88 
alkalies. They all seem to be composed of different 
proportions of hydrogene, oxygene, and carbon ; 
but are so liable to change, that few distinct ex- 
periments have been made upon their nature. In 
dyeing, they are usually applied to cloths prepared 
for receiving them by combination with certain 
saline or metaliic preparations, called mordants ; 
and, in consequence of the triple union formed 
between the cloth, the mordant, and the colouring 
matter, the tint is modified, or changed, and ren- 
dered more permanent. 
11. The bitter principle is very extensively dif- 
fused in the vegetable kingdom ; it is found abun- 
dantly in the Hop ( Humilus lupilus ), in the 
common Broom ( Spartium scoparium ), in the 
Chamomile ( Anthemis ?iobilis') 9 and in quassia , 
amera , and excelsa . It is obtained from those 
substances by the action of water or alcohol, 
and evaporation. It is usually of pale yellow 
colour ; its taste is intensely bitter. It is very 
soluble, both in water and alcohol ; and has 
little or no action on alkaline, acid, saline, or me- 
tallic solution. 
An artificial substance, similar to the bitter 
principle, has been obtained by digesting diluted 
nitric acid, on silk, indigo, and the wood of the 
white willow. This substance has the property of 
dyeing cloth of a bright yellow colour ; it differs 
from the natural bitter principle in its power of 
combining with the alkalies : in union with the 
fixed alkalies, it constitutes crystallized bodies, 
which have the property of detonating by heat or 
percussion. 
