difference.

"It is proper to add, that the experiment of the ftriped ribbon was made in the day-time, and in a good light."

COLOURS for flaining different kinds of Stones. CHEMISTRY, n° 753.

See

COLOUR, in dyeing. See DYEING. COLOUR of Plants, is an attribute found to be very variable. Different colours are obferved, not only in different individuals of the fame fpecies, but likewife in different parts of the fame individual. Thus, marvel of Peru, and fweet-William, have frequently petals of different colours on the fame plant. Three or four different colours are frequently found upon the fame leaf or flower; as on the leaves of the amaran thus, tricolor, and the flowers of the tulip, auricula, three-coloured violet, and others. To produce the most beautiful and ftriking variety of colours in fuch flowers, is the principal delight and bufinefs of the

florift.

The primitive colours, and their intermdiate fhades or gradations enumerated by botanifts, are as follow.

Water-colours, hyalinus.
WHITE.
Lead-colour, cinereus.
BLACK, niger.

Brown, fufcus.
Pitch-black, ater.
• YELLOW, luteus.

Straw-colour, flavus.
Flame-colour, fulvus.
Iron-colour, gilvus.
RED.

Flefh-colour, incarnatus.
Scarlet, coccineus.

PURPLE.

Violet-colour, cæruleo-purpureus.
BLUE, caruleus.
GREEN.

These colours seem to be appropriated to particular parts of the plant. Thus, white is moft common in roots, fweet berries, and the petals of fpring flowers. Water-colour, in the filaments and ftyles. Black, in the roots and feeds; rarely in the feed-veffel, and scarce ever to be found in the petals. Yellow is frequently in the antheræ or tops of the ftamina; as likewife in the petals of autumnal flowers, and the compound legulated flowers of Linnæus. Red is common in the petals of summer flowers, and in the acid fruits. Blue and violet-colour, in the petals. Green, in the leaves and calyx, but rarely in the petals. In the interchanging of colours, which in plants is found to depend upon differences in heat, climate, foil, and culture, a fort of elective attraction is observed to take place. Thus, red is more eafily changed into white and blue; blue into white and yellow; yellow into white; and white into purple. A red colour is often changed into a white, in the flowers of heath, mother of thyme, betony, pink, viscous campion, cucubalus, trefoil, orchis, fox-glove, thistle, cudweed, faw-wort, rofe, poppy, fumitory, and geranium. Red paffes into blue in pimpernel. Blue is changed into white in bell-flower, greek-valerian, bindweed, columbine, violet, N° 84.

Although plants are fometimes obferved to change their colour upon being moistened with coloured juices, yet that quality in vegetables feems not fo much owing to the nature of their nourishment, as to the action of the internal and external air, heat, light, and the primitive organisation of the parts. In fupport of this opinion, we may obferve with Dr Grew, that there is a far lefs variety in the colours of roots than of the other parts of the plant; the pulp, within the fkin, being ufually white, fometimes yellow, rarely red. That this effect is produced by their fmall intercourse with the external air appears from this circumftance, that the upper parts of roots, when they happen to ftand naked above the ground, are often dyed with feveral colours: thus the tops of forrel roots turn red; those of turnips, mullein, and radishes, purple; and many others green: whilft thofe parts of the fame roots which lie more under ground are commonly white. The green colour is fo proper to leaves, that many, as thofe of fage, the young fprouts of St John's wort, and others which are reddifh when in the bud, acquire a perfect green upon being fully expanded. In like manner, the leaves of the fea-fide grape, polygonum, which when young are entirely red, become, as they advance in growth, perfectly green, except the middle and tranfverfe ribs, which retain their former colour.

one.

As flowers gradually open and are expofed to the air, they throw off their old colour, and acquire a new In fact, no flower has its proper colour till it is fully expanded. Thus the purple flock-july flowers are white or pale in the bud. In like manner bachelor's buttons, blue-bottle, poppy, red daifies, and many other flowers, though of divers colours when blown, are all white in the bud. Nay, many flowers change their colours thrice fucceffively; thus, the very young buds of lady's looking-glafs, buglofs, and the like, are all white; the larger buds purple, or murrey; and the open flowers blue.

