens bear to each other. The moil tranfparent oil of turpentine, refembling nap- tha, may be changed into an oil re- fembling petroleum, by mixing it with a fmall portion of the acid of vitriol j with a larger proportion of the acid the mixture becomes black and tenacious, like Barbadoes tarj and the proportions of the ingre- dients may be fo adjufted, that the mixture will acquire a folid confid- ence, like afphaltum. This experi- ment teaches us to conclude that naptha, petroleum, Barbadoes tar, and afphaltum, differ chiefly from A 3 each

( 6 )

each other, with refped to the quan- tity of acid which enters into their compofition 3 andthefiabftances pro- cured by diililling pitcoaI> or refi- nous vegetables may furnifli no improbable conjecture concerning the origin of thefe bitumens.

Let us fuppofe then a fub terra- neous fire to be fituated in or near a ftratum of pitcoal, of turf, of foiTil wood, or of any other fuch bitumenous matter^ it is manifeil that the inflammable air, and the dif- ferent kinds of oils, which were col- 3e6led by diililling fmall portions of thefe fubilances, would be elevated by the heat into the crevices of the fuperineumbent ftrata j the light and pale oil v/ould be a fort of naptha,. or petroleum, the black and tena- cious oil v/ould be a Barbadoes tar,

and

( 7 )

and this might be fo dried by the

heat as to become an afphakum. The oils not being mifcible with water, would be found floating upon its lurfacej as it ilTued out of the bowels of the earth, and being very- inflammable, might conilitute burn- ing wells, fuch as have been met v/ith near Wigan, atBrofely, and in many^-other places : or v/here the oil did not m^eet with water, or was too heavy to float on it, we may conceive that it would impregnate the'porous ftrata of feveral kinds of fliones and earth. Ithasbeenobferved inanother place,*that they formerly obtained a fort of tar, from a ftone atBrofely, and the fcratum, v/hich is called JJmle in Derbyfhire is fo ftrongly im- pregnated with oil, that it will burn A 4 of

* Vol. 2. p. 347

( 8 )

of itfdf, when fet oa fire -.the work- men in digging through, the black ftone, which is incumbent on the ihale, fometimes meet with eavitie& containing a thick black oil,- which has oozed out of the furrounding ftone. One of the greateft/c'^^i^j, or Subterraneous paiTages, which haS;,, perhaps ever been formed in Great Britain, is that which is called Hell- car fough, in Derbyfhires this foiigh- is driven through a.ftratum of Ihale, and the workmen are much troubled v/i th inflammable air, which general- ly breaks into the fough, through the lame crannies which give paffage to- little flreams of water: they fecure themfelves from the air, by keeping great fans conilantly in motion 5 for the inflammable, air, being lighter tlian common air^, floats near the roof

of

( 9 )

of the Tough, and being drawn down from thence,, and mixed with the common air by the m^otion of the fans, it is circulated in the fough without danger. I am fenfible that inflammable air may be produced by various other ways, as well as by the application of heat, to bitumenous flrata; but as bitumens do yield in- flammable air by diflillation, it is probable enough, that fuch as is met with in bitumenous ftrata, may fometimes at leafl, be referred to the adtion of a lire, fituated^. per- haps, at too great a diftance from the furface of the earth, to produce any other fenfible effect.

In the Duchy of Modena in Italy,, there is a remarkable rock, which confirms very much the notion of oils and pitchy fubflancesj. being fe«^

parated

( lO )

parated from bitumens by a kind of fubterraneous difliUation. The in- habitants of the diftrict, by piercing the fides of this rock, at different diftances from its fummit, obtain oils of different natures, thickening and growing heavier and deeper coloured, as the canals through which they flow approach to the fur- face of the earth -, at the diftance of a few feet below the furface, they find a very thick oil, which in dig- ging deeper becomes foft as butter, and at ftill a greater depth, it is found to be as folid as pitch.

Befides^//C(?^/and afphaltum, there are three other folid bitumens which deferve to be mentioned — Jet — Amber— Ambergris . Jet fo much refembles cannel coal in its colour, in its hardnefs, in its receiving a

poliili.

( " )

polifti, in its not foiling the fingers when rubbed upon it, and in other properties, that many authors con- found the two fubftances together; and indeed they agree in io many qualities that it is fomewhat difficult to fay in what they difagree. Jet, however, when warmed by fridtion, has the property of attrading bits of ftraw, feathers, and other light bodies;, but I never obferved this property in any of the cannel- coals which I have tried. This property, if it may generally be relied on, as appertaining to jet, and not to can- nel coal, is a very eafy chara6leriilic, by which thefe fubftances may be diftinguifned from each other. Jet is faid to be found only in fimail de- tached pieces, and that it is thereby diflinguifhable from cannel coal,

which

( 12 )

which Is found in large beds. Some think that the woody fibrous tiflue of jet, may ferve to diftinguiih it from cannel-coal, but whoever ex- amines large quanties of this kind of coal, will fee many pieces which much refemble wood in texture. The weight of a cubic foot of can- nel-coal is 1 273 ounces; a cubic foot of jet is faid by one author to weigh i238,*by another 1 180 ounces, j

The natural hiflory of Amber is very obfcure. This bitumen was for a long time thought to be re- flrided to the coafts of Pruflia, on the Baltic Sea. It was fuppofed to owe its origin to the ex,udations of certain trees on the coaft of Sweden, v/hich falling into the fea, were there hardened by the continual adtion of

the * Martin,, f Lewis, Newm. Chem.

( 13 ) the faltSj and thence carried by par- ticular winds to the open coafls of Pruffia. This opinion was fupported by, and fornned to account for, the ants, flies, fpiders, leaves of trees, and other terrefbrial matters, which are almofl always found inclofed in pieces of amber, and which no doubt muft be admitted, as proving its be- ing originally in a -fluid ftate. In Pruffia they not only gather amber on the fea coaft, but they frequently find it at the depth of eight or tea feet beneath the furface of the earth, but at no great diftance from the fea. The fuperincumbent ftrata are fand, clay, fofnl-wood, pyrites, fand again, in which the amber is found, fome- ^ times in detached pieces, fometimes in little heaps. This diftribution of .the ftrata, where amber is found, to- gether

( 14 )

gether with their proximity to th€ fea, has madeitAvith fome degree of probability be imagined, that this mineral owed its fituation to the inundation and receffion of the fe a, and that it was derived partly from an oil arifmg from the decompofition of vegetables by fubterraneous fires, and partly -from a mineral acid. Amber is frequently found in Italy, where they have no fofTil-wood, but great ^ plenty of petroleum.

The natural hiitory of ^w^^r^m is asuncertainasthatofambei-junlefswe admit the defcription which has been lately given of its origin, as the true one. We are told that ambergris is a part of the Cachalot or Sper7naceti' whale, " It is found in this animal, in the place where the feminal vefiels are ufually fituated in other animals, I It

( ^5 ) It is. found in a bag of three or four

feetJong, in round lumps, from one to twenty pounds weight, floating in a fluid rather thinner than oil, and of a yellowifli colour. There are never feen more than four at a time in one of thefe bagSj and that which weigh- ed twenty pounds^ and v/hich was the largefl: ever feen, was found fingle. Thefe balls of ambergris are not found in ail fiflies of this kind^ but chiefly in the oldefl: and fl:rong- efl;.*" This account feems probable enough, for ambergris is a fine per- fume, and we know that other per- fumes, fuch as civet, muflc, and caf- tor, are fituated in the inguinal re- gions of the civet cat, the muflc ani- mal and the beaver.

All vegetable, and bitumenous,

and

* Goldfmith's Nat. Hift. Vol.-vi. p. 220.

( i6 )

and indeed all animal fubflances. leave, after their volatile principles have been feparated by diftillation, a black coal. Thefe coals differ fome- vv'hat from each other, with refpedt to their pronenefs to catch fire, and their ability to fupport it, but I will content myfelf with examining the nature of the refidue, from the dif- tillation of wood.

This refidue does not differ from what is generally called charcoal j the flighteft attention to the manner of obtaining this refidue, and of making charcoal, will convince us, that no difference ought to be expe6led. When the wood is diflilled, its com- munication with the external air is obllruded, its volatile parts are ele- vated from it, by the heat to which itisexpofed^ and the relidue is that

pari:

( 17 )

part of the wood which remains af- ter all the volatile parts are driven off. In making charcoal they con- ilru6t a pile of wood upon the fur- face of the ground, they cover the pile with a coating of turf, or other fubflances, and make the coating fa compadt, that it will not admit of air, except through fome little round holes, v/hich are purpofeiy made in it, and which can be flopped at plea- fure. When the pile, thus con- ftrudled, is ftt on fire, part of the oil of the wood is confumed during the burning of the pile, the other part, together with the air and water contained in the wood, is eraporatedj and there remains, when the opera- tion is iinifhed, the earthy part of the wood, called in that Hate, char- coal. Thus the making of charcoal VOL. III. B is

( i8 )

is a kind of diftiUatior>, for the coat« ing which furrounds the pile of ^ woo4s may be compared to a retort. Henckel informs us, that 150 lbs, of oal^j will produce 62 lbs. of char- coal * ; but he does not inform us whether the oak was dry or green, whether it had its bark on or was < peeled^ whether it was all heart of oak, or partly heart, and partly fap, whether the operation of making the charcoal was difcontinued as foon as the wood ceafed to fmoke, or pro- trailed feme time longer ; and yet a difference in anyone of thefe circum- llances, will fenfibly influence the weight of the charcoal, procurable from a definite weight of wood.

The woods which I converted into charcoal, were dry, and had been fel- led • * Fo.rc Satur, c. iv, p* 5^0

( t9 )

led many years, their relative weights were taken with great exa6tnefs. Weio-ht of a cubic foot of

■Water --.	iooo avbir. ounces*,
Box —	9SO ^
Oak —	892 .^—
Alh --	832 .—
- Mahogan)^ -	^ 816 ^^^-^
AValniit -	- 79^ "-—
Deal	^ 615 —
Authors differ	very much as to the
weights which	they have afligned to
definite bulks of the fan re kind oi
wood. Thus,	one efti mates the
weight of a cubic foot of dry box at
1030*3 another at 1201 ounces f:.

one puts the v/eight of a cubic foot

of dry oak at 925 J 5 another at 800

ounces II . To the more obvious

B 2 fources

* Cotes Hydros* p. 73. t Fergufon*s

Tab. p. 237, i CoteSi fj Emerfon's Mech^ p. 132.

( 20 )

fources of this diverfity, in the weights of equal bulks of the fame kind of wood, — fuch as the wood being green or dry, being cut from the boll or branch of a tree, — one may be added, which has not, I be- lieve, been fufficiently attended to — I mean the great lofs of weight which in certain circumfljances, the fame piece of wood fuftajns, by a fimple expofure to the atmofphere, in the courfe of a few days.

From the middle of a branch of an oak tree, which had been felled in April, and expofed without its bark, to the' hot fummer of 1779, I cut, Sept. 4, a round piece, about fix in- ches in diameter, and three inthick- nefs : Sept. 15;! cut from the heart of this piece of oak a fmall flip, 3 inches, in lengthy .-J; .of an inch in

thick-

( " )

ihicknefs, and 79 grains in weight 5 at tlie fame time, I cut a fimilar flip from the fap of the fame piece, the weight of which alfo was 79 grains, thefe two pieces were put into the drawer of my ftudy table, and being weighed again. Sept. 25,^ the heart of oak had loft 8 grains, or near ^^V of its weight ; the fap had loft 1 2 grains, or above ~ of its weight. Now if the weights of feveral equal bulks of thefe woods had been taken on the 15th, and on the 25th of Sep- tember^ it is obvious, (notwith- ftanding the contra6lion they might have fuffered) that there would hava been fome difference in them though the woods themfelves appeared equally dry on both days.

This fpeedy diminution of weight

which wood undergoes by expofure

33 to

C 2i2 )•

to the air, being a matter of fome' importance in an oeconomical view, I will mention another experiment which I made on tlie fiibje(it» A. piece of afh cut March ly,. 1780, from the middle of a large tree, which had been felled fix weeks be- fore,, was accurately weighed ; its- weight was 317 grains, its length 3 inches,, and its breadth 2., It was^ weighed again March 24, it had loft in the courfe of 7 days 62 grains, or near ^ of its weight. I weighed this fame piece of wood on the 25th of Auguft in the fame year, but it had not loft any thing of its weight, from the 24th of MarcL to the 25th of Auguft. The two pieces of oak,, mentioned in the laft experiment,, were weighed alfo, on the 25th of Auguftj 1780, they had neither of 3 them

( 23 )

them loft, in the courfe of eleven

months, quite i grain; hence it ap- pears ; that the matter which is dif- perfed from wood after it is cut, is foon evaporated : this matte> proba- bly confifts chiefly of water. The carriage of wood, efpecially by land, is- very expenfive : if an oak or an alh tree was cut into boards, or fcantlings, upon the fppt where it is felled, there would be a faving of the carriage of one ton in fix or feven, from the evaporation of the fubftance of the wood; to fay no- thing of chips and other refufe parts, • It is well known that all wood becomes heavier than water, by hav- ing the air extraded from the pores, either by an air-pump, or by boiling it in water. The woods of which: J' have given the relative weights, B 4 were

( 24 ) were all of them rendered heavier than water, by a long continuance in cold water ; for the heat of the wa- ter in w^hich they were put^ never exceeded 60 degrees. They funk in the water after they had been foaked in it for different lengths of time, but it required above ico days foaking before the deal would fink. After they had all lain in water for 1 10 days J I took them out, and let them dry by the gradual heat of the atmofphere for above a month; I then weighed themj, and found that box, oak, and afli, had each of them loft ^V o^ the weight they had before they were put into the water; but that mahogany, walnut, and deal, had loft only ^L. of their weight. This lofs of weight is occafioned, partly by the efcape of fome portion

of

I 25 ;

of air, and partly by a difTolution of fome of the other principles of the woods i for the water, in which they were placed, had evidently a6led upon them, its colour and confid- ence being both changed, Moft woods contain both a gummy and a reftnous part ; and gums being folu- ble, and refins not foluble in water, we can have no difficulty in appre- hending the reafon, why fome forts of wood loofe a greater proportion of their weight, by being immerfed in water, and afterwards dried, than others. Since the fame piece of wood has very different weights, when dry and when foaked with wa- ter ; the covering carts, ploughs, and other hufbandry gear, ufually made of afli, with a coarfe kind of paint which will keep out the rain.

( 26 )

IS a pradice full as iervlceable in kfTening the weight of the imple- ment which is to be moved by the llrength of a man or horfe, . as in' preferving the wood of which it is made from decay,

I took fquare pieces of the woods before mentioned, each piece being 3 inches in length, and weighing exaftly 96 grains, and expofed them^, when covered with fand, in a cru- cible, to the adtion of the fame fire, which was ilrong enough to keep the crucible red hot, for three hours ; they were, at the end of t:hat time, all of them converted into perfed charcoals ; the weights of the refpe6live charcoals were taken, whilft they were Hill warm^. from the operation,, and are exprefled in the following table :

Walnut

( 27 )

Walnut 96 grns. gave 25 grns. -of charcoal Oak — 96 — — 22 —

Box — 96 — — 20 ■

Mahogany 96 — — 20 - i\fli — 96 — — 17 —

Deal — 9.6 — — 15

There is a good reafon for remark- ing, that the charcoals were weighed whim they were warm,, for in weigh- ing them a few days afterwards, I found that they had all increafed in weight in eonfequence of Jomething which they had attra6led from the atmofphere ; their weights then were ■ — walnut 28 — oak 24 — box 23 ■ — mahogany 24 — alh 18 — deal 16 — grains.

The quantities of refidue remain- ing from the diftillation of 96 ounces of oak, box, and mahogany, were refpedively 30, 26!, and 27! oun- ces,

(28 ) ces, which numbers are feverally larger than thofe, exprefTing the quantities of charcoal obtainable from 96 parts of thofe woods ; this difference may proceed from the woods, employed in the two procef- fes, being of different qualities, or, more probably, from the heat ia which the charcoal was made, being greater than that employed in the diilillation ; for the ftronger the fire, the lefs is the quantity of charcoal, which a definite weight of wood will yield.

In making charcoal the workmen obferve, that the pile of wood is fenfibly .diminiHied in fize by the operation ; this proceeds from the fhrinking of the wood. All the kinds of wood which I charred were diitiiniflied in all their dimenfions,

the

( 29 )

the mahogany, oak, and walnut, v/ere the lead diminifhed, and the box was the moft dinr.inilhedj I thought it had lofl an eighth part of its length. This diminution not on- ly depends upon the nature of the wood, but it is influenced by the flrength and continuance of the heat, that being moil diminifhed^ which has fuftained the great^ft heat.

Though charcoal, from every fort of wood, is incapable of being de- compofed, by the ilrongeft fires in clofe velTels, yet it is a compounded body, and may be decompofed by being burned in the open air.

Van Helmont fays, that 6 2 pounds of oak charcoal will, by burning, yield only ilb. of white afhes. The other 6 1 pounds which are difperfed into the air, he confiders as a vapour

of

( JO )

of an elaftic nature, which can nei- ther be colle6i:ed in vefTels, nor re- duced into a yifible form. This va- pour he called by a new nanfie, gas^, Stahl is of opinion, that-iolbs. of charcoal made from porous woods, fuch as fir and fallow^ will not, when burned with a very flow fire, yield ^bove lib. of allies f; this quan- tity however, it mud be remarked, is above fix times the -quantity af- figned by Van Helmont to oak, which probably contains more afhes in a definite weight of charcoal, than either fir or fallow,

GeofFroy,

* Hunc fpiritum, incognitura ha^lenus, novo nomine gas, voco, qui nee vafis cogi nee incorpus vilibile reduci poteft. Van Hel, Op. om. p. 103. Some derive gas from the Dutch ghoaft-fpirit ; others from the German gafcht, a frothy ebullition.

f StahliiExper. Numero CCC. p. 17*'

( 3 1 )

GeofFroy, from ibmewhat lefs than

34 ounces of the charcoal, remaining

. after the diftillation of the heart of guaiacum, got near three ounces of white afhe^, by calcining the coal in an open fire for 12 hours. From

.near 23 1 ounces of the coal, re- maining from the diftillation of the

'fap of guaiacum^ he got near if ounce of afhes. And %gl ounces of

...the coal, from the bark of guaia-

- cum, gave him 13I ounces of white

:. afhes*.

Laftly, M. Sage aflures us that 100 pounds of charcoal will not,

•■ when burned, furnifli quite 2 ounces of alhesf.

Thefe accounts, it muft be ac-

know-

* Geof, Mat. Med. or treatife on foreign vVegeta. by Thicknefs. p. 112.

,f Exper. fur F Alk. VoUfluor. p. 2.70

( 3^ )

Icnowledged, differ very much, as to

the quantity of afhes obtainable from a definite weight of charcoal ; and the difference, I think, is much greater than what can wholly be at- tributed to the different textures of the feverai woods ; a part of this di- verfity may, probably, arife from a difference in the manner of burning the charcoal. When charcoal is burned in fmall quantities, and in a flow fire, lefs of its fubllance will be difperfed into the air, than when the quantity is larger, and the ftream of air which fupports the fire, is m.ore rapid. This feems not improbable ; but if the weight of the afhes re- maining from the burning of a defi- nite weight of charcoal, be at all in- fi.uenced by the degree of fire, it feems reafonable to fuppofe, that

what

i 33 ) ^ wliat is driven off by the violence of

the fire, is of the fame earthy nature, as that which remains when the fire is more moderate ^ at leaft it may be argued, that when charcoal is burn- ed with a. flow fire, fome of its prin- ciples, its oily principle for inflance, though it, probably, alfo contains a faline one, are more completely de- •compbfed, than when it is confumed with a violent fire, and that the d^e- 'Compofition of thefe principles, gives an additional quantity of earth or ialt to the afhes.

If there be any truth in this notion, "we muii; not fay, th^ the 6i pounds of matter which, according to Van Helmont, are difperfed into the air from 62 pounds of charcoal, are wholly of an elaftic nature ; fince they may confift principally of an VOL. Ill, C attenu-

C 34 )

attenuated earth, which being driven off by the current of air, requifite for the maintenance of the fire, re- mains for a time fufpended in the at- mofpherical air, without being in its own nature elaftic. I would not be underftood to fay, that the whole of what is dilTipated, during the burn- ing of the charcoal, is an attenuated earth, Tince it is certain, that the earth of theafhes is not inflammable, and that charcoal contains fomething which is inflammable; it is allowed alfo, that fimple earth is inodorous, and it is well known, that charcoal, during its inflammation, difperfes fomething into the air, which has a ftrong fmell -, this fomething by which charcoal is rendered inflammable, and by w^hich the air is infeded with a particular fmell, during the burn- ing

( 35 )

mg of the charcoal. Is called by moft

chemifls the phlogifton*. This c 2 phlogiilon

* PhlogiftoH is a conftituent part of me- tallic fubftances, and it feems, when fepa- rated from them, to he of an elaflic nature. I diftilled zinc wiih J^rong acid of vitriol, and obtained a portion of fulphur, produced, as it fhould feem, by the acid's uniting itfelf with the phlogifton of the zinc. No inflam- mable vapour was produced, till the fulphur began to be fublimed, then indeed, there efcaped a vapour, compofed, I think, of the attenuated parts of fulphur, which upon the approach of a candle took fire. Another portion of zinc was dillilled with iv^ak acid of vitriol J before the zinc fdt the heat of the lire, the inflammable air, feparable from zinc by a weak acid of vitriol, pafled into the receiver, and being fet on fire, biirll it with a great explofion : another receiver was ap- plied, and the diflillation continued to dry- nefs, but not a particle of fulphur v/as pro- duced, the phlogifton necefTary for its for- mation having, probably, been feparated from the zinc, by the violent action of the

acid.

( 36 )

phloglilon, whether it be an elaftic inflammable fluid, or an unelaftic earth of a particular kind, conflitutes^ probably, but a very fmall portion of the weight of what is difperfcd. into the air, from burning charcoal;: we all know what a firong fmell may be difFufed through a large room, from the ignited fnuff of a candle, or from a very fmall piece of charcoal, which has not been thoroughly burned; the vapours ifluing from thefe fubilances are of an oily faline nature, and are vifible^: the vapour of charcoal, though it is too fubtleto be feen, may be of a nature fomevv^hat fnnilar, and capa- ble

acid, and confumed at once by the inflam- maticn. May it not from the comparifon of thefe experiments be conje6liired, that the phlogifton of metals is an elaftic inflamma- ble air ?

( 57 )

He of a very extenfive diffufion

through the air. An infant has been known fuddenly to expire, from the fmoke of a candle blown out under its nofe, and the vapour of charcoal is mod dangerous, when the char- coal has not b^en thoroughly burnt.

It has been found by experiment, that the comman atmofpherical air is much altered in its properties, by being made to pafs through red hot charcoal, into the vacuum of an air pumpi it then extinguiihesthe flam.e of a candle, and animals die in it*. a fimilar change takes place, when charcoal is confumed in an apart- ment, which has not a fuflicient fup- ply of frefh air ; the inflances of per- fons who have unhappily loft their lives in fuch air, are very common in c 3 all

* Plauklbee's Exper. p. 287,

( 33 ) all countries, where much ufe is: made of charcoal, but efpe daily m Ruifia, where their apartments are heated by ovens,^ containing red hot charcoal*. The change which the atmofpherical ^ir undergoes, from the burning of charcoal, may pro- ceed either from the air, having lolt fome of its conflituent parts in com..- ing in conta£l with the burning char- coal, or from its having gained fomething from the charcoal, or from its having done both at the fame time; jufl as water which palTes through a lump of fait or fu gar, lofes

a great * Philof. Tranf. 1779, p. 325 — ^Where there is mention made of the Ruffian method of recovering perfons who have been render- ed fenfelefs by the vapour of the charcoal ; it conlifts in carrying the perfon into the opea air, rubbing him with fnov/ or cold water,, and pouring water or milk down his throat.

( 39 )

a great part of the air it contains in

its natural ftate, and gains a portion of the fait, which becomes dilTolved in it^ and upoa both accounts fufFers a change of its properties. ,

It is generally admitted, that char- coal and all other bodies, nitrous ones excepted, ceafe to burn, as foon as they ceafe to be fupplied with frefh air, and the air has, chiefly on this account, been thought to com- miinicate ibmething to the fire, by which the fire was maintained, and the air was confuted. And this opinion has. been confirmed by ob- ferving, that a definite quantity of air was much diminifned in bulk by bodies being burned in it. Thus, if lo cubic inches of air be made to pafs through red hot charcoal, diey will be reduced to nine, and there c 4 are

( 40 )

are means of making the dimintrtios ftill greater.

Dr. Hooke advances another hy- pothefis 3 he allows air to be necef- fary to the fupport of fire,, but he thinks that it contributes to this fup- port, not by imparting any thing of its own fubfcance to the fire, but by diJfGlving the inHammable principle- of bodies, as water difTolves falts *: according to the former hypothefis air is ih^food -, according to this it is' the receptacle ovjolvent of fire.

Dr. Prieflly, to whofe inventive genius and indefatigable induftry the

philo- * Hooke's Micogr. p. 103. and Pofthum„ Works p. 169. Jimcker feems to have en- tertained a iimilar notion — ingens aeris quantitas requiritur ad dljfoln^endas et recipi- €ndas ignitas illas et ultimo motu attenuatas particiilas, unde nili fat aeris lit extinguitui? ignis. Junck. Gonf» Chem. VoL I. p. 1 5.7.

(41 )

philofophic world is peculiarly in- debted for his inquiries into the na- ture of fiditious airs> has obferved^, that common air is diminifhed one iifth by the fumes of burning char- coal y and this dimunition, he thinks is fome how or other effe6Ved by the air being highly charged with the phlogiflon of the charcoal i and he obferves^which agrees very well with Dr. Hookers hypothefis, that when any definite quantity of air is fully faturated with phlogiflon from char- coal, no heat that he had ever ap- plied was able to produce any more efFedt upon the charcoal*.

Though common air is diminifhed in bulk by the fumes of burning char- coalj and of other bodies, in a ftatc of combuftion, yet a bottle or a bladder

filled

* Philof. Tranf. i-^-^J, p. 2 25 »— 230.

I 42 ;

filled with this diminifhed air, weighs lefs than when it is filled with com- mon air*, in the proportion of 1 83 to 185, That 5 cubic inches of common air, fnould be reduced by the fumes of burning charcoal to 4 cubic inches^ and that thefe 4 cubic inches of infeded air, ihould Vvxigh lefs than 4 cubic inches of common air, cannot v/eli be accounted for without admitting, that a part of the 5 cubic inches of atmofpherical air, has been, by fome means or other, taken away, at the famiC time that its bulk was reduced to 4 cubic inches. Being defirous of feeing,, whether the property 1 had obferved in char- coal, with relpe6l to its weighing lefs when it v/as quite cold, than when it was Y/arm from the fire in which

k * Prieft. Exp. and Ob. \ol. 11. p. 94.

( 43 )

it had been made, was a general pro-, perty appertaining to all hot and cold charcoal, I weighed feveral pieces when they were cold, and again, when they were fo hot as to be handled with difficulty, and found that they all loft (they were of the- fame kind of wood) about i part in 1 2 of their weight, and that being left to cool in the open air, they re- gained what they had loft in a few days. This acquifition of weight was made moft rapidly at firft, a. piece which weighed 240 grains when cold, was reduced by being heated, to 220 grains, and being left to cool, it gained 9 grains in 4 hours, and 1 5 grains in 8 hours. From the manner in which charcoal is made, it is probable that what remains ad- herent to the wood, is not greatly

differ-

C 44 )

different from what is forced from it by the lad degree of heat; now" this Gonfifts of an acid, and an oil rendered thick and pitchy by its- union with an acid; may we not hence fuppofe, that it is a portion of fixed acid, which attracts the humi-- dity of the air, or perhaps the air it- felf, when the charcoal is hot, and becomes faturated therewith, and that what was attra6ted, is again dri- ven off when the charcoal is again- heated 5 and thus the charcoal be- comes again capable of exerting its attraction, and acquiring an encreafe of weight^. It is fome confirmation of this hypothecs, that charcoal when taken out of hot fand,. takes fire upon expofure to the air, and for much the fame reafon, probably, that Homberg's pyrophorus takes

fire

( 45 )

fire in the open air*. Guaiacum

contains a flronger acid than moft kinds of wood, and GeofFroy has obferved that "the coal of guaia- cum being taken out of the retort, and expofed to the air, even two or three days after the procefs, takes £re imniediatqly of its own accord;

provid- * Homberg's Tyrophorus is known to <every fchool-boy. It is made by calcining together for a proper tinie, and in proper <iuantities, either alum or any fait containing the vitriolic acid, with honey, fugar, flour, or any animal, or vegetable fubftance, capable of being reduced to a eoal. Part of the vi- triolic acid being uncombined with the phlo- gillon of the coal, and being in a dry con- denfed flate, attrads the humidity of the at- mofphere, and generates fuch a degree of heat by its mixture with water, as is fufl[icient to 'inflame the other part of the pyrophorus. Py- Tophori may be made without the vitriolic acidj butfome acid probably enters into their cona- cpoiition«

( 46 )

provided, that when the diftillation is over, the neck of the retort be carefully flopped, and the veflels and furnace be left to cool of them- felves"*.

This property of increafing in weight by expofure to the air, be- longs to the hot coal of pitcoal, as well as to that of wood -, I took fome red hod cinders, and weighing them in that ftate, left them to cool ; in 12 hours they had gained one 75th part in weight, and in 4 days they had gained one thirtieth of their weight. Some coak whic:h had been burned with a ftrong fire, gained much lefs than the cinders.

It has been obferved in another place, that charcoal may be decom- pofed, by being diftiiled with the

acid

* Treatife on foreign vege. p, 1 1 1 .

( 47 ) acid of vitriol* ; this acid robs the charcoal of its inflammable principle, and reduces it to an earth : no other menflruum feems to have any a6cion upon it. What alteration might be produced in charcoal, by quenching it when red hot, in various menftru- umSj or by boiling it in them, or by keeping it immerfed in them, when cold, for a long time, or by other lefs obvieu5 procefTes, it does not fall ^within my defign to inquire.

Animals and vegetables are foon reduced by putrefaction to an earth.; many forts of flones and metallic fubflances are crumbled into duft by the adlion of air and water ; but char- coal remains unchanged for ages, whether it be expofed to the air, or immerfed in water, or buried in the ^arth. The. beams of the theatre

at

( 48 )

at Herculaneum were converted into charcoal by the Lava^ which over- flowed that city, and during the lapfe of above feventeen centu- ries the charcoal has remained as entire as if it had been formed but yefterday^ and it will probably con- tinue fo to the end of the world. This incorruptibility, as it may be called, of charcoal has been known in the moft diftant ages ; for it has been obferved that the famous temple of Ephefus was built upon wooden piles which had been charred on the oiatfide. The cuftom of -charring the ends of pofls which are to be fixed in the earth is very common, and I have often wondered that the fame cuftom has not prevailed with .refpe(5t to the wood ufed in mines and fubterraneaus drains. The tim- I bers

C 49 )

hers which fupport^ in many places, the roof of the foughs through which there is a current of water, are wailed away in a fev/ years, that part of them efpecially which is ex- pofed to the alternatives of moifture and drynefs by the rifmg and falling of the water is foon rotted, and this part one would think would be char- red with ,ireat advantao-e.

