DYEING. 
Tlie great fineiies!i given to it probably 
rannot be prodnecd but at the expeiice of 
the length and finnness of tlie filaments. 
A clereyman of the department of 
Somme, in France, employs a process not 
liable to the inconveniences caused by ley- 
ing the dressed hemp. He waters the. 
hemj) as soon as it is pulled, and separates 
the cortical part by a pec\iliar operation 
immediately after the watering, and having 
soaked it in a weak solution of black soap, 
be washes it with great care ; previous to 
the drying, the colouring matter, (which 
would afterwards have been soluble only 
in alkali) may he dissolved and extracted 
by water, with tlie addition of a small quan- 
tity of soap ; the hemp becomes much 
whiter, and divides better and more mi- 
nutely, without, however, having been in- 
jured; and the leys preparatory to the 
bleaching become unnecessary. ITiread 
and linen contain then a colouring sub- 
stance, most of which may be extracted by 
simple leys, but there is a part of it, which 
is really combined with the vegetable fibres, 
and which can only be taken away by the 
destruction of its nature, effected by the 
combustion it undergoes during its combi- 
nation with oxygen. Tlircad loses by the 
operations employed in bleaching from one- 
fourtli to one third of its weight. 
Flax or linen, intended to be dyed, must 
be subjected to the same operations of 
scouring, aluming, and galling which cotton 
undergoes. 
The well-known greater difficnlty with 
which linen, cotton, and silk, take dyes 
than wool, have been accounted for by sup- 
posing the pores of their fibres to be smaller ; 
this, however, appears not to be true, from 
the greater quantity of colouring matter 
which tliey absorb. Unbleached cotton is 
always preferred for dyeing Turkey red, 
because in this state its colour is more per- 
manent. The -same thing is observed of 
raw or unscoured silk, which is found to 
combine more easily with tlie colouring 
matter, and to receive a more permanent 
colour in this state, than after it has been 
scoured and whitened. This has been ac- 
counted for also on mechanical principles, 
but it more probably is owing to the dilfer- 
ence of the affinity, which exists between 
the colouring matter and the substance 
separated from the silk or cotton in bleach- 
ing or scouring. This substance acts pro- 
bably the part of a mordant, and having a 
stronger affinity for the stuff and the co- 
louring matter, than the stuff has for the 
VOL. II. 
latter, the colour communicated is more 
durable, when the silk or cotton is dyed in 
the unbleached or imscoiired state. 
Of the Processes for dyeing black. 
According to the method described by 
Hcllot, woollen cloth to be dyed black 
ought to have received the deepest blue 
tint, to have been washed in the river as 
soon as taken out of the vat, and to have 
afterwards been cleaned at the fulling- 
mill. 
For an hundred pounds of the stuff, ten 
pounds of logwood, and ten pounds of Alep- 
po galls powdered, are put into a bag, and 
boiled for twelve hours in a middle-sized 
copper, with a sufficient quantity of water. 
One-thirif of this bath is put into another 
copper, witli two pounds of verdegris, and 
into this the stutf is immeised, stirring it 
continually lor two hours, and observing to 
keep tlie bath very hot, witliout letting it 
boil. The stuff is then taken out, and a 
portion of the bath equal U> the former is 
put into the copjier, witli eight poiiiKls of 
vitriol, or sulphate of iron. Tlie fire is now 
to be diminished, and the bath suffered to 
cool fur half an hour, whilst tlie vitriol dis- 
solves ; the stuff is then put in again, moved 
about well fur an hour, and afterwards taken 
out to air. Lastly, the remainder of the 
bath is added, taking care that the bag be 
well pressed out. Fifteen or twenty pnends 
of sumach are now put in, and tlie ha i U 
made to boil oiicc, and tlien iniinedia ely 
stopped with a little cold w~dter; two pounds 
more of the sulphate of iron are added, and 
the stuff is kept another hour. The stutf is 
now washed, aired, and again put into the 
copper, constantly stirring it tor an hour . 
it is then carried to the river, well washed, 
and then fulled. fVhen the water comes off 
clear, anotlier bath is prepared witli weld, 
which is made to boil for a moment, and 
after being cooled, the stuff is passed through 
it, to soften it, and render the black mons 
firm. lu irds manner a very beautiful black 
is obtaiued, without making the stutf too 
harsh. 
In general more simple processes are 
employed. Cloth previously dyed blue is 
merely boiled in a bath of galls fur two 
hours ; it is then kqit two hours in the bath 
of logwood and sulphate of iron without 
hnilinir, and aftcrwaixls washed and fulled. 
M. Hellot has also fuiiiid tlie following 
method to succeed. For fifteen ells of deep 
blue cloth a bath is to be made with a 
pound and a half of yellow wood, five 
Pp 