With respect to the colours of the juices of plants, we may obferve, that most refinous gums are tinctured; fome, however, are limpid; that which drops from the domeftic pine is clear as rock water. The milk of fome plants is pale, as in burdock; of others white, as in dandelion, euphorbium, and fcorzonera; and of others yellow, as in lovage, and greater celandine. Mot mucilages have little colour, tafte, or fmell. Of all the colours above enumerated, green is the moft com. mon to plants, black the most rare.

Colour being a quality in plants fo apt to change, ought never to be employed in diftinguishing their fpecies. These ought to be characterised from circumftances not liable to alteration by culture or other accidents. The fame inconftancy of colour obferved in the flowers, is likewife to be found in the other parts of plants. Berries frequently change from green. to red, and from red to white. Even in ripe fruits, the colour, whether white, red, or blue, is apt to vary;

particularly

forrel, and bloody dock. Green indicates a crude al- Colour. kaline tafte, as in leaves and unripe fruits. A pale colour denotes an infipid tafte, as in endive, afparagus, and lettuce. White promises a fweet luscious taste; as in white currants and plums, fweet apples, &c. Laftly, black indicates a harfh, naufeous, difagreeable tafte; as in the berries of deadly nightshade, myrtleleaved fumach, herb-chriftopher, and others; many of which are not only unpleasant to the taste, but pernicious and deadly in their effects.

To be afcertained of the acid or alkaline property of any plant, expréfs fome of the juice, and rub it upon a piece of blue paper; which, if the plant in queftion is of an acid nature, will turn red; if of an alkaline, green. For the methods of extracting colours from the different parts of plants, fee the article COLOURMaking. See

Colour particularly in apple, pear, plum, and cherry trees. Seeds are more conftant in point of colour than the veffel which contains them. In the feeds, however, of the poppy, oats, pea, bean, and kidney-bean, variations are frequently obferved. The root, too, although not remarkably fubject to change, is found to vary in fome fpecies of carrot and radifh. Leaves frequently become spotted, as in a fpecies of orchis, hawk-weed, ranunculus, knot-grafe, and lettuce; but feldom relinquish their green colour altogether. Those of fome fpecies of amaranthus, or flower-gentle, are beautifully coloured. The fpots that appear on the furface of the leaves are of different colours, liable to vary, and not feldom disappear altogether. The leaves of officinal lung-wort, and fome fpecies of fowbread, forrel, trefoil, and ranunculus, are covered with white fpots. Thofe of dog's-tooth violet, with purple and white. Those of several species of ranunculus, and orchis, with black and purple. Those of amaranthus, tricolor, with green, red, and yellow. Thofe of ranunculus acris, and a fpecies of bog-bean, with red or purple. The under surface of the leaves of fome fpecies of pimpernel and the fea-plantain is marked with a number of dots or points; a white line runs through the leaves of Indian reed, black-berried heath, and a fpecies of Canary grafs and the margin or brim of the leaf, in fome fpecies of box, honey-fuckle, ground-ivy, and the evergreen oak, is of a filver-white colour. The whole plant is often found to affume a colour that is unnatural or foreign to it. The varieties in fome fpecies of eryngo, mug-wort, orrach, amaranthus, purslane, and lettuce, furnish examples.

Such being the inconftancy of colour in all the parts of the plant, fpecific names derived from that quality are, very properly, by Linnæus, deemed erroneous; whether they refpect the colour of the flower, fruit, feeds, root, leaves, or exprefe in general the beauty or deformity of the entire plant, with a particular view to that circumftance. Of this impropriety committed by former botanists, Linnæus himself is not always guiltlefs. Thus the two fpecies of farracena, or the fide-faddle flower, are distinguished by the colour of their petals into the yellow and purple farracena; although the fhapes and figure of the leaves afforded much more conftant as well as ftriking characters. The fame may be faid of his lupinus albus and luteus; refeda alba, glauca, and lutea; angelica atro-purpurea; dictamnus albus; lamium album; felago coccinea; fida alba; paffiflora rubra, lutea, incarnata, and cœrulea; and of many others, in which the specific name is derived from a character or quality that is so liable to vary in the fame fpecies.