I) "ESSAY

ESSAY II

©P THE QlTANTITr OF WATER EVA- PORATED FROM THE SURFACE OF THE EARTH IN HOT WEATHER.

^I^HERE are many operations- JL conftantly carrying on by na- tural means, v/hich, though they cfcape the ordinary obfervation of our fenies^ fufficiently excite our a- ftonilhment when once difcovered. The vafl: quantity of a particular kind of air, with which the atmof- phere is daily impregnated, from she combuilion of all forts of f jel, is- E> 2 one

( 52 ) one inftance of this kind ; and the water which is raifed into the attnof- phere fronn the furface of the earth, is another. Who would have con- jedured that an acre of ground,, even after having been parched by the heat of the fun in fun^imcr, dif- perfed into the air above 1600 gal- lons of water in the fpace of tv/elve of the hotteil hours of the day ? No vapour is {een to afcend, and we little fuppofe that m the hotteft part of the day, more ufually does afcend than in any other. The experiment from which I draw this conclufion, is fo eafy to be made, that every one may fatisfy himfelf of the truth of it. On the 2d of June, 1779, v/hen the fun ilione bright and hot, I put a large drinking glafs, v/ith its miouth downw'iro''. u-'/on 3 o-n^-rlr^t wj^^rh

C 53 )

was mown clofe , there had been no

rain for above a month, and the grafs was become brown ; in lefs than two minutes the infide of the glafs was clouded with a vapour,

and in half an hour droDS of v^ater

i.

began to trickle down its infide, in various places. This experiment was repeated feveral times with the fame fuccefs.

That I might accurately eftimate the quantity, thus raifed, in any cer- tain portion of time, I meafured the area of the mouth of the glafs, and found it to be 20 fquare inches : there are 1296 fquare inches in a fquare yard, and 4840 fquare yards in a ftatute acre -, hence, if we can find the means of meafuring the quantity of vapour raifed from 20 fquare inches of earth, fjppofe in D 3 one

( 54 )

one quarter of an hour, it will be an eafy matter to calculate the quantity which would be raifed with the fame degree of heat, from an acre in 1 2 hours. The method I took to mea- fure the quantity of vapour, was not perhaps the mod accurate which might be thought of, but it was lim- pie and eafy to be pradtifed : when the glafs had flood on the grafs-plat one quarter of an hour, and had collected a quantity of vapour, I wiped its infide with a piece of muf- -lin,, the weight of which had been previoufly taken ; as foon as the" glafs was wiped dry, the muHin was weighed again, its increafe of weight fhewed the quantity of vapour which had been collefted. The medium increafe of weight, from feveral ex- periments made on the fame day, J between

< 55 )

b-etween 12 and 3 o'clock, was 6

grains colleded in one quarter of an hoiir^ from 20 fquare inches of earth. If the reader takes the trou- ble to make the calculation, he wilf find that above 1600 gallons, reck- oning 8 pints to a gallon, and efli- mating the weight of a pint of wa- ter at one pound avoirdupoife, or 7000 grains troy \7eight, would be raifed, at the rate here mentioned^ from an acre of ground in 24 hours. It may ealily be conceived that the quantity thus elevated, will be greater v/hen the ground has been well foaked with rain, provided the heat be the fame ; I did not happen to mark the^hrat of the ground v^hen I m.ade the forementioned experi- ments i the t^o following are more circumllantial : the ground had been D 4 wet^

(56 )

wetted the day before I made them

by a thunder fhower^ the heat of the earth at the time of making them, eftimated by a thermometer laid on the grafs, was 96 degrees ; one ex- periment gave 1973 gallons from an acre in 1 2 hours, the other gave 1905. Another experiment made when there had been no rain for a week, and the heat of the earth was no degrees, gave after the rate of aSoo gallons from an acre in 12 hours ', the earth was hotter than the air, as it was expofed to the reflec- tion of the fun's rays from a brick wall.

The heat in Bengal in the fummer months is variable, in the fhade from 98 to 120 degrees,* and in the fun it probably does not fail Ihort of

140 * Phllof. Tranf. 1767, page 218, and for the year 1775, P« *02,

(57 )

140 degrees j hence, after the earth

has been well drenched by the over- flowing of the Ganges^ immenfe quantities of vapours mufl be daily raifed, to the amount, perhaps, of five or fix thoufaitd gallons from an acre, in twenty-four hours. The rainy fcafon in Bengal lafts from the beginning of June to the middle of October, all this interval isconfidered as an unhealthy time, but efpecially the latter part of it , for then the earth begins to grow dry, the flime left upon its furface, confifting of decayed vegetables and other putref- .cent bodies, begins to corrupt, and the fun by its violent and continued action raifes up into the air, not a pure water, but water impregnated -with putrid particles of all kinds. Whether a merely raoill fituation

be

( 58 )

^e unwholefome may be mtvch queflioned, but that moifture arifing from earth or water in a ftate of pu- trefadion is fo, cannot well be doubted. The overflowing of the Nile puts a ftop to the plague in Egyp^ infomuch, probably, as it puts a ftop to the putrefadlion of the ca- nals of Grand Cairo and other places. Agues and putrid fevers are much more frequent in the fens of Gam- hridgefnire and LincolnJInre in very- dry, than in wet years ^ the Irijh^ who annually come to reap the harveft in the fens of Cambridgefhire, have tieen fo fenfible of the difference, that for the three or four years laft ^aft, which have been very dry, they Have entered upon their tafk with great reludance and apprehenfion of what they call the Fen-Jhake, The

States

( S9 )

States o( Holland y in the year 174.S,

laid the country around Breda under water, and ordered the water to be kept up till the wineer, in order to flop a ficknefs which had arifen from the moiil and putrid exhalations of half-drained grounds.* The Arabs are faid to take a horrid kind of vengeance when they think them- felves injured by the ^urks at Bajfora ; they contrive to overflov\^ the adjoin- ing country: a peftilential fever be- gins to Ihew itfelf as the land begins to grow dry by the evaporation of the water, and it rages with fuch violence as to carry off many thou- fands of the inhabitants of that city. f The nature of the foil muft have a great influence on the health of the

people

* Sir J. Pringle's Dif. of the Army, p^ 63* f Ptiilol. Tranf. 1778, p. 215.

( 6o )

people who inhabit it, fo far as that is dependent on the moifture or dry- nefs of the air. There is, probably, as much water raifed into the air, in a hot day, from an acre of ground in the fens of Camhridgejhire^ as is raifed in two or three days from an equal furface in the fandy parts of Norfolk and Suffolk^ Not but the moft fandy country may have a very moift atmofphere, when water hap- pens to be found near the furface j for the heat of the fun will penetrate through the fand, and raife the water in vapour, which will find an eafier palTage through the fand than it would do through a lefs open foil. Thus the foil in fome parts of Dutch Brabant is a barren fand, but water is every where to be met with at the depth of two or three feet, and in

propor-

( 6i )

proportion to its diflance from the furface the inhabitants are free from difeafes.*

Vegetation muft be greatly influ- enced by the quantity of water which is raifed from the earth ; fome foils retain humidity much longer than others, and one great ufe of marles and other manures, is to render the foil on which they are put lefs liable to be deprived of its moiflure by the heat of fummer. The water in af- cending from the bofom of the earth, moiftens the roots, and in being dif- folved in the air, it affords nutriment to the branches of vegetables ; but as vegetation may be injured either by a defe6t, or an excefs of moiflure, and as different plants require dif- ferent quantities of it, for attaining

dieir

* D&f. of the Ari-v, d, 62.

C 62 )

their utmoil- perfe6tion^ it merits tne attentive obfervation of the farmer to fuit his plants and his manures to- the nature of the foil. There aremany^ fandy and limeftone foils, which are covered almoft with flints or lime- ftone pebbles;- the crop of corn would, probably, be lefs, if thefc :0:ones were removed ; for they are ferviceable^ not only in fheltering the firft germs of the plant from^ cutting winds, but they impede the efcape of moiflure from the earth ; the afcending vapour ftrikes upon^ that furface of the ftone which i^ eontiguous to the earth, and is there- by condenfed, and thus its further af- cent is for a time, at leaft,. prevented,. Upon the fame grafs-plat, and contiguous fto the glafs ufed in the experiments^, I placed a filver cup,.

with.

( 63 )

with its mouth downwards, of a

fhape fimilar to that of the glais, and nearly of the fame dimenfions 3 but I could never obferve that its infide had colleded the leaft particle of vapour, though I frequently let it Hand on the grafs for half an hour,. or more..

By means of a little bee's wax, I fattened an half crown very near, but not quite contiguous, to the fide of the glafs, and fetting the glafs, with^ its mouth downwards, on the grafs,, it prefently became covered with va- pour, except that part of it which was near to the half crown. Not only the half crown itfelf was free from vapour, but it had hindered any from fettling on the glafs which was near it, for there was a little ring of glali lurrounding the half

crowa

( 64 )

crown to the diflance of I- of an Inch which was quite dry^ as well as that -part of the glafs which Vv^as imme- diately under the half crown; it* feemed as if the filver had repelled the water to that diflance. A large red wafer had the fame effe6t as the half crown, it was neither wetted itfelf nor was the ring of glafs contiguous to it wetted. A circle of white paper produced the fame efte6l, fo did feveral other fubilances, which it would be tedious to enumerate.

Thefe phenomena, refpedlingthe different difpofitions of different bo- dies to attradl the rijing vapour, are fimilar to what others have taken notice of concerning the falling of dew, and are, probably, to be ex- plained upon the fame principles, whatever they may be. Mufchen-

bro-k

ibroek placed on the leaden terras of the Obfervatory at Utrecht velTels <of glafs., china, yarniflied wood, po- lifhed brafs, and pewter 5 he found . .that in the courfe of a night the glafs, .china, and vflrniihed wood, had col- Jedied a great abundance of dew, •but that not a drop had fallen on any cof the poiifhed metals*. M. du Fay expofed to the air, when the dew was falling, two large funnels, one made of glafs the other of po- iifhed pewter; the necks of the fun- nels being inferted into velTels pro- per to retain any moiilure which might be colleded by them.; he fometimes found in the morning that ■ the veiTel under the glafs funnel con- tained an ounce or more of water^ VOL. in. E but

"" In trod* ad Philof. Nat, Toixi. 2. p. 990.

t 66 )

fent lie never obferved fo much as & drop in the other*.

A great part of the water which is raifed into the air from the per- fpiration of the earth during a hot day, defcends down again upon its furface in the courfe of the night; and this is the reafon that the dews are the greateft in the hotteft wea- ther, and In the hotteft climates. The earth retains the heat it receives in confequence of the fun's adtion longer than the air does; water, moreover, is evaporabie in all de- grees of heat; hence water may con- tinue to rife from the earth, when the air, being cooled by the abfence of the fun, is no longer able to fuftain what is thus raifed, or to retain what

. * Hift. <Ie I'Acad; des Scien. i:749»

( 67 )

it had taken up during the day tinae, and a dew from thefe different caufes may, under <:ertain circumfliances, be found both to rife and fall during the whole night.

Egypt, at one feafon of the year, is fo parched up by the hear, thar the furface of the ground becomes quite rugged with fiffures; at this time the dew, proceeding from the vapour exhaled from the earth, is very plentiful, and by its plenty pre- vents the total deilruction of the country. ^' This dew is particularly ferviceable to the trees, which would otherwife never be able to refift the heat; but with this alTiftance they thrive very well, blolTom and ripen their fruit. Therefore, the upper parts of the Egyptian trees, at one time of the year, do the office of E 2 roots,

( 68 )

roots, attradling nourifliment by their abforbent vcflels, the leaves, from the moift air."*

The quantity of water which was condenfed on the infide of the glafs, I found to be accurately proportion- able to the time . during which it flood on the grafs ; for in one ex- periment 6 grains were collected in lo minutes, and in another 15 grains were collected in 25 minutes; now the proportion of 6 to 10 is the fame as that of 15 to 25.

•In order to fee whether the copious vapour colledled by the glafs was owing to the natural perfpiration of the grafs, or to a kind of mechanical dillillation from the body of the earth, I put the glafs upon a foot- path which was dry,, and had no

grafs * HafTelquiA^sVoy. p. 455.

( 69 )

grafs growing upon it,, the vapour rofe from the footpath as well as from the grafs, but not fo abun- dantly.-

From what has been advanced, it may, probably, be juftly inferred, that the air contiguous toy or not far removed from, the furface of the earth, whether that furface be plain or mountainous, barren, or covered with vegetables, will be much more loaded with the vapour which arifes conftantly from the earth, than that which is at the diftance of even a few yards from the furface. This point may be illuftrated by the fol- lowing hypothecs Suppofe the

earth to be a globe of rock fair, and to be covered with water to the •height of a mile; imagine the wa^ ter*to-bc divided into four: fpherical E 3 Ihells,

( 7° )

fliells, each ^ of a mile in thicknefs.

ISow the firft fhell, which is fup- pofed to be contiguous to the fur- face of the fait, v/ould foon faturate, Jtfelf with th^ fait, and becoming thereby heavier than, the water at a greater dlftance, it would not, by the ordinary motion of the winds and tides, foon mix itfelf with the whole mafs of water ; . but it would contain far more fait in folution than the fecond fhell, and the fecond would contain more than the third, and the third more than the fourth. Let us further fuppofe the fait con- tained in the v/hole of the water to be precipitated, and the precipita- tion to begin from the flieli fartheft removed from the furface of the earth ; it is evident, that the quan- tity of the precipitate will increafe, a not

C 7' )

not fimply with the increafe of Ipace through which it has defcended, but in a much higher proportion, inaf- much as the lad (Bell,, through which it defcends, may be fuppofed to con- tain three or four times as much fait as the uppermoft. In like manner,, it feems reafonable to fuppofe that the air which is near the furface of the earth will be greatly^ more charg- ed with water,, which it diffolves as water diflblves fait, than that which is fituated at the diftance of even a- few yards from the furface.

Dr. Heberden was the firft perfon^ who took notice^ that a. much larger quantity of rain falls into a rain- gage fituated near the furface of the earth, than into one of the fame di- menfions^ fituated a few yards above E 4 its

( 7i ) it*; and he thinks that this differ- ence is to be explained fronn fome unknown property of eledlricity. The fad is placed beyond contro- verfy, by experiments which have been made at various places ; at Liverpool in particular it has been obferved, that ^^ a veflel (landing on the ground in a fpacious garden, re- ceived douhle the quantity of rain which fell into another veffel of equal dimenlions placed near the fame fpot, but eighteen yards high- €r"f . I am far from thinking that the foregoing obfervations, relative to the quantities of water contained

in equal bulks of air at different

heights

* Phil. TrarX 1769. p; 361. ^ See an ingenious eflay on the fubje6t, by Dr, Percival, who has -explained the pheno- menon from the known principles of eledtri- city. Eflays by Dr. Perci, p. 112.

( n )

lieights from the furface of the earth, contain a fatisfa6tory explanation of this phenomenon ; yet it may be re- marked:, that rain gages placed at -equal diftances from the furface of the earth, colle6ted nearly equal quantities of rain, though one of them was fituated on a plain, and the other on a mountain 450 ; yards in height above the plain* : this obfer- vation is fome confirmation of the hypothefis v/hich has been mention- ed, as on that fuppofition it follows, that the air at the fame diftance from the furface of the earth, is equally impregnated with water, other cir- cumilances being the fame, and therefore equal quantities of rain ought to be coUefted by vefTels plac- ed at equal diftances from the fur- face

* Philof, Tranf. 1772, p. 294,

( 74 )

face of tbe earth; though according to the fame fuppofition, a much larger quantity ought to be colie6ted by a vefiel placed on the furface,, than by one placed a few yards above it. Thus this hypothefiSj. admitting its truth, (v/hich future experiments will perhaps eftablifh) feems as if it was fufHcient for explaining the phe- nomenon i I would be underftood however to mention it witb much diffidence, and was I as nauch fkilled in ek6tricity,,as the very worthy and ingenious perlbn, who' firft noticed the fa6l, is in every branch of natu- ral philofophy,, I might probably have feen reafon not to mention it at all.

ESSAY

ESSAY m<

OF WATER DISSOLVED IK AIR.

W^E have fecn, m the precedr- ing ElTay, that large quan- tities of water are railed from the earth in the hotteft weather ; the wa- ter, which is thus elevated, is no more vifible in the air, than a piece of fu gar is vifible in the water where- in it happens to be diflblved, nor is the tranfparency of the air injured by the water it has received from the

earthj,

( 76 )•

earth, and therefore we conclude,. that the water is not merely mixed with the air, but really dijblved m its a perfed tranfparency of the fluid, in which any body isdifTolved, being efteemed the moft unequivo- cal mark of its folution.

The caufe of the afcent, fufpen- fion, and defcent of vapours, is not yet fully determined -, many think that eledricity is the principal agent - in producing^ thefe phenomena * i •whiift others are of opinion, that wa- ter is raifed and fufpended in the air, much after the fame manner in which falts are raifed and fufpended in wa- ter i and it muft be owned that this

opinion

* Philof. Tranf. 1755. p. i24.-*'Elec^ tricitas, vapores ia atirem extoUit,. in aer« (fufpendit, et ex acre in teilurem depluit. Prof. pavers Exp, de Elec. Theo»p. 106.

'( 77 5

opinion (which future experience :may fliew not to be wholly incon- fiftent with the other) has a great appear-ance of probability.

Salts, in general, are more fpeedi - ly dilTolved in warm water than in cold 3 and water, in like manner, is more fpeedily diflblved in warm air than in cold. We have a fenfible proof of this, in the exhalation of dew, it being much fooner dried up in places expofed to the diredl rays of the fun, than in the fhade ; be- caufe the air in the ihade, being fome degrees colder than that in the fun, is not able to diflblve the fame quantity of water in the fame time.

When water is faturated with any kind of fait in a definite degree of heat, then will it retain the fait as long as it retains its heat s but if the

3 i^^^

C 78 )

heat be lefTened, the tranfparency of the folution will be deftroyed, a part of the fait will become viflble, and fall to the bottom, in confequence of its fuperior weight ; what falls to the bottom will be rediflblved, as Toon as the water regains its heat. It is obvious that the quantity of the fait, which is precipitated from the cooling of th-e water, will depend partly on the degree of heat in which the folution is fatu rated,- and partly on the degree of cold to which the folution is reduced* Thus' water of Bo degrees when faturated with fait, contains more fait than it would do if it had only yodegrees of heat, and in being cooled to 50 degrees, the precipitation of fait will be greater in the firft inftance, than in the fe- cond; though it might, probably, be

the

( 79 )

the fame, if the folution of 80 de- grees was cooled only to 60, and that of 70 to 50. Something very- analogous to all this may be obfer- ved, with refpedl to the folution of -water in air. In mifty weather, we frequently fee the milt of the morn- ing intirely vanishing towards the middle of the day, and coming on again towards the evening ; the rea- fon of which feems to be, that the air being warmed by the approach of the fun to the meridian, is able to diffolve the morniiig mifl, but ^ the air grows colder again towards the evening, the water which had been perfedtly dilTolved by the mid- day heat begins to be precipitated, the tranfparency of the air is deftroy- ed, and an evening mift is formed. This phenomenon has been ob-

ferved

:( 8o )

ferved to prevail, in the coldell ac- mofphere that has ever yet been taken notice of, on the furface of the globes for in January 1735, when the cold in Sikeria was equal to 157 degrees below the fre^zijig point in Farenheit's thermometer, the low- er region of the air was obfcured by a perpetual cloud, which was very- thick in the morning, thinner to- wards noon, and thicker again at night*.

Mifts and dew will, generally fpeaking, be the greatefl when the •difference between the heat of the airj in the day time, and at nighty is the greateft, becaufe the hotter the day, the greater is the quantity of water which is diffolved -, and the colder the night, the greater will be

the

* Novi Commem Petrap, Tom. vi. p. 429*

( 8i )

the quantity which is precipitated. It often happens that there is no mifc obfervable towards the clofe of the day, this may be occafioned, either by there being little difference in the heat of the air at noon, and at night ; or, though that difference be confiderable,. yet the air may chance not to be faturated with water, and in that cafe it may, even in the night, be warm enough to retain all the water it had difToIved in the day time. In cold weather the breath of animals becomes vifibie, becaule the air is not warm enough to. dif- folve the moiflure which is exhaled from the lungs*.

VOL. III. F It

^ The breath is vifible if the temperature of the air be colder than 6i degrees. Caval, on air p. 400. The degree of cold in which it is vifible, depends partly on the humidity, or'drynefs of the air.

( ^\ } -

It is not unufual for a river irr ^vinter tlme^ to be much warmer than the aif;, hence^ the vapour which rifes from the river is condenfedy the air not being able to diiToIve it, and a- cloud or mifl of fmall elevation^ is fi^cn to accompany the fiver in its- courfe t this appearance ceafes, as foon as the river is frozen, becaufe the ice, though it be fubjeft to eva- poration, yet it does not yield fo much vapour as water does^.-

A cubic inch of rock fait, nitre,- or any other kind of fait, is much longer in being diffolved, when it is in a compa6l (late, than when it is r^;duc€d into a fine powder, becaufe the fair, when in the form of a pov/-

der^

■•* Angara fiuvius node glacle confiilit, quo Kido nelula ilia perpetiia, hue ufque ex fluvio hoc eveda cclTavit. Novi Comp. Fetrop, 'Vo. \1. p. 436.

( 83 )

licr, has a much Lirger furface ex- poicd, to the adlion of the water, than h^it was In one folld luiTip. In like manner^ the air will diffolve any definite quantity of water fooner, when the furface of the water is in^ creaK^d by its being in the form of a vapour, than it would do {( the wa- ter was either in thtt form of ice;> or 'u> its ordinary fluid fjate. The fmoke of a .chimney confifcs principally of water, in the ilate of vapouFj and it is really arconifning, to {ce how quiclcly, in particular flates of the atmofphcre;, it is difk)]red in the air. It has been remarked, that the fmoke of miOunt Vefiruius is miuch more ftrong and viffble in rainy, tiian in fair weathers* if this phe- F 2 nomenon

"" Lett, fur. La Tviine-.-ak par. M. Ferbcr> . p. :S8.

( H )

nomenon does not proceed from the greater quantity of water, which is raifed from the mountain in wet, than in dry weather -, it may be ac~ counted for, from the greater facility with which aqueous vapours are dif- Iblved in a dry ferene air, than in one which is fo faturated with water^ that it can diflblve no more ; which is the cafe, in general, of air, which parts with its water, in the form of rain or mifi.

In riding upon wet fand in a hot day, a kind of tremulous motion in the air, to the height of a foot or more above the fand,. may be obfer- ved 5 this appearance may proceed from hence, that the water in riling from the fand, is not immediately difTolved in the air. A fimilar appear- ance may often be obferved on land>

efpe-

( 85 )

efpecially in corn fields towards au* tumni the water which is exhaled from the (landing corn, not mixing itfelf at once, fo effedually with the air, as to conftitute with it an appa- rently homogeneous fluid. Some- thing of the fame kind happens, when either faline folutions, wines, or vinous fpirits of any kind, are poured into a glafs of water, the compound fluid mufl be agitated, or the mixture will not at firil be uniform.

The quantity of water contained in the air, even in the driefl weather, is very confiderable. We may be faid to walk in an ocean ; the water indeed of this ocean, does not ordi- narily, become the objed of our fenfes, we cannot fee it, nor, whilft it continues diifolved in the air, do F 3 we

( 86 )

we feel that it wets us, but iris frill v/ater, thou2;h it be neither tan.Q-ible nor vifible ; jufc as fugar, when dif- folved in water;, is ftili fugar, though we can neither fee it nor i'ttl it.

Some philofophers have doubted, whether the weight of the air, may not chiefly be attributed to the wa- ter which is conilantly fufpended in it *. But whether this conjedture be admitted or not, the power which the air has of keeping a great quantity of water difTolved in it, may very properly be applied to the illuftra- tion of that text, in which it is faid, Gcd divided the waters which were under the firmament^ from, the waters which were above the firmament \^ without having recourfe with Efif-

, co^^iuSy

* Boerh. Chem. Vol. I. p. 461. f Gen. i. 7.

C ^7 )

'i'OpiuSy to the very unphilofophlcal

fuppoficion of the blue ficy being a foliti fubllance compofed of con- gealed water*. Some are puzzled to find water enou2;h to form an iiniverfal deluge -, to ajQiil their en- deavours it may be remarked^ that was it all precipitated which is dif- folved in the air, it might probably be fumcient to cover the furface of 'the whole earth, to the depth of above thirty feet.

The sir not only diirolves water,

but various other vapoursj -wliich con^

F 4 fiil

^^ Extinia iiv-e fuprema hajns al'ris regio attingit fornicem aihim c^ruleiira, in quo poitca die quarta il;ellse fixss collacatse fifc- runt ; qui fornix csraleus mini efie videtiir aquarum in akum elevataruiHj et cryftalli im niorem feu condenfatarum, feu conglaciata- rum, cccruleoque colore radiantium, compa- ,ge==. Epia, Ins. Theoli Lib. iv. d. 3.

( 88 )

fill partly of water, and partly ofvola- tilefalts and oils. All vegetables, whe- ther aromatic or not, are found toper- fpire verygreatly,and thematterwhich they perfpire, could it be condenfed, would, probably, be fo far different from pure water, as to have both a tafle and fmell. The nrratter per- fpire d by animals, without f^veating, confifts principally of water, but the water is ilrongly impregnated with odorous particles. It has been faid of Baron Halkr, that he could fmell the perfpiration of old people, at the diflance of ten y^rds -, this is by no means incredible, for the human body is conftantiy enveloped in an tnvifible cloud, arifmg from the great quantity of matter which is infenfibly perfpired. Sa7i^orius cM- iTiares the /e/iJU'Ie excretions of a

perfon

( 89 )

perfon who eats and drinks 8 lbs of

food in 14. hours, at 3 lbs, and the injenfihle perfpiration at 5 Ibsj but if we fuppofe the infenfible perfpira- tion in this clinfiate (which is colder than that of Venice^ where he made his experiments) to amount only to one half of our'food, we cannot but csnclude, that it muft form a great icioud around us ; for 4 lbs of matter converted into a vapour as heavy as air, would occupy a great fpace, amounting to above 50 cubic it^u The heat of the human body is ge- nerally between 90 and 100 degrees, this degree of heat is fufficient to raife frorri it, by a kind of diililla- tion, a copious vapour, which would become vifible, if the heat was in- creafedi I remember having been greatly heated and fatigued in af-

■cenaiiig

( go )

cending the ladders from the bottom of the copper mine at E^cn \ when ;I got to the top \ obfervedj by the light of a candle, a thick vapour reek-ing from the body, and vifible around it, to the diflance of a foot or more.

The difpofition of the air for dif- folving either pure water, or the matter perfpired ^by vegetables, or .animals, is very various, depending chiefly on its dcnfay-, heat^ and dry^ nejs. The power which dogs have of fcenting the animal they are in purfuit of, m'Uil be much anecfted by this difpofition of the air ; for the air through which the animal has pafied, is impregnated with the matter perfpired from its body \ and this matter may in one ftate of the air be fo fpeedily dilTolved, and fo "X muck

( 91 )

much as. it were diluted with airj as to make either no impreflion, or a very flight one, on the olfadory nerves of the dog-, v/hihl: in another, it may make a very fenfible one. And if we fuppofe the perfpirable matter not to coniiil chiefly of wa- ter*, but of fuch particles as are throv/n off by perfumes, without their lofing fenfibly of their weight, frill it will be true, that the ftate of the air mufc have a great influence

in * If the whole body of a naked .man, ex- cept his mouth and nofcriis, was flint np in a glafs cafe, fo thr^t no air could enter, the matter of the infenfible perfpiration, w^ould, probably, be condenfed, and ftand as dew on the inflde of the glafs ; and I apprehend it %vould not differ much from the matter of the j\'?ij%le perfpiration, or fvveat. But if any • one be difpofed to confider the infenfible jperfpirauon, as an uncondenfable fluid, or a

• - kinjd

( 92 )

in rendering them fenfible ; fince it

has been found, that on the tops of very high mountains, where the ftate of the air is very different from what it is in the valleys below, the moft odorous bodies lofe either in- tirely, or in a great degree, their powers of exciting a fmelL — The exiftenee of water in air is made ap- parent various ways.

If a bottle of wine be fetched out of a cool cellar, in the hotteil and drieft day in fummer, its furface will prefently be covered. with a thick vapouc, which, when tailed, appears

to

kind of air iimilar to that which arifes from vegetable fluids, in a ilate of fermentation, (the heat of fermenting wort, being much the fame as that of an animal body) ftili its mixture with the atmofpherical air, muil. de- pend very much on the weight, humidity, and other properties of that air«

( 93 )

to be pure water. This watery va- pour cannot proceed from any exu- dation of the wine, through the pores of the bottle, for glafs is im- pervious to water,, and the bottle remains full, and when wiped dry, it is found to weigh as much as when taken out of the cellar. The fame appearance is obfervable on the outfide of a filver, or other vef- fel in which iced water is put in fummer timej and it is certain, that the water which is condenfed on the furface of the veiTel, does not pro- ceed merely from the moiflure ex- haled by the breathing of the people in the room, where this appearance is moft generally noticed, becaufe the fame effed will take place, if the velTel be put in the open air. Water which is cooled by the folu-

tion

( 94 ) tion of any fair, or even ipring wa*^

ter, which happens to be a few de- grees colder than the air, produces a limilar condenfafion of vapour on the outfide of the veiTel in which it is contained. Thefe and other. ap- pearances of the fame kind, are to be explained on the fame principle. Warm, air is able to retain more wa- ter in foiution than cold air can ; when therefore warm air becomes contiguous to the outv/ard furface of a veiTel, containing cold liquor, it is prefently cooled to a certain de- gree^ and in being cooled, it is forc- ed to part v/ith fome of the water which it had diiTolved, and this wa- ter, ceafing to be fufpended by the air, attaches itfelf to the furface of the cold velTel.

The more ancient pliilcfophers,

not

( 95 )

not fufpeftiilg that water might be

diflblved in air^ were of opinion that the moidure which they obferved adhering to the outfides of velTels^. which had' been cooled by having Ihowput into them, proceeded from a tranfmutation of air into water*- But there fecms to be no more rea- son for this fuppofition, than there would be for laying, that water waa changed into faltpetre, from obferv- ing that w^-ater which had diiTolved as much faltpetre as it could, in a

certain * Naturae myftss arcano modo, fed faciii a'irem in aquam medlis caloribiis cogere doce- bit abjeda hsc nix, li vitro conicse figure, intra tripodem, apice deorfum vergente, Hif- penfo indatur nivis vel glaciei fruilum. Quippe fubjetSlo vafciiio excipiuntur, exteri- ore vitri frigiditate collects, et laterum dc- clivifate mahantes aqiis giittre. Bartholinus tie figiira Nivis p. 5. See alio Boyle'^ Works, Vol. II. p. 297.

(96)

certain degree of heat, depofited a

part of it, when that degree of heat was lefTened.

