C H E M ] 
The concentrated fulphuric acid attacks indigo brifkly, 
and the mixture becomes opaque and black ; it water be 
added, it clears, palling fucceflively through all the (hades 
of blue, according to the quantity of water. Ifthelul- 
phuric acid be weakened with water, it only attacks the 
earthy principle, which in indigo is confounded with fome 
of the mucilaginous parts. 
Concentrated nitric acid attacks indigo with fuch vio¬ 
lence, that it burfts into flame ; if weakened to a proper 
degree, it a£fs lefs brifkly ; the indigo becomes ferrugi- 
ginous ; the refidue, after the operation, has the appear¬ 
ance of umber, making only a third part of the indigo. 
Fixed alkali precipitates from the nitric acid, which has 
added upon indigo, a little oxyd of iron mixed with calca¬ 
reous earth, &c.but, if too much alkali be added, part of the 
precipitate will be diffolved again, and the colour of the 
liquor becomes darker than before. 
Muriatic acid, digefted or boiled with indigo, takes to 
itfelf the earthy part of the iron, and a little of the ex- 
traftive matter, which gives it a yellowilh-brown colour, 
but does not affeft the blue colour of the indigo at all. 
If the indigo is precipitated from fulphuric acid, then the 
muriatic acid will diffolve a certain portion of it, and 
make a liquor of a dark-blue colour. The other acids, 
as the tartareous, acetous, and phofphoric, have the fome 
effedfl upon indigo as the muriatic acid ; they diffolve it 
very well when precipitated. The oxygenated muriatic 
acid has little a< 5 iion on the indigo in fubftance; but it de- 
ftroys its colour when infolution. Indigo detonates ftrong- 
ly with nitre. 
Of Woad.—T his is a plant of the family of the cruci- 
feres. The colour is extradled by fermentation from the 
bruifed leaves of the plant; the fermentation is promoted 
by wetting them with the mod tainted or flunking water 
that can be procured. The (Irongeft kind of woad is cal¬ 
led pafleli the weaker fort mouede. 
Of Madder. —This is the'rootof a plant of which 
there are two kinds. Madder, as prepared for the dyers, 
has different qualities. That which is prepared from the 
main root, is called clafie red.madder ; the other fort, or 
not clujlered, comes from thefe twigs or runners which 
ereep underground, and have there become roots. 
, The red colour of madder is foluble in alcohol, which, 
by evaporation, leaves a refiduum of a deep red. Fixed 
alkali makes a violet precipitate from this folution, ful¬ 
phuric acid a fawn-colour, fulphat of potafh a beautiful 
red; and precipitates of different colours are obtained 
with alum, nitre, chalk, acetit of lead, muriat of tin, See. 
Of Cochineal. —Cochineal is an infe6l brought from 
America. They collect two forts of cochineal at.Mexico; 
the wild or wood infect, called in Spanifn grana fyl-vejlra ; 
the other is called grana fina. On the word grana it is 
neceffary to obferve, that cochineal was long conlidered 
as a,vegetable grain ; father Plunder was among the firfi 
who detefted this error. 
The decoftion of cochineal produces a crimfon colour 
inclining to violet. A fmall quantity of fulphuric acid 
gives the liquor a red colour inclining to yellow ; and a 
flight precipitate is formed of a beautiful red colour. 
The muriatic acid produces nearly the fame change of 
colour, but without any precipitate. A folution of tar¬ 
tar changes the liquor to yellowifli red ; a fmall precipi¬ 
tate of a pale yellow is gradually formed; but thefuper- 
natant liquor remains yellow. By pouring in a little al¬ 
kali it becomes purple ; the alkali quickly diffolves the 
precipitate, and the folution is purple. A folution of 
tin gives a role-coloured precipitate, and makes the liquor 
yellow. The folution of alum brightens the colour of 
the infufion, and makes it redder : a crimfon precipitate 
falls down, and the liquor preferves a crimfon colour in¬ 
clining to red. Various other phenomena are produced 
by different folutions, as detailed by Berthollet. 