We fhall conclude this article with obferving, that of all fenfible qualities, colour is the least useful in indicating the virtues and powers of vegetables. The following general pofitions on this fubject are laid down by Linnæus, and feem fufficiently confirmed by experiment. A yellow colour generally indicates a bitter tafte; as in gentian, aloe, celandine, turmeric, and other yellow flowers. Red indicates an acid or four taste; as in cranberries, barberries, currants, rafpberries, mulberries, cherries; the fruit of the rofe, fea-buckthorn, and fervice-tree. Herbs that turn red towards autumn, have likewife a four tafte; as forrel, woodVOL. V. Part I.

COLOUR of the Human Species, Difference of COMPLEXION.

COLOUR, in heraldry. The colours generally used in heraldry are, red, blue, black, green, and purple ; which the heralds call gules, azure, fable, vert or finople, and purpure; tenne, or tawny, and fanguine, are not fo common: as to yellow and white, called or and ørgent, they are metals, not colours.

The metals and colours are fometimes expreffed in blazon by the names of precious ftones, and sometimes by thofe of planets or ftars. See BLAZONING.

Enomaus is faid firft to have invented the diftinction of colours, to diftinguish the gundille of combatants of the Circenfian games; the green for thofe who reprefented the earth, and blue for those who re prefented the fea.

COLOURS, in the military art, include the banners, flags, enfigns, &c. of all kinds, borne in the army or fleet. See FLAG and STANDARD.

COLOURS, in the Latin and Greek churches, are used to diftinguish several mysteries and feasts celebra

ted therein.

Five colours only are regularly admitted into the Latin church: thefe are white, green, red, violet, and black. The white is for the myfteries of our Saviour, the feaft of the Virgin, those of the angels, faints, and confeffors; the red is for the mysteries and folemnities of the holy facrament, the feafts of the apoftles and martyrs; the green for the time between pentecoft and advent, and from epiphany to feptuagefima; the violet in advent and Christmas, in vigils, rogations, &c. and in votive maffes in time of war; laftly, the black is for the dead, and the ceremonies thereto belonging.

In the Greek church, the ufe of colours is almoft abolished, as well as among us. Red was, in the Greek church, the colour for Christmas and the dead, as black among us.

To COLOUR Stranger's Goods, is when a freeman allows a foreigner to enter goods at the custom-house in his name.

COLOUR-Making, the art of preparing the different kinds of colours used in painting.

This art properly belongs to chemistry; and is one of the moft curious, though leaft understood, parts of it. The principles on which colour-making depends are entirely different from thofe on which the theory of other parts of chemistry is founded; and the practiU

cal

Colour cal part being in the hands of those who find it their making intereft to conceal their methods as much as poffible, it thence happens, that there is not only no diftinct theory of this art, but fcarce a fingle good receipt for making any one colour hath ever appeared.

I

Division of

to opaque and tranfparent.

The first general divifion of colours is into opaque colours in- and tranfparent. By the firft are meant fuch colours as, when laid over paper, wood, &c. cover them fully fo as to efface any other painting or ftain that might have been there before; the others are of fuch a nature as to leave the ground on which they are laid vifible through them. Of the firft kind are whitelead, red-lead, vermilion, &c.; of the latter kind are the colours ufed for illuminating maps, &c.

2

Oil and wa

Another divifion is into oil-colours and water-coter colours lours; by which is meant, fuch as are appropriated to painting in oil and in water. Moft of those which are proper for painting in water, are alfo proper for being ufed in oil. There is, however, this remarkable difference betwixt colours when mixed with water and with oil, that fuch as are quite opaque in water will become perfectly tranfparent in oil. Thus, blue verditer, though exceedingly opaque in water, if ground with oil, feems totally to diffolve, and will become very tranfparent. The fame thing happens to fuch colours as have for their bafis the calx of tin, alabafter, or calcareous earth. The moft perfectly opaque colours in oil are fuch as have lead, mercury, or iron, for their bafis to the latter, however, Pruffian blue is an exception; for though the bafis of that colour is iron, it proves quite transparent when ground with oil. In water-colours, thofe prepared from metals, Pruffian blue alone excepted, are always opaque; from vegetables or animals, tranfparent. Coals, however, whether vegetable or animal, are opaque both in water and

ones.