Another method of proving the exiftence of water in the cleareftair, is, to obferve the increafe of weighty which certain bodies acquire by ex- pofure to the open air. I put upon a plate 8 ounces of fait of tartar, which had been well dried on a hot iron ; the day was without a cloud, and the barometer flood at 3oinGhes> in the fpace of three hours, from II to 2 o'clock in the afternoon, the fait had increafed in weight two ounces ; in the courfe of a few days its weight was increafed to twenty ounces, it was then quite fluid, and being diftilled it yielded a pure wa- ter equal in weight nearly to the increafe it had acquired from the air,,

and

(97)

and therefore it is rightly inferred, that water was the fubflance which it had attradted from the air.

Strong acid of vitriol is another body which very powerfully attradls humidity from the air. An ounce of this acid has been obferved to gain, in 1 2 months, above fix times its own weight.* The power of the acid to attrad water from .the air, depends upon its flrength, for it may be fo far diluted, that inftead of attrading any more water from the air, it will, by evaporation lafe a part of that which it had acquired; when sit ,is in this flate^ its .weight varies with the dry nefs or moiftnefs of the atmofphere, and it becom.es, when accurately balanced in a good f>air of fcales, no bad kind of an hy- voL. HI. G grometer,

* Newm, Chem, by Lewis, p. 161.

( 93 )

grometer. The time in which any definite quantity of acid acquires its greateft weight from the air, depends partly upon the quantity of water which is diffolved in the air, and partly upon the furface of the acid which is expofed to the air, it hav- ing been afcertained by experiment, that the quantity attra(5led from the air, in a definite portion of time, is greater as the furface is greater. Hence, inflead of a twelve months expofure to the air being requifite to make one ounce of acid of vitriol acquire fix ounces of water, it might pofTibly acquire that weight in a few minutes, if its furface was enlarged in a due proportion. ^ Onions and other bulbous roots, "^hen hung up in a room Sheltered from rain and dew, are obferved. to

germi«

( 99 )

germinate-, and to acquire a great

mcreafe of bulk, and it might thence have been fufpeded, that they at- tracted much water from the air, and were increafed in weight. But though they may increafe in bulk, they are found to decreafe in weight; the root itfelf in becoming rotten, fupplies nutriment to the germinat- ing plant; and if it imbibes any thing from die air, it lofes that and more by perfpiratian. An onion on the 26th of January, when it had fcarce begun to fliew any figns of vegetation, weighed 2^6 grains; on the i6thof the following May, after having put forth feveral ftem.s in the open air, it weighed only 145 grains,*

The increafe of weight which the G 2 human

* Novi Com. Pctrop, Toi-ti* 2. p. 22^,

( lod )

human body, in nnany cafes, experi- ences from the water which the pores of the body fuck in from the air. is another very fenfible proof of the great quantity of water which is conflantiy diflblved in the air. *' Keil has proved, that a young man weakened from want of nou- rifhment, but in other refpedls healthy, added eighteen ounces to his weight, in the fpace of one night, and this by the abforption through his pores. Another perfon has been feen to gain 4olbs. weight, in the fame manner, in the fpace of a day. M. de Haen, is of opinion, that dropfical patients abforb more than loolbs. weight every day. It is fuppofed, that in general, the body abforbs more than ilb. every day

by

( loi )

by the pores.*" The (kin of a middle-fized man, is equal to about 1 5 fquare feet, and if we fuppofe the ikin of a dropfical perfon to be 20 iqviare feet, then will each fquare foot imbibe 5lbs. or pints of water in one day.

In addition to thefe inftances I will fubjoin the following account, which was given me by a perfon of credit and judgment. A lad at New- market, a few years, ago, having been almoft flarved, in order that he might be reduced to a proper weight for riding a. match, was weighed at 9 o'clock in the morning, and again at 10, and he was found to have gained near 30 ounces in weight in the courfe of an hour, though he G 3 had

* Treatife of Phyfic by Zimmerman* Vol. II. p. 128.

had only drank half a glafs of wine in the mterval. The wine probably ftimulated the action of the nervous iyftenn, and incited nature, exhaufted by abftinence, to open the abfor- bent pores of the v/hole body, in or- der to fuck in fome nourifhment from the air. Something fimilar to this was the cafe of the negro, who,, being gibbetted alive,, regularly^ voided every morning a large quan- tity of urine,, but difcharged no more till about the fame hour the next day,* The dews of the even- ing at Charles Town in South Ca- rolina, imbibed by his body, fupply- ing a fuperabundance of fiuids in the night,, and a fufhcient quantity ta fupport perfpiration in the day. It laasbeen obferved that "neither hogs

nor

* Me^kal Tranf. VoL II. p. £05*

( I03 )

nor beails of burden ever drink ia Jamaica^ and yet they are continu- ally fweating. The air is fo moift, that the abforbi ng pores of thefe animals imbibe a fufficiency of wa- ter.*" The imbibition of water through the pores of the flcin is an

acknowledged fa61: '-^ it is well

known, that perfons who go into a warm bath, come outfeveral ounces heavier than they went in, their bodies having imbibed a correfpon- dent quantity of water. f Part of the utility of medicated .and vapour baths, depends upon this prmciple of imbibition by the pores : and it is faid that thirft may be allayed by bathing in warm fea water^ th€ pores G 4 im-

♦ Treatife of Phyf. Vol. II. p. loi. t Goldlmith's Hiil. of the Earth. Vol. I. p, 238.-398.

( 104 ) imbibing^ the water and carrying it to the inteftines, but not fuffering the diffolved fait to accompany the water.

With refped to the quantity of water fufpended in the whole atmof- phere, or even in a column of the atmofphere, of a definite bafis, in- cumbent on any particular Ipot, it cannot be afertained with precifion, unlefswe knew fome method of de- priving the air of all the water it contains, and could at the fame time make the experiment at different diftances from the furface of the earth. For it is not only probable, that a cubic yard of air, contiguous to the furface of the earth, contains .at different times very different ^quantities of water, even at the fame place, according as the ^rround is 3 moift

( I05 )

moid or dry, or the temperature of the weather warm or cold ; but we have great reafon to believe, that at the fame inflant of time, a cubic yard of air which touches the furface of the earth, contains as much wa- ter as three or four cubic yards, which are fituated at the diilance of thirty or forty yards above it. For the water which rifes from the fur- face of the ocean, from the perfpi- ration of organifed bodies,, whether vegetable or animal, or from the mere a61:ion of the fun on a moifl earth, in being diiTolved in the air as foon as it rifes, makes the air near the furface, heavier than that which is at a diftance from it,, and on that account the motion of the air, unlefs it be violent, will not readily mix the lower and heavier air, with the

higher

( io6 )

higher and lighter^ and the lower air will confequently contain nn ore water in a definite bulk, than the higher. To what has in a former EfTay been obferved on this fubjedt, the follow- ing illuftration may be added. If into a deep drinking glafs half full of water, you gently pour a glafs of port or claret, you v/ill fee the wine mixing indeed itfelf flowly with the water, but that part of it which is near the water, will be much more impregnated, in any definite portion of time, with water, than the more- remote parts ; it will be a confider- able time before the water will be uniformly difFu fed through the wine,, if they are left undifturbed ; nor does a gentle undulating motion foon mix them, and this difficulty of mixing them vyoiild be Hill much

greater.

( I07 )

greater, if there was a greater dif- ference in their refpedlive weights,,. or if the upper parts of the wine were kfs denfe than the lower. Now this is the cafe in the air, which is not only above 800 tincies lighter than water, but its parts, which are far removed from the furface, are much lefs denfe than thofe which are con- tiguous to it. That denfe air holds more water in fokition than rarefied air, is proved from hence j that v/heo. common air is rarefied ^under the receiver of an air pump, a part of the water which is contained is pre- eipitated^ in the form of dew; this anfwers to tlie precipitation of fait from a faline folution, when part of the water is taken away, which held the fait in folution. Hence, as cold teudj^ to render the air mare dtnfc^

it

C i<58 ) itcertainly contributes to its holding- more water in folution than it would' do, if it was more rarefied under the fame degree of heat : but as- hot air diflblves more water than cold air, and as air is rarefied by heat, it is evident, that the denfity and heat of the atmofphere in fome meafure counteract each other, with refpe6t to the power the air has in diflblving water: the law according to which this power varies, in different de- grees of heat and condenfation, is- not determinable from any experi- ments which have yet been m.ade.

It may not be improper to take notice in this place, of an obje<5lion v/hichisufuaily made to the dodrine here advanced, — - — of water being fufpended in the air by folution — It is alTerted, that water is . as evapor-

able

( 109 )

able in an exhaufted receiver, where there is no air, as in the open air *. It is certain, that heat will evaporate water, and great degrees of it may, probably, evaporate it fader in vacuOy than in the open air, inafmuch, as the prefTure of the air may tend to :obflru(St the adion of the heat, in converting the water into vapour. Thus, quickfilver is not, I appre- ;hend, evaporable in the open air, yet it has long been remarked to be ccvaporable ini;^f//^, as may be col- le6ted from th^ little globules of quickfilver, generally found adher- ing to the upper part of a barome- ter, and which arife from the vapour which infenfibly efcapes from the :furface of the quickfilver in the

tube.

• Berlin Mem. 1746. Waller de .afcem ivapo. in vacuo.

( no )

tute. But though heat may be one caufe of the evaporation of water, the attradlion between air and water, upon whatever principle it depends, may be another. The fad moreover, upon which the objedion is found- ed, is very quellionable, and not ge- nerally to be admitted. A china faucer which contained 3 ounces of water, lofh nothing of its weight un- der an exhauiled receiver in the fpace of 4 hours ; whilft a fimilar faucer, containing an equal quantity of water, loft, in the fame time, in the open air, one drachm and eight grains ; the heat of the atmofphere being between 48 and 50 degrees *. Many readers are gratified with feeing the general progrefs of any

philo-

* See Dr. Dobfon's ingenious Obferv^- tions in Philof. Tranf. 1777, p. 256,

( "I )

philofophical opinion, from its being firft fuggefledj till its being general- ly admitted. The hiftory, indeed, of philofophy, is one of the moil pleafing purfuits which a fpeculative mind can be engaged in, but it re- quires great leifiire and ability to cultivate it with fuccefs. It is not every diftant hint which he throws out, that can entitle a philofopher to the credit of being the firfl: framer of an hypothecs ; nor on the other hand are w^e haftily to reje6t the maxim, that ^^ all novelty is but ob- livion", inafmuch as we frequently fee old opinions putting on the ap- pearance of new difcoveries, from their being drefifed out in a new form.

Natural philofophy principally confiils in exploring by experiment,

the

( 112 )

tlie phenomena refulting from the mutual aflion of different bodies upon each other. Thefe phenomena are innumerable, no arithmetic can reckon up the various ways in which terreftrial bodies may, by natural or artificial means, be brought to ope- rate on one another. To this caufe may we attribute the immenfe num- *ber of volumes on experimental phi- ■lofophy, which have been publifhed in Europe fince Bacon pointed out the proper method of ftudying na- ture. This circumflance, joined to the uniformity which muft ever at- tend the operations of nature in fimilar circumftances, may juflly in- title different men to the honour of having made the fame difcoveries, it being much eafier to make an ex- periment, which may have be^n

made

( 113 )

made before, than to read all that has been written in different ages and countries on natural appear- ances.

Bo^or Halleyy in the year 1691^ propofed to the Royal Society, his opinion concerning the origin of -fprings : in this trad he exprefTes •himfelf in the following manner, « the air of itfelf would imbibe a certain quantity of aqueous vapours, and retain them like f alts dijfolved in water ^ the fun warming the air, and raifing a more plentiful vapour from the water in the day time, the air would fuftain a greater portion of vapour, as warm water would hold more diflblved falts, which upon the abfence of the fun, in the nights, would be all again difcharged in

VOL, \iu H dews.

( "4 )

dews^ analagous to the precipitation of falts on the cooling of liquors."*

M. Le Roy pubiifhed an ingeni- ous difiertation on the foiubility of water in air^ in the year 1 7 5 i ; among other experiments, by which he ii- lufcrated his hypothefis, he obferves that if a large, new, hollow, globular glafs veflel, with a narrow neck, be clofely corked up in a clear hot day, the water contained, in the apparent- ly dry air, will be precipitated, and form a dew in the infide of the velTelj whenever the velTel is cooled, and that this dew will vaniih, being re- difTolved by the air included in the veiTel, as foon as the air regains its ,heat.

Do of or Franklin further illuilrated ithis principle, of water being foiuble

in * Philof. Traaf. No, 192.

( "5 )

in air, in a paper which was read be- fore the Royal Society in 1756, and afterwards printed in his works *.

In the French Encyclopedicy pub- liflied in 1756, we meet with the following pafiage — on voit par la combien fe trompent ceux qui s* imaginent que Fhumidite qu'on voit s' attacher autour cFun verre plein d'une liqueur glacee ell une vapeur condenfee par le froid : cet tf^tty de meme que celui' de la formation des nuages de la pluie, et de tous les meteors aqueux, eft une vraie preci- pitation chimique, par un degre de froid qui rend V air incapable de tenir en difiblution toute T eau dont il s' etoit charge par V evaporation dans un terns plus chaud ; et cette precipitation eft precifement du me- H 2 me

* Franklin on Elec. p. 182.

C "6 )

me genre que celle de la creme dc tartre, lorfque V eau qui la tenoit en diflblution s' efl refroidie.*

Mufcbenl^roeky ^mongHothcY caufes which he affigns for the fufpenfion of vapour evidently alludes to the folution of water in air, and com- pares it to the folution of falts in v/ater.f

But though a great many philo- fophers had Ipoken of the folubility of water in air/ before I>o5for Hamil- ton^ yet in juilice to him it muft be ov/ned, that no one has treated the fubject more diftindly, or applied it more fuccefsfully to the explanation of various phenomena than he has done, in an elTay which was read to

the

* Ency. Fran. T. 6. p. 583. Fol. Ed. f Introd. ad Phil, Nat, Vol. II. p. 965, pub. 1709.

( "7 )

the Royal Society in 1765, and afterwards publifhed with other ef- fays, by the fame author.* The reader will be very well pleafed with feeing this principle illuftrated in an effay by Mr. White, publiihed in 177 15 in the elegant colledion of Georgical EiTays by BoEior Htinter-\.

* Philo. EfTays by Hugh Hamilton, D. D. F, R. S.

f Georgical ElTays by Do(5tor Hunter. Vol.11, p. 15.

ESSAY

E S S A Y IV,

OF G0LD PRODUCED DURING THE EVAPORATION OF WATER^ AND THE SOLUTION OF SALTS.

ON the 27 th of March 1779, when the weather had been for fome time very dry, I put a thermometer into a glafs of water, which had been heated to 87 degrees, by Hand- ing expofed to the dire6t rays of the fun. The thermometer was then taken out, and its bulb was held op- pofite to the fun which ihone very H 4 bright 3

( MO )

bright j as the bulb grew dry by the evaporation of the water, the mer- cury in the thermometer funk very fafii it continued for a moment fta- tionary at 76 degrees, and then it rofe rapidly to 90 ; fo that 1 1 de- grees of cold had been produced during the evaporation of the water. On another day in the fame month, when the heat in the Ihade was 6S degrees, I put a thermometer into a glafs of water, it Hood at 50 degrees -, upon taking it out, the mercury ia- ftead o^ finking from the eifed of evaporation, began immediately to rife from the efFea of the heat of the atmofphere upon it. I put the ther- mometer into the fame water, heat- ed to 55 degrees, and taking it out, the mercury zoYiimwtd ftationary for fome time, and afterwards it began.

to

( 1"-I )

to rife. It was put into the fame water heated to 58 degrees, and up- on being taken out, the mercury did not either rife or continue ftationary, but it funk one degree ; when the water was heated to 60 degrees, the thermometer upon being talcen out, funk 3 degrees before it began to rife. Thefe experiments were all made in the fhade, and it feems as if we might conclude from them, that, 57 was the degree of heat in the wa- ter, in which the cold produced by evaporation, was jufl equal to the heat produced by the atmofphere which then furrounded the ball of the thermometer.

The degree of cold produced by evaporation,- depends, probably, up- on the quicknefs with which that is accomplifhed : now the quicknefs

with

( 122 )

with which water, of a definite tem- perature, is evaporated, is influenced, partly by the degree of heat pre- vailing in the atnaofphere ; partly by the wind blowing upon the thermo- meter ;^ partly by the drynefs or moiftnefs of the air ^ and by other caufes.

September 30th of the fame year, when the heat in the Ihade was 64, degrees, and the heat of the water 60, the thermometer upon being taken out, flood ftationary for three minutes, and then it rofe 3 there was a gentle fouth wind. On the next day there was a cold dry wind from the north, the water and air were both at 56 degrees, and the thermo- meter on being taken out funk to 52.

Spirits of wine, ether, and many

other fluids, produce cold by being

3 cva-

( 123 )

evaporated, and they produce a much greater degree of cold than water, in confequence, probably, of their be-, ing more evaporable. Thus, vitrio- lic ether*, which is one of the moil volatile fluids in nature, has been obferved to lower Reaumur's ther- mometer 40 degrees below the freez- ing point (which anfwers to 90 de- grees of Fahrenheit's fcale)-]-. The experiment is mofl: commodioufly made, by applying a piece of fine linen wetted with ether upon the bulb of the thermometer, accelerat-

ing

* Ether is made by difhlling a mixture of fpirits of wine and oil of vitriol. — Ether may be made alfo by diftilling fpirits of wine with the feveral acids of nitre, fea fak, and vine- gar, and it is then called he nitrous, marine, acetous ether.

f Chem. Dia. art. Ether. Or Manuel de Chymie. par. M, Baume, p, 375,

( 124 )

ing the evaporation by blowing on the linen with a bellows, and moift- ening the linen as it becomes dry, or exchanging it for a frefh piece which is wetted with ether. Who- ever attenipts to afcertain the degrees of cold refpedively produced by dif- i ferent fluids, would do well to re- mark particularly the ftate of the atmofphere with refped to other cir- cunnilances, as well as to its heat.

Sailors have a cuftom, in a calm, to hold a v/et finger up into the air, and if one fide of it, in drying, be^ comes colder than another, they ex- peft wind from that quarter. This cuftom is not without its foundation ; for an almofl infenfible motion of the air, will evaporate the water from one fide of the finger fooner

than

( 125 )

than from another, and thus pro* duce a degree of cold.

There is a fimilar experiment, by which anyone may convince himfelf that cold is produced by evapora- tion ; let him wet a finger by putting it in his mouth, and then hold it up in the air, even in a warm room where there is no current of air, he will find that it grows cold as it be- t:omes dry by the evaporation of the humidity.

" The method our gentlemen make ufe of to cool their liquors, is to wrap a wet cloth round the bot- tle and fet it in the land wind : and^ what is very remarkable, it will cool much foonerby being expofed thus to this burning wind, than if you take the fame method, arid fet it in

the

( ii6 )

the cold fea- breeze."* — The cold is produced by the evaporation of the water from the wet cloth, and as the hot land-wind will evaporate the water fooner than the cold fea-breeze^ it is not to be wondered at, that the liquor is fooner cooled when placed in the former wind than in the latter. " Kempfer relates, that the wind? are fo fcorching on the borders of the Perfian gulph, that travellers are fuddenly fufFocated, unlefs they co- ver their heads with a wet cloth ; but if this be too wet, they immedi- ately feel an intolerable cold, which would become fatal to them if the moiflure were not fpeedily diffipated by the heat. "J The cold, which i$

pror

•^Ives's Voy. p. 77. - ■

I Treatife of Phyfic by Zimmerman, Vol. II, p. 151.

( 127 ) produced by the ad of evaporation^ ceafes as Toon as, that is finifhed, by the cloth becoming dry.

The manner of making ice in the ;Eafl Indies, has an evident depend- ence on the principle of producing cold by evaporation here mentioned; On large open plains the ice makers dig pits about 30 feet fquare and 2 deep; they ftrev/ the bottoms of thefe pits, about eight inches or a foot thick, with fugar canes, or with the dried ftems of Indian corn. Upon this bed they place a number of ungiazed pans, which are made of fo porous an earth, that the water penetrates through their v/hole fub- flance. Thefe pans, which are about a quarter of an inch thick, and an inch and a cpiarter deep^ are filled, towards the duik of the even-

ing

( I2S )

ing in the winter feafon, with water which has been boiled^ and then left in that fituation till the morning, when more or lefs ice is found in themj according to the temperature of the weather; there being more formed in dry and warm weather, . than in that which is cloudy, though it may chance to be colder to the feel of the human body.* Eve- ry thing in this procefs is calcu- lated to produce cold by evapora- 1 tion, the bed on which the pans are placed, fufFers the air to have a free paflage to their bottoms, and the pans, in conflantly oozing out water to their external furface, will be cooled in confequence of that watej being evaporated by a gentle ftream of warm dry air, the power of

the '^ Philof, Tranf, for 1775, p, 2^2,

( 129 )

the air to evaporate water depending much upon its warmth and drynefs.

They have a kind of earthen jar in fome parts of Spain, called Buxa- ros which are only half baked, and the earth of which is io porous, that the outfide is kept moift by the wa- ter filtering through ; though placed in the fun,, the water in the pots re- mains as cold as ice :* and it probably is colder from the jar being placed in the fun, becaufe the evaporation is thereby increafed.

The Blacks at Senegamhia have a fnnilar method of cooling water. «^ They fill tanned leather bags with it, and hang them up in the fun 5 the water oozes more or lefs through the leather, fo as to keep the out- ward, furface of it wet, which, by its

quick

* Swinburne's Trav. p, 305. VOL. III. I

( 130 )

quick and continued evaporation^^ occafions the water within the bag to grow confiderably cool."-j-

It is common enough for labour- ing people, in the height of fummer, to drink feveral quarts of beer or other beverage in a d-ay ; this quan- tity is principally difcharged from the body by perfpiration ; and the cold which is generated during the evaporation of the fweat, greatly contributes to keep the body cool. Thus has Providence contrived to render the heat of the torrid zone Jefs infupportable to the inhabitants j an intenfe heat bathes the body in iweat, but the fweat being evaporated by the fame heat which occafioned it, a degree of cold is generated on

the

+ Philof. Tranf. 1780. p. 486.

( IJI )

the furface of the body, which would not otherwife have been produced.

It feems reafonable to attribute the cold, which is produced in thefe and other fimilar circumftances, to the evaporation of the water, rather than to any other caufe -, becaufe when the bulb of a thermometer is wetted with different fluids, the cold produced has a manifeft dependance on the evaporability of the fluid with which it is wetted. Thus, more cold is produced when the thermometer is wetted with fpirits of wine, than when it iz wetted with water, becaufe fpirits of wine are more evaporable than watery and more is produced when it is wetted with ether, than with fpirits of wine, becaufe ether is more evaporable than fpirits of wine. No cold is pro- I 2 duced

( 13^ )

duced when the thermometer is

fiiieared with Ihiieed oil, or other oils of a fimilar nature, becaufe thefe oils are not fenfibly evaporable in the ordinary heat of the atmofphere. Strono; acid of vitiiol when expofed to the air, infread of lofing any thing of its weight, acquires an increafc, by attracting the humidity of the atmofphere j and as ilrong acid of vitriol when mixed with water, ge- nerates a degree of heat, fo the bulb of the thermomieter, v/hen Vs^etted •with flrong acid of vitriol, infiead of being cooled, is warmed, and the merciary afcends, in confequence of the heat produced from the union of the acid of vitriol with the water contained in the air.

When water is refolved into va- pour, by the violence of a fall from

a con-

( U3 )

a confiderable height, the air will difTolve it fooner -, and in diiTolving it Iboner, it will, probably, produce more cold than it would have done, if the furface of the water had not been broken : hence natural and arti- ficial cafcadeSj may, probably, be fer- viceable in cooling the air furround- ing them. This obfervation is pur- pofely exprefied in different terms, becaufe, having more than once fprin- kled the floor and fides of a room with water in the fummer time, when the heat of the air in the room and of the water was 68 degrees, I could not obferve that a thermometer, hung in the middle of the room, changed its degree of heat whilfl the room grew dry. In very hot climates the effe6b may, probably, be different -, thus we are told, that in I 3 the

C 134 ) _

the ifland of 6'/. Lewis., m the river Senegal, ''' water poured on the floor of a room for the purpofe of cool- ing the air^ is dried up in an inftant> and there \s/ome efe5l on the thermo- meter placed in fuch a room/'*

This phenomenon of producing cold by evaporation, had been men- tioned by M. Amontons in the year 1699.-1* It had been noticed alfo by M. Mairan in i749^t and by Miijf- chenhroeky in his EiTai de Phyfique. Profefibr Richmany at Peterfburgh, gave an account of feveral experi- ments^ which he had made on this fubjed in 1747 and i748j|| but he

did

* Philof. Tranf. 1780. p. 485.

f Mem. de V Acad, des Scien. a Paris, 1699.

X DiiTertation fur le Glace.

il Novi Comment. Petrcp. Tom. I. for 1747 and 174S.

(• 135 ) did "not explain the finking of the

mercury in the thermometer^ whilft its bulb grew dry, on the principle of evaporation. Dr. Cuilen\\d,s very particularly iiluftrated this principle, in a paper publifhed in 1756; and he has there Hiewn that the cold produced was greater, when the evaporation was made in vacuo, than in the open air.* Laftly, Pro- feiTor Braun, to whom the world is indebted for the difcovery of freezing quickfilver, has made a further in- veiligation of this matter, by pub- lifhing a table of the degrees of cold produced during the evaporation of different fluids. f

During the folution of falts in wa- ter

-* Effays, Physical and Literary, Vol. II. Edinb. 1756. p. 145.

t Novi Commen. Petrop. Tom. X. 1764,'

I 4

( 136 )

ter either cold or heat is generally produced, but more commonly cold. Fixed alkaline falts^ Glauber's fait, and white vitriolj produce fmail de- grees of heat during their folution, Sal ammoniac produces the greateil degree of cold, of any fait hitherto knov/n.

When Fahrenheit's thermometer flood at 68 degrees-^ both in the open air, and in the water which v/as ufed for the experiments-, I faturat- ed equal portions of water with fal ammoniac, with faltpetre, and with fea fait. The fal ammoniac made the m.ercury fink from 68 to 42 de- grees, hence, 26 degrees of cold were produced ; the nitre produced 17 degrees, and the fea fait produced only 2 degrees of cold. I repeated the experiment v^^ith the fea fait feve-

ral

( /37 )

ral times, and with different forts of

it, but I could never obferve that it produced above 2 or at mofl 2|- de- grees of cold. The experiments with fal ammoniac and faltpetre, agree very well with thofe made by M. Eller^ and mentioned in the Ber- lin memoires for 1 7 50 ; fince he pro- duced almoil 27 degrees with fal ammoniac, and 1 8 with faltpetre. Boerbaave, indeed, made the ther- mometer defcend through £8 de- grees by diffolving fal ammoniac in water ; but he had reduced his fait to a very fine powder, and dried it well before he ufed it; and a differ- ence in the finenefs of the powder to which the falts are reduced before they are diffoived, may make a dif- ference of a degree or tv/o in the cold produced ; for the finer the fait,

the

( '38 )

the more furface has the water to a6t upon, and the quicker will the folu- tion be performed -, and as the cold is produced only by the ad of folu- tion, the fooner that is accomplifh- ed, the lefs effect will the heat of the atmofphere have, in reiloring to the water, during the time of the folu- tion, any part of the heat it may have been deprived of, during the immediate a6lion of the water upon the fait.

Does any given kind of fait, dur- ing its folution in water, produce the fame number of degrees of cold, whatever be the temperature of the water before folution ? I have only endeavoured to refolve this queflion with refpe6l to fal ammoniac, and it feems to me that the quantity of cold produced, is not influenced by the

tempe-

( ^39 )

temperature of the water. In the

lummer feafon when the temperature of the air^ water^ and fal annmoniac were each of them 70 degrees, the water fank during the folution, of as much fal ammoniac as would fatu- rate it, to 44 degrees, or through 26 deirrees. I thawed fome fnow in winter, the thermometer ftood in the fnow water at the freezing point, or at 32 degrees -, by putting fai am.mo- niac, which was equally cold, into the water, the thermometer defcend- ed during folution to fix degrees, or through 16 degrees.

The pofTibility of freezing water in the middle of fummer, is rightly enough inferred from this experi^ ment. In a tub, fuppofe of 3 feet in diameter, place a bucket, a little taller than the tub, of i foot in dia- 3 meters

( I40 )

meter ; in the bucket hang a Florence fiafk, or a flat lavender water bottle, fo that the mouth of the bottle may be above the rim of the bucket : fill thefe veiTels with v/ater heated, fup- pofe, to 70 degrees. Saturate the water in the tub VN^ith fal am.moniac, then v/iil the 70 degrees of heat be reduced to 44, the v/ater lofing, dur- ing the folution of the fait, 26 de- grees. The water in the bucket being furrounded with this cold fluid, will itfelf be cooled ; fuppofe it to be cooled only to 50 degrees, then by faturating it with fal ammoniac, it will lofe 26 degrees more of its heat, and be cooled to 24 degrees. The water in the bottle being im- merfed in a fluid, heated only to 24 degrees, will foon be cooled below

the

( '41 )

the freezing pointer 32 degrees, and confeqiiently will concrete into ice. The cold, in all thefe cafes, is ge- nerated only during the time of the folution. The water recovers the temperature of the atmofphere fooner or later, according as its quantity is lefs or greater, and as the furface ex- pofed to the air is greater or lefs ; it is here fuppofed, that the heat of the atmofphere remains the fame. The different degrees of cold produced by different falts, do not depend up- on any general caufe which has yet been difcovered, nor is there any very fatisfaftory reafon given for thefe, and other fimilar produdtions of cold or heat. The time may come when we fliall be able to compre- hend the reafon wliy the acid of ni- tre has fuch different efFeds when

mixed

( 142 )

mixed with fnow from what it has when mixed with fnow water ; when mixed with fnow water it excites a very great degree of heat ; and when mixed with fnow it produces the greatefl degree of cold that has ever yet been obferved *. Rejourn natura Jacrafua nonfimul tradit, Initiatos nos credimuSy in veftihulo ejus haremus. Ilia Arcana non promifcue nee omnibus patent s reduEla et in inferiore Jacra- rio claujajunt. Ex quihus aliud h^c ^etas, aliud qu^ foft nos Juhibit, ad/pi- ciet.

f Vol. I.J). 267.

ESSAY

E S S A Y V.

OF THE DEGREES OF HEAT IN WHICH WATER BEGINS TO PART WITH ITS

THE air bubbles which^ in fum- mer time, adhere to the iniides of decanters, water glalTes, and other vefiels filled with water, cannot have efcaped the obiervation of any ones -I have endeavoured to afcertain the degree of heat in v/hich thefe bub- bles begin to be formed.

Into

( 144 )

Into a water glafs filled with wa- ter I immerfed a thermometer -, the heat of the water was 64 degrees ; the water was fet in a clofet, where the fun never fhone, for two days 5 the heat remained much the fame during that period, and there was no appearance of bubbles. The glafs^ with the immerfed thermometer, was then {(^t in the fun, and when the heat amounted to about 90 de- grees, feveral air bubbles were found adhering to the graduated fide of the thermometer, and fome wTre begin?- ning to be formed on the bottom and fides of the glafs.

