Trip′o-li.
1. A siliceous polishingma-terial first imported from
Tripoli, Africa.
The
tripoli of Bilin in Bohemia has been ascertained by
Professor Ehrenberg of
Berlin to consist of the siliceous plates or frustules of animalculae and diatomaceae.
They are divested of everything but silex, are hard but fragile, and are of different species.
Of one kind there are 41,000,000,000 in a cubic inch, weighing 220 grains; 187,000,000 to a single grain.
Infusorial earth has been employed in the manufacture of
fire-brick and for the lining of furnaces; its adaptation for this purpose is owing to the fact that it contains but a very small proportion of material capable of acting as a flux, being composed of nearly pure silica.
Floating bricks were made by the ancients, according to Posidonius, from a kind of argillaceous earth, which was employed for cleaning silver-plate.
As tripoli is too heavy to float in water,
M. Fabbroni experimented with a number of mineral substances, which it seemed might be adapted for making brick of this kind, and at last succeeded in producing them by using fossil meal, a kind of earth abundant in
Tuscany, containing, according to
M. Fabbroni, 55 parts of siliceous earth, 15 magnesia, 14 water, 12 alumina, 3 lime, and 1 iron.
It is infusible in the fire, loses about 1/8 of its weight in baking, and but little of its volume.
Bricks made of this substance float in water, either burned or unburned, and 1/20 of clay may be added without destroying this property.
They resist water, unite readily with lime, and are nearly as strong as common bricks, with but about 1/6 of their weight.
They are such bad conductors of heat that one end may be made red-hot while the other is held in the hand, and are well adapted for furnaces and where great heat is to be sustained, as well as in constructions where extreme lightness is desirable, as for domes, etc.
2. Rotten-stone.
A light-brown siliceous earth used as a polishing-material.
Sometimes made from
clunch or
separia. One analysis gives: —
| Silica | 81 |
| Alumina | 1.5 |
| Iron | 8 |
| Sulphuric acid | 3.45 |
| Water | 4.55 |
| —— |
| 98.55 |
[
2629]
It is now found in numerous localities.
It is prepared by calcining and grinding, and has various colors.
