Ill 
mid Dyeing Turkey Red. 
mined tlie just proportion to be employed : in general, I 
take one part for four, five, or six, of madder. 
In order to obtain the brightest madder colours, it is 
not sufficient to attend to the quality of the water and of 
the madder : it is necessary also to observe the degree of 
the heat of the bath : a low temperature will check the 
attraction of the colouring parts, and prevent them from 
being extracted, while one too high will favour the adhe- 
sion of the yellow particles of the madder, which obscure 
and tarnish the shades intended to be produced. The 
only colour which gains by increasing the heat is black. 
I have always observed, that on, withdrawing the fire 
from below the boilers, when the hand can no longer be 
held in the aqueous vehicle which they contain, if the 
maddering be then continued for two or three hours, the 
most satisfactory results will be obtained, as the furnace 
still retains a sufficient quantity of heat to maintain the 
vehicle at the same temperature, especially when, accord- 
ing to custom, large boilers are employed. Besides, it 
would be very difficult to fix a determinate degree of heat 
by the thermometer when the furnaces are large. 
The yellow parts of the madder as well as of other 
colouring substances are, it is probable, nothing else than 
the colouring parts themselves combined with oxygen. 
The product of this combination, by acquiring greater 
solubility, suffers itself with more difficulty to be taken 
away by clearing, if the heat has not been properly regu- 
lated during the process of dyeing. I have often ob- 
served that madder, and other colouring substances, when 
long exposed to the atmospheric air, do not give colours 
of the same intensity and the same brightness as before ; 
either because these substances absorb the oxygen of the 
atmosphere, or that they procure this radical from the wa- 
ter which they attract, or which they naturally contain as 
a constituent principle, and which is decomposed by a 