Having frequently {ctn the in- fides of veiTels containing water, ftudded with bubbles, when the heat, it was apprehended, was much lefs than 90 degrees ^ I put a thermome- ter

( 145 )

ter into a water glafs at a time when it abounded with bubbles, and found that the heat of th^e water was not above 64 degrees.

The refult of this experiment be- ing very different from that of the preceding, in which the air did not begin to feparate itfelf from the wa- ter till the heat was about 90 de- grees, I was for fome time at a lofs how to account for the difference 5 recollecting, however, that the water which required 90 degrees of heat before it parted with its air, was pumped from a well fed by a ftream, which had run four miles in the ■open air ; and that the other water, which let go its air at 64 degrees, was pumped from a well fed by fubterraneous fprings, I attributed the difference in the degree of heat

VOL. III. K reaui-.

( '46 )

rcquifite to make thefe waters part with their air, to the diiTerent qua- lities of the waters.

In order to try thefe waters under fimilar circumftances, two water glaflfes were filled, one with common well water, another with that which had been fupplied by the ftream; on being expofed to the air, bubbles began to be formed in the well wa- ter when the heat amounted to 60 degrees, the other did Bot part with any of its air in th€ fame degree of heat.

I v/as at firfl difpofed to thirik, that thefe experiments pointed out a general difference between river wa- ter and well water, with refpedb to their difpofition for retaining or part- ing with their air ; but the following experiment, made at a different fea- I foil

( U7 ) foil of the year, convrnced me tliat the conjedure was not well founded.

In November, when the heat of the air had been for fome time about JO degrees, I took three water glafles, one was filled with rain water imme- diately after it had fallen, another with the common well water, the ■third with the water which came from the ftream : the heat of thefe feveral waters was the fame, namely 48 degrees ; they were all gradually warmed, by fetting the water glafTes in hot water, and they all began to exhibit bubbles when the heat was about 60 degrees ; I thought the rain waters ihew*ed the moil bubbles.

Hence it is plain^ that the flreia:m

water does not differ from rain or

well water, except accidentally, as to

the degree of heat in v/hich it parts

K a with

(.148 )

with its air. The firft experiment, ill which the bubbles were not form- ed till the heat was 90 degrees, was made after there had been feveral days of very hot weather^ and the water in being expofed, during its courfe, to the adion of the fun, had probably loft a confiderable portion of its air before it arrived at the well. All river water has a vapid tafte in fummer lime, which is in part, probably, occafioned by having loft fome of its air, in confequence of its being expofed to the rays of the fun. Water drinkers are defirous of having water frefti from the well ; efpecially in fummer time, and not without reafon, for the heat in that feafon being generally above 60 de- grees at our principal meal time, the water^ if it has been long expofed

to

( 149 )

to the air, muil have fuffered a change of quality, not only from its increafe of heat, but from a confe- quent lofs of a portion of its air. The water which fupplies the warm bath at Matlock, and which is drunk by invalids, is 68 degrees warm i hence it has loft a part of the air which it would naturally contain, and, except in very hot weather, it does not exhibit any air bubbles in the decanters.

The air begins to be mfihly fepa- rated when the heat is about 60 de- grees 5 but it begins, probably, to be inviftbly feparated when the heat is much lefs : and the leaft heat will be requifite to feparate it, when the weight of the atmoiphere is the leaft.

Phiiofophers have invented vari- ous methods, equally cone lu five, of K 3 fhevv-

r 150 _) _

{lewing^ that water in its ordina^ ftate^ contains diflblved in it a por- tion of air. And they have fhewn^^ that water which has loil a portion of this air, either fey hting frozeny or heated J or by longcontinued agitation y or by other means, has the property^ ©f re-abforbing as much air from the atmofphere as it had loft ; and they have fhewn, th^t this abforption is the ftrongeft at firft,. and becomes lefs and lefs r)Owerful, as the water .becomes more and more impregnated with air. Thefe and fimiik-r obfer- vations renderitprobablcy that water is as capable of diiToiving a certain portion of air, as it is of diiToiving a certain portion of any particular kind of fait. Thr quantity of air, vv^hich water is capable of diiToiving and retaining m folutionj depends partly

( '5' )

upon the temperature of the water, partly upon the weight of the at- mofphere, and partly, I conceive, upon the water's purity. From thefe circumftances, as well as from fome others which might be attended to in making the experiment, it has happened, that authors have given very different accounts of the quan- tity of air contained in water. Boerhaave has an experiment*, from which he infers, that there may be feparated. from v/ater a quantity of air equal in bulk to the water s the experiment is ingenioufly contrived, but the conclufion,,! think, is liable to fome objedtions.. T\\t Abbe Nollet fays, that water which has been pre- vioufly purged of air, abforbs, in fix days, one thirtieth of its bulk.f

Docfor

* Boerh. Chem. Vol. I. p. 521,

t Hift, del' Acad. 1743. k:4

( H^ )

Do5for Hales obtained by diftillation one cubic inch of air from fifty-four cubic inches of water*. Mr. Eller is of opinion that the portion of air contained in water does not exceed the 150th part of its bulkf. Dr. Prieftley found that a pint of his pump water contained about one fourth of an ounce meafure of air, that is, the bulk of the water was to that of the air it contained, as 64 to i§.. M. Fontana fays, that the wa- ter of the Seine at Paris, after being long boiled, abforbs in forty days one twenty eighth of its bulk of common air J. Lailly, M. Cavallo obferves, that in a temperate degree of heat, and when the barometer is

about

* Veg. Stat. c. 6. f Berl. Mem, 1750. § Philof. Tranf. 1772. p. 248, I Fhiiof. Tranf. 1779. P* 439*

( ^S3 )

about 29I inches, water abforbs

about one fortieth of its bulk of common air*.

It has been remarked in another placet, that the atmofpherical air con- fifts, in part, o^ fixed air ; and fome of the moll ftriking differences be- tween fixed and atmofpherical air were there mentioned. If a bubble of atmofpherical air of a definite bulk, fuppofe it equal to eleven pints, be expofed to the aftion of a fulHci- ent quantity of water, which has been purged of its air by boiling, the zvhole of the bubble will, in a proper length of time, be abforbed by the water 5 but when about fevea pints, or even a lefs portion, have been abforbed, the remaining part

will

* Cavalla on air. p. 213. f Vol. II. p* 247.

( 154 )

will refemble fixed air in this — that

a candle will not burn in it*. It is very probable that water which has not been boiled may have a fimilar efFedt under certain circuinftances. — " The wells at Utrecht are from 8 to 20 feet in= depth ; it has been the cuftom to make ufe of pumps to raife the water, and they are then covered over with, a kind of arch. When, after a certain period of time> the wells are opened, on any account, it is necefifary to leave them un- covered for 12 hours, before any perfon defcends into them ; whoever fhould venture to go down into them fooner, would expofe himfelf to immediate death. The air of thefe wells extinguilhes candles -like that acquired from fermentation or

cffer- * Philof. Tranf, 1772. p. 247,

( ^S5 >

cffcrvefcence."* — Stagnatmg^ airj,

which has brooded, though but for a fhort time, even over running wa- ter^ is found to be fo greatly altered in its quality, that it will extinguifh flame,, though it be fufficiently pure to fupport animal life. I was in- formed of this f^d by a miner in Perbyfhire, who had frequently ve- rified it by his own experience. In order to free a mining diftridt from water, they frequently dig for miles together ftibterraneous a<jueduds; fupporting the fides and roof with timber or done. The mouths or outlets of thefe aqu^duds or /oughs^ being below the level of the diftridt to be drained, there- is a conftant ilream of water flowing through them. Thefe Joughs are many of

thenai?

* LaY€>ifier''sEirays, p, ii8»

( 156 )

them high enough for a man to walk upright in them^ the water reaching to his middle or higher; and men with lighted candles fre- quently walk through them from one end to the other, in order to prevent obftru6lions ; it fometimes however happens, that by the falling in of the roof, or other accidents, the fough is in part dammed up : when this is the cafe, the water beyond the place where the obflru6lion is, rifes to the roof of the fough, and thus prevents a circulation of air, though there is ftill a difcharge of water through the mouth of the fough. When an accident of this kind happens, men are fent with candles in their hands to find out and remove the ob- ftru(5lion, but before they have walk- ed fifty yards from the mouth of the

fought

C 157 )

fough, the candles go out, though they perceive no difficulty in breath- ing, and this extin6l!on of the can- dles will take place in 24 hours, af- ter the lloppage of the water has commenced^

Fahrenheit^ Boerhaav£y and other philofophers, had obferved that the degree of heat, requifite to make water boil, was variable according to the purity of the water and the weight of the atmofphere. Within the ufual limits of 28 and 3 1 inches in the barometer, Boerhaave was of opinion*, that there would be a va- riation in the heat of boiling water, amounting to 8 or 9 degrees. This fubjed ha« of late been examined with great accuracy by Mr. de LuCy and Sir George Shuckhtirg ; and Mr.

Cavallo

^ Chem. Vol. I. p. 171.

( i5« )

t^avalto has given us the refult of

their experiments in the annexed table, which is formed according to the fcale of Fahr£nheit'% ther- mometer*.

TABLE,

Height of the	Heat of boiling water accordino; to
Barometer.	Mr.de Luc	Sir G. Shuckburg
	Parts of	Parts of a
	aDeg.deg.	Deg. deg.
26 1	205,17 206,07 206,96 207,84 208,69	204,91 205,82 206,73 207,63 208,25
29	209»55 210,38	209,41 210,28
^9i	210,2	211,15
30	212	212
30I 31	212,79	221,85 213,69

* CavaUo on air, p. 215,

The

( '59 )

The following experiment is curi- ous in itfelf, and it illuftrates both the nature of boiling in general, and what is here advanced relative to the heat of boiling water under dif- ferent preiTures of the atmofphere. I hit upon it many years ago, when I had another objecl in view. My tdefign was to exhibit a flriking in- ftance of the increafe of dimenfions produced in fluids by various de- grees of heat : in order to this, I took a large glafs veflel, refembling in fhape, fuch mercurial thermometers as have a bulb at the bottom*, the hu\b of this velTel held above a gallon, and the ftem had a fmall dia- meter, and was above two feet in length. Into this vefTel I poured

boiling

* A velTei of this fhape is -ufually called a Maira/s,

C i6o )

boiling water, and having filled it up to the very top of the ftem, I corked it with a common cork as ciofe as I could. The water and the cork were at firft contiguous to each other ; but in a very little time the water began to grow cold, and as it grew'cold, it contracStcd itfelf and funk very vifibly in the ftem ; and thus the firft intention of the experi- ment was fully anfwered. But an unexpe6ted phenomenon prefented itfelf, — the water, though it was re- moved from the fire, — was growing cold, — and had for fome time en- tirely ceafed from boiling, began to boil afrefh very violently, the bubbles were large and numerous, and continued to afcend, into the fpace between the furface of the wa- ter in the ftem, and the cork, where 2 the

( i6i )

they burfl, for above two hours. When a hot iron was applied to that part of the flem, through which the water, in contradiing itfelf, had de- fcended, the ebullition prefently ceafed; it was renewed when the iron was removed; and it became more than ordinarily violent, when, by the application of a cloth dipped in cold water, that part was cooled. There is no great difficulty in accounting for thefe feveral appearances : by the finking of the water in the fleni a kind of vacuum is left between its furface and the cork ; water and other fluids boil with lefs degrees of heat, when the prefTureon their furface is diminifhed ; here the preffure of the atmofphere is wholly removed by means of the cork, and the water continues to boil, though its heat be VOL. Ill L con*

C r6i )

eondantly decrcaiing. The interval between the water and the cork U not, as will be ihewn prefently, a ferfe^ vacuum ; it is occupied cither ^ by the vapour of the water^ or hy a filial 1 portion of r^ir, or by both ; heat increafes the elaflicity of both air and vapour, and thus augments the preiTure upon the fur face of the water, hence, the ceafir.g of the ebullition on the application of the hot iron; cold dim inifhes the elalH- city of air, and condcnfes vapour, and thus, the preflure upon the fur- face being Icffcned by the applica- tion of the Goldcloth, the ebullition of the v^atcr became more violent. When the water ceafed boiling I poured it on the bulb of a thermo- meter, and found that its heat was only 130 degrees.

- Another

( »63 ) .

Another circumflance defervirig of notice remains to be mentioned* When the water was become cold^ it had funk through the whole flem, and through part of the bulb, I then inverted the veffei which contained it, into a tub of water, and obferved upon the bottom of the bulb a large circular fpot void of water, I con- fidered this fpot as a perfed: va- cuum, for it anfwered to the fpace which the water, in contracting it- felfj had deferted ; and the vapour which^ whilil the water was w^arm, might have been fuppofed to occu- py that fpace, I was perfuaded, was condenfed by the cold : in order to fee whether it was a vacuum or not, I pulled out the cork, whilfl it was under the furface of the water into wiiich the veffei w^s inverted, being L % certain

( i64 )

certain that if it was a vacuum, it would be inftantly filled with water, which the prelTure of the atniof- phere would make to afcend through the ilem. In fad, the circular fpot was greatly diminlihed bytheafcent of the water, but never (for the ex- periment w^as often repeated) taken wholly away ? what remained mufi have contained either air, or fome other fluid, whofe elaflicity was a counterpoize to the preiTure of the atmofphere, on the furface of the water in the tub. It v.'ould be too haily a conclufion, from this circum- ilancc, to attribute the formation of . the bubbles to the particles of air, from which water cannot "be fepa- rated by long boiling'* ; for it may

be,

* Licet diu ebuUieriet aq\ia noa erit Reris cxpers. Mufchen, de Aqua.

_( i65 )

be, thnt this fmall portion of air arofe from the fubitance of the cork, or from the air in the water of the tnb, that water having: not been boiled ; or it may have been intang- led in the parts of the boiling water, as it was poured into the veiTel, and not have had time to efcape before the cork was inferted ; or, laftly, which is the lead probable fuppofi- tion, the vapour ariiing from the water may not be capable of being totallv condenfed.

The phenomenon of the boiling of fluids is not very fatisfadtorily explained. It is clear, I think, from the experiment of which I have given an account, that it cannot be attri- buted, in ail cafes, either to the efcape of air from the interflices of water, or to the matter of fire, as it L 3 is

_ ( i66 )

is called, pervading the water ; for the water continued boiling for two hours after it was removed far from the fire; and the air, if it contained any, was utterly inadequate to the formation of the numerous bubbles* .Bc?(?;'^i3^'yd' has remarked, that bubbles of the kind here fpoken of contain no air, but he has not affigned the caufe of their origin ; Dr. Hooke af- cribes them to the fubtle parts of the water, which, when the prelTure of the air is removed, (probably by means of an air pump) are able to -acquire the form of vapours, by thac fmall degree of heat which is left in the ambient air *: and other philo- fophers -f have adopted this idea, without hinting, at what Hooke fup-

pofed,

^ See Birch's Hift. of the Royal Society. f The Abbe Nollet and Dr. Hamilton.

( i<J7 )' pafed, a different degree of volatiliry in the parts of the water.

Froin what has been advanced we may conclude, that the Ahnightyr when he feparated the chaotic mafs into air and water, did not render ihefe two oceans of matter fo wholly heterogeneous from each other, as that they fliould be incapable of Gontrad:lng any union together ; they have, on the contrary, fuch a difpo- fition to unite, as feems t6 indicate their having had a common origin; and were it not for the intervention of heat, they would, probably unite and again compofe a common mafs. The water on the fur face of the earth is conftantly replete with air, and the atmofphere is replete with water.The Bumerous tribe of aquatic animals, L 4 which

( i68 )

which inhabit the ocean of water^, would perilL, if it contained no air ; and it it is not an improbable conjec- ture, that the animals which exiil in this ocean of air, would pcrifn if it contained no water. The air, more- over, b)^ being abforbed into the w^ater, and afterwards feparated from it by the ad:ion of the fun, to which it is daily expofed, is rendered abun- dantly more fit fol* animal refpira- tion than common air ; and this purified air (the quantity of which, confidering the great extent of the furface of the earth which is covered v^'ith w^ater, muil be very coniider- able) cannot but be one great means of reftoring to the whole mafs of air, thofe falubrious qualities of which it is daily deprived, by the rejpration

of

( i69 )

of animals, ihQ putrefaBicn of bodies, the ccmbiiftion of fuel, and other caufes.

* Dr. Prieftley has obferved, '^ that the fame water, which, if examined immedi- ately, gives only a fmall quantity of bad air, y\fiS.^% fpontaneouJJy about ten times the quantity of pure dephlogiilicated air, after ilanding fome time expofed to the funJ^^ Phil. Tranf. 1779, p. 377. An animal w'ill live five times as long in what is called here dephlogifticated air, as it v/ill in com- mon air of the befl quality.

fiSSAY

ESSAY VI.

OF WATER IN A SOLID STATE; OF THE HEAT OF SPRING WATER; AND OF A PROBABLE CAUSE OF THE IMPREGNATION OF SULPHU- REOUS WATERS.

TH E mind of man admits with great reluctance, the truth of every tellimony concerning matters of fad, which happen to be repug- nant to the uniform experience of his fenfes ; hence the general back*

wardnefs

( 17^ )

wardnefs to believe the miracles re- corded in the bible; and hence the Dutchman who informed the king of Siain, that water in his country, would fometimes, in cold weather, be fo hard that men walked upon it^ and that it would bear^an elephant, if he were there, was cfleemed a per- fon unworthy of credit, the king, as Mr. £cfy^^ relates the flory, faying to him, " Hitherto I have believed the ftrange things you have told me, becaufe I look upon you as a fober man, but now I am fure you lie,"-'^

Mahine, the native of Borahora^ could fcarcely be perfuaded, even by the information of his fenfes, of the reality of the fame effedl. The ap- pearance of " white flones," as he

called

* Locke's ElTay on the Hum. Und. B. IVi C. XV.

( 173 )

colled hail, which melted in his hand was altogether miraciilous to him ; and when he had been with difficulty convinced that an exten- live field of ice was not common land, he was determined at all events to call it '' white land," by way of dillineuiihine: it from all the reil''^.

This dc term inatioii of the favage was made in the true fpirit of philo- lofophv, for ice in fm.all particles is afpecics of earth, and in folid maiTes it may be conlidered as a kind of tranfparent ftone. The waters, fays Job, "j- fpeaking of the eired of froil^ ere hid as with aftoiie^ that is, vs^a- ter conceals its nature, by afluming a Hone-like hardnefs and conliftence when it becomes ice. The Ruffians

applied

* Forilei's V^j. Vol. I, p. 530. I Chap. >jcxviii. 30,

c 174 )

applied ice to the fame purpofes ■with flone, at the whimficai mar- riage of Prince Gallitzen^ in 1739; an houfe, conlifting of two apart- ments, was bnilt with large blocks of ice, the furniture of the apart- ments, even to the nuptial bed, was made of ice ; and the icy cannon and mortars, which were iired in honour of the day, perform.ed their office more than once without burilino;. *

Ice, however, differs from all other earths and ftones, not only in its melting in a much lefs degree of heat than any of them, but in its being fubjedl tOr a conftant diminu- tion of its weight when expofed to the open air, in the greateil degree of cold. It generally becomes fluid in the 33d degree of heat, as indi- cated

* Manftein's Mem. of Ruffia*

( '75 )

cated by Fahrenheit's thermometer ; and Mr. Boyle, by expofing in a good balance fomewhat lefs than two ounces of ice to a fharply freezing air, a little before midnight, found it in the morning diminifhed in weight ten grains. * It is probable, that this diminution of the weight of ice, is owing to the abrafion of its parts by the adlion of the air. The particles of air are thought to be larger than the particles of water, and may by their motion acquire force enough to feparate the particles of ice, or if this ihould not be ad- mitted, it muil be remembered, that the air always contains a great quan- tity of water, the particles of which when converted into particles of ice, though in this country they are fel-

doni * Boyle's Works, Fob Vol. III. p. 66.

( 176 )

doni large enough to be feen, always make themfelves felt by impinging Upon our ikin : thefe icy particles wben put in motion may abrade the furface of a mafs of ice, and caufe thereby a conRant diminution of its weight. In confirmation of this explanation it may beobferved, that ice fuiTers no lofs of its weight in a velTel devoid of air, nor in a clofe veffel full of air.* That the icy particles, contained in a freezing atmofphere, ihould be able to a<5l upon ice, cannot be a matter of dif- ircult conception to thofe who recol- lect, that the hardeft bodies in na- ture fuffer a diminution of their w-eight, by the fridion of the minute parts of the fame kind of liodies;

dia-

* Hamilton on the Afcent of Vspours,- p. 71.

f 177 )

cFiamond duft being eflentlally ne- cefTary for the cutting or polifhing. of diamonds.

That water was diminifhed in quantity by being frozen was known to Hippocrates;, for he exprefsly fays,, that if a given quantity of water be frozen, and afterwards thawed, it will not fill the fame vefTel it would have done before it was frozen *- Pliny was of the fame opinion with. Hippocrates, and they both of them attribute this diminution of weight ta the feparation of the more fubtile parts of the water during congela- tionf . The principal caufe of the lofs of weight,: fuflained by water when : changed into ice, feeras to be the-

inceffant

* Hippoc. de Aqua.>

t Plin. Hifl. Nat, Lib. II. S. 61.. & Lib,. JXXI. S. 3.

VOL. IIU M.

( 178 )

incefTant adion of air upon its fur- face 'i it is true, however, that water is, by freezing, deprived of the great- eft part of the air with which, in its fluid ftate, it is ordinarily faturated; and this feparation of its air may contribute fomething towards the diminution of the water's bulk -, fince water when faturated with air, is fomewhat greater in bulk than when deprived of it.

It is eafy to apprehend, that the lofs of weight which any given quan- tity, fuppofe a cubic foot, of ice will fuffer by expofure to the air in a given time, will depend, partly upon the hardnefs or foftnefs of the ice, partly upon the temperature of the atmofphere, with refpedl to the de- grees of cold and humidity, partly upon the velocity of the wind which

bruihes

( 179 )

brufhes its furface, and probably enough upon the agency of other caufes with which we are lefs ac- quainted. Some philofophers have efbimated in general terms^ the lofs of weight fuftained by a certain weight of ice, without fpecifying the magnitude of the ice's furface -, others, with more accuracy, have mentioned both the weight and furface of the ice expofed to the air, but then they have either omitted to fpeak of the ice's confiftency : the temperature of the atmofphercj the force and diredlion of the wind ; or they have expreffed themfelves in very indefinite terms concerning thefe points, fo that we cannot be faid to have hitherto gained, from their experiments^ any precife information upon the fubjedl. As to the fad itfelf, the moft com- M 2 mon

( 38o ) _

mon obfervation is fufficient to af-; certain us of its truth. In long con- tinued frofts, the ice formed in ponds and other fmall colle6tions of water, is fenfibly diminifhed every day, and often v/liolly evaporated ; and a flill of fnow may be feen confider- ably wailed in a few days, in the fever ell feafon.

Notwithflanding this diminution of weight, to which both ice and fnow are fubje6l in the coldeil weather, and the thaw v/hich they experience in the hottefl, yet fome have doubted whether the quantity of congealed water, be not an increafing quantity upon the furface of the earth ; and have even thought, that the globe of the earth mufl in procefs of time refemble 'an egg, having its diameter from pole to pole, longer than the

equa-

( i8i )

equatorial diameter^ on account of the conftant accumulation of frozen water at the two poles. — '^ After fo many years lapfe it cannot be, I think, but that the diameter of the earth from pole to pole, from the top of the fnow at one end of the earth, to the top of it at the other end, is much longer, than in any part under the equator, though at the creation it were (as I believe) made fpherical."*

In fome mountainous countries, the proportion between the fnow which falls at one feafon of the year, and that which is diffolved in an- other, approaches fo near to an equality, that upon the fame fpot, the fnow may in one year be {gqti quite through the year, in another,

the * Childrey's Brit. Bacon, p, 148, M 3

( I82 )

the laft fpeck of it will vanilli in a few weeks or days, before a new fupply is brought by the approach of winter. In colder climates, the utmoft power of the fumn:ier fun is not able to melt all the fnow which falls in the winter. In afcending mount Etna^ the Jlps, or the Andes y though the lower parts are found to be rich in vegetation, yet you foon come to a region covered, as it fhould feem, with everlafting fnow : the height at which this region com- mences, does not admit much varia- tion in the fame latitude, but is very different in different latitudes. It begins at the diftance of near three miles above the level of the fea, un- der the equino6lial line \ and at each pole, probably, it is not removed from that level fo many hundred

feet ;

( i83 )

feet ; it is found to be 600 yards nearer to the level of xhc/ea at 'Tene- riffe than under the equator ^ and above 1 200 yards nearer in Switzer- land than at 'Teneriffe^,

Not only the tops of high moun- tains in every quarter of the globe are covered at all feafons of the year with fnow, but the ocean both in the northern and fouthern hemifphere is, in high latitudes, replete with im- menfe mountains, and extenfive plains

of

* Hifto. Nat. des Glaciers Suifle the

author fays, enlin la plupart des Montagnes volines des poles font convertes jufqu' a leiir pied de neiges perpetuelles. This obferva- tion muft not be admitted without reilridion, if it be at all true, lince in Greenland, and in the latitude 79 degrees, 44 minutes north, the feet of the mountains are in certain fea- fons freed from fnow. See Crantz Hill, of Greenland, Vol. I. p. 30. and Phipps's Voy, p. 52 and 70.

M 4

C 1 34 )

of ice, in the greateft heats of fum- mer ; and hence it has appeared pro- bable to many, that both the fnow upon the land, and the ice upon the fea, receive an augmentation every year, from the continued agency of the fame caufe which firfl: produced 'them.

.A philofopher, well acquainted with the natureof the Alps, expreffes himfeif upon this fubjed in the fol- lowing manner, " one cannot doubt concerning the increafe of all the Glaciers of the Alps : for their very €xiftence is a proof, that in preced- ing ages the quantity of fnow which has fallen during the winter^ has ex- ceeded the quantity melted during the fummer. Nov/ not only the fame caufe flill fubfifls, but the cold, oc- cafioned by the.mafs of ice already

formed.

( i8s )

formed, ought to augment it ftill farther, and thence both more fnow ought to fall, and a lefs quantity of it be melted."* If this be admitted, the time will undoubtedly come when the fea will be diminiflied in depth, if not dried up by the con- verfion of the water, which is daily raifed from it, into fnow or ice ; and had the world been as old, as fome are fond of fuppofing it to be, we fhould, probably, have had no wa- ter upon its furface at the prefent day. However, it mud be owned, that no argument can be drawn a- gainfl the antiquity of the world, from thisconfideration, becaufe there is reafon to believe that the ice and fnow upon the furface of the ^arth, ^re not annually increafing in quan- tity. * DeLuc de rAtmofphere, Vol. 11, p. 328.

( i86 )

tity. For, befides the heat of the air in fummer, there is another caufe which tends to prevent an indefinite augmentation of congealed water — the internal heat of the earth. The general heat of th€ fprings of water, fituated deep in the bowels of the earth, is 48 degrees; in mountainous countries, I fufpefb it to be fome- what lefs, but fufficient, notwith- ftanding, for the purpofe here men- tioned. When the fnow, incum- bent on any fpot of ground, is but thin, it may fo far cool the earth, that its internal heat may not be able to difToive it ; but when the bed is thick enough to prote6t the earth from the influence of the atmof- phericai cold, that furface of the fnow which is contiguous to the fur- face of the earth, may, even in the

coldeft

( i87 )

coldeft winters, receive more heat from the earth than it does cold from the atmofphere, and, on that fuppo- fition, I fee no abfurdity in admit- ting, that it may be diffolved at all feafons of the year.

The fadl I believe is certain, that ftreams of water iffue from the bot- tom of the Glaciers in the Alps^ in the greatefl feverity of winter; fo that whether the internal heat of the earth be admitted or not, as a caufe fufficient to explain the phenome- non, a con ft ant thaw of the ice or fnow, which is contiguous to the furface of the earth in the Alps can- not be denied ; and this, added to other caufes, may render it proba- ble, that the quantity of congealed water has its limits even in the cold- eft climates.

The

( i88 )

The ardinary heat of fpring water, which does not feel the yiciflitudes of the temperature of the atmof- phere, is here faid to be 48 degrees of Fahrenheit's thermometer ; it may be worth while to add a few remarks on this fubjedl.

In Auguft 1778, when the heat of the air was 7 2 degrees, I tried on the fame day, the temperature of feveral fprings, reputed cold, in the neigh- bourhood of Matlock 5 and I found them varying in heat from 50 to 54 degrees. This variation, pro- bably, proceeds from their fubterra- neous pafTages being fituated at dif- ferent diflances from the furface of the earth, which was then much warmed by the heat of the fummer. Or it may proceed from the fprings being more or lefs mixed with the

water

( i89 )

water which fupplies the warm baths^ the heat of that water being 68 de- grees. There is a fubterraneous pafTage upon the fide of the hill near the new/h2Lth at Matlock, which ter- minates in a large cavern, fituated under one of the fields in the midway between the new and the old b3,th ; and from this cavern, which is always full, iflues the warm water which fupplies both the baths ; and it may probably ooze out in different direc- tions, and in different quantities, fo as to make the neighbouring fprings participate more or lefs of its warmth. At Lord Godolphin's houfe on Gcg- magog hills, near Camhridgey there is a well, above 230 feet in depth, which is dug through a ftratum of- chalk 3 I have frequently examined the heat of the water of this well,

and

( I90 )

and conftantly found it to be 50

. degrees. At Cherry Hint on, a village fituated at the bottom of thefe hills, there ifTues from the chalk a very copious fpring, the heat of this water as it bubbles out of the earth, is, at all feafons of the year, t^o degrees. I have tried the heat of fome deep wells dug in chalk at Bury St, Ed- munds, and found it variable from

50 to 52 degrees. «^ It has

been long and generally obferved, that as far as the limeftone extends, that tra6t of ground makes the fnow that falls on it, thaw or melt fooner than it does on the neighbouring lands."* This is Mr. Boyle's ob- fervation concerning fome limeftone land in Ireland, and he fays its truth was confirm-ed to him by a Derby-

fhire

* Boyle's Works, Vol. IV. p, 278.

( 191 )

jfhire miner, who aiTured him, that

on contiguous diftrids of land, fnow was obferved to diiTolve much foon- er on the foil which covered lime- ftone, than on that which covered freeftone. If thefe obfervations may be depended on, we may, per- haps, in general infer, that the heat of calcareous ilrata is greater than that of other kinds of Ilrata, and this would furnilh a reafon for the fprings in chalk countries being of the v/armth of 50, though the ordinary heat of fprings be not above 48 degrees.

