Encyclopaedia Britannica > Volume 7, ETM-GOA

FLU [3°8] FLU
FluM, fe&s, too fmall to be fingly the obje&s of our view,
Fluidity. yet are t0 us w[iat the clouds of gnats would be in the
v» former cafe.
Nervous Fluid. See Anatomy, p. 761. col. 2.
Elajlic Fluids. See Aerology, Air, Fixed Air,
Gas, Vapour, &c.
FLUIDITY, is by Sir Ifaac Newton defined to
be, that property of bodies by which they yield to
any force impreffed, and which have their parts very
eafily moved among one another.
To this definition fome have added, that the parts
of a fluid are in a continual motion. This opinion is
fupported by the folution of falts, and the formation of
tinctures. If a fmall bit of faffron is thrown into a
phial full of water, ^ yellow tinfture will foon be
communicated to the water to a confiderable height,
though the phial is allowed to remain at reft; which
indicates a motion in thofe parts of the fluid which
touch the faffron, by which its colouring matter is
carried up.
With regard to water, this can fcarce be denied;
the conftant exhalations from its furface Ihow, that
there muft be a perpetual motion in its parts from the
afcent of the fteam through it. In mercury, where in-
fenfible evaporation does not take place, it might be
doubted; and accordingly the Newtonian philofophers
in general have been of opinion, that there are fame
fubftances effentially fluid, from the fpherical figure of
their conftituent particles. The congelation of mer-
• See Cowg*-cury, however, by an extreme degree of cold *, de-
fatioii. monftrates that fluidity is not effentially inherent in
mercury more than in other bodies.
That fluids have vacuities in their fubftance is evi¬
dent, becaufe they may be made to diffolve certain bo¬
dies without fenfibly increafing their bulk. For ex¬
ample, water will diffolve a certain quantity of fait ;
after which it will receive a little fugar, and after that
a little alum, without increafing its firft dimenfions.
Here we can fcarce fuppofe any thing elfe than that
the faline particles were interpofed between thofe of
the fluid ; and as, by the mixture of fait and water, a
confiderable degree of cold is produced, we may thence
eafily fee why the fluid receives thefe fubftances with¬
out any increafe of bulk. All fubftances are expand¬
ed by heat, and reduced into lefs dimenfions by cold ;
therefore, if any fubftance is added to a fluid, which
tends to make it cold, the expanfion by the bulk of
the fubftance added, will not be fo much perceived as
if this effeft had not happened ; and if the quantity
added be fmall, the fluid will contradt as much, per¬
haps more,from the cold produced by the mixture, than
it will be expanded from the bulk of the fait. This
alfo may let Us know with what thefe interftices be¬
tween the particles of the fluid were filled up; namely,
the element of fire or-heat. The farine particles, up¬
on their folution in the fluid, have occupied thefe fpa-
ces ; and now the liquor, being deprived of a quantity
of this element equal in bulk to the fait added, feels
fenfibly colder.
As, therefore, there is fcarce any body to be found,
but what may become foKd by a fufficient degree of
cold, and none but what a certain degree of heat will
render fluid ; the opinion naturally arifes, that fire is
the caufe of fluidity in all bodies, and that this ele¬
ment is the only effentially fluid fubftance in nature.
3
Hence we may conclude, that thofe fubftances which Fluidity
we call jluids are not effentially fo, but only affume that 11
appearance in confequence of an intimate union with Flumirerg.
the element of fire ; juft as gums affume a fluid appear- * f
ance on being diffolved in fpirit of wine, or falts in
water.
Upon thefe principles Dr Black mentions fluidity
as an effeift of heat *. The different degrees of heat * See
which are required to bring different bodies into
ftate of fluidity, he fuppofes to depend on fome Par-
ticulars in the mixture and compofition of the bodies
themfelves: which becomes extremely probable, from
confidering that we change the natural ftate of bo¬
dies in this refpe6t, by certain mixtures ; thus, if two
metals are compounded, the mixture is ufually more fu-
fible than either of them feparately. See Chemistry,
n° 542-
It is certain, however, that water becomes warmer
by being converted into ice f; which may feem con-’f See Conge*
tradidtory to this opinion. To this, however, the Doc- lalton‘
tor replies, that fluidity does not confift in the degree
of fenlible heat contained in bodies, which will affedt
the hand or a thermometer; but in a certain quantity
which remains in a latent ftate This opinion he { See Eva-
fupports from the great length of time required to melt 'porati.n.
ice; and to afcertain the degree of heat requifite to
keep water in a fluid ftate, he put five ounces of wa¬
ter into a Florence flafk, and converted it into ice by
means of a freezing mixture put round the flaflt. Into
another flalk of the fame kind he put an equal quanti¬
ty of water cooled down nearly to the freezing point,
by mixing it with fnow, and then pouring it off. In
this he placed a very delicate thermometer; and found,
that it acquired heat from the air of the room in
which it was placed : feven degrees of heat were gain¬
ed the firft half hour. The ice being expofed to the
fame degree of heat, namely, the air of a large room
without fire, it cannot be doubted that it received heat
from the air as fail as the water which, was not fro¬
zen : but, to prevent all poflibility of deception, he put
his hand under the flaflt containing the ice, and found
a ftream of cold air very fenfibly defcending from it,
even at a confiderable diftance from the flalk ; which
undeniably proved, that the ice was all that time ab-
forbing heat from the air. Neverthclefs, it was not
till 11 hours that the ice was half-melted, though in
that time it had abforbed fo much heat as ought to
have raifed the thermometer to 140°; and even after
it was melted, the temperature of the water was found
fcarce above the freezing point: fo that, as the heat
which entered could not be found in the melted ice,,
he concluded that it remained concealed in the water,
as an effential ingredient of its compofition. See Con¬
gelation.
FLUKE, or Flounder, in ichthyology. See
Pleuronectes.
FLuxE-Worm. See Fasciola.
Fluke of an Anchor, that part of it which faftens in
the ground. See Anchor.
FLUMMERY, a wholefome fort of jelly made of
oat-meal.
The manner of preparing it is as follows. Put three
large handfuls of finely ground oat-meal to fteep, for
24 hours, in two quarts of fair water: then pour off
the clear water, and put two quarts of frelh water to
it^