a4. RHUS RADICANS. 
various unsuccessful experiments with a view to. 
ascertain the nature of this colouring principle,. 
and the means of fixing it on stuffs. He found 
that the juice, expressed from the pounded leaves, 
did not produce the black colour, and that strong 
decoctions of the plant, impregnated with various 
chemical mordants, produced nothing more than 
a dull yellow, brownish or fawn colour. The 
reason of this is, that the colouring principle 
resides not in the sap, but in the succus proprius 
or peculiar juice of the plant, that this juice 
exists only in small quantity, and is wholly insol- 
uble in water, a circumstance which contributes 
to the permanency of its colour, at the same time 
that it renders some other medium necessary for 
its solution. 
» With a view to ascertain the proper. menstru- 
um for this black substance, I subjected bits of 
cloth stained with it, to the action of various 
chemical agents. Water, at various temperatures 
assisted by soap and alkali, produced no change 
in its colour. Alcohol, both cold and boiling, was 
equally ineffectual. A portion of the cloth, di- 
gested several hours in cold ether with occasional 
agitation, was hardly altered in appearance. 
Sulphuric acid reddened the spots, but scarcely 
rendered them fainter. The fumes of oxymuriatic 