oil. Simple and Colours again, may be confidered as either fimple or compound compound. The fimple ones are fuch as require nothing to be fuperadded to them, in order to make a full ftrong colour, without regarding whether they are formed of many or few ingredients; and in this view, white-lead, red-lead, vermilion, calces of iron, &c. are fimple colours. The compound ones are formed by the union of two or more colouring fubftances; as blue and yellow united together to form a green, red and yellow to form an orange, a white earth or calx with the red colour of cochineal or brazil to form a lake, &c.; and thus carmine, lake, rofe-pink, Dutch-pink, English-pink, &c. are compound colours.

falfe co

lours.

The laft and most important divifion of colours is True and into true and falfe. By the former are meant thofe which retain their colour under every poffible variety of circumstances, without fading in the leaft: the others are fuch as do not; but either lofe their colour altogether, or change to fome other. What is chiefly apt to affect colours, is their being expofed to the fun in fummer, and to the cold air in winter: but to this there is one exception, viz. white-lead; which, when ground with oil, retains its whitenefs if expofed to the weather, but degenerates into a brownish or yellowith colour if clofe kept. In water this fubftance is very apt to lofe its colour, whether expofed to the air or The great defideratum in colour-making is to produce the first kind of colours, viz. fuch as will not fade by expofure to the weather; and indeed it is to

not.

the fun and

The great difficulty of knowing à priori whether a colour will fade or not, is owing to our ignorance concerning the nature of colouring fubftances. With all our disadvantages, however, we may observe, that whatever change of colour is produced in any fubftance by expofure to the fun and air, that colour to which it changes will bid fair for being permanent, and therefore ought to be employed where it can be done. Of thefe changes the inftances are but very rare. Inftances of One is in the purple of the ancients, which affumed co ours 110 its colour by expofure to the fun, and confequently duced by was exceedingly permanent. Another is in the folu- expofure to tion of filver; which, being mixed with chalk, the air. precipitate turns to purplish black where it is expofed to the fun. A third is in folutions of indigo by alka line fubftances, which conflantly appear green till expofed to the air by fpreading them very thin, upon which they become almoft inftantaneously blue, and continue fo ever after. Sometimes, though ftill more By the mir rarely, a very remarkable change of colour happens, ture of two upon mixing two vegetable juices together. Almost vegetable juices. the only inftance of this we have on the authority of Mr George Forfter, who informs us, that the inhabitants of Otaheite dye their cloth of a crimfon colour, by mixing together the yellow juice of a fmall fpecies of fig with the greenish juice of a kind of fern. But the most remarkable alterations of colour are effected by different metallic and faline folutions mixed with certain animal or vegetable fubflances; and with these the colour-maker will be principally converfant.

6

༡

It is a common obfervation in chemistry, that acids Effects of mixed with blue vegetable juices turn them red, and acids and alkalies on alkalies green. It is equally certain, though not fo colours. generally known, that acids of all kinds generally tend to heighten red colours, fo as to make them approach to the fcarlet or true crimfon; and alkalies to darken, or make them approach to blue or purple. Mixed with yellow colours, acids alfo univerfally tend to brighten the yellow; and alkalies to turn it to an orange, and make it become more dull. But though this is very generally the cafe, we are not to expect that all acids are equally powerful in this refpect. The nitrous acid is found to heighten the moft of any, and the marine acid the leaft of the mineral ones. vegetable, as might be expected, are lefs powerful than the mineral acids. Thus, if with a tincture of cochineal, either in water or fpirit of wine, is mixed the pure nitrous acid, it will change the colour to an exceeding high orange or flame colour, which it will impart to cloth. If the vitriolic acid is ufed, a full fearlet, inclining to crifon rather than orange, is produced. With marine acid a true crimfon colour, bordering on purple, is the confequence. Alkalies, both fixed and volatile, change the colour to a purple, which is brighter with the volatile than the fixed alkalies.

