spar
is the " blue John " of Derbyshire-earths ; and the " kann" of Cornish
miners. It phosphoresces when exposed to light, and exhibits electrical
phenomena.
Flourine forms
with hydrogen, both in nature, and in the chemical laboratory,
hydrofluoric acid, the use of which, through its power of acting on
glass for etching purposes, has been in vogue since the year 1670.
Most kinds of clay are composed of decayed feld-spar. Various physical
effects on the body as wrought by medicinal uses of hydrofluoric acid,
when diluted to a degree almost infinitesimal, have been faithfully,
and reliably recorded. Similar effects may be reasonably expected to
attend, in some measure, at any rate, the personal wearing of jewels
which by analysis are known to contain fluorine as a constituent. By
the hydrofluoric acid, given as described, varicose veins about the
limbs have shrunk to half their size, fresh hair has grown on a bald
head, whitlows on the fingers have been blighted, and a chronic
soreness inside the nostrils has been cured. After smelling the strong
acid a sense was felt in the brain as if on the verge of being struck
with apoplexy. M. Maumene has been led by observations, and
experiments, to conclude that the main cause of goitre is a presence
of fluorides to excess in the drinking-water ; these being particularly
abundant in the water of goitrous districts.
Borax (whereof
boracic acid is a product) has been found in certain mineral waters ;
as in those of Ischia, Thibet, and Persia. Pliny has described this
substance under the name of " Chrysocolla," which is thought to be
identical with our biborate of soda. The term " Baurach," from which
our word " Borax " is derived, first occurs in Arabian writings. Native
boracic acid