In the middle of fummer, v/hen the air was 7 2 degrees hot, I tried the heat of fome fprings at Harrow- gate in Yorkfhire. Pump water at the Granby Inn 48 degrees. — Old Spaw 48 degrees. — Pewit or ^ewit

well

( ^92 )

well 48 degrees. — -Sulphur well 50 degrees. The cold well at Buxtoriy examined at the fame tune of the year^ was 48 degrees, and the famous Spaw^ at Llanrbaid'r in Venhighjhire was alfo 48 degrees; St. Winifred's, well at Holywell in Flintfhire, was con- fiderably v/armer, the thermometer^, when held in the fpring as it rofe out of the earth, (landing at 54 de- grees. I have tried a great many other fprings in different parts of Great-Britain, and found the heat of moil of them to be included be- tween the limits of 48 and 54 de- grees, the mean of which is 51. Springs on the fides of high moun- tains, may, probably, participate of the cold which is found to be greater in elevated than in low fituations.. There is a fpring by the fide of the

turn-

C m )

• turnpike road Icadmj^qser the high ground called Otky Sk^vin in York- fliirci I obferved the heat pf this fpring in September, when the air was warmed to 62 degrees, to be not 485 but only 45 degrees. The mean heat of fprings near Edinburgh is faid to be 47, and at Lundo'd 51 degrees : f this diverfity depends, probably, on the different elevations of London and Edinburgh above the level of the fea.

I have mentioned the Sulphtir . well at Harrowgate^ according to its ufual appellation at that place, with- out taking upon me to decide the long controverted queftion, concern- ing the existence of fulphur in that and other waters of the fame kind. '^^ Sulfhur has been long efteem-ed a

mincrar t Philof. Tranf. 1775, p. 46-cv. VOL. III. N

( ^94 ) niineral body very common to be ' met with in waters; and all thofe waters which have a flrong fetid fmell, refembling that of a foul gun, have been efteemed to be more or lefs impregnated with fulphur.. However, Dr. Hoffman feems to doubt much of its exiftence in the greater number of fuch waters ; and Dr. Lucas has affirmed, that it is not to be found in the form of fulphur in any water whatever; not even in that of j^ix- la- Chape Iky where a true and perfedl fulphur is found on the up- per parts of the conduits through which the water pafles ; for he fays, that, flridiy fpeaking, thefe waters do not contain fulphur fubftantially difiblved in them, but are impreg- nated with a phlogiilon and an acid, the principles of fulphur ; which be- 2 ing

( 195 )

ing in a volatile ftate, are fublimed,, meet on the furface of the conduits, ■ and there unite into a true and per- fe6l fulphur, which did not naturally exifl in the water." f The author, from whom I have made this ex- tradi informs us that . Dr. Rutty maintains the exiilence of fulphur in mineral waters; and that both Dr. Shaw and Dr. Short found fulphur in Harrowgate water. Notwithftand- ing the teilimony of fuch eminent phyficianSj the mose recent opinion of a phyfician, whom Dy, Monro con- fulted on the fubje6l iri 1768, is againft the exiftence of fulphur in fuch w^aters. " I have taken parti- cular notice of every appearance of the Harrowgate waters, and muft

own f Monro on Mineral Waters, Vol. I. p. 30. and 196.

N 2

( 196 )

own I never obfcF-yed any appear- ance of fulphur floating in them, nor any fcum at the top of the well ; nei- ther could I meet with any perfon in that quarter, who remembered the appearance of real fulphur fublimed, upon taking up the ftones at the bottom of the well, as mentioned by Dr. NeaL^'X — I beg leave to add my own obfervation on the fubjeft, which I made in 1780. The v/ater in the well rifes into a circular ftone bafon ; a whitifh crull adheres to the ftone, where it is contiguous to the furface of the water i I fcraped off a portion of this cruft, and put- ting it on a hot iron, I found that it burned with the flame and fmell of Julphur, I do not think that this experiment abfolutely warrants us to

conclude,

% Id. p^ 196.

( '97 )

c'o« elude, that a5fualjulphur is con- tained in this and other waters ge- nerally denominated fulphureous |, we juftly infer from it, that fome- thing is fublimed from the water, which either of itfelf is. fulphur, or which in conjundion.with tne air, or fome other principle,- conflitutes ful- phur.

The profecution of this fubje(ft would lead: to fpeculations too ab- flrufe for mydefign; the following experiment, however,, which I have frequently made,^ will, I hope, throw no inconfiderable light on the caufe of the impregnation of fulphureous waters in. general.

The acid of vitriol does not afl:

upon the common Derbylliire lead

ore, except when it is afiified by

. heat, it then. difTolves it, and a. great

N 3 efcape

( 198 )

cfcape of air is obferved ; I made this air, as it was difcharged from ihe ore, pafs through a high bended tube into a bottle full of pump wa- ter: the water;, in a very littk time,, acquired the fetid Jmelloi Harrow- gate water, — its tafte was the fame as that of fuch fulphureous waters as contain no fait, — it was perfectly iranj^arenty but in the courfe ©f t\ hours it became cloudy y and loft moft of its fmell,— it did not fufter any 'preclptaHon by the addition af the acid of vitriol,— ^/^'^r was blackened both hj being ,put into this v/arer, and by being expofed to the vapour which arofe from it ; from all thefe cicumflances, it may properly enough, I think, be called an ariifi^ cial fulphureous water.

I have obferved the fame pheno- mena

( J99 )

mena when, inftead of lead ore^ I iifed black jacky and I remember that once having placed a bottle, containing black jack and acid of vitriol, fo that its neck leaned againft a plaiftered wall, 1 obferved fome days afterwards,, that the wall was flained, to the diftance of above a foot from the mouth of the bottle, of a purple colour, refembling the purple fediment often found in ful« phureous wells.

Air of the kind here ipoken of^ may be feparated from other fub- flances, as well as from lead ore and black jack, and by other means, as- well as by the acid of vitriol j and it feems very probable, that the wa- ters ufually called fulphureous, are impregnated with this kind of air,, which has been feparated, in the N 4 bowels;

( 2rOO )

bowels of the earthy from particular minerals J efpeciaily fulphureousones. It has been remarked of Harrowgate water;, that as it fprings up it is clear 2iwdjfarkli7igy and throws tip a quan- tity of air bubbles.

During the procefs of impregnat- ing water with air, by difTolving lead ore in the acid of vitriol, a part of the glafs tube "was coated with a thin pellicle of falphur, which had accompanied the air in its afcent : May not the fulphur fubiimed from Harrowgate waxer, have accompanied the air which -gives it its fm.ell? Is it certain that this kind of air does not confift of attenuated parts of ful- phur, which have acquired an elallic force, and which cannot be con- denfed in v;ater? Or is it not more probable^ that this kind of air is one

of

( 20£ )

of the conftituent parts of fulphnrv than fulphnr itfelf? Does this air^ and the inflammable air feparable from fome metallic fubftances, by folutioa in acidSjXonfift o^ oleaginous partix:Ies in an elaftic ftate I

If the reader wiflies to impregnate comiTion water with the fulphureons properties of Harrowgate water, he may do it in the following fimple manner. — Into an apothecary's vial> holding four or five ounces> put fome pounded lead, ore, and pour upon it fome acid of vitriol j (there is no occalion to be foiicitous about the proportions of the lead ore and acid, for if there be more or lefs ore thaathe acid can difTolve, ftill air enough for the purpofe will be difcharged j.) wrap a. fev/ folds of wet linen round one end of a bended

tube^

( 202 )

tube, infert this end into the neck of the vial fo clofely, that no air may pafs out of the vial except through the tube -, the end of the tube Ihould be at fome diftance from the fur face of the acid. Put the other end of the tube into a bottle full of water, then, by fetting the vial on the hot bar of a grate, or by fome other means, heat the acid, and as foon as it is heated, it will begin to a6t on the lead ore, and a great quan- tity of air will be difcharged, which will pafs through the tube into the water in the bottle, and in a few mi- nutes the water will be ftrongly im- pregnated with the fulphureous pro- perties of Harrowgate water. Be- fides its fulphureous impregnation, Harrowgate water contains fea fait ; and moft other fulphureous waters

contain

( 203 ) contain fome fait or otherj fb that^: to make a complete imitation of them/the falts which they feverally hold fhould be added in due propor- tion, to the water impregnated with the air here fpoken oL

Though I am greatly difpofed tO' believe, that fdlphureous waters are- impregnated with their peculiar fmell and taile, after the manner I have defcribed ; yet, to aifift the rea- der's conjedtures concerning the ori-. gin of this impregnatian,, I will men- tion another way in which it may be fuppofed to arife, and which will ac-' caunt for the faline taile as- well as the Imell of the water.

I know not whether any fpecies- of maritime plants, containing fea fait, will impregnate water with a. fulphureous fmell by means ofpitre-

fa^ion y

{ ^04 )

foMioriy nor whether all of them will do it by means of combujlion^ but that one of them will do it I can haye na doubt : I allude to the bladder fticus or Jea wracks which is burned on our coalls for the makincj o{ Kelp.. It has been mentioned be- fore,* that fe a wrack when burned to a black coal, will yield, by being boiled in v/ater,, a great quantity of common fait; and I would now re* mark, that the water extrads from the black ai^es, not only a great quantity of common, fait, but fome- thing elfe alfo, by which, without lofing its tranfparency,: it aGq,uires both the fmell and fulphureous tafte of Harrowgate water -, and by which it is enabled, like that water, to blacken iilver and white paint.

This

* Vol. L p. 137.

( 2G5 )

This Jomething I am fenfible may be what chemifts call liver of/ulphurf or an union of fulphur with fixed alkali, and it would not be difficult to explain its formation during the combuftion of the fea wrack ; no ful- phur however can be precipitated from the water by the acid of vitriol, though that acid turns it, as is the cafe with Harrowgatc water, a little cloudy. The air extra6led from iron by the acid of fea fait, impregnates water with a fmell fomewhat refem- bling that of Harrowgate water, but its difference both from the natural and the artificial fulphureous waters, may be eafily diftinguifhed, efpecial- ly after the water has Hood a few hours expofed to the air.

ESSAY

ESSAY VII*.

OF DERBYSHIRE LEAD ORE.

LEAD ore, as dug out of the mine, is generally much mixed with ipar, lime{lone,.and other fub- fiances, bulk for bulk, lighter than the ore itfelf. It undergoes various drefTings before it becomes a mer- chantable commodity, the general tendency of which is to free it, as much as poffible, from every hetero- geneous impurity,

Suppofe

* The fubftance of this EfTay was printed in the Philof. Tranl". 1768.

( !208 )

Suppofe that a cubic foot of lead bre, which contained no fpar or other extraneous matter^ wouldweigh 7 800 ounces^ and that a cubic foot of fpar, which contained no lead ore or other foreign fubflance, would weigh 2700 ounces, then would a mixture, con- fiftmg of a cubic foot of pure lead ore, and a cubic foot of pure fpar, weigh 10500 ounces, and one cubic foot of fucli a mixture would weigh 52 sO. ounces. It is obvious tliat according to the different propor- tions in which the particular kinds of fpar and lead ore here aiTumed, are fuppofed to be mixed together, a cubic foot of the mixture will have different weights, the limits of which are on the one hand 7800, and on the other 2700 ounces; it never can weigh fo little as 2700 ounces, for

then

C ^09 )

then It would confid intirely of fpar without any lead ore -, nor can it ever weigh fo much as 7800 ounces, for then it would confift intirely of lead ore without any fpar.

From this view of the matter it is evident, that the purchafing of lead ore by the meafure, which is the general, though not the univerfal cuftom in DerhyJIjire^ is a mode lia- ble to fome exception j fmce a dilli, containing any definite meafure, muft have d liferent v/eights^ according 'as -the ore with which it is filled is more or lefs free from fpar. And it is fcarce poiTible, by repeated dref- fings, to feparate all the ipar U'om. an ore, or equal portions of it from equal portions of ore.

There is a diverfity, however, in the weights of equal meafures of lead

VOL. HI, . O ore.

C 210 )'

ore, which, probably, does not arife from fparry or other heterogeneous accretions, but from the nature of the ore itfclf. I have carefully cal- culated the weight of a cubic foot of many of the Derbylhire lead ores ; the weight of a cubic foot of the lighted which I met with was 7051 ounces, and the weight of a cubic foot of the heavieft was 7786 ounces ; the difference amounting to between a ninth and a tenth part of the weight of the lighteil. There are, proba- bly, other ores of lead, the weights of equal bulks of which differ more than thefe here mentioned ; but the <lifference between thefe is fufhcient to fliew the great uncertainty of pur- chaiing lead ore by the meafure, iince ten difhes of one fort of ore may not weigh more than nine diflies

of

( 211 )

of another fort, though both the forts are equally well drefled.

Lead ore is not always of the fame goodnefs in the fame min.c, nor even in the fame part of the fame mine ; and, what is more remarkablej the different parts of the fame lump of ore have in equal bulks different weights. I could not eafily have believed this, unlefs a variety of ex- periments had convinced me of the fad.

They wereemployed lately ^.tHoly- w^//infmelting a lead ore from xh^IJle of Man \ the ore was rich in filver. A lump of this ore, weighing about ten ounces, was broken into fcveral pieces, and fuch of the pieces were fcleded as appeared to the eye to be wholly pure. I eftimated the weight of a cubic foot of fix of thefe pieces, o a and

( 212 )

mnd found that a cubic foot of the ilightefl khid would have weighed ■^5^5 ounces, and a cubic foot ^of the heavieft kind would have -weighed 7636 ounces, Suppofing (the weight of a cubic foot of water to be denoted by 1000, the mean weight of a cubic foot of the fix 'different pieces of this ore, may be vexpreffed by 7 115 avoirdupoife ounces,

A very pure fpecimen of telTella- ted lead ore, from a mine near Ajhover in Berhyjhirey was broken into fix pieces, weighing near one ounce each. A cubic foot of the lightefl of thefe pieces would have weighed 7326 ounces, and a cubic foot of the heavieft would have weighed 7786 ounces. The mean weight of a cu-' bic foot of the fix pieces was 7566. 2 At

C 213 )

At the fame mine they frequently meet with fmall quantities of fteel* grained lead ore. Six different pieces' of the fame lump of this kind of ©re were chofen, each of which ap-- peared quite free from fpar and^ every other impurity. A cubic foot- of the lighten of thefe pieces would^ have weighed 7188 ounces^ and a eubic foot of the heaviefl would, have weighed 7442 ounces. The- mean weight of a cubic foot of the^ fix pieces was 7342.

Other lumps of ore, from different mines, were refpedtively broken into* different pieces^ and fcarcely any two equal pieces of the fame lump^ were obferved to agree in weighto^ This diveriity in the weights of equal bulks of the feveral pieces oB the fame lump of ore may be owinge,. o 3^ either:

( 214 ) ^either to the different proportions in which the conftituent parts of the pre are combined in the fcveral pieces ; or to the different quantities of extraneous fubilances impercepti- bly mixed with them^ or, which feems iiK)ft probable, to a diveriity in the fize or configuration of their pores.

But be the caufe of this diveriity what it may, the fatt^ I believe, is certain, and by no means fingular> for not to mention the varieties ob- fervable in the weights of equal bulks of different pieces of roll brimftone, of corrofive fublimate, of cad ileel, and other factitious fub- fiances, the natural fpars generally found along with lead ore are fub- jedt to a flmilar diverfity, though not, perhaps, in an equal degree.

A piece-of rhomboidal, otberways

called

C 215 )

called ref railing or lantern fpary waJJ broken into four fm^ller pieces, the weights of a cubic foot of each of which were 2675, 2687^ 2715, 2723 ; the mediuin of the four is 2700 ounces. Mr. Cotes fixes the weight of a cubic foot of Iceland cryftal at 2720, and JVallerlus fixes it at 2700 ounces.

The weights of a cubic foot of four pieces of the fame lump of cu- bical fpar were 3204, 3218, 3222^ 3231 ; the medium of the four is 3219 ounces. — Moil of the fpars met with in Derby/hire are either rhomboidal or cubical; they are eafily diftinguiflied from each other by a view of their Ihape^ when their an- gles can be difcerned ; and when the Ihape cannot be cafily feen, the na- ^ ture of the fpar may be afcertained o 4 by

( 2i6 ) by touching it with an acid; the rhomboidal fpar always effervefcing with an acid, and the cubical refill- ing its action. The lead fnielters make great -ufe of the cubical fpar as a flim for fuch lead ores as do not readily melt ; it is curious to fee its cifed:; a few fhovels full of ir,.. thrown upon a heap of red hot ore,, immediately melting down the ore into a liquid, though the^ longed continuation of the fame degree of heat^ without the addition of the fpar, would not have been fufficienC for the purpofe.

Six ounces of fine teffellated lead ore were put into a crucible and ex- pofed, at firil, to a gentle, and after- wards to a flrong fire : the ore grew red, and emitted fumes which fmel- led of fulphur ; ac length it melted,

and

( 2^7 ) and the fumes became very copious *;

they were accompanied with a yel- lowifh flame upon the furface of the melted ore, and when collected had: a whitiih appearance. The crucible,, after the ore had continued a full hour in perfect fuiion was taken from the fire, and when.it was cold it was broken. The mafs which it contained weighed five ounces and, an half; there was no fcoria obferv- able on its furface, nor were any particles of metal formed^ it was^ ftill an ore of lead..

The mafs remaining from the lafl: experiment was put into a freih cru- cible, and expofed to a flrong melt- ing heat;, the fumes which arofe from ir feemed to be heavy; they brooded over the furface of the: melted mafs in undulating flames^.

which

( 2l8 )

which now and then appeared like burning zinc* The lead was now formed, and many particles of it were fublimed to at leafl fix inches above the furface of the liquid in the crucible. After letting the cru- cible continue two hours in this Itate, I poured out its contents, and found them confifting partly of lead, partly of lead ore, and partly of a very minute portion of brownifh fcoria. I repeated this experiment with the fame fuccefs.

Thefe experiments prove, that fome fubftance or other is contained in lead ore, which muft be difperfed before the ore can be formed into lead ; and they fhew too, that it re- quires

* It may deferve to be inquired whether zinc may not be contained in lead, iron and ©ther ores, more frequently than is fuppofed.

C 219 )

quires a coniiderable lime to effedl: the difperfion of this fubflance^fince fix ounces of ore, though kept three hours or more in complete fufion, were not wholly brought into the form of lead ; they inflrud: us alfo to believe that the lead in this kind of ore is in its metallic ftatc, as the ore was changed into lead without the addition of any fubllance containing the inflammable principle; and, laft- ly, they render it probable, that the fumes, arifing from melted ore, carry off with them no inconiiderable por- tion of the lead itfelf. At the great fmeking houfes in Derbylhire, they put a ton of ore at a time into the furnace, and work it off in eight hours ; the ore might be wholly melted in one hour, but the lead, perhaps, is not formed in the great-

( 220 }

ell poflible quantity in eight h(mm Some fine teifellated lead ore from Derbyfhire was pounded into fmall lumps, each about the fize of a pea,, and carefully picked from fpar and other impurities. Sixteen ounces^ of this ore, thus previouily cleanfed,, were diililled in an earthen retort;. as foon as the ore felt the fire, the ftopple of the quilled receiver had a. ftrong fmell, refembling that of the- inflammable air, feparable from fome:^ metals by folution in acids ; foon af- ter a fmall portion of a liquid came over into the receiver ; the fire was- then raifed till the retort v/as of a white heat, when a black matter be- gan to be fublimed into the neck of the retort ; the operation was then difcontinued'.. This experiment was undertaken with a view of feeing,

wLe-

( 221 )

•whether fulphur could be feparatecl from lead ore, as it may be from fome fpecles of the pyrites, by diilil- lation, and it appears from the iffue of the experiment that it cannot, at leaft in the degree of heat which is requifite for fubliming the ore. Up- on breaking the retort I found, that the ore had been melted during the operation, for there was a confident cake of ore of the figure of the bot- tom of the retort ; the weight of this cake was fifteen o unces and an half, the weight of the liquid in the re- ceiver, and of the black matter which had been fublimed, did not together amount to one quarter of an ounce, fo that a quarter of an ounce or more had been difperfed, probably, in the form of air, or fome elaftic fluid. The ore by this pro-

cefs

( 222 )

cefs had loft one thirty-fecond part of its weight. The liquid did not cffervefce with either acids or alka- lies ; nor did it produce any change in the colour of blue paper, yet I am certain, from experiment, that one drop of oil of vitriol, though diluted with two ounces of water, would have produced a fenfible red- nefs on the blue paper which I ufed. The liquid, notwithftanding, had an acid tafte, and a pungent fmell, re- fembling that of the volatile vitriolic acid. The black matter which had been fublimed ii^to the neck of the retort, was examined with a microf- cope, and it appeared to be pure lead ore. The melted ore which was found at the bottom of the re- tort, had not any appearance of fcoria, or of lead^ upon its furface.

Some

( 223 ) ^

Some phenomena attending this experiment deferved, I thought, a further invelllgation, I therefore diftilled another i6 ounces of ore, but with a fire flronger and continu- ed for a longer time, than in the pre- ceding experiment : the quantity of liquid was much the fame, there was a fmell of fulphur, and, perhaps, to the amount of half a grain of ful- phur was found in the receiver ; the ore was in this experiment fublimed into the neck of the retort, to the thicknefs of one fourth of an inch. There was found, as before, a cake of melted ore at the bottom of the retort, but no fenlible portion of either lead or f carta ; '^ fo that we may

fafely

* I have faid no fenlible portion ; there

^vas, however, an appearance of fcoria ad-

liering to the fide, and an appearance of lead

adhering

X ■^24 ) fafely conclude, that lead ore cannot 'be decompofed by the ftrongeil fires in clofe velTels, but that it may be fublimed in them. The ore had loll near an ounce of its weight.

Though the experiment is fuffici- ently troublefome, I was not deter- red from making it once more ; for I wanted to fee whether lead ore could be wholly fublimed ; as I thought that philofophers might 'thereby form fome conjedturcs of the efhcacy of fubterraneous fires in

fubliming ^adhering to- the bottom of the retorf; but the quantity of each vvus exceedingly fmall, and they were both, probably, produced from that minute decompofition of the ore i^hich produced the fulphur, and which would not, I think, have taken place in any degree, had there been no communication with the external air ; but the orifice of the quilled receiver was not always clofely flop- ped during the difdllation.

( 225 )

in lead ores, and, perhaps, ores of other metallic fubftances. The event of this third experiment was perfect- ly correfpondent to that of the two former, with refpedt to the produc- tion of liquid, and the reparation of air, which w^as caught in a bladder, but was not found to be inPiamma-' ble : the lead ore too was fo plenti- fully fublimed into the neck of the retort, that it quite plugged it up for above three inches in length. Upon difcontinuing the fire, which had been raifed to a degree of heat exceedingly great, I found the retort was cracked, and that the cake at its bottom was very different from v/hat was found at the bottom of the other retorts, which had flood the fire without cracking ; for this cake was covered with a black glaffy fco- VOL. III. P ria

( ii6 ) iria ^ of an inch in thicknefs, -and the ore which laid under it, was in part changed into lead, and the whole of the ore did not weigh quite ten ounces, fo that above 6 ounces had been loft by efcaping through the crack. By a communication with the air through the crack, the ore was decompofed, and thus both lead znd/coria were formed, which in the other experiments, for want of fuch a decompofition, could not be form- ed. There was a thin coat of ful- phur aifo which lined the infide of the receiver, and this fulphur, pro- ,bably,, arofe from the decompofition of the ore, fince none, or next to none, was obferved in the other di- ftillations of the ore. I found that the weight of a cubic foot of the ore, which had been fublimed into 3 the

( ^^7 ) the neck of the retort, was 7500 ounces ; which fuificiently agrees with the weight I had before afcer^ tained of this kind of ore. A cubic foot of the black glafly fcoria Vv^eigh- ed 3233 ounces ; and the metailiG cake which laid under it, and which confifled partly of lead, and princi- pally of ore not quite changed into lead, gave 87 38 ounces to the cubic foot.

Finding that fulphur could not be feparated from lead ore by diflilling it in clofe veffels without addition,, and yet being much difpofed to think, that it contained a confidera- ble portion of fulphur, I firil thought of diftilling it with charcoal dull:, iron filings, fand, and other addi- tions; but recolle6ting that fulphur might be feparated from antimony p ^ by

( 228 )

by folution in acids, I thought it not improbable, that it might be feparated from lead ore by the fam.e means, and the luccefs of the follow- Lng experiment abundantly juflified the conje6]:ure.

Upon ten ounces of lead ore, cleanfed as in the preceding experi- ments, I poured five ounces of the ilrongeft fuming fpirits of nitre ; this ftrong acid not feeming to a6l upon the ore, I diluted it with five ounces of water ; a vfolent ebullition, ac- companied with red fumes, immedi- ately took places the folution of the ore in this meyiftruu77i becam.e mani- feit, and when it was finifhed, there rem.ained floating upon the furface of the menftruum a cake of fine yel- low fulphur, perfedly refembling common ililphur.

I re-

( ^29 ) I repeated this experiment a great many times, in order to afcertain the quantity of fulphur contained in lead ore, and feparable therefrom by fo- lution in acid of nitre. The refults of different experiments were feldom the fame i the matter feparable from the ore by folution, after being re- peatedly wafhed in large quantities of hot water, in order to free it from every faline admixture, fometimes amounted to more, fometimes to lefs than one-third of the weight of the ore. This matter may, for the fake of diffin6lion, be called crude fulphur* Its apparent purity might induce a belief that it contained no heterogeneous mixture, yet the fol- lowing experiments (hew how much we fliould be deceived in forming p 3 fuch

( ^30 ) ftich a conje6lure, and how rightly it is denominated crude fulphur.

From one hundred and twenty parts, by weight, of lead ore, I ob- tained, by folution in acid of nitre, fubfequent walhing in hot water, and drying by a gentle fire, forty parts of a fubftance which looked like ful- phur : thefe forty parts were put on a red-hot iron, the fulphur was made manifefc by a blue flame and pun- gent fliiell. "When the flame went out, there remained upon the iron unconfum.ed twenty-fix parts of a greyifh calx-, the weight of the ful- phur which was confumed muil there- fore have amounted to fourteen parts, or between one eighth and one ninth part of the weight of the ore. It has been obferved, that the weight of the matter, feparable from lead ore

by

c m 1

by folutlon in acid of nitre, fome- times exceeded, and fometimes fell fhort of, one third part of tlie weight of the ore -, this variety, as far as I have been able to obferve, does not extend to the quantity of fulphur contained in a given quantity of ore, it depends upon the quantity of calx remaining after the burning of the fulphur. Different lead ores will doubtlefs contain different quantities of fulphur i but that the fulphur contained in the lead ore which I examined, conilitutes between one eighth and one ninth part of the weight of the ore, is a conclufion upon which, from a variety of expe- riments, I am difpofed to rely.

There are faid to b^ annually fmelted

inDerhyJlme about ten thaufand tons

p 4 of

( 232 ) of lead ore j* now if means could be invented (which I think very pofTi- ble) of faving the fulphur contained in ten thoufand tons of ore^ fuppof- ing that the ore fhould only yield one tenth of its weight of fulphur, though it unqueilionably contains more^ Derhyjhire alone w^ould furnifh annually one thoufand tons of ful- phur, the value of which would an- nually be about fifteen thoufand pounds. ] mention this circum.ftance thus publicly3 in hopes that the lead fmelters rnay be induced to profe- cute the fubjeft. If the fulphur contained in the lead ore could be col- le6led^ it would not only be a lu- crative bufmefs to the fmelters, but a great faving to the nation. We at

prefent

* This efliii^ate is I have resfon to think too high.

( ^33 )

prefcnt import the fulphur we nfe,

and the confumption 6f this com- modity is exceeding great^ in the making of gunpowder, in form- ing the mixture for covering the bottom and fides of fhips,. * and in a great variety of arts. The fmelters need not be apprehenfive lefb the quality of the ore Ihould be injured by extra6ling the fulphur. Eighteen hundred weight of ore, from which the fulphur has been extracted, will certainly yield as much lead as twenty hundred weight of ore, from which the fiilphur has not been extracted, and it will, pro- bably, yield more. Arfenic is ex- traded * This mixture is made of one part of tallow, of one part of brimflone, and of three .parts nearly of rolin. The tallow and rofin are melted together, and the brimftone is llirred into them ; 140 pounds of brimftone i§ enough for a veffel of 1 40 tons.

( 234 ) trafted from a particular ore in

Saxony, by roafting the ore in a fur- nace, which has a long horizontal chimney ; the chimney is large, has many windings and angles, thai the arfenical vapour which arifes from the ore may be the more eafily con- denfed : the arfenic attaches itfelf like foot to the chimney, and is from time to time fwept out. It is very probable, that by fome fuch con- trivance the fulphur contained in lead ore might be colle6ted. The fmelters call every thing fulphur v/hich is volatilized during the roafting or fluxing of an ore -, but none of thofe with whom I have converfed, had any notion that com- mon fulphur could be feparated from lead ore.

The greyifh calx which remained

upon

( ^3S ) upon the iron after the fulphur was

confumed, was put upon a piece of lighted charcoal ; the heat of the charcoal being quickened by blow- ing upon itj a great nunnber of glo- bules of lead were formed upon its furface. From hence it appears, that this calx is not an unmetallic earth contained in the ore, which the acid of nitre could not diffolve -, but a calx of lead, probably pro- duced by the violent a6lion of the acid, and which, by the addition of phlogifton, may be exhibited in its metallic form. The quantity of this calx depends much upon the adion of the acid upon the ore -, if that a6lion is violent, the calx is in greater abundance than if it be mo- derate ; and I am not certain whe- ther the experiment might not be fo

managed.

( ^36 y

managed, that there would be little: or no calx remaining; that is, a given quantity of ore might be io dilTolved in the acid of nitre, that nothing would remain undilTolved except the fulphur. But I have not yet perfectly fatisfied myfeif as to the conftituent parts of lead ore. I am certain that it contains lead, and Julphur, a liquid, ^,nd air :■ of the ex- iftence of the three firft there can be no doubt, from what has been faid, and the air is rendered beautifully apparent by the following experi- ment.

Let fome lead ore be reduced into a fine powder, put it into a narrow- bottomed ale glafs, fill the glafs three parts with water, drop into the water a portion of the ftrong acid of nitre, you may judge of the requi-

lite

( ^37 ) fite quantity by feeing the folution

commence, and you will obferve the ore univerfally covered with bubbles of air, thefe will buoy the ore up in large tufts to the furface, and the air will continue to be feparated from the ore till the acid becomes faturated with the lead. The fait arifing from the union of the nitrous acid to the lead often appears cry- ftallized upon the furface of the menftruum in this experiment; and if, when the menftruum is in that ftate, a little frelh acid be added, the fait inftantly cryftaliizes and falls down to the bottom of the glafs, the acid having abforbed the water which held it in folution. When lead is difiblved in the m^anner here menti- oned, by a very diluted acid of ni- tre, there is no appearance of ful-

phur

( 233 )

phur upon the furface of the men- ftruum, there is found at its bottom a black matter, which is the fulphur. But though lead, and fulphur, a liquid, and air*, are unqueilionably conftituent parts of lead ore, I do not take upon me to fay, that they are the only conflituent. parts : it is well known, that, during the foelt- ing of lead ore, a third part or more of its weight is fome how or other loft, fince from one and tw^enty hun- dred weight of ore, they feldom ob- tain above fourteen hundred weight of lead. What is loft partly confifts of a fcoria which floats upon the furface of the lead during the opera- tion of fmelting, and partly of what

is

* I have feparated inflammable air from lead ore, by diflTolving it in the acid of lea fait.

