14 5 
D Y I N G. 
louring matter of the leaves, flowers, See. of vegetables; 
of the green inner bark of elder, the green juice of the 
berries of the rhamnus catharticus, and of the orange 
dyed from the quercitron bark. Arid among animal co¬ 
lours, numeroivs inftances may be alleged of fimple or 
uncompounded greens, oranges, purples, and violets: 
even the liquor of the v purpura, from which the Tyrian 
purple was produced, pafies quickly through all the 
(hades of yellow, green, violet, and purple, upon being 
expofed to the fun in atmofpheric air; and thefe mult 
neceiTarily be deemed fimple, not compound colours, 
but on the oilier hand, dyers, painters, Sec. daily pro¬ 
duce, orange, green, purple, and violet, by mixtures of 
the blue, yellow, and red. 
The colouring matter with which cloth is dyed, does 
not cover every portion of its furface ; but its particles 
attach themfelves to the cloth at certain difiances from 
each other ; for cloth is dyed different (hades of the fame 
colour, lighter or darker, merely by varying the quantity 
of colouring matter. With a final I quantity the (hade is 
light; and it becomes deeper as the quantity is increafed. 
Now this would be impolTible, if the dye-liuff covered 
the whole of the cloth. Newton has demonftrated, that 
colours are rendered faint when the rays of light which 
occalion them are mixed with white rays. Consequently, 
from cloth dyed of a light (hade, a contiderable quantity 
of white rays pafies off unchanged : but this could not 
be the cafe if the (luff were covered with coloured mat¬ 
ter ; becaufe all the white rays would be decompofed as 
they pafs through the coloured matter. Therefore, in 
light (hades, the colouring matter does not cover the 
cloth ; its particles adhere to it, at certain difiances from 
each other; and from every part of the cloth which is 
uncovered, the white rays pafs off unchanged. Even 
when the (hade of colour is as deep as poflible, the co¬ 
louring particles do not cover the whole of the cloth, 
but are at a certain diftance from each other. This dis¬ 
tance, undoubtedly, is diminifhed in proportion to the 
deepnefs of the fhade : for the deeper the (hade, the 
fmaller is the number of white rays which efcape unde- 
compofed ; the more, therefore, of the furface is cover, 
cd, the fmaller is the diftance at which each of them is 
placed. A fhade may be even conceived fo very deep, 
that not a particle of white light efcapes the adfion of 
the colouring matter ; in which cafe, the diftance between 
the particles of colouring matter could not exceed dou¬ 
ble that diftance at which a particle of matter is able to 
aft upon light. 
That the particles of colouring matter, even when the. 
fhade is deep, are at fame diftance, is evident from this 
well-known faff, that cloth may be dyed two colours at 
the fame time. All thofe colours to which the dyers 
give the name of compound ', are in fact two different co¬ 
lours applied to the cloth at once. Thus cloth gets a 
green colour, by being firft dyed blue, and then yellow'. 
The rays of light that pafs from green cloth thus dyed 
are blue and yellow ; by the mixture of which it is well 
known that green is produced. In this cafe it is clear, 
that each of the colouring matters perforins the very fame 
office as if it were alone ; and that the new colour is not 
produced by the combination of the two colouring mat¬ 
ters. That part of the white light, reflected from the 
cloth, which pafies through the blue colouring matter, 
is decompofed, and the blue rays only tranfmitted ; and 
that part of the white light which paffes through the 
yellow colouring matter is alfo decompofed, and only the 
yellow rays tranfmitted. It is clear, therefore, that both 
of the colouring matters equally cover the naked fibres 
of the cloth; confequently the one mud be placed in the 
intervals of the other: wherefore the panicles of each 
of the colouring matters are at fome diftance. Now the 
fame eft'eft happens how deep foever the fhade be; and 
it makes no difference which of the two dyes be firft 
given. Nay, if one of the dyes have a ftrong affinity for 
VOL. VI. No. 338. 
the cloth, and the other only a weak affinity, the latter 
will foon difappear, and leave the cloth of the colour 
which the firft dye gives it. The difference, then, in the 
fliades of colour, and alfo the compound colours which 
cloth may receive, depend entirely upon the diftance be¬ 
tween the particles of the colouring matters attached to 
the cloth, and the poffibility of partly filling up the in¬ 
tervals, either with the fame colouring matter, or with a 
different one. 