The

8 Permanen

lours, by

Here it is obvious, that whatever colours are produced by the mixtures of different fubftances together, cy of cothe permanency of thefe colours can only be in pro- what deter portion to the ability of fuch mixtures to refift the mined. weather.

Colour weather. Thus, fuppofe a high fcarlet or orange comaking. lour is produced by means of fpirit of nitre, it is plain that, was fuch a colour expofed to the air, it could remain no longer than the fpirit of nitre which produced it remained. In proportion, therefore, as the fpirit of nitre was exhaled into the air, or otherwise destroyed, it behoved the colour to fade, and at laft to be totally deftroyed; and thus, in proportion to the deftructibility of the fubitances by which colours are produced, will be the difpofition of fuch colours to fade, or the contrary. In this refpect alkalies are much more deftructible than acids, and confequently lefs proper for the preparation of colours. With regard to acids, the nitrous feems most deftructible, the vitriolic lefs fo, and the marine the least of all. From the extreme fixity of the phofphorine acid and fedative falt, perhaps they might be of fervice in preferving colours.

how formed.

As all colours, whether derived from the animal or vegetable kingdom, must be extracted either by pure water or fome other liquid menftruum, they cannot be used for the purpofes of painting till the colouring fubitance is united with fome earthy or folid matter, Opaque or capable of giving it a body, as the workmen call it; tranfparent and according to the nature of this substance, the cocolours, lour will be tranfparent or otherwife. This bafis ought to be of the most fixed and durable nature; unalterable by the weather, by acids, or by alkalies. It ought alfo to be of a pure white colour, and easily reducible into an impalpable powder. For this reafon all earthy fubitances fhould be avoided as being acted upon by acids; and therefore, if any of thefe were added to heighten the colour, they would not fail to be deftroyed, and their effect totally loft. Precipitates of lead, bifmuth, &c. though exceedingly fine and white, ought alfo to be avoided, as being apt to turn Caly of tin, black by expofure. The only fubftance to be chofen the most in preference to all others, is calx of tin, prepared proper bafis either by fire or the nitrous acid. This is fo exceed

10

for fine colours.

IT

ingly refractory as not only to be unalterable by alkalies, acids, or the fun and weather, but even by the focus of a very large burning mirror. It is befides white as fnow, and capable of being reduced to an extreme degree of finenefs, infomuch that it is made ufe of for polishing metalline fpeculums. For these reafons, it is the moft proper bafis for all fine coPrecipitate lours. For coarse ones, the white precipitate of lead, of lead moft mentioned under the article CHEMISTRY, n° 703, will proper for anfwer very well. It hath a very firong body, i. e. is very opaque, and will cover well; may be eafily ground fine, and is much lefs apt to turn black than white lead; it is befides very cheap, and may be prepared at the small expence of 3d. per pound.

coarfe ones.

12

If what we have juft now obferved is attended to, General method of the general method of extracting colours from any preparing vegetable or animal substance, and fixing them on a colours. proper bafis, muft be very easily understood. For this purpose, a quantity of calx of tin is to be procured in proportion to the quantity of colour defired. This must be well rubbed in a glafs mortar, with a little of the fubftance defigned for brightening the colour, as alum, cream of tartar, fpirit of nitre, &c. after which it must be dried, and left for fome time, that the union between the two fubftances may be as perfect as poffible. If the colour is to be a very fine one, fuppofe from cochineal, the colouring mat

ter must be extracted with fpirit of wine without Colourheat. When the fpirit is fufficiently impregnated, it making, is to be poured by little and little upon the calx, rubbing it conftantly, in order to ditribute the colour equally through all parts of the calx. The fpirit foon evaporates, and leaves the calx coloured with the cochineal. More of the tincture is then to be poured on, rubbing the mixture conftantly as before; and thus, with proper management, may very beautiful colours, not inferior to the belt carmine, be prepared at a moderate expence. If, inftead of cochineal, we fubftitute brazil-wood, turmeric, logwood, &c. different kinds of red, yellow, and purple, will be produced. For the coarfer colours, aqueous decoctions are to be used in a fimilar manner; only as thefe are much longer of evaporating than the fpirit of wine, very little must be poured on at a time, and the colours ought to be made in large quantity, on account of the tedioufnefs of the process.