( n9 )

is fublimed up the chimney and dif- fipated in the air. The fcoria, I ap- prehend, would be very little, even from a ton of ore, if the ore was quite free from fpar : it is the fpar which is mixed with the ore that con- ftitutes the main portion of the fco- ria*. I have in my poiTefTion a folid mafs of fcoria, which accidentally flowed out from a fmelting furnace, and which in colour and confiftency perfedly refembles grey lime-ilone, it receives a polifli as fine as marble, and it might perhaps with advan- tage be cad into moulds for paving ftones, chimney pieces, and other

matters.

* The fpar without queflion augments the quantity of the fcoria, yet the lead ore, which appears to the eye to be quite free from fpar, yields a conliderable portion of a black glafly fcoria, when urged with a liifficient fire.

( 240 ) matters. It arifes from the fpar mix- ed with the ore^ and, by the addition of cubical fpar to the ore during its fufion, its quantity might be increaf- ed at no great expence, in any pro- portion. That part of the ore which is fubiimed and difperfed in the air^ confiils partly of the fulphur which is decompofed, and partly of lead j this fubiimed lead attaches itfelf in part to the fides of the chimney of the fmelting furnace ; the reft of it flies lap into the air, from whence it falls upon the ground, poifoning the wa- ter and herbage upon which it fet- tles. This fubiimed lead might be collected either by making it meet with water, or with the vapour of water, during its afcent, or by iriak- ing it pafs through an horizontal chimney of a fufficient length.

It

( ^41 )

It is not eafy to determine with precifion the quantity of this fublim- ed lead ; a general guefs, however, may throw fome light upon the fub- jed. They ufually at a fmelting houfe work ofF three tons, or fixty hundred weight, of lead ore every twenty-four hours ; the fulphur con- tained in fixty hundred weight of ore, we will fuppofe to be feven hundred weight, and the lead to be forty hundredweight; the air, liquid, fco- ria, and fublimed lead muft toge- ther, upon this fuppofition, amount to thirteen hundred weight -, now, admitting three hundred weight of the thirteen to be fublimed lead, it is evident that, could it be colleded, there would be an annual faving at ^ach fmelting houfe of above fifty tons, which, fuppofing it to be

VOL. III. Q^ worth

( 242 )

>worth four pounds per ton, would amount to above two hundred pounds a year. The price, if not the quantity of lead fublimate, here -afiTumed, is, probably, below the truths but my end is anfwered in giving this hint to perfons engaged in the fmelting bufinefs.

The following experiments, though upon a different fubjedt, may ;not be unacceptable to the lovers of chemiftry, as I do not remember to have any where met with them.

It is commonly known, that the furface of melted lead becomes co- vered with a pellicle of various co- lours. I undertook fome experi- . ments in the courfe of laft winter, with a view to afcertain the order in which the colours fucceeded each .other. The lead which lines the

.boxes

( 243 ) boxes in which tea is imported from China happening to be at hand, fome of it was melted in an iron ladle; but I was much furprized to find that its furface, though it was prefently covered with a duiky pellicle, did not exhibit any colours. Imagining that the heat was not fufHciently ftrong to render the colours vifible, the lire was urged till the ladle be- came jed hot, the calcined pellicle upon the furface of the lead was red hot alfo, but it was ftill without co- lour. The fame parcel of lead was boiled in a crucible for a confider- able time ; during the boiling a co- pious fteam was difcharged, and the furface of the lead, as is ufual, be- came covered with a half vitrified fcoria. The lead which remained unvitrified was then examined, and it ct, 2 had

( 244 )

had acquired the property of form-' ing a fucceflion of coloured pellicles, during the whole time of continuing in a ftate of fufion.

Another portion of the fame kind df lead v/as expo fed to a llrong cal- cining heat for a long time ; the part which rem,ained uncalcined did, at length, acquire the property of ex- hibiting colours fufiiciently vivid.

Thefe experiments induced me to conclude, that the Chinefe lead was mixed with fome fubftance from Vv^hich it was neceflary to free it ei- ther by fublimation or calcination, before it would exhibit its colours. It would be ufelefs to mention all the experiments which I made be- fore I difcovered the heterogeneous fubflance with which I fuppofed the Chinefe lead was mixed. At laft I

hit

( 245 ) hit upon one which feems fully fuf- ficient to explain the phenomenon. Into a ladle full of melted Derby- fhire lead, which manifefted a fuc- cefTion of the mod vivid colours, I put a fmall portion of tin, and ob- ferved, that as foon as the tin was melted, and mixed with the lead, no more colours were to be feen. I do not know precifely the fmalleft poffible quantity of tin, which will be fufficient to deprive a given quantity of lead of its property of forming coloured pellicles, but I have reafon to believe that it does not exceed one five thoufandth part of the weight of the lead.

Derby (hire lead, which has lofb

its property of exhibiting colours by

being mixed with tin, acquires it

again, as is mentioned of the Chinefe

0^3 lead.

lead, by being cxpofed to a calcining heat for a fi^f^cient time 3 the tin, it is fappoiedj being feparated from the lead by calcination, before all the lead is reduced to a calx.

Some calcined Chinefe lead was reduced to its m.etallic form by burn- ing fomiC taliow over it. The re- duced lead gave, when melted^ co- loured pellicles ; ' the calx of tin, which we fuppofe to have been mix- ed with the calcined lead, not being fo eafily reducible as that of lead.

I find that %inc is another mxetallic fubftance which has the fame pro- perty as tin v^ith refped to the de- priving lead of its power of forming coloured pellicles 3 but it does not, I think, pofiefs this power in fo eminent a degree as tin. I put fmall portions of hifmuth alfo into melted

lead,

' ( m f

lead, but the lead ftill retained its ■ quality of forming colours. I melted together fome filver and lead, but the lead did not thereby lofe its power of forming colours. A little tin added to a mixture of lead and bifmuth, or to a mixure of filver and lead, immediately takes away from the refpediive mixtures the fa- culty of forming coloured pellicles.

This quality of tin has hitherto,, as far as I know, been unobferved -, but every new fa6l, relative to the actions of bodies one upon another, ought to be recorded. The change, produced in lead by the admixture of a fmall portion of tin is much felt by the plumbers, as it makes the metal fo hard and harfli, that it is not without difficulty they can eaft it into Iheet lead. If their old 0^4 lead

lead does not work fo willingly, nof exhibit colours fo readily, as new lead, they may refer the difference to the fmall quantity of tin contained in the folder, from which old lead can feldom be thoroughly freed.

With refpe6l to the order in v/hich the colours fucceed one an- other upon the furface of melted lead, it feems to be the following one ; yelloWy purple, hluey — yellow^ 'purple y green y — pink^ green, — pinky green. Upon exhibiting the bright furface of melted lead to the air, I have often obferved thefe ten changes to follow one another in a more or lefs rapid fuccefiion, according to the degree of heat prevailing in the lead. If the heat is but fmall, the fuccef- fion flops before it has gone through all the changes 5 but v/ith the great- eft

( 249 )

eft heat I did not obferve any fur- ther variation. All the colours are very vivid, and each feems to go through all the fhades belonging to it before it is changed into the next in order.

The formation of thefe colours may be explained from what has been advanced by Sir Ifaac Newton^ and illuftrated by the very ingenious experiments o^yiwDelavaly relative to the fize of the particles confti- tuting coloured bodies.

ESSAY

ESSAY VIII.

OF THE SMELTING OF LEAD ORE, AS PRACTISED IN DERBYSHIRE.

THERE IS a certain ftandard of perfedtion in the exercife of every art, which is not always well undcritood ; and after men do fuffi* ciently comprehend it, many ages often pafs away before they are for- j tunate or ingenious enough to attain it. To extract the greatcfl poffible

quantity

( 252 )

quantity of metal, from any parti- cular kind, and any definite quantity of ore, is a problem of great iPxi- portance, whether it be confidered in aphilofophical or a commercial light; yet he who fliould apply himfelf to the folution of it, v^nth an expedta- tion of being ufeful to mankind, muft take into confideration another circumflance, of as much importance as the quantity of metal to be ex- traded,— the expence attending the procefs. For it is obvious, that a great quantity of metal extrad:ed at a great expence, may not produce fo much clear profit, as a lefs quantity procured at an eafier rate ; there is a beneficial limit between the quantity to be obtained, and the expence at- tending the operation, which nothing but experience can afccrtain.

It

( 253 ) It has been proved, by experi- ments made in France^ * that lead ore when fmelted by a fire made of wood, yielded one tenth more lead, than in the ordinary method of fmelting by means of piccoal ; yet pitcoal is fo much cheaper than wood, in Derby- ihu-e, and moil other parts of Great Britain, that the lofs of a tenth of the lead, is probably, more than compenfated, by the ufe of pitcoal inftead of wood or charcoal. It is pollible, ^perhaps, even with the ufe of pitcoal, by an alteration in the procefs of fmelting, to cxtra(ft from every twenty tons of ore, one ton more of lead than is any where ex- traded at prefent ; but whether the price of one ton of lead, would be

more

* Effais des Mines, par M. Hellot, Vol. :H. .p. 114,

( 154 ) moi-e than fufficient to defray the extraordinary expence attending the alteration of the procefs, muft be left to the decifion of thofe who are interefted in the fuccefs of fuch in- quiries.

The art of fmelting the ores of all metallic fubflances, was, probably, at firfl very imperfe6t in every part of the world ; and this doubtlefs has been a reafon, why the ufe of iron has every where been of a more re- cent date, than that of the other metals, fince it requires the applica- tion of a much ftronger fire to fmelt the ores of iron, than thofe of any other mietal.

We have no certain account when,

or by whom, the feveral metals were

<lifcovered 3 Wdllerius fays, that, as

far as he knew, Pliny was the fir ft

3 who

( 255 )

who enumerated the fix metals:"^ Pliny may, probably, be the firft Natural Hiftorian who mentioned them, but they were certainly known long before the age of Pliny, and were mentioned both by Horner^ "ssidi by an author far more ancient than Homer — Mojes. — " Only the goldy and the^/ter, the brafs {cofper)^ the irony the//;^, and the lead^ every thing that may abide the fire, ye fhall make it go through the fire, and it fhall be clean." f From this tcflimony we are certain that all the metals were known, at leafl in the country of the Midianites, above 1450 years before the birth of Chrift, or near 900 years

after

* — Primus (fcil Plliiius) quantum mihi conftat, fex metalla enumeravit. Waller, de Syf. Minera. p. 10.

f Numb. xxxi. 22,

( 2J6 )

after the deluge. When I fay all the metals, I mull be underftood to mean, all thofe which were anciently- known ', for plalina, the feventh me- tal, has been but recently difcovered, and is not yet brought into general ufe ; and quickfilver or mercury is not admitted by mineralogifts into the clafs of metals i though it has a good right to be admitted, fince in a fuffi- cient degree of cold, it poflefTes the great charaderiftic property of a metal, as diftinguillied from zfemi- metal — malleability. This property of malleability, as conftituting the x:riterion by which metals differ from femimetals, is not over rigidly to be infifted on, fince iron, when firfl fluxed from its ore, or when con- averted into fleel, and hardened by being fuddenly immerfed when red

hot

( m )

hot in water, is lefs malleable than ]zincy which is always clafled amongft the fern i metals.

It has been contended, that copper Was one of the firft metals which was ufed as money, and that gold and filver were, in very remote ages, of little account in that view. In many inftances the greatnefs of the Roman name has made us forget the sera when that people began to be di- itinguifhed in hiilory, and induced us to confider their cuftoms, as the firfl which prevailed amongft man- kind. It is granted, that Servius Tullius firft coined copper, and that the Romans ufed no other currency till the four hundredth and eighty- fifth year of their city,* when filver began to be coined 3 but from this

con* * Plin. Hift. Nat. Lib. XXXIII, S, 13.

VOL. Ill, R

( 2s8 )

concefTion, no argument can be de- duced for the foie ufe of copper as a currency, in the firft ages of the world. We know, from undoubted authority, that filver was ufed in commerce, at ieafl: eleven hundred years before even the foundation of Rome. — And Abraham weighed to Ephroriy theftlver which he had 'named in the audience of the Jons ofHeth^ four hundred fljekels of filver^ current money with the merchant^. About 60 years before Abraham paid this fum for a piece of land in Canaan ^ he is faid, upon his return from Egypt ^ to have been rich, not in copper and iron, but in filver and gold f.

Iron and copper were certainly. knovv'n before the deluge ; and it is probable, that ail the other metals,.

every * Gen.xxHK 16, f Gen. xiii. 2,

C ^59 ) every one of which is more eafily €xtraded from its ore than iron and copper are from their's, were known slIio to the Antediluvians ; we have proofs how^ever, that in the time of Abraham, gold and filver were cfleemed;, as they are at prefent^ pre- cious metals ; and hence it feems reafonable enough to conclude, that Noah was able to inilru61: his de- fcendants in the art of fmelting me- tallic ores : but, though this be ad- m.itted, we need not be furprized at the ignorance of many barbarous na- tions in this particular. For the va- rious colonies which, either by com- pulnon or choice, quitted the plains Q^Afidy in fearch of fettlements, may not always have had in their compa- ny men who had been indrudled in the art of fmelting ; and thofe who R 2 did

( 26o )

did underftand it, when the colony firft migrated, may, in many in- llances, have died before any ores were difcovered, upon which they might have exerted their Jkill -, and thus the art of fmelting being once loft, it is eafy to conceive that many nations may have remained for ages without the ufe of metals, or with the u{e of fuch only as are found ready formed in the earth, or are eafily fluxed from their ores.

The earth in a little time after tht deluge, and long before it could have been peopled by the pofterity of Noah, mull have become covered Tvithwood; tlie moft obvious me- i.hod of clearing a country of its wood, is t:l:e flatting if on fire : nov/ in m.oft mineral countries there are veins of metallic ores^ wliich lie

con-

( a6i )

contiguous to the furface of the earth, and thefe having been fluxed whilft the woods growing over them were on fire, probably, fuggefled to many nations the firil idea of fmelt- ing ores.

Powerful gold firfl raifed his head.

And brafs, and lilver, and ignoble lead. When iliady woods, on lofty mountains grown^ Felt fcorching fires ^ whether from thundeir

thrown, Or elfe by man's defign the flames arofe*

Whatever 'twas that gave thefc flames t^r

birth, Which burnt the tov/ering trees and feorch^d

the earth, Hot flreams of filver, gold, and lead, and

brafs, (copper) As nature gave a hollow proper place, Defcended down, and form'd a glitt'^ring;

mafs*..

There * Lucretius by Creech, VoLII. p. 572^ ^ 3

( 262 )

There is no natural abfurdity in this notion of the poet; and indeed it is confirmed by the teilimony of various ancient hiftorians, who fpeak of filver and other metals being melted out of the earth, during the burning of the woods upon the Alps and the Pyrenees, A fimilar circum.-- ftance is faid to have happened in Croatia in the year 176 1 ; a large mafs of a mixed metal, compofed of copper, iron, tin and filver, having been fluxed, during the conflagra- tion of a wood, which v/as acciden- tally fct on fire. *

The putting a quantity of ore up- on a heap of wood, and fctting the pile on fire, in conformity to the manner in which ores were melted during the burning of foreits was,

it * Annual Repiflerj 1761, p. 138.

J

( ^62 )

it may be conje^lured, the firfl rude procefs by which metals were ex- tra6ted from their ores. But as the force of fire is greatly diminiflied, when the flame is fuffered to expand itfelf, and as the air a6ls more forci- bly in exciting fire, when it rufheg upon it with greater velocity, it is likely, that the heap of wood and ore would foon be furrounded with a wall of ftone, in which fufiicient openings would be left for the en- trance of the air, and thus a kind of furnace would be conftruded. The Peruvians we are told " had difcover- ed the art of fmeltinc-^ and refininor filver, either by the fimple applica- tion of fire, or ^yhere the ore was more ftubborn and impregnated v/ith fo- reign fubllances, by placing it in fmall ovens or furnaces on high R 4 e-rounds^

( s64 )

grounds, fo artificially conflru6led that the draught of air performed the fundlion of a beU4)wS;, a maGhiiie with which they were totally unac- quainted." *

This method of fmelting ores on high grounds> without the affiftance of a bellows, at lead of a bellows moved by water, feems to have been formerly prad:ifed in other countries as v/ell as in Peru, When M. Belon travelled into Greece^ he found the furnaces placed on the fides of ri- vuletSj and obferves, that all their bellows played with v/heels turned by flream^s ^f v/ater, yet formerly they had fmelted their ores in a dif- ferent manner : for upon the m.oun-

tains

* Robertfon's Hill, of America. — Alonfo Barba, Treatife of Metals, French Tranf- Vol, I, p. 272,

( 265 )

ta^ins of Macedonia^ where mines had been wrought in the time of Philip tlie father of Alexander y great heaps of flag have been difcovered, which are fituated fo far above any river of the country, that the furnaces from which they were formed, muft,. pro- bably, have been wrought by the wind. There are feveral places in Derby/hire called Boles by the inha- bitants, v/here lead has been ancient- ly fmelted, before the invention of moving bellows by water. Thefe places are difcovered by the flags of lead, which are found near them ; there is no certain tradition concern- ing the manner in which the ore v/as fmelted at thefe boles, it was, probably, as fimple as that of the Peruvians ; for in Berhyjhirey as well 'Ss in Pe-ru^ they feem chiefly to have

relied

( a66 ) relied upon the ftrength of the wind for the fuccefs of the operation; the boles being always fituatedupon high grounds, and moflly upon that fide of a hill, which faces the weft. This fituation was not fixed upon with- out defign, fmce the wind blows in England, in the courfe of a year, near twice as many days from that quarter as from any other.* A me- thod is mentioned by Ercker7t f of fmelting bifmuth ore by the wind, and it feems as if the ore of lead might have been fmelted at thefe

boles, * As may appear from the following abridged Hate of the winds at London in the years 1774 and 1775.

	N	s	E W	NWJ 8E NE	sw
^774	25 ;Tr	21 21.^ anf.	171^4 II i8|- 1774—5	43i 30 74 391-13^1172	126.^ 148"	dys
f See Fleta Minor, by Sir John Pettus,
p. 30

( ^67 ) boles, after the fame manner. This method confifls in putting the bif- murh ore, when beat to a proper fize, into fmall flat iron pans, thefe are fee in a row contiguous to each other, in an open place -, and when there is a flrong wind, a fire of dry wood is made clofe to the pans, and on that iide of them from which the wind blows, by this contrivance, t\\t wind driving down the flame of the w^ood upon the pans, the ore contained in them is quickly melted, A pig of lead was dug up at one of the boles in the year 1766 on Crcm- ford moor near Matlock^ upon its un- der furface there is an infcription in relievoy from which it appears to have been fmelted in the age of the Emperor Adrian ; it is not very dif- ferent in fn.ape from the pigs which

arc

( 268 ) are caft at prefent ; it confifls of fe- veral horizontal layers of unequal thicknefies, and there is an irregular hole in it running from the top to near the middle of its fubftance 5 from thefe appearances it feems as if it had been formed by pouring into a mould, at different times,- feveral quantities of lead ^ and if lead had been fmelted after the manner before mentioned of fmelting bifmuth ore, the feveral pans being emptied, at different times as they became ready, into the fame mould, would have yielded a mafs of lead divided into layers of unequal thickneffes, and refemblingthis Roman pig; for the hole in its furface was, probably, made accidentally, from the unequal cooling of the lead, or from fome extraneous matter being lodged in it.

The

( 269 )

The boles in Derbyfhire are, pro- •bably, many of them of high anti- quity, as appears from the pig of lead before mentioned -, yet I have met with a pafTage in a writer of the lail century^ from which it is evident, that the method of fmelting lead on high grounds was then pradlifed in the Peak. " The lead-ftones in the Peak lye but juft within the ground next to the upper cruil of the earth. They melt the lead upon the top of the hills that lye open to the weft wind i making their fires to melt it as foon as the weft wind begins to blow 3 which wind by long experi- ence they find holds longeft of all others. But, for what reafon I know not, fmce I ihould think lead were the eafieft of all metals to melt,

they

( 270 ) they make their fires extraordinary

great." *

The fmelting of ore by the varia- ble and uncertain a6lion of the wind, mull have been a troublefome pro- cefs. It has therefore been univer- faliy difufed, and the more regular blail of a bellows has been intro- duced in its fcead. The invention of the bellows is attributed by Straho to Anacharfis the Scythian : j but it is more probable, that he was the in-. ventor of fome improvement of this machine, than of the machine itfelf; for Horner^ v/ho lived long before the age oi Anacharfis^ defcribes Vulca7C2j^ employing twenty pair of bellows at once, in the formation of Achilles^

fnield.

* Childrey's Britan. Bacon, i66i« f Strab. Geog. Lib. VII,

( 27. )

Ihield. * It is difficult to fay when the art of moving bellows, by means of a water wheel, was firft difcovered; it is pretty certain, that the ancients did not know it; and that it was very generally known, amongil the Germans at leafc, in the time of i^gricola, one of the firft of our metallurgic writers, for he fpeaks of it in feveral places without any hint of its being a recent invention, f The heat of the fire in a furnace de- pending much upon the force of the blaft of air impelled againft the fuel ; and that force, other circumftances remaining the fame, being in pro- portion to the quantity and velocity of the air ; the application of a power

able * Iliad. Lib. XVIIT. V. 470. t Agric, de Re Metal, pubiiflied in 1550, p. 165. 33S.

( 2/2 )

able fuddenly to comprefs the largeft bellows when fwelled with air, could not fail of being confidered by nie- tallurgifts, as an invention, whenever it was niade, of the 1 aft importance. The moderns accordingly have, in many ihftantes, worked over again, with confiderable profit, the heaps of iron and other kinds of flag, from which the metal had been but im- perfectly extraded, before the mov- ing of bellows by water was difco- vered.

It is not fifty years fince the hlafl or hearth furnace, was the only one in ufe for fmelting lead ore in Der- hyjhire. In this furnace ore and charcoal, or ore and what they call white coal, which is wood dried but not charred, being placed in alter- nate layers, upon a hearth properly

con-

( ^73 ) conllrudied, the fire is raifed by the

blail of a bellows, moved by a water wheel ; the ore is foon fmelt- ed by the violence of the fire, and the lead as it is produced trickles down a proper channel, into a place contrived for its reception. There are not at prefent, I believe, above ©ne or two of thefe ore hearths in the whole county of Derby; this kind of furnace, however, is not likely to go entirely out of ufe, fince it is frequently applied to the extracfling lead from the flag which is produc- ed, either at the ore hearth , or the cupola furnace, and it is then called 2. flag hearth I and the lead thus ob- tained is CcxWtdi flag lead': the fire in a ilag hearth is made of the cinder of pitcoal inftead of charcoal.

The furnace called a cupol or cu- VOL. 111. S pola^

I ^74 )

'pohy in which ores are fmelted by the flame of pitcoal, is faid to have been invented, about the year 1698, by a phyfician named TVright^ * though Beecher may, perhaps, be thought to have a prior claim to its invention or introdudion from Ger- many. -\' But whoever was the firfl inventor of the cupola, it is now in general ufe^ not only in Derbyfhire and other countries for the fmelting of the ores of lead, but both at home and abroad, where it is called the Engliih furnace, for the fmelting of copper ores. This furnace is fo contrived, that the ore is melted, not by coming into immediate contad; with the fuel, but by the reverbera- tion of the flame upon it. The •bottom of the furnace on which the.

lead ■^' ElTais dcs Mines, Vol. II. p. 114. 'i See Vol. I. p. 3%

( ^75 _) lead ore is placed, is fomewhat con- cave, flielving from the fides towards the middle; its roof is low and arch* ed, rcfembling the roof of a baker's oven , the fire is placed at one end of the funtace^ upon an iron grate, to the bottom of which the air has free accefs ; at the other end^ oppo- fite to the fire place, is a high per- pendicular chimney ; the dirediion of the flame, when all the apertures in the fides of the furnace are clofed up, is neceifarily determined, by the fi:ream of air which enters at the grate, towards the chimney, and in tending thither it fi:rikes upon the roof of the furnace, and being reverberate4 from thence upon the ore, it foon melts it.

It is not always an eafy matter to

meet with a current of water, fuffi-

s 2 cient

( ^76 )

clent to move the bellows required

in fmelting on an hearth furnace; and to carry the ore from the mine where it is dug, to a confiderablc difiance to be fmelted, is attended with great ex pence ; this expence is faved by fmelting in the cupola furnace, which not requiring the life of bellows, may be conflrudied any where. Wood is very fcarce in every mining country in England, and though pitcoal cofls ten or twelve Ihillings a ton in Derby- ihire, yet they can fmelt a definite quantity of ore in the cupola, at a far lefs expence by means of pit- coal, than of wood.— The flame^ which plays upon the furface of the . ore and fmelts it in a cupola fur- nace, is not driven againll it with much violence ; by this means

fmall

I

( 277 ) jinall particles of ore, called beU land, may be fnielted in a cupola furnace with great convenience, which would be driven away, if expofed to the fierce blait of a pair of bellows in a hearth furnace. — Thefe are fome of the advantages attending the ufe of a cupola in pre- ference to a hearth furnace ; and to thefe may be added one fuperior to all the reft, — the prefervation of the workmen's lives ; the noxious particles of lead are carried up the chimney in' a cupola, whilft they are driven in the face of the hearth fmelter at every blaftof the bellows. They generally put Into the cu- pola furnace a ton of ore, previoufly beat fmall and properly dreifed, at one time; this quantity they call a charge ; if the ore is very poor in lead they put in fomevvhat more^and they s 3 work

( 278 >

work off three charges of ore in every twenty -four hours. In about fix hours froLB the time of charg- ing, the ore becomes as fluid as milk. Before the ore becomes fluid^ and. even whiift it continues in a flate of'iufion, a confiderable por- tion of its weight is carried off through the chimney ; what remains in the furnace con fills of two dif- ferent fubilancts, — of the lead^ for the obtaining of which the procefs was commenced^ — -and of the Jlag ox Jcorla, The proportion between thefe parts is not always the fame, even in the fame kind of ore; it depending much upon the management of the fire. The lead, being heavier than the flag, finks through it as it is formed, and fet- tles into the concavity of the bot- tom of the furnace. The pure flag,

accord-

< 279 ) according to the idea here given, is that part of the ore of lead which is neither driven* oif by the heat of the furnace, nor changed into lead. In order to obtain the lead free from the flag which fwims over it, the ' fmelters ufually throw in about a bufhel of lime; not, as is ufually fuppofed, in order to contribute to- wards the more perfedt fulion of the ore., but to dry up the flag which floats upon the furfaee of the lead, and which, being as liquid as lead, might otherwife flow out along with it. The flag being thus thick- ened by an admixture of lime, is raked up towards the fides of the furnace, and the lead is left at the bottom. There is a hole in one of the fides of the furnace, which is pro-. perly flopped during the fmelting^ s 4, of

( aSo ) ©fthe ore; when the Hag is raked off, this hole is opened, and being iitu-ated lower than the lead in the furnace, the lead gufhes through it into an iron pot placed contiguous to the nde of the furnace ; from this pot it is laded into iron mouMs^ each containing what they call a pig of lead, the |)lgs when cold, being or- dinarily flamped with the maker's name, are fold under the name of ore lead,. After the lead has all flowed «aut of the furnace, they Hop up the lao hole, and drawins: down the Hag and liQ:te into the middle of the furnace, they raife the fire till the mixture of flag and lime, which they limply term flag, is rendered very liquid, upon this liquid mafs, they throw another quantity of lime to dry it up as in the former

part

( '^8i ) part of the procefs. This fecond mixture of flag and lime is then raked out of the furnace, and the fmall portion of lead feparated from the fufion of the firfl, generally to the amount of twenty or thirty pounds, being Let out of the fur- nace, a nev7 charge of ore is put in,, and the operation re-com.menced. In, order to fpare the lime, and the expence of fuel attending the fiiix- ing of the mixture of lime and flag, they have in fome furnaces lately contrived a hole,,, through which they fuffer the main part of the li- quid flag, to flow out, before they tap the furnace for the lead -, upon the little remaining fl.ag they throw a fmall portion of lime, and draw the mixture out of the furnace without fmelting it. This kind of

fur-

( 282 )

fiitnace they have nick-named a Maccaroni,

The procefs of fmelting here'de-. fcribed, appears to be defeftive iii fonne points, which I will take the liberty to mention, and at the fam© time fuggeft the means of improve- ment; without, however, prefuming to fay, how far it may be expedient to adopt the propofed alterations ; being fenfible that what m^ay appear very feafible in theory, or m^ay even anfwer in fmall affays, may not be practicable in large works.

The firft alteration which I v/ould propofe to the confideration of the lead fmelters, is to fubilitute an ho- rizontal chimney of two or three hundred yards in length, in the^ place of the perpendicular one now in ufe. In the preceding EfTay,

which

( 583 )

which was firft publiHied in 177^^^ mention is made of the probability of faving a large quantity of fub- limed lead, hj making the fmoke, which rifes from the ore, pafs through an horizontal chimney, with various windings to condenfe the vapour. I have fmce converfed with fome of the principal lead fmelters in Derhyjhirey and find that I had over-rated the quantity of this fublim.ed lead 3 the weight of the Jcoria from a ton of ore, amounting to m^ore than I had fuppofed ; they were all of them, however, of opi- nion, that the plan I had propofed for faving the fublimate, was a very rational one. But fo difficult is it to wean artifls from their ancient ways of operating, that I queftion very much whether any of them

would

( 2§4 )

would ever have adopted the plan they approved^ if an horizontal Ghimney, which was built a iittk time ago in Mid die ton dale^ for a quite different purpofe^ liad not given them a full proof of the pra(5l:iGability of faving the fubli- mate of lead, which, is lofi: in the ordinary method of fmelting. This chimney was built on the fide of an hill, to prevent fome adjoining paf- tures from Being injured by the fmoke of the furnace. It not only anfwers that end, but it is found alfo to colle£l confiderable quanti- ties of the lead, which is fublimed during the fmelting of the ore \ this fublimed lead is of a whitifh cafr, and is fold to the painters at ten or twelve pounds a ton s it might per- haps be converted into red lead with. ftill more profit,

A f€.-

C ^«5 )

A fecond circumftance to ht at- tended to in the fmelting of lead ore, is the faving the fulphur contained in it. The pure lead ore of Derbylliire contains, between an eighth and a ninth part of its weight of fulphur; but as the ore which is fmelted is never pure, being mixed with par- ticles o(/par, cawky limeftone^ brazily and other fubftances, which the mi- ners call deads y we fhali be high enough in our fuppofition, if we fay that the ordinary ore contains a tenth ' of its weight of fulphur ; it may not, probably, contain fo much, but even a twelfth part, could it be col- le6led at a fmall expence, v/ould be ..an obje6h of great importance to the fmelter. In the common method of fmelting lead ore there is no ap- |)earance of the fulphur it contains,

it

( 286 ) it is confumed by the flame of the furnace, as foon as it is feparated from the ore ; an attentive obferver may, indeed, by looking into the furnace diflinguifn a diverfity in the colour of, the flame, at diflferent pe- riods of the procefs ; during the flrfl: three or four hours after the ore is put into the furnace, the flame has a bluifli tint, proceeding no doubt from the fulphur which, in being fublimed from the ore, is inflamed ^ after all the fulphur is feparated fromi the ore, the flame has a whi- tifn call, and then and not before the fire may be raifed for flnifliing the operation ; for if the fire be made flirong before the fulphur be difperf- ed, the quantity of lead is Icfs, pro- bably, for two reafons; the fulphur unites itielf in part to the lead which

( 237 )

is formed, and by this union be* comes infeparable from it ; for the fulphur cannot without much diffi- culty be feparated from an artificial mixture of lead and fulphur, when the two ingredients have been fufed together -, — 2. The fulphur, whilil it continues united to the lead in the natural ore, renders the ore vo- latile, ib that in a flrong heat a great portion of it is driven off. Hence, very iulphureous ores fhouid be roailed for a long time with a gen- tle heat, and in this proper mianage- ment of the lire, principally confifbs the fuperiority of one fmelter above another.