Several attempts have been made to arrange and clafs 
the different fpecies of colouring matters employed for 
dying and callico printing ; but none feems to accord 
with, or give any juft ideas of, their feveral natures and 
properties. Mr. Berthollet, indeed, alleges many rea- 
fons for not dividing thefe matters, as Mr. Macquer did, 
into extractive and refinous, and alfo for not making their 
effefts depend, as Mr. Poerner has done, upon the muci¬ 
laginous, earthy, faline, refinous, or oily, parts, of which 
they were fuppofed to be compounded ; yet without 
propofmg any fuitable arrangement of his own : nor does 
it appear at all neceffary, fince the colouring matters fall 
of their own accord under two general and diftinCt claffes; 
the firft including thofe colouring matters which, when 
put into a ftate of folution, may be permanently fixed, 
and made fully to exhibit their colours in or upon the 
dyed fubftance, without the interpolation of any earthy or 
metallic bafis or mordant ; and the fecond, comprehend¬ 
ing all thofe colouring matters which are incapable of be¬ 
ing fixed, and made to difplay their proper colours with¬ 
out the mediation of fome fuch bafis or mordant. The firft; 
clafs, indeed, appears to confift of very few articles; fince 
it is much to be queftioned whether any other dye-ftuff 
at prefent known, except the liquor of the purpura and 
fome other fhell-filh, the genuine indigo, and paftel or 
woad, will communicate a permanent dye to any kind of 
material, without the aid or adtion of fome chemical 
bafe. Every other colouring matter belide the ahuve, 
mu ft therefore rank in the fecond clafs, and be confidered 
as fugitive colours. Hence the technical phrafes adopted 
in the dye-houfe, of great, and little, dye. That com¬ 
pounded of the firft clafs of colouring matters is called 
the great or permanent dye ; and colours communicated 
by it are faid to be fajl, or in grain. That compounded 
from the fecond clafs, without the agency of a chemical 
bafe, is termed the little or falje dye : a prohibition of 
which, by the interference of the legiflature, might an- 
fwer a very defirable purpofe, by preventing the frauds 
and impofitions of thofe who fell piece-goods manufac¬ 
tured with the falfe dye, for that of the permanent. This 
evil calls the more loudly for a remedy, becaufe, fince 
the difeo^ery of fo many effectual chemical bafes or mor¬ 
dants, there feems now to be fcarcely any colour, either 
fimple or compound, but what may be rendered periga- » 
nent through their agency: the mo ft important part of 
dying feems therefore to depend on a complete know¬ 
ledge and judicious application of thefe bafes. 
Of MORDANTS. 
All thofe earthy and metallic fubftances ufually em¬ 
ployed in a ftate of folution or combination with acids, 
were, from that circumftance, called by the French dyers, 
mordants , i. e. biters or corroders; and from them the 
term has been adopted in other countries. Some mo¬ 
dern writers, however, prefer the term bafe, or bafis ; 
whi 1 ft others indifcriminately make ufe of both. Almoft 
the only fubftances 11 fed as mordants are, earths and me¬ 
tallic oxyds. Of earthy mordants., by far the mo ft im, 
portant and mod generally ufed is alumina. It was ufed 
as a mordant in very early ages, and feems indeed to 
have been the very firft fubftance employed for that pur¬ 
pofe. Alumina has a very ftrong affinity for wool and 
for filk ; but its affinity for cotton and linen is a good 
deal weaker. It is ufed as a mordant in two ftates; 
either in the ftate of alum, in which it is combined with 
P p fulphuric 