Carmine.—I s the lake obtained from cochineal by means 
of alum; but the cochineal is mixed with a certain quantity 
Vol. IV. No. aoi. 
s T R Y. " 345 
of the bark of a tree from the Levant, called aulour by the 
French ch'emifts, of a colour fomewhat paler than cinna¬ 
mon ; and alfo with chouan, a leed quite unknown to us, 
but brought likewife from the Levant, and of a yellow- 
ifli-green colour. It appears that thefe two lubftances 
form with the alum a yt liow precipitate, which ferves to 
brighten the colour of the lake; and part of the yellow 
colouring matter communicates a flame colour to the 
1'carlet. Carmine was formerly prepared from kermes , 
whence the name. 
Of Kermes.— This is an infeft alfo, though formerly 
conlidered as a tubercle, or excrelcence of plants ; it is 
found in feveral parts of Alia, and the fouth of Europe. 
If the living infedl be crulhed, it yields a red colour; its 
fmell is not di(agreeable; the tafte is bitter, acrid, and 
pungent. When dried, it communicates the fome odour 
and tafte to water and alcohol, with a dark red colour; 
the extra£l obtained by thefe infufions retains the fame 
colour. 
Of Lac.— This is a fubftance of a red colour, 
brought from India in different lhapes. It is formed 
in cells like a bee-hive, being the work of a kind of flying 
ants, who fix it on the fmall branches of a fpecies of 
croton, hence called croton laciferum. There are feveral 
fpecies of lac; the principal kinds are, i. Stick-lac; 
which is what the infefts build round fmall (ticks or 
branches which the inhabitants place on purpofe to fup- 
port their work : this is the richeft in colour. 2. Seed- 
lac; this is not fo high coloured. 3. Shell-lac; this is 
brought over in pieces of various fizes, more or lefs 
tranlparent; it is thought that the Indians have previoufly 
extradited the colouring matter. 
Of Archil. —The archil ufed in’dying is a pafte of a 
violet red colour. There are two forts, prepared from two 
fpecies of lichen. The molt efteemed is made from the 
lichen roccella, growing on rocks near the fea at Cape Verd 
and the Canaries; the other, from the lichen parellus, 
growing on the rocks of Auvergne in France. 
Prepared archil gives its colour very quickly to water, 
ammoniac, and alcohol. Its folution by alcohol is ufed 
for thermometers ; and, if the air be clofely (hut out, the: 
liquor lofes its colour in a few years ; air reftores the co¬ 
lour, which is again deftroyed by time. The aqueous 
infufion lofes its colour in a few days if deprived of air. 
The infufion of archil is of a crimfon inclining to vio¬ 
let ; acids give it a red ; as it contains ammoniac, which, 
has already modified its natural colour, fixed alkalis pro¬ 
duce but little alteration; they make it lomewhat darker, 
and more inclined to the blue tinge. Alum makes a pre¬ 
cipitate of a brown red ; the liquor remains of a yellowilh 
red. The folution of tin gives a reddifti precipitate which 
falls down very (lowly. 
Of Carthamus. —Carthamus, or bafe laffron, cartha - 
tnus tinBorius, of which the flower only is ufed in dying,. 
is an annual plant cultivated in Spain, Egypt, and the 
Levant. Carthamus contains two colouring parts: one 
yellow, the other red ; the firlt only is foluble in water ; 
its folution is always thick; acids render it clear; alkalis 
make it of a deep orange-colour; both produce a fawn- 
coloured precipitate, by which the liquor becomes clear. 
Alum makes a (light precipitate of a deep yellow colour. 
I11 order, to obtain the red colour, the foluble part of 
the carthamus muft firlt be carefully waffled away. The 
remainder is mixed with the cendres gravelees, or fait of 
(oua; and the mixture, being lixiviated, forms a bath. 
But as the alkali alters the colour, and renders it dull, the 
dyed (tuff is plunged in water rendered acid by lemon 
juice : the acid leizes the alkaii, and ieaves the colouring 
matter, which it enlivens, and caules to become red. A 
coloured fecula is obtained by a fimiliar procefs, which, 
mixed with Brianeon chaik in powder, compofes the rouge 
uled by the ladies. 
Of BrazilWood.— This wood, which is of great ufe 
in dying, takes its name from that part of America 
4 T whence 