An old lead fmelter informed me that he had often reduced a ton of ore to 16 hundred weight bjy roafl- ing it;, but that he did not obtain

more

( 283 ) more metal from it by a fubfequent fufion, than if he had fluxed it with- out a previous roafting. This may be true of fome forts of ore, but it is not true of very fulphureous ores. Indeed the lire may be fo regulated in a cupola furnace, as to make it anfwer the purpofe of a roafting and a fmelting furnace at the fame time : I have feen much lead loft by fmelt- ing a ton of fulphureous ore in eight hours, which might have beenfaved, if the fire had at firft been kept fo gentle as to have allowed twelve hours for finifhing th€ operation.

Sulphur cannot be feparated from lead ore in clofe vefTels, and the lead ore melts with fo fmall a degree of heat, that there may be more diffi- culty in procuring the fulphur from the ores of lead, than from thofe of

copper

( 289 )

copper or iron, however, I am far from thinking the matter impra6:i- cable, though I have not yet hit up- on the method of doing it ; and the following refiedions may, perhaps, tend to fuperfede the neceffity of colledling the fulohur in fubftance.

When it is faid that the fulphur is confumed by the flame of the fur- nace as fooTi as it is feparated from the ore, the reader Vv^iil pleafe to re- colled, that fulphur coniiils of two parts, — of an inflammable part hy which it is rendered combuflible, — and of an acid part which is fet at liberty, in the form of vapour, during the burning of. the fulphur. Now this acid, though it may be driven out of the furnace in the form of a vapour, yet it is incapable of being thereby decompofed ; it Hill vol. HI. T con-

( 290 )

continues to be an acid ; and, could the vapour be condcnfed, might an- fwer all the fame purpofes as the acid of vitriol ; iince all the acid of vitriol, now ufed in commerce, is adrually procured from the burning of fulphur. That the faft, with refpedt to the acid not being decom- pofed, is as I have ftated it, may be readily proved. The fmoke which iiTues out of the chimney for fom.e hours after each freili charge of ore has a fufFocating fmell, perfectly re- fembling the fmell of burning brim- ilone, and if a wet cloth, or a wet hand be held in it for a very ihort fpace of time, and afterwards appli- ed to the tongue, a Urong acid will be feniibly perceived. Various me- thods may be invented for conden- iing this acid vapour, and, probably,

more

( 291 )

more commodious than the follow- ing one, which, however, I will juft take the liberty of mentioning, as, if it fhould not fucceed, the trial will be attended with very little expence. Suppofing then an horizontal chimney to be built, let the end far- thefl from the fire be turned up, by a tube of earthen ware, or otherwife, fo that the fulphureous acid may ilTue out in a direction parellel to the £ue of the chimney, and at the dis- tance of about a foot and an half a- bove it. Let a number of large globular veffels be made of either glafs or lead, each of thefe globes muft have two necks fo as to ba capable of being inferted into one another ; let thefe veiTels be placed on the flue of the chimney, the neck of the firft beins: inferted into T 2 the

( 292 )

'the tube through which we have fuppofed the fulphureous acid to -iffue, and the neck of the lad being left open, for fear of injuring the draught of the furnace. Let each of thefe globular veflels contain a fmall quantity of water, then it is con- ceived, that the heat of the flue will raife the water into vapour, and that this watery vapour will be the means of condeniing the fulphureous acid vapour, if not wholly, at lead in fuch a degree as may render the un- dertaking profitable. When the ful- phur is all confumed, the draught of the furnace may be fufiTered to have its ordinary exit at the end of the horizontal chimney, by a very ilight contrivance of a moveable damper. Since the firll publication of the preceding Effay, I have feen

C 293 >,.

an horizontal chimney at the copper works near Liverpool, where every- thing J had faid concerning the pro- bability of faviiTg fulphur by roail- ing lead ore, is verified with refpedt to copper ore-: and I believe a patent has been^ granted to fome individual for this mode of collediing fulphur. Sulphur might be obtained witb equal facility from the fyrites which is found amongil coal, and this ap- plication of the pyrites might, pro- bably, be more lucrativ^e than the prefent one — -making green vitriol/^ A third circumftanee, which re- quires the utmoft care of the lead fmelter, is the leaving as little lead aS' poffible in the flag. Near ever3r fmelting houfe there are thoufands- of tons of flagjVvhirGh, when properly^ T-3, allayed^

* Vol. I. p. 229,

( 294 ) aflayed, are found to yield from one eighth to one tenth of their weight of lead ; though no perfon has yet difcovered a method of extrad:ing, fo much from them when fmelted in large quantities ; and indeed the fmelters are fo little able to obtain, all the lead contained in them, that in many places they never attempt to extradt any part of it : in fome places, where they do attempt it, I have known the proprietor of the Hag allow the fmelters 20s. for every pig of lead they procured of the va- lue of 38s. befides furnifliing them with fuel J and' yet the men employ- ed in fuch an unwholefome bufinefs, feldom made above ys. a week of their labour. This fufion of the Hag of a cupola furnace is made, as has been mentioned, at a hearth fur- "^ nace ;

C 295 )

nace ; the coal cinder, which they ufe as fuel, and the flag are foon melted by the ftrong blaft of the bellows- into a black mafs, which, when the fire is very ftrong, becomes a pcrfedt glafs ; this black mafs, even in its moll liquid ftate, is very tenacious, and hinders many of the particles of lead from fubfiding, and ic being from time to time removed from the furnace, a coniiderable quantity of lead is left in it^ and thereby loll^ A principal part of the lead con-- tained in the flag of the cupola fur- nace, is not, I apprehend, in the form of a metal, but in the form of a, litharge or calcined lead ; a portion of the lead, in being fmelted from its ore, is calcined by the violence of the fire ; this calcined lead is not only very vitrifiable of itfelf, but it T 4 helps:

( 296 )

helps to vitrify the fpar which k mixed with the ore, and thus eonfli- tutes the liquid fcoria ; might it not be ufeful to throw a quantity of char- coal duft upon the liquid fcoria in the cupola furnace, in order that the calcined lead might be converted into lead, by uniting itfelf to the iniiammable principle of the char- coal ? — Iron will not unite with lead, but it readily unites with ful- phur, and when added to a mixture of lead and fulphur, it will abforb the fulphur, leaving the lead in its metallic form ; might it not be ufe- ful to iiux fulphureous lead ores in conjund:ion with the fcales or other xefufe pieces of iron, or even with fome forts of iron ore ? ■ The

fmelter's great care ihould be to ex- trad as much lead as pofTible at the

firft

( 297 ) firft operation of fmelting the ore, and to leave the flag as poor as pof- fible; but if he fliould ilill find either the flag of the cupola furnace, or that of the hearth furnace, contain- ing much lead, (as that even of the hearth furnace certainly does),, he may, perhaps, find it v/orthhis while to reduce the flag into a powder by a (lamping mill, or by laying it in highways to be ground by the carts, or by fome other contrivance^ and then he may feparate the ftony part of the flag from the metallic, by waflii-ng the whole in water, inafmuch as the metallic part is far heavier than the other.

I eftimated the weights of feveral pieces of flag, and found them to differ very much from each other ; this difference is principally to be

at-

( 29S )

attributed to the different quantities of lead left in them.

Weight of a cubic foot of

Avoir, oz. Slag from a cupola furnace, where 1

no lime was ufed - - - J ^ ' ^

Black flag from a hearth furnace - 3652

Another piece - « - - 3612 Black flag from another hearth fur- I g

nace — ftruck fire with fleel J ^^'

Blafs glafs flag - - - - -, 3371

This may not be an improper place to add a word or two concern- ing the Derhyjhire 'Toadfioney which- conftitutes one of the principal flrata in the mining country,* and which is fuppofed to have been in its origin a flag thrown out by a volcano. It perfedtly refembles fome of the fpe- cimens, I have feen, of one of the forts of the lava of Vefuvius, not only

in- * See Vol. II. p. 2o6r

C ^99 )

m the hardnefs of its texture, and

blacknefs of its colour, but in its weight ; a cubic foot of fome forts of Derbyihire toadllone weighing more, and of other lefs than a cubic foot of the Vefuvian lava, which it - refennbles. The ftreets of London have fome of them been paved, of late years, with a toadftone from Scot^ land, of the fame nature as the Der- byihire toadftone ; and the ftreets of Naples have for many centuries paft^ been paved with the lava from Ve- fuvius which refembles toadftone^ Neither the Derbyihire toadftone, nor that fort of Vefuvian lava which refembles it, feem to have experienced in their formation any great degree of heat, they are but in a half vitri- fied ftate ; the toad-Hone I have fre- quently melted in a fmith's forge

inta

( 300 ) into a black glafs, and the Vefuvian lava gives a glafs of the fame kind. The air has a manifeft adtion upon tlie Derbyfhire toadftone, for it not only waftes away the fpar which is found in the blebs of fonfie forts of toadftone, but it reduces into a browniih mouldy fit for vegetation, the moil hard and compad: forts i the Vefuvian lava is fubjcdt to the fam.e change from the optcration of the fame eaufe.

Weight of a cubic foot of

Avoir. oXi

Toadllone hard and free from blebs 2884

Vefuvian la\'^ refembhng toadftone 2865

Iron flag, a greenilh glafs - » - - 2843

Iron flag, a brov^'nilh glafs - - - - 2729.

Iceland cryflal —-- Mr. Cotes - - - 2720

Toadllone, decaying - - - - - - 2680

Another piece -- 2662

Another piece - - - ^ - - - - 2558

ESSAY

E S S A Y IX.

^OF SILTERXXTRACXEID FROM LEAD,

WE have no filver mines, pro- perly fpeaking, in Great Bri- , ■tain^ but we have plenty of lead, from which filver is, in fome places, .extra6led with much profit. If the method of doing this had been known to the 2inc\ent Britons, it might have freed our country from the reproach of Cicero, who tells his friend Jtticus, that there was not a fc-rupie of filver 2. in

( 302 )

in the whole ifland ; * and in another place^ he fays, that he had heard there was neither gold nor filver in B7'itain., f The Romans had a very imperfecc knowledge of this country in the time of Cicero ^ fo that his ac- count of the matter may not, per- haps, deferve to be much relied on ; we are certain, at leail, that about fifty or fixty years afterwards, both gold and filver were reckoned by Strnho amongft the products of Bri- tain-,% hence, if the Britons did not tinderftand the art of extracting fil- ver from lead at the firfl invafion of

the

* ., — etiam illud jam cognitum eft, ne cfae argenti fcrupulum effe ullum in ilia infula (Britann.) Epifl^adAtt. L. IV. E. XVII.

t Epift. Fam. L. VII. E. VII.

:*: L. IV. p. 305, .-- See alfo Tacitus' Life ^f Agricola.

( 3^3 )

the Romans, they foon learned it from their conquerors, and this be- comes more probable, if it be ad- mitted, that filver v/as coined in Bri- tain in the time oi Auguftus.^

Silver is fo commonly contained in lead, that it is eileem^d a very great curiofity to meet with lead which is entirely free from it: it has even been afTerted, that there is no lead in the world, except that of Villach in Ca- rinthia^ which does not contain fil- ver. t

The more ancient alchemifls, not knowing, probably, that fiiver was fo generally contained in lead, and

yet

* Sir John Pettiis Fod Reg.

f II n'y point de plomb au monde, hor- mis celui de Villach que ne contienne de V argent. Lehmao fur les Mines, Vol. I. p. 174. —See alio Philof, Tranf, for 1665. p.

10*

( 304 )

yet obferving, that lead, when treated according to their procefTes, often gave a portion of filver, were of opinion, that they could convert lead into filver.* This was an eafy miilake, and if they had obtained a portion of gold, they would, no doiibt, have concluded, that they had tranfinuted the lead into gold ; fince there is no metal, perhaps, which does not coii- tain a fmall quantity of gdld, or from which gold may not h^ feparated hj long calcination.

Lifler had long ago obferved, that all thfC Englifh lead contained filver; and he fpeaks as having, by his own experiments, proved the exiflence of filver in the lead of at leafl thirty difiTerent mines 3 f nor has any per-

fon

* GebriChem. L. 1. C. XIX.

f Lifler de Fontibus, Cap. 11. S, 9, 10.

( 305 ) Ion fince his time, found lead wholly free from filver. The Z)^r^jvy^/>d' lead has been faid to contain, two grains of filver in a pound of lead. * Every general obfervation of this kind is liable to much contravention from particular fafe ; becaufe the quantity of filver contained in lead,, is not only different according as the lead is fluxed from the ore of differ- ent mines, but it is very poflible in an affay of the ore of the fame mine,, to meet with one piece of ore which Ihall afford a lead yielding eight or ten times as much filver,. as another piece would do< This diverfity arifes from the ore itfelf being variable in quality indifferent parts, of the fame mine ; and even different lumps of ore, though contiguous to each other^

, will * Oper. Min, Explicata, p. 263,

'^ol. III. U

( 3o6 )

^ill often yield very diiferent quaft^ titles of filver, from the fame quan- tity of lead. This obfervation may- explain the reafon of the very oppo* iite teflimonies, which have been fometlmes given in courts of juflice^ concerning the richnefs of a mine from particular allays ;. the plainriffs and defendants^ where the iffue to be tried was the quantity of filver^ having been fevcrally interefted in getting the beft and the worfl pieces of ore aifayed, in order to fupport their refpedive claims. There was a notable ini^ance of this with refped: to the lead mine of EJi-kyr-kyr in Cardigar/JIjirey which was dlfcovered in 1690. The law at that time ad- judged every mine to be a royal mine the metal of which contained enough of gold or filver to compenfate the

charges

C 307 )

charges of refining, and the lofs of the bafer metal in which they were contained. In confequence of this law the patentees of royal mines laid claim to the mine of EJi-kyr-kyr which was rich in fllver, and they produced proof in Weftmtnfter-hallj thai the lead of that mine contained to the value of (ixty pounds of iilver in every ton, whilil the proprietor, produced proof that it only contain- ed to the value of four pounds of Iilver in a ton. * '

I have been informed by an in- telligent perfon, that there are fome lead ores in Great Britain^ which, . though very poor in lead, contain ' between three and four hundred' ounces of filver in a ton of the lead. It is not to be expeded that the pro- -

prietors > * Some Account of Mines, p. 27. U 2

C 3oS ) pEietors of thefe^ or of any othsr mines rich in iilver^ Ihould be for- ward in declaring, to the world the quantity of lilver which they con- tain. The proprietor indeed of a lead mine containing filver, may work the fame^ without any appre- henlion of its. being taken from him^ under the pretence of its being a royal mins; yet the crown^ and pep- fons claiming under it, have the right of pre-emption, of all the ore which may be raifed. There was an adt of parliam.ent paiTed in the fixth year of JVilliam and Mary^ intitJed,— An adt to prevent difputes and contro- verfies concerning royal mines. — This ad: gave great quiet to the ful> ied by declaring, that every propri- etor of a mine of copper, tin, iron^ or leadj^ Ihould continue in pofleffion

of

( 309 )

of the faid mine, notwithflanding its

being claimed as a royal mine, from its containing gold or filver : but it .further enadted, that their majeflies, their heirs and fucceffors, and all claiming under them, fhould have the privilege of purcliaiing all the ore whicii fhould be raifed out of fuch a mine, at the following prices; this is to fay, paying for all ore wafhed, made clean and merchant- able, wherein is copper, after the rate of fixteen pounds a ton ; for tin ore (except that raifed in Devonlhire and Cornwall) forty fhillings; for iron ore forty fhillings ; and for lead ore nine pounds a ton. This ftand- ard price of nine pounds a ton for lead ore was, at the time it was fix- ed, much higher than the ordinary price of ore^ ^n which there was no u 3 filver

( 310 )

filver worth extradlng ; the beft kind of Derbyfhire lead ore, being at prefent, generally worth no more than feven pounds a ton. It may deferve however the coniideration of the legiilature, whether the elaufe in the forementioned at3: refped:ing the right of pre-emption ihould not be wholly repealed; as there may be many lead mines in England very rich in filver, but which, on account of the difficulty of working them., cannot.be entered upon with advan- tage, whilft this right fubfifts. At many lead mines, moreover, there are large, quantities of fteel-grained ore raifed together with the ordinary fort, now it generally happens that the fteel-grained ore is much richer in filver than the ordinary diced ore -of Derbyfhire ; and it might, if fepa-

ratcd

( 311 )

rated from the reft, be worked for filver ; but whether from an appre- -henfion of the operation of the claufe we are fpeaking of, or from mere ignorance or inattention," all the forts of ore are mixed and fmelted together.

Silver has formerly been cxtradted from lead in a great many places ia this iiland. In the reign of Edward I. near 1600 pounds weight was ob- tained, in the courfe of three years, from a mine in Devon/bire, which had been difcovered towards the begin- ning of his reign ; this mine is called a lilver mine by the old writers, but it appears to have been a mine of lead which contained lilver.* The

lead

* Hollingfhed's Chron. Vol. II. p. 316.

See alfo in the fame author a further account

of XJ 4

lead mimes in Cardiganjhire have at

different periods afforded great

quantities of filver : Sir Hugh Mid-

4leton is faid to have cleared from

them two thoufand pounds a

month, '^ and to have been enabled

thereby to undertake the great work

of bringing the new river from Ware

to London ; and in allufion, probably,

to thefe two great circumftances of

his life, there are painted upon fome

of his piiftures the two termS'—fonfes

— -fodin^, Thefe fame mines yield-

^d^ in the time of the great rebellion,

eighty ounces of iilver out of every

ton of lead, and part of the king's

:army was paid with this Iilver, which

was loF filver extraded from the lead in Devonfhire •and* Corn vvali 'in the time of Edward I'll. p«

^13.

* .Oper, Min. explic. p. 245.

( 313 )

ivas minted at Shrewjhury* -f- A minit for the coinage of Welch filver had before that time been eftabliihed in i6'^y at AheryftwHh\ the indenture was granted to "Thomas Bujhel for the coining of half-crowns, Ihillings, fix-pences, two-pences, and pennies, and the monies were to be ftamped with the oftrich feathers on both fides*. In the year 1604 near three thoufand ounces of this Welch bul- lion were minted, at one time, at the tower if. Wehfter in his hiftory of metals, publiihed in 1671, makes mention, from his own knowledge, of two places in Craven^ m the weft- riding of Torkjhhe, where formerly good filver ore (lead ore abounding

ia

-f- Sir J. Pettus, Effay on Metal. Works, * Rym. Faed. Tom. XX. 164. % Some Account of iviiues. p. 6.

( 3H )

in filver) had been gotten. One .of

the places was Brunghill moor in the pariih of iS/^/W^«r;/, the ore of which held about the value of fixty^feven pounds of filver in a ton : the other was Skelkorn field within the townlhip oi Rimmington in the parilh of Gif- hum I it had formerly belonged to one Pudfey^ who is fuppofed to have coined the filver he got out of- his mine, there being many ihillings in that country which the common people called Pudfey 'schillings.*

There is not at prefent any place in Derhyjhire where filver is extradled from lead. A work of this kind was eftabliihed a few years ago not far from Matlock^ and the lead yield- ed fourteen ounces of filver from a ton; but the mine which afforded

the f Webfler's Metal, ^lu

( 3^5 )

the ore was foon exliaufted, or be- came too difficult to be worked with profit. There is a lead mine in Patierdale ne^v Kefwick^ which yields between fifty and fixty ounces of fil- ver from a ton of the lead, the ore of this mine is reckoned to be poor in lead; and indeed it is very common- ly obfervedj that the pooreft lead ores yield the moft ftlver, fo that much filver is probably thrown away, for want of having the ores of the pooreft fort properly affayed. The quantity of lead fmelted an- nually in Derbyfhire, may be efti*^ mated at 7500 tons upon an average,; fifty years ago the average was, pro- bably 1 0000 tons a year, but we put it high enough in fuppoiing it, at prefent, to amount to 7500 tons : I have never been able to get any I proper

( 31^ )

iproper information, concerning the

quantity of lead annually fmelted in other parts of Great Britain, but for the illuftration of the fubjedt we are upon, let us fuppofe that in the whole kingdom 30000 tons of lead are annually fmelted, and that at a medium each ton of lead would yield 12 ounces of filver ; then would there be, if all the lead was refined, a faving of three ounces of filver from each ton of lead, or ninety thou- fand ounces in the whole ; our Eng- lifh workmen reckoning that nine ounces of filver are full adequate to the expence of refining a ton of lead, added to that of the lead which is loft during the operation. ^ The general manner of extrading lilver from lead is every where the fame ; it is very fimple, depending

upon

C 317 ) ^

upon the different effential proper- ties of the two metals. — It is an^ effential property of lead, when melted in the open air^ to> lofe its metallic appearance, and to- burn away into a kind of earth.-— It is- an effential property of filver not to:^ burn away, or to lofe its metallic ap-- pearance when expofed to the adtion of the ftrongeft fires, in the open air.. Hence,, when a mafs of metal con- fining of lead and filver, is melted^ in the- open air, the lead will be burned to afhes, and the filver re- maining unaltered, it is eafy to un- derftand how the filver may be es- tradted from the lead; for being hea- vier than the afhes of the lead, and incapable of mixing with them,, (fince no metal is mifcible with an earth), it will fmk to the bottom of

tha:

( 3^8 )

the veffel in which the mafs is melt- ed. Iron, tin, and copper, refera- ble lead, in being convertible into a kind of aihes, when t xpofed to the adtion of air and fire,, and gold re- fembles filver in not undergoing any change from fueh adlion ; hence ei- ther gold or filver, or a mafs con- lifting of both, may be purified from any or all of thefe metals by the mere operation of fufion ; . for thefe metals will rife to the top of the vefFel, in which the fufion is made, in the form of an earth or drofs, leav- ing the gold or filver pure at the bottom.

The ancients certainly knew that filver could be purified from the bafe metals by the force of fire.— ^e houfe of IJrael is to me become drojs : all they are hrqfsy (copjier) and

titiy

( 319 )

tiHy and iron^ and lead^ in the tnidfl of the furnace ; they are even the drofs of filver:-^ And as we read of filver being purified feven times in a fur- nace of earth, "i- it may, perhaps, jbe inferred, that the method of refining filver which was then in ufe, con» fifled in reducing the bafe metals into earth, by a repetition of the procefs of fufion. This inference^, it mufl be owned, is rendered doubt- ful by a paffage in Jeremiah \—the lellows are burned i the lead is confumed of the fir e^ the founder melteth in vain.^ — This paffage is fomewhat ambi- guous, and interpreters tranfiate the original Hebrew differently, buc inoil of them coHed: from it, that the

founder

* Ezek. xxii. i8. f Pf, xii. 6,

% Jerem. vi. 2^

C ?20 )

founder added lead to the mixetf mafs which he wanted to refine..

Lead, when reduced to an eartk by being^ burned in the open air^ may, in a ftronger degree of heat, be converted into a yellowilh glafs, *

which

* Other metallic fubftances yield coloured glafles, either when vitrified alone, or in- conjundion with pure glafs. In enamel and china painting they prepare rofe red and purple colours from gold ; fcarlet reds from iron, or vitriols that partake of it ; greens from copper ; blues from cobalt ; blacks from magnefia, zafTer, and fcales of iron ; yel- lows from filver antimony, Naples yellow, and crocus martis j white from tin. Tb^ fame fubftance yields different colours, ac- cording to the degree of heat to which it is expofed ; thus, the green colour of common glafs bottles, which proceeds from the iron, contained in the fand and vegetable alhes from which the glafs is made, is changed, into a blue by a Wronger degree of heat.

C 321 )

•which has the property of greatly contributing to the eafy vitrification of all earthy fubftances ; hence, when gold or filver are mixed with iron, copper, or tin, it is ufual to add to the mixed mafs a quantity of lead, in order to accelerate the purifi- cation; for the lead will be converted into glafs, and this glafs will vitrify all the extraneous fubftances with which the gold or filver are polluted, v/ithout exerting the leaft adion upon the precious metals themfelves.

I do not know upon what grounds one of the moft diftinguifhed cho- mifts of the age has afferted, '^ that the refining of gold and filver mere- ly by the adion of the fire was the only method anciently known ; " f

and

>t Chem. Did. by M. Macquer. artic. Refining.

VOL. irr. X

( 0^2 )

and that the doing it by the addition of. lead, is a difcovery with which the ancients were unacquainted. Not to inlift upon what has been quoted from Jeremiah -, in Diodorus Skulus there is a very minute de- scription of the m.anner of working fome gold mines in the confines of Egypt and Arabia \ this defcription was probably written on the fpot ¥/hen he vlfitcd that country, but the mode of operation feems to have been derived from a more early pe- riod 5 as the difcovery of the mines is attributed by him to fome of the moft ancient JEgyftian kings ; amongft other particularities, he takes notice of their melting the mineral in con- jun6lion with a little tin, fome fmall portion of fait, and a lump of lead, *.

Strabo • Diod, Sic. Lib, HI. p. 183 — ^^189,

C 3^5 ) Straho quotes Poly bins as fpeaking of •a filver ore, which, after being five times waihed, was melted with lead^, and became pure filver. Unfortu- nately this part of the works of Po- lybius is loft, or we might have had a more circumftantial knowledge of the proceffes by which the ancients extraded filver from its ores, as Strabo fays, that he omitted Poly- bius^ account of this matter, becaufe of its prolixity, f PJiny probably has an allufion tx) the ufe of lead in refining filver, when he fays, that a filver ore in the form of an earth could not be melted except in con- jun6lion with lead or the ore of lead.* a more diligent fearch into the writ- tings of the ancients, would, doubt-

lefs, f Strab. Geo. Lib. II. p, 221, * Plin, Hifl, Nat. Lib, XXXIIL C. VI. X 2

( 3^4 )

lefs, jfurniili more authorities upon the pointy but thefe may be fuffi- cient to induce us to believe^ that they.were not unacquainted with the ufe of lead in refining gold and fil- ver. — But to return to the manner of extracting filver from lead.

The veiTel in which the work- men melt the mafs of filver and lead is. of a fhallow form, that a large fur- face of the melted mafs may be ex- pofed to the air, it is made ufually of four meafures of the ajQies of calcined ^bones, and of one meafure of un- i^^afh.ed fern afhes, and is called a 4eft-.^ This vefTel is very porous^

but

* Tefts are fometimes made of clay and other materials, and tnetaliurgic writers of- ten order the wood afhes to be wafhed, left the alkaline falts which they contain fhould .tend -to nitrify the tefl j but a very good re- finer

C J^5 )

but not fo much as to imbibe the metal, whilft it continues in the form of a metal -, but as the earth, into which the lead is foon reduced by the adlon of the fire, becomes melt- ed, the tefl imbibes a portion of it in that liquid ftate, the other por- tion is driven off (as cream is blown off from mxilk) from the furface of the melted mafs, by the blaft of a. bellows. The liquid, half vitrified^, earth of lead, which is thus driven, off, concretes into hard, maffes of a- fcaly texture, and is called in that flate litharge, or filver ftone,^ from, the manner of its being produced,, or from an idle notion of its con-

taining

finer at Holywell informed me, that he al- ways ufed the aflies without wafhing them, as the velTel became thereby lefs apt to crum- ble into pieces-.

X 3

( J26 )

faining much filver. The litharge which is nril fomned is whitiih, that which experiences a greater degree of heat is red 3 the colour of the litharge is aifo influenced by that of the other metals;, v/hich may chance to be mixed with the mafs of lead and iilver. When the furface of the melted mafs becomes white, and throws up no more litharge, the ope- ration is finiilied; but as the re- maining filver is not quite pure,. fmce it contains a fmall portion of lead, from whicli the degree of heat re qui free fljr melting the mixed m.afs cannot readily fi^ee it^ it is taken to a refining furnace, and r'endered quite pure, at leafl fi-om lead, by cup ell a- tion. This procefs confiils in miclt- ing. the iilver obtained from the firft operation^ in a vefTel made of the

fame

( 3^7 )

fame materials as the teft, and which, from its refemblance to a wide mouthed cup^ has been called a cupel. The cupel being expofed to a ilronger heat than the tefl:, the lead which had efcaped the a6lion of the fire on the tell, is now driven out from the filver, and being converted into litharge, is abforbed by the cu- pel, and by this means the filver'is purified from every mictal except gold; for it is not neceffary, on this occa- fion, to remark, that a minute por- tion of copper, when there happens to be any in a mafs of filver and lead, probably efcapes the a6lion of the fire in cupelling gold or filver.

There are feveral fmelting houfes at Holywell in Flintjhirej where filver is extraded from leads Mr. Fenncnt^

has

* Tour through Wales.

X4

( 3^8 )

has given the following account of the" quantity of filver extra6t€d at one of the largeft of thefe houfes in the courfe of fix years.

ounces. ounces.

Year 1754 - 12160 Year 1774 - 5693 3755 - 1276 1775 - 6704

^756 - 7341 1776 - 4347

The filver obtained from lead at Holywellj is chiefly fold to the ma- nufadurers at Birmingham and Shef- field, Much filver is alfo extradled from lead in Northutnherland.

At Holywell they ufually work off three tons of lead at one operation, the quantity of filver which they procure^ is variable according' to the richnefs of the leadj a few years ago they were refining lead from an ore found in the Ifle of Man^ and it gave them about 60 ounces at every

ope-

( 3^9 )

operation, or 20 ounces in a ton of the lead.. The litharge ordinarily obtained from three tons of lead amounts to 58 hundred weight; this litharge may either be changed into red lead by calcination, or it may be reduced into lead again by being fluxed with charcoal, or any other m.atter containing, the inflammable principle ; * but when it is reduced they feldom obtain more than 52 hundred weight of lead, f fo that by

ex-

* Lead from litharge is, generally fpeak- ing, worth five fhillings a ton more than ore lead, as the plumbers elleem it fofter and litter for making fheet lead; yet the litharge lead from the ore of the Ifle of Man here mentioned, was found quite unfit for making fheet lead, on account, probably, of the ore having held other metals belides iilver and lead.

f In the foreign works they eflimate the lofs of weight, which the litharge fuflains in

being:

( SS'^ ) extradling the filver^ there is a lois

of eight hundred weight in three tons of lead. It has been faid that the Dutch can extradl: the filverfrom three tons of lead> and not lofe above G.ii- hundred weight * upon convert- ing the litharge into lead, and that this fuperior fkill, : aided, probably, by their fuperior induflry, enabled them to purchafe our lead, and to extra 61 the filver from fuch as could not be refined here with advantage : I have been informed^ however, by an experienced refiner in Derbyfhire, that he could extract the fdver with- out ioling quite fo much as fix hun-

being reduced into lead, at a lixth part of the weight of the litharge, or 9I hundred weight from 53 hundredweight of litharge. Ellais des Mines, Tom. II. p. 401. * Webller's Metal, p. 233.

