76 TRIPOLI* 
exposed to heat in the furnace. The colours used for the 
painting of it are all derived from metals ; and many of 
them, though dull when applied, acquire considerable 
lustre by the action of the fire. The colours are always 
mixed with some kind of ftus, such as a mixture of 
glass (204>), borax (208), and nitre, melted together, 
and afterwards ground, 
Gum or oil of lavender is used for mixing up the 
colours When the painting is finished, the pieces 
are exposed to a heat suftieient to melt the fiux, and 
thus fix the colour. 
1 19. TRIPOLI is a kind of clay of yellowish grey y brazen, 
or zvhite colour, sometimes striped or spotted, and of an earthy 
texture. 
It feels harsh and dry to the touch ; is soft, scarcely adheres 
to the tongue, and will not take a polish from the nail. 
This substance obtained its name from having for- 
merly been imported into Europe from Tripoli, on the 
north coast of Africa. It is, however, now found ira 
several parts of Germany ; and a granulated kind has 
been discovered in England. 
Tripoli is used for the polishing of metals and stones. 
For tltis purpose, it is, mixed with sulphur, in the propor- 
tion of two parts of tripoli to one of sulphur. These are 
well rubbed together on a marble slab, and are applied 
to the stone cr metal \vixh a piece of leather. 
When tripoli is combined with red ironstone, it is 
used for the policing of optical glas&es. It i& some- 
times made into moulds, in which small metallic or glass 
figures and medallions are cast ; and a kind of tripoli is 
found near Bucg&s, in Spain, which is- used as an ingre- 
dient in the manu&ctare of porcelain* 
In Derbyshire, and several parts of Staffordshire, is 
dug, a kind of tripoli which has the name of rotten stone. 
This is considered to be a produce of limestone shale, 
which has undergone a decomposition by exposure to 
the air and moisture. It is used for most of the same 
purposes as tnpoli. 
