Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 5, BUR-CHI

C H E M
picric. Time the Caloric il’tfj in paffing into the Thermometer.
Tempera¬
ture.
fherm. rofe
from 3 a0
to 200°, iu
Fherm. rofe
8o°, viz
from 8oc-
to 1600, in
Through
the Water
and Starch
Seconds.
n©9
34i
Through the
Water and
Eider down.
Seconds.
949
269
Through
ftewed
Apples.
Seconds.
IO964
335
Through
pure
Water.
Seconds.
597
172
Time the Caloric was in pajjing out of the Thermometer.
Tempera¬
ture.
Through
the Water
and Starch.
Therm, fell
from 2000
to 40°, in
Therm, fell
8o°, viz
from 1600
to 8o°, in
Through the
Water and
Eider down.
Seconds.
*548
468
Seconds.
1541
460
Through
ftewed
Apples.
Seconds.
1749^
520
Through
pure
Water.
Seconds.
IO32
277
253
I S T R Y.
perature, or brought into ceMact with each other,
they acquire in a certain time the fame tempera¬
ture. Thus, if one body be raifed to the tempera¬
ture of 2oo°, another to that of ioo°, and a third to All bodies
the temperature of 6o° ; and if thefe three bodies be acquire the
placed in the temperature of 8o°, they all indicate, in ^ame tem."
a fhort time, the fame temperature. The bodies which m
were at the temperature of 200° and JOO° are reduced mediuxn.
to 8o°, and the temperature of the body at 6q° rifes
to the fame. This is called the diftributmn, or the
equilibrium, of caloric. To whatever degree bodxei
are heated or cooled, they all acquire in time the
temperature of the furrounding medium, as it is indi¬
cated by the thermometer. It may therefore be re¬
ceived as a general law, that all bodies which commu¬
nicate freely with each other, and are fubjeSl to no ine¬
quality of external a Elion, acquire the fame tempera-
turei
1. Bodies are deprived df calorie, hot only by radia-
tion from their furfaces, but it is alfo conducted by Radiation
thofe bodies w ith which the heated body comes in con- not the foie
taft, and this depends greatly ort the nature of the fur- caufe
rounding cold body. The experiments of Profdlor coo^ng*
Piftet and Count Rumford, however, fhew, that radia¬
tion is not the only caufe. By thofe of the former it
appeared, that hot bodies fufpCnded in the vacuum of
an air pump, cooled more flowly than in the open air j
and by thofe of the latter, the cooling vtas ftill flower
in the Torricellian vacuum.
The fubftances which were added to the water in
thefe experiments, by diminiftimg its fluidity, had the
effect of retarding the internal motions or currents by
which the caloric is conduced through fluids. Thus,
when ftareh was mixed with water, it required nearly
double the time to raife the thermometer to the fame
degree, as with pure water. From thefe and from fome
other experiments, Count Rumford concluded, that
fluid bodies are heated in a different manner from folids y
that caloric is not commtmicated through fluids from
particle to particle, but that all the particles!- indivi¬
dually come in contaft with the heating body, and this
is fuppofed to be the caufe of the currents'which are
obferved during the heating of the fluids.
5. Fluids no doubt acquire great part of their tem¬
perature in this manner y but it has been clearly proVed
by the experiments of others, that they are alfo con-
duftors of caloric exactly the fame way as folid bodies-,
but in an inferior degree. This has been eftabliflied
m the moll fatisfa£tory manner by the experiments of
Dr Thomfon * and Mr Murray f, whichwere publifli-
wol. iv. eA in Nicholfon’s Journal y and alfo by another fet of
t 29. experiments by Mr Dalton, which were publifhed in
| ^ the Manchefter Memoirs J. By thefe experiments it
j - is demonftrated, that fluids conduft caloric from the
| ol. v. farface downwards y which could riot be the cafe, were
^ 73. it only communicated through them by the afeending
I currents of particles, in the way Count Rumford fup-
J n f0]jjs pofed: but they are worfe conductors of caloric than fo-
’ lids 5 that is, it paffes through them much more flowly.
.
Sect. IV. Of the Distribution of Caloric.
- :Uf
If a number of bodies be expofed to different
temperatures, and then be all placed in the fame tem-
2. The time requilite for the heating or cooling of
bodies depends much on their conducing power. Acoodcon*
fubftance which is a good conductor of caloric cools dueftors
much more rapidly than a bad conduftor. Mercury co°l
and water heated to the fame temperature cool in very raP^ly*
different times y the mercury cools more than twice as
fall as the water in the fame circumftances. The time
of the cooling of fluids has been confidered as nearly in
the inverfe ratio of their conducting power.
3. This equal diftribution of caloric was attempted ,
to be explained by Boerhaave, Mufchenbroeck, andDiftdbu-
others, by fuppofing that there is an equal quantity of tion of ca-
ealoric in every equal meafure of fpace, however that lori.c ex*
Ipace might be filled up with different bodies, and that Plained by
thefe bodies floated, as it were in this caloric. From gj.0" iaave?
this equal diftribution of caloric in fpace, they con¬
cluded that there was an equal quantity of caloric in
all bodies, becaufe, whatever was the denfity or differ¬
ent circumftances of bodies, they always indicated the
fame temperature to the thermometer. A cubic foot
of gold, and a cubic foot of air, according to this theory,
contained the fame quantity of caloric.
Profeffbr Piftet gave another explanation of this
phenomenon. He fuppofed that the accumulation of
caloric in- a body inefeafed the repulfive force between
ks particles, by the diminution of the diftance between
them. By the aflion of this repulfive force, the par¬
ticles are driven off in all direftions. This repulfion
continues to aft till it is oppofed by a new force, which
is the force of repulfion between the particles of calo¬
ric feparated from another body j and, till thefe two
forces acquire the fame intenfity, the particles of calo¬
ric continue to fep&rate from the hotter body. When
the two forces are balanced, the bodies are of the
lame temperature. Thus, if two bodies of different
temperatures