140 Observations on Maddening* 
same with the Prussic acid, which communicates a co- 
lour to different metallic oxides., from which it can be se- 
parated cold by alkaline leys. 
To judge of the fixity of colours arising from animal 
and vegetable substances, the best method is to employ a 
ley of oxygenated muriate of potash or soda, with excess 
of alkaline carbonate. The longer or shorter resistance 
which the colours make in this ley, will indicate what 
they will make when acid, alkaline, saponaceous^ and 
other reagents are employed. 
In the art of dyeing, and that of cotton-printing, the 
name of mad dering is given to that process by which the 
colouring parts of madder are transferred, by means of 
water with the aid of heat, to ai undue, or to the oxide of 
iron fixed in any kind of stuff. 
The brightness and fixity of the colours obtained from 
maddering depend not only on the process, but also on 
the state and purity of the water as well as of the mad- 
der. It is therefore absolutely necessary to avoid or to 
render inactive every acid, alkaline, or saline substance 
that may be contained in the water, or in the madder it- 
self. I have shown that, by adding carbonate of lime, 
(pounded chalk,) madder which I suspected to contain 
gallic acid was corrected ; but that my friend Charles 
Bertholdi, professor in the central school of the Upper 
Bhine, afterwards found that it was sulphuric acid united 
to magnesia. 
The important discovery of this addition of chalk, 
which I made twenty-five years ago, has given birth to 
many manufactories, and improved all those established 
near waters which do not run over or hold in solution this 
earthy salt, without which it is absolutely impossible to 
obtain beautiful and fixed madder colours. This chalk 
since that time has become a new object of commerce ; 
and as the price is very moderate, I have not yet deter- 