13

kinds of

Hitherto we have confidered only the effects of the Effects of pure and fimple falts, viz. acids and alkalies, on differ- different ent colours; but by combining the acids with alka- falts. lies, earths, or metals, thefe effects may be varied almost in infinitum; neither is there any rule yet laid down by which we can judge a priori of the changes of colour that will happen on the admixture of this or that particular falt with any colouring fubftance. In general, the perfect neutrals act weakly; the imperfect ones, efpecially thofe formed from metals, much more powerfully. Alum and fal ammoniac confiderably heighten the colour of cochineal, brazil, turmeric, fuilic, madder, logwood, &c. The fame thing is done, though in a lefs degree, by common falt, Glauber's falt, faltpetre, and many other neutrals. Solutions of iron in all the acids ftrike a black with every one of the above-mentioned fubftances; and likewife with fumach, galls, and other aftringents. Solutions of lead, or faccharum faturni, univerfally debafe red colours to a dull purple. Solution of copper changes the purple colour of logwood to a pretty good blue; and, in general, folutions of this metal are friendly to blue colours. The effects of folutions of gold, filver, and mercury, are not so well known; they feem to produce dark colours of no great beauty. The moft powerful folution, how-Solution of ever, with regard to a great number of colours, is tin the moft that of tin, made in aqua-regia. Hence we may fee powerful. the fallacy of Mr Delaval's hypothefis concerning colours*, that the leaft refrangible ones are produced See Chro by the most dense metals: for tin, which hath the leaft matics, denfity of any metal, hath yet, in a state of solution, n°8. the most extraordinary effects upon the leaft refrangible colours as well as thofe that are most fo. The colour of cochineal is changed by it into the most beautiful scarlet ; a fimilar change is made upon the colouring matter of gum-lac. Brazil-wood is made to yield a fine purplish crimson; logwood, a beautiful dark purple; turmeric, fuftic, weld, and all yellowcolouring woods and flowers, are made to communicate colours far more beautiful than can be got from them by any other method. The blue colour of the flowers of violets, eye-bright, iris, &c. are heightened fo as to equal, if not excel, the blue produced by a folution of copper in volatile alkali. In fhort, this folution feems to be of much more extenfive use in colour-making, U 2

when

14

pended upon for eftablishing a general theory of co- Colourfour-making, we fhall now proceed to give an account making. of the different pigments generally to be met with in the colour-fhops.

Colour when properly applied, than any thing hitherto thought making. of. It is not, however, univerfally ferviceable. The colour of madder it totally deftroys, and likewife that of faf-flower, changing them both to a dull orange. It likewife fpoils the colour of archil; and what is very remarkable, the fine red colour of tincture of roses made with oil of vitriol, is by folution of tin changed to a dirty green.

