POTASH. 135 
it or flowing from it. The water is salt to the taste, and 
contains both borax and common salt ; and the edges 
and shallow parts are covered with a stratum of this 
substance, which is dug up in considerable masses for 
exportation. It has here the name of tinkal, and is 
usually brought into Europe enveloped in a kind of fatty 
substance. The mode of refining it was for a long time 
kept, by the Dutch and Venetians, amongst those se- 
crets which a want of sufficient research alone prevented 
from being generally known. When refined, it is called 
borax. 
The uses of borax are numerous. It is employed as a 
flux for metals, being found to produce a more perfectly 
limpid fusion than any other substance. For the same 
reason it is made an ingredient in the finest kinds of glass, 
and particularly in some of the coloured glass pastes 
which are manufactured in imitation of gems. But its chief 
use is to jewellers and goldsmiths, to facilitate the sol- 
dering of gold and silver. Borax is also used in medicine. 
205. POTASH FAMILY. 
Potash is an alkaline substance (42), of white colour, and 
of smell somewhat resembling that which is perceived during 
the slacking of quick-lime (137). It is extremely corrosive, 
and remarkably acrid to the taste. 
In a mineral state it is found only in combination with ni- 
tric acid (30). 
Potash principally exists under the form of a salt, in 
vegetable substances ; and is obtained by burning them, 
afterwards repeatedly washing the ashes with water, and 
then filtering and evaporating these to dryness. The 
appellation of potash was given to this salt from its hav- 
ing formerly been prepared in large iron pots. 
The uses to which it is applied are numerous. In 
chemistry it is employed for a variety of purposes ; and 
also in many arts and manufactures, in scouring, wash- 
ing, bleaching, dyeing, glass-making, and several others. 
Its corrosive property is such that it is often used by 
