120 BARYTES* 
The acid produced from fluor spar is called fluoric 
acid (27), and has the peculiar property of corroding 
glass and flint, and consequently cannot be kept in 
glass bottles. Artists, by means of fluoric acid, are 
enabled to etch on glass, in the same manner as, with 
aqua fortis (nitric acid), they do on copper. The pro- 
cess is sufficiently simple. The glass is first a little 
heated, for the purpose of covering it thinly over 
with wax; then, with a needle or other fine point the 
drawing is to be made, by cutting through the wax to 
the surface of the glass. The edges are next to have a 
little wall of wax raised upon them. This done,, the 
glass must be placed in an horizontal position, and 
sifted over with fluor finely pounded; and lastly, a mix- 
ture of one part of spirit of vitriol or sulphuric acid (24-) 
with two or three parts of water is to be poured gently 
upon it. The acid will be prevented from running 
off by the wax; and, in the course of a little while, 
if these be cleared away, the glass will be found cor- 
roded in all the lines along which the needle passed. 
The mode of obtaining fluoric acid for chemical pur- 
poses is, by pouring sulphuric acid upon powdered spar 
in a leaden retort, and applying to it a gentle heat. 
This acid should be used with great caution ; for, when 
applied to the skin, it instantly disorganizes it, and 
produces very painful sores. , 
195. BARYTES FAMILY. 
These minerals are sometimes called ponderous earths, and 
have their name from a Greek word signifying heavy. They 
comprehend all the combinations of barytes with acids. 
When purified, they form a greyish white, porous substance, 
which is easily reducible to powder; has no perceptible 
smell, but has a harsh and more burning taste than lime, and 
changes the blues of vegetable colours to green. 
Although barytes is one of the most useful chemical 
tests that we are acquainted with, it is not much em- 
ployed in the arts, because, when purified, it is found 
too expensive. It is capable of being made into a very 
