FLU 
FLU 
tance in chemistry. But the attention of the 
chemist is chiefly directed to the state of 
fluidity as it may affect the component parts 
of bodies. 
A solid body may be converted into a 
fluid by heat. The less the temperature at 
which this is effected, the more fusible the 
body is said to be. 
All fluids, not excepting the fixed metals, 
appear, from various facts, to be disposed 
to assume the elastic form, and this the 
more readily the higher the temperature. 
When a fluid is heated to such a degree as 
that its elasticity is equal to the pressure of 
the air, its interior parts rise up with ebul- 
lition. 
The capacity of a dense fluid for caloric 
is greater than that of the same body when 
solid, but less than when in the elastic state. 
If this were not the case, the assumption of 
the fluid and elastic state would be scarcely 
at all progressive, but effected in most cases 
instantly as to sense. See Caloric. 
The state of dense fluidity appears to be 
more favourable to chemical combination 
than either the solid or elastic state. In the 
solid state, the cohesive attraction prevents 
the parts from obeying their chemical ten- 
dencies ; and in the elastic state, the repul- 
sion between the parts has, in a great mea- 
sure, the same effects. Hence it has been 
considered, though too hastily, as a che- 
mical axiom, that corpora non agunt nisi 
Jluida. 
FLUOR spar, the native fluate of lime, 
See the next article. 
FLUORIC acid, in chemistry, is obtain- 
ed from tiuor spar, or, as it is technically 
called, fluate of lime. It has not yet been 
decomposed, unless it be among the grand 
discoveries of Mr. Davy, not yet announced 
to the world. We have attended the lec- 
tures of this professor, and think, in one of 
them, he said, he had decomposed the fluoric 
acid: for want, however, of any written 
document on the subject, we must content 
ourselves with a summary account of the 
properties of this acid, which were investi- 
gated with accuracy and precision by 
Scheele and Priestley. The spar was not 
distinguished from others of a similar ap- 
pearance till about the year 1768, when 
Margraff attempted to decompose it by 
means of the sulphuric acid. He found 
that it consisted of a white sublimate, and 
a peculiar acid ; the sublimate proved after- 
wards to be lime, and the acid being deno- 
minated fluoric acid ; it is now called the 
fluate of lime. Margraff found, to his asto- 
nishment, that the glass retort in which the 
experiment had been made, was corroded, 
and even pierced with holes. 
Fluoric acid may be obtained by putting 
a quantity of the spar in powder into a re- 
tort, pouring over it an equal quantity of 
sulphuric acid, and then applying a gentle 
heat. A gas ensues, which may be received 
in the usual manner, in jars, standing over 
mercury. This gas is the fluoric acid, which 
may be obtained dissolved in water, by 
luting fo the retort a receiver containing 
that fluid. The distillation is to be con- 
ducted with a very moderate heat, to allow 
the gas to condense, and to prevent the 
fluor itself from subliming. 
Soon after the discovery of this acid, it 
was doubted whether it possessed those 
properties that rendered it different from 
all other, acids. Scheele, however, who 
had already investigated the subject, in- 
stituted another set of experiments, which 
completely established the fact. 
The properties of this acid are, that, as 
a gas, it is invisible, and elastic like air : but 
it will not maintain combustion, nor can 
animals breathe it without death. In smell 
it is pungent, something similar to muri- 
atic acid. It is heavier than common air, 
and corrodes the skin. When water is ad- 
mitted in contact with this gas, it absorbs it 
rapidly ; and if the gas be obtained by 
means of glass vessels, it deposits at the 
same time a quantity of silica. Water ab- 
sorbs a large portion of this gas, and in that 
State it is usually called fluoric acid by che- 
mists. It is then heavier than water, has an 
acid taste, reddens vegetable blues, and has 
the property of not congealing till cooled 
dow'n to 23°. The pure acid may be ob- 
tained again from the compound by means 
of heat. Fluoric acid gas does not act 
upon any of the metals ; but liquid fluoric 
acid is capable of oxyding iron, zinc, cop- 
per, and arsenic. It does not act upon the 
precious metals, nor upon platina, mercury, 
lead, tin, antimony, cobalt. It combines 
with alkalies, earths, and metallic oxides, 
and, with them, forms salts denominated 
fiuates, of which the true fluor, Derbyshire 
spar, or fluate of lime, consists of 
Lime 57 
Fluoric acid 16 
Water 27 
100 
The most remarkable property is that 
already alluded to, viz. the facility with 
which it corrodes glass and siliceous bodies, 
