FLU 
FLU 
FLU 
75 1 
t'ons, Mr. Scheele instituted and published 
a new set of experiments ; which not only 
completely established the peculiar nature of 
the fluoric acid, but once more displayed 
the unrivalled abilities of the illustrious dis- 
coverer. It would be needless to enumerate 
these objections, as they originated entirely 
from want of precision, and did not produce 
a single convert. 
2. Fluoric acid gas is invisible and elastic 
like air; it does not maintain combustion, 
nor can animals breathe it without death. It 
has a pungent smell, not unlike that of mu- 
riatic acid. It is heavier than common air. 
It corrodes the skin almost instantly. 
3. Neither caloric nor light produces any 
alteration on it. 
4. When water is admitted in contact with 
this gas, it absorbs it rapidly ; and if the gas 
has been obtained by means of glass vessels, 
it deposits at the same time a quantity of 
silica. 
Water absorbs a considerable proportion of 
this gas, but the precise quantity has not been 
determined. The compound is usually term- 
ed fluoric acid by chemists. It is specifically 
heavier than water, has an acid taste, reddens 
vegetable blues, and does not freeze till 
cooled down to 23°. When heated, the acid 
gas is easily expelled, except the last por- 
tions of it, which adhere with great obstinacy. 
5. Neither oxygen gas nor any of the 
simple combustibles or incoijibustibles pro- 
duce any change on fluoric acid, either in 
the gaseous or liquid state. 
6. Fluoric acid gas does not act upon any 
of the metals, but liquid iiuoric acid is capable 
of oxiding iron, zinc, copper, and arsenic. It 
does not act upon gold, platinum, silver, 
mercury, lead, tin, antimony, cobalt. 
7. It combines with alkalies, earths, and 
metallic oxides, and forms with them salts 
which are denominated floats. See Fluat. 
means of it, to engrave, or rather etch, upon ! ores, and other substances which are diffi- 
glass. The glass is covered completely with ! cullly fusible in assays, and in the reductions 
wax; and then that part where the letters or j of ores. We shall here describe the fluxes 
figures are to appear is laid bare, by remov- 
ing the wax. The whole is then exposed 
for some time to the hot vapours of fluoric 
acid. This simple process is employed with 
advantage in writing labels on glass vessels, 
and in graduating thermometers, and other 
similar instruments. The discovery is by no 
means new ; it has been shewn by Beckman 
and Accum, that this acid was employed for 
that purpose by Henry Swanhard, an artist 
of Nuremberg, as early as 1670. He seems 
to have kept his art for some time secret, 
but the receipt was made public by Pauli in 
1725. See Etching on Glass. 
FLUSTRA, a genus of insects of the order 
zoophyta; an animal of the polypus kind, 
proceeding from porous shells ; stem fixed, 
foliaceous, membranaceous, consisting of 
numerous row r s of cells united together, and 
woven like a mat. There are many species. 
The verticillata is found in the Mediterra- 
nean, ‘adhering to fuci: the cells, when mag- 
nified, appear surrounded by sharp denticles, 
with a long bristle in the front of each, bend- 
ing inwards like a horn ; the mouths incline 
forwards, and their whole substance appears 
full of small points. 
FLUTE, fistula, an instrument of music, 
the simplest of all those of the wind kind. It 
is played on by blowing it with the mouth, 
and the tones or notes are changed by stop- 
ping and opening the holes disposed for that 
purpose along its side. The antient fistula?. 
recommended by Bergman, in vol. ii. 
1. The phosphoric acid, or rather the mi- 
crocosmic salt, as it is called, which contains 
that acid partly saturated with mineral, 
I partly with ammonia, and loaded besides with 
! much water. This salt, when exposed to 
! the flame, boils and foams violently, with 
a continual crackling noise, until the water 
and ammonia have flown off ; afterwards it 
is less agitated, sending forth something 
like black scoriae arising from the burned 
gelatinous part: these, however, are soon 
dispelled, and exhibit a pellucid sphericle 
encompassed by a beautiful green cloud, 
which is occasioned by the deflagration of 
the phosphorus, arising from the extrication 
of the acid by means of the inflammable 
matter. The clear globule which remains, 
upon the removal of the flame, continues 
longer soft than that formed by borax, and 
therefore is more fit for the addition of the 
matter to be dissolved. The ammonia is ex- 
pelled by the lire; therefore an excess of acid 
remains in what is left behind, which readily 
attracts moisture in a cool place. 2. Soda, 
when put upon charcoal, melts superficially, 
penetrates the charcoal with a crackling 
noise, and then disappears. In the spoon it 
yields a permanent and pellucid sphericle, as 
long as it is kept fluid by the blue apex of the 
flame; but when the heat is diminished, it 
becomes opaque, and assumes a milky co- 
lour. It attacks several earthy matters, par- 
ticularly those of the siliceous kind, but can- 
or flutes, were made of leeds, atteiwaids of i no ^ be em pj 0 yed on charcoal. 3. Crystal 
wood, anu last oi metal ; but how they were i j lzec j borax, exposed to the flame urged by 
blown, whether as our flutes, or as hautboys, 1 - • 
does not appear. 