I dred

C 331 )

drcd weight in three tons of lead; I make no queftion that the lofs de- pends, in fome meafure, on the qua- lity of the lead. It has been re- marked before, that lead, which does not contain nine ounces of filver in a ton, is not thought v/orth the re- fining ; the fmailefi: quantity which can be extradbed .with profit, m^uil depend much upon the price of lead, all expences attending the feveral proceiTes being the fame. For eight hundred weight of lead, which may be aiTumed at a medium as the lofs fuftained during the operations of refining and reducing^ is worth 6L when lead is at 15I. a ton, and it is worth only 4L 16s. when it is at 12I. a ton. The value of 27 ounces of filver, which we fuppofe to be the quantity feparable from three tons

of

C 3J2 3

of lead, is 7I. los. 9d. at 5s. yd.

an ounce; hence^ the difference be- tween the value of the filver obtain- ed, and that of the lead loft, would, when lead is at 15I. a ton, be il. I OS. 9d. and when lead is as low as 12I. a ton, it would amount to al. 14s. pd. In the times of Sir John FettuSy the ufual allowance for wafte in refining and reducing of lead, was three hundred weight in a ton, or nine hundred weight in three tons,, and the lead was valued at 12I. a ton,* fo that lead has altered very little in its price in the courfe of above one hundred years.

Silver is here valued at 5s. yd. an ounce; this requires fome ex- planation. A pound of fiandard filver in England, confifts of i.i

ounces

* Fodinae Reg. p. 10,

( 333 ) •ounces and 2 penny weigb-ts ^i fine filver, and of 18 pennyweights of copper \ in other words, every mafs of ftandard filver confiiling of 40 parts by weight, is compofed of 37 parts of fine filver, and of 3. parts of copper ; the copper is called the al- loy. All nations ufe fome alloy both in their gold and lilver ; partly with a view of rendering thefe metals harder, -and partly becaufe it would require much labour and expence to free them wholly from that fmall portidh of copper, which, in their ordinary flate, as fluxed from their ores, they are generally found . to contain. . A pound of ftandard {A^^v is coined into 62 fhillings, hence the Mint price of an ounce oi. ftandard filver would be a twelfth part of 62 Ihillings, or 55. izd. From hence

. ' it

( 334 ) it might be lliev/n, by the rule of proportion, that the -^z/?ri^^/ price of an ounce of fine filver, which con- tains no copper, will be 5s. yd. at the lead. The market price of fil- ler bullion does not wholly depend on the mint price^ it can never be lower than that, but, from the ope* ration of various caufes, it may ex- ceed it. •\— -Standard gold with us confifts of 1 1 parts o^ fine gold, and .of I part of copper^ or of a mixture of filver and copper -, and a pound or 12 ounces of Handard gold, is ^coined into 44I guineas 3 hence the price of an ounce of ftandard gold is ^1. 17s. lofd. and the prke of an ounce Q^ fine gold is 4I. 4s. iijd. Foreign gold trinkets llain the liand^ more> and have a more cop- pery f EfTay on Money and Coins, p. 2. & 55,

( 33S ) pcry look than Englilli ones; and

in fa6t they are made of gold which is alloyed with a much greater pro- portion of copper, than the.ftand- ard gold of England ; yet, when an enamel is to be fixed on gold, one of the mofb experienced of the fo~ reign enameilers, f recommends the •ufe of gold, which has the fame al- >loy as the Englijfh ftandard gold, or two parts alloy, and twenty-two parts of fine gold.

Copper communicates a fmell both to gold and filver. Tht Ro- .man fpecula,^ which they ufed as look- ing glaffes, in Fltny^.% time wer^ commonly made of filver, but the fdver was alloyed with much cop- per; for we find a cunning waiting .maid in Plautus advifing her mif-

trefs

.f M. de Montamyj Traite des CoLeurao

i S36 )

tre{s to wipe her fingers after hav- ing handled a fpeculum^, left her paramour from the fmell of her fingers fhould fufpedt her of having received filver from fome other lover.

Ut fpeculum tenuifli, metuo ne oleant argene

turn manus. Ne ufque argentum te accepifle fufpicetur

Philolacles. *

* Plant, Mofl. Aa. I.

ESSAY

ESSAY X.

OF RED AND WHITE LEAD,

IF the reader does not know what minium or red lead is, I v/ould wifh him to fend for a few ounces of it to his painter or apothecary. — Suppofing him to have a parcel of ••ed lead before his eyes, the firft tning which will fl-rike him is its vi- vid colour .verging a little towards oranges if he crumbles it betwceu VOL. III. Y b.i^

( 33^ ) _ his fingers, he will find it to be an

almoft inapalpable powder ; if he poizes it in his hand, he will per- ceive it to be much heavier than either brick dufl or red ochre, with which fubftances it is fomc- times adulterated ; if he compares it with a piece of lead, he will be aftonifhed how it can be either pro- duced from lead, or be capable of being, by a very flight operation^ reduced into lead again.

It has been mentioned in the pre- ceding EfTay, that red lead is made from litharge at Holywell : this red lead which is made from litharge is not perhaps, in all its properties, of quite the fame kind with that which is made diredly from lead; at leaft I have been informed, that the mak- ers cf flint dafs, who ufe much red

lead

( 339 )

lead in the compofition of that glafs, are of opinion, that the litharge red lead does not flux fo well as that which is made from the dired calci- nation of lead, as is praftifed in Derhyjhire, There are in that county nine red lead mills or furnaces, all of which are much upon the fame conflru6lion.

The furnace is very like a baker's oven, its vaulted roof is not at a great diilance from the bottom or floor, on each fide of the furnace there are two party v/alls, rifing from the floor of the furnace, but not. reach- ing to the roof; into the intervals between thefe walls and the fides of the furnace the pit- coal is put, the flame of which being drawn over the party walls and firiking upon the roof, is from thence refleded y 2 down

( 340 ) down upon the lead, which is placed in a cavity at the bottom, by which means the lead is foon melted. The furface of melted lead, when expofed to the open air, inilantly becomes covered with a dufky pellicle ; and this pellicle being removed another is formed, and thus by removing the pellicle, as faft as it forms, the great- c^ part of the lead is changed into a yellowifh green powder. This yeilowifh powder is then ground ve- ry fine in a mill, and being wafhed, in order to feparate it from fuch parts of the lead as are ftill in their m,e- tallic ftate, it becornes of an uni- form yellow colour, and, when it is dried to a proper confiftency, it is thrown back again into the furnace, and being conftantly llirred, fo that all its parts may be expofed to the

adlion

( 34t )

adlion of the flame of the pit coal, in about 48 hours it becomes red leady and is taken out for ufe.

The colour of the red lead admits fome variety, which is occafioned by the different degrees of heat. If the heat is too fmall, inftead of red it is yellow or orange coloured j if it is too great the red colour is changed into a dirty white, between thefe tv/o extremes it is fubjed to fome diver- fity of fhades of red, which cannot well be noticed or defcribed, except by thofe who are engaged in the making of it.

It has been alTerted, that the re- verberation of the flame and fmoke upon the furface of the lead, is not & a neceflary circumftance in giving it ■jka red colour,* but that it will ac-

i

quire * Infllt, de Chym. par M.Demachy, p. 522, Y 3

( M^ ) quire t!iis colour by a long calci- nation without coming into contact with the flame- The truth of this -afiertion I think may be doubted. I have more than once calcined lead for above 60 hours^ without fuffer- ing the flame of the fire to touch it during any part of the procefs, but by this method I could never obtain any thing better than a dirty red, refem.bling the red of brickduil, which is very different from the colour of red lead; and even this dirty red was changed into a yellow colour, by augmenting the degree of heat with which the lead had been calcined. The method of making red lead is very well underftood in England and Holland y but not in France; and the French workmen are

of

( 343 ) of opinion, that it cannot be made by the flame of wood fires. *

During the making of red lead, part of it is volatilized, there rifes up from it a vapour, which attaches itfelf to the roof of the furnace, and forms folid lumps. Thefe lumps arc of a yellowifh white colour mix- ed with pale green and fome reddilli itreaks, wherein are frequently fmall red cryftals, refembling fuch as may be artificially formed by fubliming fulphur and arfenic together. The workmen call the whole of what is feparated from the lead in the form of fmoke, fulphur : when this fub- limed matter is detached from the roof of the furnace, the red parts

* Mem. de I'Acad. des Scien. 1770.— Elemens de Mineral, par M, Sage. Vol. II. p. 248.

y 4 are

( 344 ) are converted, by a fubfequent pro- cefs, into red lead ; and the yellow ones are fent to the fmelting fur- naces, to be run down again into lead. The quantity of this fubli- mate announts to about five hundred weight in making one hundred tons of red lead. The proportion here afiigned is not wholly to be relied on, fince the frnoke arifing from the lead forms itfelf into larger mafTes, and in lefs time, when it is not con- flantly fwept from the roof of the furnace than when it is -, and the workmen endeavour to keep the roof as free from it as they can, be- caufe a fmall portion of it injures the colour of a large quantity of the red lead with which it happens to be mixed^

A ton or twenty hundred w^eight

of

( 345 )

of lead generally gives twenty- two hundred weight of red lead, notwith- flanding the lofs of fubftance which the lead evidently fuftains from the copious fmoke which arifes from it during the operation. Some authors tell usj that the increafe in the v/eight of the red lead is double what I have here mentioned : thus, Or/iri^^Z/fpeak- ing of the red lead made at Nurem- berg^ alTures us, that loo pounds of lead yield 120 pounds, and fome- times even more, of red lead.* It is not impofTible that, according to the different manners of condudins; the procefs, there may be a differ- ence in the quantity of weight v/hich the red lead acquires : I had my in- formation from fome of the mofl

expe-

* Orfch. Metal. French Tranf. p. ico.

M. Sage's Mine. Vol. II. p. 384,

( 346 )

experienced makers of red lead in Derbyiliire. There have been great difputes amongil philofophers, to vvhat principle this increafe of weight fhould be afcribed^ fome have attri- buted it to what they call the matter of fire; others are upon good grounds convinced, that it is owing to the abforption of the air itfelf, or of fome of the principles of which the air confiils. This hypothefis con- cerning the fixation of air during the calcination of metals, is faid to have been firft advanced by John Rey, a French phyfician, ini630j Dr, Hales was partly of the fame opinion;* and Dr. Pemherton very exprefsly af- firms, that calcined metals receive their increafe of weight from the air, -which " by a6ting on the inflamma-

able *r Veget. Stat,

( 347 ) ' able fubilance^ either^ in metals or other bodies, expels its from them, and unites itfelf (in part at leaft) to the remains of the body." * The ingenious labours of Dr. Prieftley and of M. Lavoifier have confirmed the conje6tures and experiments of for- mer philofophers, for they have clearly proved two points — firft, that a large portion of air may be JeparaUd from red lead, by reducing it to the ftate of a metal ^ — and fecondly, that a large portion of air is ahjorhed by lead during the calcination, by v/hich it is reduced to the ftate of red lead.f

During the calcination of lead, it is certain, from what has been faid,

that

* Pember. Chem, p. 24^. f Prieflley's Exper. and Lavoifier's EiTays, franilated by Renry,

( 34^ )

that much of its fubftance is difperf- ed into the air -, this fubftance may indeed be feen afcending as a fmoke from the furface of the lead, if the heat be fo great as to make it boil ; and in a lefs degree of heat, the va- pour which afcends from it, may be rendered vifible, by holding over it a wet iron ladle to condenfe it. But at the fame time that the lead lofes confiderably of its weight by the voladlization of part of its fubftance, it receives fuch an accellion of new matter from the air, as renders the v/eight of the part which remains, much greater than that of the whole lead which was expofed to calcina- tion. This accefiion of aerial matter may be driven off from red lead, by reftoring to it the inflammable prin- ciple which was confumed during 3 the

( ^49 ) the calcination -, but after this extra- neous matter is driven otT, by re- ducin^r the lead, Vv'e ought not to cxpe6l that the lead, which is thus .brought back to its former Rate, fhould weigh as much as it did be- fore it was calcined j becaufe that part of it which was volatilized anvi difperfed into the air cannot be reco- vered. And in fact, it was obferved in the laft ElTay, that three tons of lead, when converted by calcination into litharge, had loft two hundred weight ; this quantity, and, probably much more than this, had been vo- latilized and loft, for the rem.aining fifty-eight hundred weight confifted partly of the earth of lead, and partly of the air which had been fixed in it during the calcination J and hence, when it was reduced, it did not give

above

( 3S0 )

above fifty-two hundred weight. In calcining then, and reducing fixty hundred weight of lead, there is a lofs of eight hundred weight : a great part of this lofs is rightly referred to the volatilization of the lead, but a part alfo may juftly enough be re- ferred to the fcoria which remains after the reduction of the litharge into lead, that operation being fel- dom performed fo accurately as not to leave fome part of the litharge unreduced. I have here fpoken of the lofs of weight, fuflained during the redudion of litharge, as if it was the fame as that which red lead fuilains ; there, probably, may be fome difference between them, but the general inference is the fame s and I have been informed moreover, that there is neither increafe nor

decreafe

( 3S^ )

decreafe in weight, in converting litharge into red lead. *

In making red lead in Derbyfhire, the workmen mix one hundred weight o( flag lead with about eigh- teen hundred weight of ore lead f and they are perfuaded that this flag lead has a great efixct, in accelerating the converfion of the other lead into an earth. 5"/;/, when mixed with lead, very much promotes its calci- nation 5 and the flag lead has this

property

* This obfervation does not accord with that of the author of the Familiar Difcourfe

concerning Mines, p. 34. "20 hundred

weight of this litharge will produce. 22 hun- dred weight of red lead." Another author informs us that 20 pounds of lead will by a long calcination give 25 pounds of allies, and that thefe 25 pounds of alhes will, when ]-educed, give 19 pounds of lead, Lemery Cours de Chym. p, 145.

( 3S^ ) property In coiriinon with a mixture of tin and lead, that it does not, when melted, exhibit any colours on its furface : may not its properties, by which it is diftinguifhable from ore lead, arife from its containing zinc or tin ? We are too apt, I think, to look upon the ores of lead as con- taining only one metal; fince we are certain that they all contain two, namely, lead and filver ; and it may be, that they contain other metallic fubftances, particularly zinc and tin. In converting a ton of lead into red lead, the workmen obferve, that towards the end of the operation, a few pounds of lead are always found to remain, which cannot be changed into red lead, with the fame facility with which ordinary lead is changed. When I was firil inform- ed

( 353 ) cd of this circumltance, I confidered it in the following manner. — Der- bylhire lead, though it does not con- tain filver enough to render the ex- traction of it profitable, yet it gene- rally contains five or fix ounces in a ton : filver is not capable of being converted into an earth by the ac- tion of air and fire, when therefore a ton of lead is converted, as to its greatefl part, into red lead, why may not the fix ounces of filver contained in that lead, be left unaltered ? and may not the fuperior difficulty of reducing the laft portion of the lead into red lead, proceed from hence, that it is much more impregnated with filver, than ordinary lead is ? Under the influence of this conjec- ture, I procured from Derbyfliire, fome of the lead which remained VOL, III. Z un-

( 354 1

uncalcined in the making of reki lead, and I afTayed it for filver j but it did not contain more filver, than many fpecimens of ore lead contained.

It has been remarked, more than once, that red lead may be reduced into lead, by being melted v/ith roiin, tallow, charcoal, or any fubftance containing the inflamimiable princi- ple. The proof of this is very eafy ; a few grains of red lead being fcat- tered on a piece of red hot charcoal, will be changed into globules of kadi or if the reader, burns a com- mon red wafer in the ilamiC of a candle, holding a piece of v/hite paper under it; he will fee many red hot globules falling upon the paper, and thefe globules he will find to be lead : this lead proceeds from

the

( 3S5 )

the red lead with which ordinary wafers are coloured^ being reduced into the ftate of a metal, by uniting itfelf with the inflamnaable principle. The beil wafers are coloured with vermilion — powdered cinnabar. *

Having been difappointed in the cxpeftation of finding a large pro- portion of filver;, in the fm.all refidue of lead remaining after the conver- fion of ordinary lead into red lead \ and being unwilling to give up the notion, I v/as defirous of convincing myfelf that I had not been guilty of any miftake in the allay that I had made, by trying whether red lead it- felf did not contain filver -, for if red lead contained filver, I faw no reafon

to

* Cinnabar is an ore of quickfilver ; it is compofed of quickfilver and fulphur ; gene- rally of 7 parts of quickfilver to i of fulphur.

Z 2

( 35^ ) to be furprifed at the refidue, before mentioned, not containing more than I found it to do. I therefore re- duced a quantity of red lead into the Hate of a metal, by melting it with rofm; this reduced lead was carefully afTayed more than once, and It always afforded a portion of filver. Hence we may conclude, that the filver contained in lead, though it be not fubje6l to calcina- tion during the procefs of making red lead, iSf neverthelefs mixed with the calcined lead in fuch a commi- nuted ilate, as to efeape our fenfes ; the filver, probably, is ftill in the form of filver, but its particles are fo indefinitely fine, that they can- not be diflinguifhed in the mafs of red lead, which contains them. The method of making flag lead

has

( 357 )

has been defcribed before ; I affayed

this kind of lead feveral times, and I fometimes obtained from it a glo- bule of filver, at other times there was no appearance of filver. This difference in the refult of the afTays, is not to be attributed to any differ- ence in the quality of the flag lead which was affayed^ for all the pieces which I tried were cut from the fame lump, but to the different de- grees of heat ufed in the aperation ; when the fire was too ilrong, the filver, I conceive, was volatilized. Silver I know is looked upon as a fixed metal, and not capable of being volatilized ; and the lofs of filver when the fire is too flrong, has been attributed to its being not volatiliz- ed, but abforbed by the cupel-, I have no objedion to this account; z 3 but

( 35§ )

but that the volatilization of filver

on the cupel is no unwarranted con- je6bure, appears from hence^ that in the iail procefs of refining lead for filver at Holyv/ell, fo much of the filver is carried into the chimney of the furnace, that they have pro- cured a filver cup from melting the fweepings.

A great quantity of lead is annu- ally imported in the tea boxes from China, a Congo box contains about lo pounds, and an Hyfon box about 4 pounds of lead j I have frequently allayed this lead, and always found that it contained filver, but not in quantity fufficient to quit the ex- pence of extrading it.

Pure lead is heavier than pure fil- ver, and the purer the lead the great- er is its weights I calculated the

weight'

( 359 )

weight of a cubic foot of five differ- ent forts of lead :

Weight of a cubic foot of

Avoir, oz.

Lead from the reduclion of red lead 1 1460

Lead uncalcined in making red lead 11331

Lead fmelted from an ore - - - 11262

Lead from the flag of a cupola furn. 11212

Lead from a tea box - - - - 11 176

The experiments from which I form- ed this table^ were repeated at dif- ferent tim.es, and the m.ean of feve- ral trials in the refpedlive forts is expreffed. A cubic foot of fine filver weighs 1 1091 ounces, *

The following aiTays of the feveral leads here mentioned, were made by an experienced afiayer in London -, they are very little different from

thofe * Cotes.

z 4

( 36o ) ,

thofe which I myfelf had made, but I was defirous that the reader might rely upon the authority of a peribn verfed in the particular bufmefs of allaying, rather than upon mine.

Fine filver in a pound of

Grains.

Lead from the redu6lion of red lead 1 1

Lead uncalcined in making red lead 1 1-

Lead fmelted from an ore - - - - i J

Lead from the flag of a cupola furn. i|

Lead from a tea box ----- jl

From comparing the two tables together, we fee that the heavieft lead contains the lead filver. I do not think, that perfons interefted in knowing the quantity of filver con- tained in any particular fpecimen of lead, ihould reft fatisfied with affay- ing fo fmall a portion as a pound, efpecially if no notice is taken of

any

( 36i )

any weight lefs than one fourth of a grain.

White lead or cerufe^ is lead cor- roded by vinegar. Thin plates of lead are rolled up in a fpiral form, and placed in earthen pots contain- ing vinegar ; thefe pots being ranged on proper llages, and their mouths being covered in fuch a manner, as to permit the vapour of the vinegar to efcape, and at the fame time to prevent any impurity from falling into them, a quantity of horfe dung is thrown in amongft them ; by the heat of which, as it grows putrid, the vinegar is raifed in vapour, and this vapour attaching itfelf to both fides of every fpiral of the lead, which is fo placed as not to touch the vinegar, it corrodes the lead into white fcales, which being beat off

from

( 3^2 )

from the plates, wafhed and ground in a mill, conftitute the white lead of the fhops, excepting that this is generally, even before it gets into the hands of the painters, adulterat- ed with chalk. Cerufe was for- merly made by the vapour of putrid urine inflead of vinegar. The time when this preparation of lead v/as firil difcovered is wholly uncertain i Diqfcorides fpeaks of its being made in great perfedion ^t Rhodes^ Corinth and Lacedemon^ and of an inferior fort of it at Puteoli', * and Pliny defcribes two ways of condu6ting the opera- tion, both of v/hich are now in ufe J. The Roman ladies were well ac- quainted with the ufe of cerufe as a cofmetic : Plautus introduces a wait-

ing

* Diof. Lib. V. C. 103, { Lib. XXXIV, S. 54,

( 3^3 )

ing woman refufing to give her mi- ftrefs either cerufe or rouge ^ becaufe, forfoothj in the true fpirit of a flat- tering Abigail, Ihe thought her quite handlbme enough without them. * I fuppofe the Chriftian ladies in the days oi St, Jerome J were given to this pagan cuftom, for the venerable fa- ther inveighs very forcibly againil

the

* — — non do, fcita es tu quidem, Nova pidura interpolare vis opus lepidiffi-

mum, Non iflanc ^tatem oportet pigmentum allem

attingere, Neque cerufam, neque melinum, neque alium ullam ofFuciam.

Plaut. ]\Ioft. Acl. I. Quid facial in facie Chriftianae purpurilTus ct cerufa, quorum alterum ruborem genarum, labiorumque mentitur, alterum candorem oris et colli, ignis juvenum, fomenta libidi- num, impudicse mentis judicia. Hieron, ad Fufcum.

( 364 )

the life of rouge for the lips and cheeks, and of cerufe for the face and neck, as incentives to luft, and indi- cations of unchafte defires. With- out prefunning to explore the arcana of a lady's toilet, or to reveal the arts by which my fair countrywo- men endeavour to improve charms naturally irrefiftible, I would add to the admonition of St. Jerome, a caution more likely, in thefe dege- nerate times, to be attended to — the certain ruin of the complexion, to fay nothing of more ferious mala- dies, which muft ever attend the conftant application of this drug. Nor is the magiftery of bifmuth or SpaniJIj white^ as it is called, much lefs pernicious than cerufe, notwith- ftanding its being in fuch repute in London, that the chemifts can hardly

pre-

( 365 )

prepare it faft enough to fupply the demand for it.* But if, as is moft probable, they will negle6b this cau- tion, I warn them, however, to for- bear the ufe of fuch wafhes at Har- rowgate, Moffat, and other places of the fame kind, left they fhould be in the ftate of the unlucky fair one, whofe face, neck, and arms were fuddenly defpoiled of all their beau- ties, and changed quite black by a fulphureous water. Indeed, all phlo- giftic vapours, and even the fun it- felf, tends to give both the magiftery of bifmuth, and cerufe, a yellow co- lour : this obfervation may explain

a line

* The magiftery of bifmuth is made by dilTolving that femimetal in aqua fortis, and precipitating the dilTolYed bilmuth from the acid, by water.

( 366 )

a line in Martial ^ where a cerufed lady is faid to fear the fun.*

Other fluidsj befides the vapour of vinegar^ corrode lead into a kind of cerufe. When plumbers ftrip the roofs of churches, or other build- ings covered with lead, which has lain undiilurbed for many years, they ufuaily find that fide of the lead which is contiguous to the boards, covered with a vvhite pellicle, as thick fometimes as an half crown; this pellicle is corroded lead, and is as ufeful for painting, and other purpofes, as the beil white lead. The lead on the fouth fide of any build- ing is found to abound mofl with

this

* .- cretata timet FabuUa, nimbum,

Cerufata timet Sabelia, folem.

Mar. Ep. Lib. 11. E. XLL

3

( 367 )

this white crufl -, that on the nortfl

fide having very little, or none at all of it. It is believed alfo, that lead which lies on deal boards, is not fo apt to be covered with this white in- cruftation, as that which lies upon oak ; if there be any truth in this obfervation, it may, perhaps, be ex- plained from hence, that oak con- tains a much ilronger acid than deal, and this ftrong acid being diililled, as it were, by the heat of the fun in fummer, attaches itfelf to the lead and corrodes it : or this ccrrofion may be the effedt of the fun and air, v/hich, by their conilant adion, cal- cine or corrode the lead; and this calcined lead not being wafhed off by the rain, may, in the courfe of a great many years, form the cruft here fpoken of. It might be worth

v/hile

( 368 )

while, in a philofophical view, to examine more minutely than has been done, the difference between old lead which has loft fome of its parts by long expofure to the air, and new lead. The plumbers have affured me that if a pig of old lead, and an equal pig of new lead, be put together into the fame iron pot, and expofed to the fame degree of heat, the new lead will be melted much fooner than the old lead. An- other difference betwixt them, re- Ipedts the quicknefs with which they may be reduced to a calx, the new lead being obferved to calcine much f after than the old.

Neither cerufe, nor litharge, nor minium, have any tafte, but any of thefe fubftances being boiled in di- ftilled vinegar, which has an acid

tafte.

(3% )

tafte, will be diffolved in it ; and the folution being cryflallized will give one of the fweeteft fubftances in na- ture, called Saccharum Satiirnij or fugar of lead. It is this property which lead has of acquiring a fv/eet tafle by folution in an acid, that has rendered it fo ferviceable to thofe wine merchants who, refpecling their own profit more than the lives of their cuflomers, have not fcrupled to attempt recovering v/ines, v/hich had turned four, by putting into them large quantities of cerufe or li- tharge. I believe this adulteration is puniihed with death in fome parts of Germany 5 and it is to be wifhed that it met with that puniihment every where. In 1750 the farmers general in France being aftonifhed at the great quantities de v in gate which VOL. Ill, A A were

( 370 ) ^ were brought into Paris y in order to be made into vinegar, redoubled their refearches to find out the caufe of the great increafe in that article ^ for near thirty thoufand hoglheads had been annually brought in for a fev/ years preceding th€ year i75o> whereas the quantity annually brought in forty years before, did not exceed 1200 hoglheads. They difcovered, that feveral wine merchants, aiTum- ing the name of vinegar merchants, bought thefe four wines (whicPi were ilill rendered more four by the cuf- torn of pouring into each hogfhead iix pints of vinegar before it was fold,) and afterwards, by means of litharge, rendered them potable,, and fold them as genuine wines,*

Our * Exam. Chy, de Differ. Subf. par. M.

( 37^ )

Our Englifh vintners, there Is rca- fon to fear, are not lefs fcrupulous in the ufe of this poifon than the French wine merchants ; for it not only corre£ts the acidity of four •wines, but it gives a richnefs to meagre ones> and by this property the temptation to ufe it is much increafed.

The reader may foon furnifli him- feif with the means of detecting lead when dilToived in viiHQ, Let him boil together in a pint of water, an ounce of quicklime and half an ouTice of flowers of brim.llone, and when the liquor, which will be of a yellow colour, is cold, let him pour it into a bottle, and corking it up, referve it for ufe. A few drops of this liquor, being let fall into a glafs of wine or cyder containing lead,

A A 2 Will

( 372 ) will change the whole into a colour more or lefs brown^ according to the quantity of lead which it contains; if the v/ine be wholly free froni lead, it v/ill be rendered turbid by the li- quor, but the colour will be rather a dirty white than a blackiih brown. Van Helmo?it^ was of opinion, that Varaceljus made no vain boail, in faying that he could cure r^vo hun- dred difeafes by preparations of lead; but he does not tell us of x\it many hundred perfons he, probably, fent to their graves by his attempt. But it is beyond m.y ability, and falls not within my defign, to difcufs ei- ther the falubrious or poifonous qualities of lead ; efpecially as the

labours

* Adeo lit non friillra Paracelfus glorietiir Iblo pliimbo forte ducentas morborum clalTes {iiperare polTe. Helm. Op. p. 561.

( 373 ) labours of Sir G. Baker * and Dr. Per civ al f have fo fully illuilrated that fubjed.

Having accidentally heard, during the printing of this volume, that Dr. Prieftley had difcovered a method of reducing red lead to its metallic form, by melting it, in conta6t with inflammable air, by means of a burning glafs, I was very defirous of having lb remarkable a fad: confirm- ed by other experiments. But being prevented by a bad ftate of health from venturing into an elaboratory myfelf, I communicated my wifhes and ideas to an ingenious gentleman of this univerfity> ^ who has for fome years been cultivating chemiftry with

a pro-

* Med. EfT. f Eir. on the Poifon of Lead. : Rev. Mr. Milner, A. M. Fellow of Queen's College.

( 374 )

a proper degree of enthufiafm, and he has fucceeded in reducing red lead by means of inflammable air in the following manner. To one end of a glafs tube, into the middle of which fome red lead had been put, an empty bladder was tied ; to the other end a bladder full of inflam- mable air, obtained from a folution of iron in the acid of vitriol, was lailened very clofe : that part of the tube, in which the red lead was principally lodged, being heated al- mofl red hot, by being held over a fmall crucible full of burning char- coal, the inflamimiable air was preiTed out of the bladder; at its flrft paffage through the tube the red lead be- came brown, as if it had been mixed v/ith fome oleaginous particles; and by prelfing the bladders alternately for

a (hort

( 37S ) a fhoft fpace of time, the red lead was reduced into fmall globules of lead; the quantity of inflammable air was fenfibly diniiniilied, a part of it having been abfbrbed by the red lead, when it became a metal.

Occafion v/as taken in another place to remark,, the inflammable air, as a conftituent part of ccxn- bufbible bodies, bore a great refem- blance to phlogiilon, * and a doubt alfo has been expreflfed, whether the phlogiflion of metallic fubllances be not an elailic inflammable fluid -, this experiment, in which lead is reduced by abforbing inflammable air, tends very much to fcrengthen that hypo- thefls, and I doubt not we fhall fee reafon to adrniit it without hefitation,, when the fubjed: has been more in-

vefliigated * VoLIL p. 35U

( 376 ) veftigated -, at prefent I do not know whether it has been proved that the whole of any definite quan- tity of inflammable air can be ab- forbed by a metallic earth -, nor, if it cannot, what the nature of the remainder is : but the removal of thefe, and other doubts, will be beft accomplifhed by the ability of him, to whom we owe the firfl fuggef- tion, of the phlogiflon of metallic fubftances, being an inflammable air.

END ©F VOL. III.