15 Directions for the

any

The molt important confideration in colour making is to make choice of fuch materials as produce the choice of moft durable colours; and if these can be procured, colouring an ordinary colour from them is to be preferred to materials. a bright one from thofe which fade fooner. In what the difference confifts between the colours that fade and those which do not, is not known with degree of certainty. From fome appearances it would feem, that thofe fubftances which are moft remarkable for keeping their colour, contain a viscous glutinous matter, fo combined with a refinous one as to be foluble both in water and spirit of wine. The most durable red colour is prepared from gum-lac. This is very ftrongly refinous, though at the fame time fo far glutinous, that the colouring-matter can be extracted from it by water. Next to gum-lac are madder roots and cochineal. The madder is an exceedingly penetrating fubftance, infomuch that, when given to animals along with their food, it tinges their bones of a deep red colour. Its colouring-matter is foluble both in water and spirit of wine. Along with the pure red, however, there is in madder a kind of viscous aftringent substance, of a dark brown colour, which feems to give the durability to the whole. The colouring-matter of cochineal, though soluble both in water and spirit of wine, is very tenacious and mucilaginous, in which it bears fome resemblance to the purpura of the ancients, which kept its colour exceedingly well. Where the colours are fugitive, the tinging fubitance feems to be too refinous or too mucilaginous. Thus the colours of brazil, turmeric, &c. are very refinous, especially the latter; infomuch that the colouring-matter of turmeric can fcarcely be extracted by water. Both these are perishable, though beautiful colours; and much more are the red, purple, and blue flowers, commonly to be met with. Thefe feem to be entirely mucilaginous without the leaft quantity of refinous matter. The yellow flowers are different, and in general keep their colour pretty well. Whether it would be poffible, by adding occafionally a proper quantity of gum or refin, to make the fugitive colours more durable, hath not yet been Mr Hellot's tried, but feems to have some probability. What method of tends a little to confirm this, is a process given by Mr improving Hellot for imparting durability to the colour of brathe durabi- zil. It confifts only in letting decoctions of the wood lity of brazil-wood. ftand for fome time in wooden cafks till they grow ftale and ropy. Pieces of woollen cloth now dyed in the liquor acquired a colour fo durable, that they were not in the leaft altered by expofure to the air during four months in the winter feafon. Whether this change in the durability of the colour was effected by the ropinefs following the fermentation, or by fome other cause, or whether the experiment can be at all depended upon, must be referred to future obfervation.

16

17

Prepara tion of dif

ferent coJours.

Having thus collected all that can as yet be de

18

1. Black. Thefe are lamp-black, ivory-black, blue- Lanipblack, and Indian-ink. The first is the finest of what black. are called the foot-blacks, and is more used than any other. Its preparation is defcribed in the Swedish Tranfactions for the year 1754, as a procefs dependent * on the making of common refin: the impure relinous juice collected from incitions made in pine and fir trees, is boiled down with a little water, and ftrained whilft hot through a bag: the dregs and pieces of bark left in the ftrainer are burnt in a low oven, from which the fmoke is conveyed through a long paffage into a fquare chamber, having an opening on the top on which is a large fack made of thin woollen ftuff: the foot, or lamp-black, concretes partly in the chamber, from whence it is fwept out once in two or three days, and partly in the fack, which is now and then gently ftruck upon, both for fhaking down the foot, and for clearing the interitices betwixt the threads, fo as to procure a fufficient draught of air through it. In this manner lamp-black is prepared at the turpentine houfes in England, from the dregs and refufe of the refinous matters which are there manufactured.

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On this fubject Dr Lewis hath fome curious obfer- Dr Lewis's vations. "The foot (fays he) arifing in common obferva. chimneys, from the more oily or refinous woods, as the tions. fir and pine, is obferved to contain more diffoluble matter than that from the other woods: and this diffoluble matter appears, in the former, to be more of an oily or refinous nature than in the latter; fpirit of wine extracting it moft powerfully from the one, and water from the other. The oilyness and folubility of the foot feeming therefore to depend on those of the fubject it is made from, it has been thought that lampblack muft poffefs thefe qualities in a greater degree. than any kind of common foot. Nevertheless, on examining feveral parcels of lamp-black, procured from different fhops, I could not find that it gave any tincture at all, either to spirit or to water.

"Sufpecting fome miftake or fophiftication, or that. the lamp-black had been burnt or charred, as it is to fit it for fome particular ufes, I prepared myfelf fome foot from linfeed oil, by hanging a large copper pan. over the flame of a lamp to receive its smoke. In this manner the more curious artifts prepare lamp-black for the nicer purposes; and from this collection of itfrom the flame of a lamp, the pigment probably received its name. The foot fo prepared gave no tincture either to water or to fpirits, any more than the common lamp-black of the shops. I tried different kinds of oily and retinous bodies with the fame event; even the foots obtained from fifh-oils and tallow did not appear to differ from thofe of the vegetable-oils and refins. They were all of a finer colour than the lampblack commonly fold.

"Some foot was collected in like manner from fir and other woods, by burning finall pieces of them flowly under a copper-pan. All the foots were of a deeper black colour than those obtained from the fame kinds of woods in a common chimney; and very little, if at all, inferior to thofe of the oils: they gave only

a