ON MADDER. 
131 
dry, its weight is taken. This represents the proportion of 
red tinctorial principle contained in the madder. 
This process is rather long ; it does not give, especially on 
a small scale, the absolute proportion of coloring principle 
contained in the madder ; there is a slight loss, but by acting 
comparatively a sufficient approximation is obtained. 
Such are the different methods for ascertaining the quality, 
the purity, or the adulteration of the madders. In most 
cases calcination is sufficient, and rigorously, calcination and 
the test by dyeing made conjointly, allow the practitioner to 
form a positive opinion of the value of the madders sub- 
mitted to examination. 
Considering the minutias and the number of operations 
which it is necessary to have recourse to, in order to form 
a just estimate of the relative worth of the madders, it is 
evident that an examination of the madders by simply look- 
ing at them, as is customary with the merchants, can afford 
no precise information, and must indeed lead in most cases 
to erroneous conclusions. The process in use amongst mer- 
chants consists in spreading samples of madders of about 30 
to 40 grammes side by side on a sheet of paper, which small 
heaps are flattened and their surfaces rendered smooth with 
the back of an ivory spatula. The samples are then placed 
in a cellar, or some moist situation, where they remain from 
twelve to fifteen hours. At the expiration of this time the 
quality is judged of according to the brightness and tint of 
the powder. 
But as M. H. Schlumberger has already observed, this 
method does not even approximately show the richness of 
color of the madders, since a somewhat long contact with 
the air is sufficient to render them darker, and many cir- 
cumstances may change their tint, without thereby causing 
their tinctorial value to vary. On the other hand, the old 
madders, of a dull tint, may be far superior to others of a 
more beautiful color. The merchants' and brokers' method 
of trial often places the manufacturer in a false position, by 