Flute, German, is an instrument entirely 
different from the common flute. It is not, 
like that, put into the mouth to be played, 
The most singular property of fluoric acid , but the end is stopt with a tampion, or plug, 
is the facility with winch it corrodes glass and | and the lower , ip app i ied to a hole about , 
, , -. ... . ’ ai . K ,. ,e ! two inches and a half, or three inches, distant j 
it hokb silica in solution j from tju , cnd . This imminent is usually 
... . AT*’ +i • V S cl | U ’, lty : about a foot and and a half long, rather larger 
ior silica is so great, that the thickest glass : at the upper end than thti j 0 ® e r, and peifo- 
cl 1 rated with holes, besides that for the mouth, 
siliceous bo-dies, especially when hot, and the 
ease with which it holds silica in 
even when in the 
vessels can only withstand its action for 
short time; and the greatest precautions are 
scarcely sufficient to obtain it entirely free 
from siliceous earth. 
8. It produces no change, as far as is 
known, upon any of the acids already de- 
scribed. 
9. Its affinities are as follows : 
Lime, 
Barytes, 
Strontian, 
M agnesia. 
Potass, 
Soda, 
Ammonia, 
Glucina, 
Alumina, 
Zircon ia. 
Silica. 
10. As fluoric acid produces an insoluble 
compound with lime, it may be employed 
with great advantage, as Pelletier has ob- 
served, to detect the presence of that earth 
when held in solution. A drop or two of the 
acid causes a milky cloud or precipitate to 
appear, if any lime is present. The property 
which this acid has of corroding glass, has in- 
duced several ingenious men to attempt, by 
the lowest of which is stopt and opened by 
the little finger’s pressing on a brass, or some- 
times a silver key, like those in hautboys, 
bassoons, &c. It is found exceedingly sweet 
and agreeable, and serves as a treble in a 
concert. 
Flute, or Fluyt, (originally perhaps 
float) is a kind of long vessel, with flat 1 
ribs, or floor timbers; round behind, and 
swelled in the middle; serving chiefly for 
the carrying of provisions in fleets, or squa- j 
ch ons of ships, though it is also used for mer- 
chandize. 
Flutes, or Flutings, in architecture, 
perpendicular channels, or cavities, cut along 
the shaft of a column, or pilaster. See Ar- 
chitecture. 
FLUX, in medicine, an extraordinary 
issue, or evacuation, of some humours of the 
body. See Medicine. 
Flux, in metallurgy, is sometimes used 
synonymously with fusion: for instance, an 
ore, oj rather matter, is said to be in liquid 
flux, when it is completely fused. But the 
w r ord flux is generally used to signify certain 
saline matters, which facilitate the fusion of 
the blow-pipe or charcoal, first becomes 
opaque, white, and excessively swelled, with 
various protuberances, or branches proceed- 
ing out from it. \V hen the water is expell- 
ed, it easily collects itself into a mass, which, 
when well fused, yields a transparent sphe- 
ricle, retaining its transparency even after 
cooling. If calcined borax is employed, the 
clear sphericle is obtained the sooner. 
Having provided every thing necessary, 
the following directions are next to be at- 
tended to. 1. A common tallow candle, not 
too thick, is generally preferable to a wax 
candle, or to a lamp. The snuff must not 
; be cut too short, as the wick should bend to- 
| wards the object. 2. The weaker exterior 
: flame must first be directed upon the object, 
j until its effects are discovered; after which 
- the interior flame must be applied. 3. We 
j must observe with attention whether the 
matter decrepitates, splits, swells, vegetates, 
boils, &c. 4. The piece exposed to the 
flame should scarcely ever exceed the size of 
a pepper-corn, but ought always to be large 
enough to be taken up by the forceps. 5. A 
small piece should be added separately to 
each oi the fluxes; concerning which it must 
be observed whether it dissolves wholly or 
only in part; whether this is effected with or 
without effervescence, quickly or slowly; 
whether the mass is divided into a powder, 
or gradually and externally corroded; witi> 
what colour the glass is tinged, and whether 
it becomes opaque, or remains pellucid. 
Having given tliese directions, Mr. Berg- 
man proceeds next to consider the subjects 
proper to be examined by the blowpipe. 
These he divides into four classes: 1 Saline; 
1 
