CHEMISTRY. 
182 
Jey, fynonymous with the igneous fluid of Lavoifier, 
with the abfolute heat of Dr. Crawford, and with 
the matter of heat of La Place. Th'efe terms exprefs a 
particular kind of matter, or a particular quality of 
matter, which exills under a variety of modifications 
that are mutually convertible. One of thefe modifica¬ 
tions is free caioric. It is in this (late that caloric affefts 
animals with the fenfation of heat, and that it expands 
in every direftion the bodies into which it enters. Free 
caloric is fynonymous with the exprefilons of interpofed 
caloric, uncombined caloric, thermometrical (ire, and 
caloric of temperature ; and was formerly called fenjtble 
heat. It is communicated in general to bodies in three 
ways : 1. By contaft with a heated body. 2. By friftion. 
3. By the aft of combination. Dilatable bodies are fo 
only by the caloric palling from one body to another; 
according to which circumftances we have dilatation or 
condenfation of liquids; an operation which points out 
the conftruftion of thermometers. The aftion of caloric 
may be confidered as tending to deftroy aggregation, and 
to promote combination: this happens from melting. 
This objeft may be explained under four principal 
heads: x. There are bodies which are not altered, but 
only, dilated, by heat. 2. Caloric caules bodies to pafs 
from the (olid to the fluid (late: this'phenomenon is 
called fufon, and thofe bodies are called fifible bodies: 
1 'uch are fulphur, lead, &c. This fuflbility, when carried 
farther, is called volatilization ; and bodies fufceptible of 
this property, are called volatile bodies : Inch are benja¬ 
min, boiling water, &c. Thofe which have not this pro¬ 
perty are called fixed. There are feveral degrees of this 
volatility: the ultimatum' is bodies melted into gas. 3. 
Bodies decompofable without alteration, which confti- 
tutes the true analyfis. One of the bodies is always fix¬ 
ed; the other volatile : as, oxyd of red mercury, &c. 
4. If bodies expofed to the aftion of caloric, be com- 
pofed of feveral principles, volatile and fixed, the vola¬ 
tile parts unite,'and the fixed combine alfo ; hence new 
compofitions are produced : this is called falfe analyfis. 
All bodies contain two diftinft portions of caloric ; viz. 
the combined caloric, and the interpofed or difeagaged 
caloric. Combined caloric is that which is fixed to bo¬ 
dies by the force of affinity or attraftion, conilituting a 
part cf their fubftance, even of their folidity. Interpofed 
caloric is that which, without being engaged in any com¬ 
bination, is found between the molecules, or elementary 
particles, of bodies. A familiar example will render the 
difference between thefe two portions of caloric more 
clear. A piece of bread put into water contains two 
diftinft portions of water; one portion is in a Hate of 
combination, and forms a conftituent part of the bread 5 
the other is only interpofed between the particles ; it ap¬ 
pears as water, and efcapes by prefl'ure. 
Caloric is alfo to be diftinguifiied from heat, becaufe 
we mull not confound the cffedl and the caufe under the 
fame denomination. Heat is only the effeft produced 
upon our organs by the pafiage of the caloric which is 
dil'engaged from the furrounding bodies. When we touch 
a cold body, the caloric pafles from the hand into the 
body we touch, and we feel the fenfation of cold ; when 
we touch a hot body, the caloric pafles from the body to 
the hand, and we have the fenfation of heat. But ail 
bodies do not furnilh equally a free and eafy pafiage to 
caloric. Here, then, we mud diftinguifh, 1. Caloric con- 
dufted; 2. Caloric flopped or obftrufted. Metals, and moil 
liquids, furnifii examples of the firft point. If one end 
of an iron wire be held in the flame of a candle, the per- 
fion loon feels a fenfation of heat. If, on the contrary, 
3 r ou take a coal, lighted at one end, and touch at a little 
dillance from the burning end, no fenfation of heat will 
be produced. The reafon of thefe effefts is, that the 
caloric is quickly propagated or conducted through the 
elementary particles of the iron, while the particles of 
the coal refill its pafiage. Glals, refins, filk, wool, ft raw, 
&c. refill the pafiage of caloric more or lefs 5 or, in other 
words, they are good or bad conduftors of heat. From 
a due confideration of thefe effefts, it may be feen what 
ufeful applications may be made in the arts, and even 
in the common concerns of life, by the medium of thefe 
properties. The property which bodies have of abforb- 
ing a quantity of caloric, is called their capacity. Thus, 
to raile to the fame number of degrees the temperature 
of two bodies equal either in mals or in volume, it is 
generally necefftry to communicate to them unequal 
quantities of caloric. Regarding caioric as an eminent¬ 
ly elaftic fluid, which is always tending to expand, ac¬ 
cording to certain laws peculiar to itfeif, it is faid that 
caloric tends conllantly to the Hate of equilibrium ; and 
upon this property of caloric is founded the ufe of ther¬ 
mometers. When a mercurial thermometer is immerfed 
in water, the caloric of the water makes an effort to dif- 
fu(e itfeif through the mercury, and the caloric of the 
mercury makes an effort to cliffule itfeif through the 
water. If the tendencies to expand be equal in thefe 
two quantities of caloric, both quantities will remain at 
reft; the mercury will neither be expanded by the en¬ 
trance of caloric from the water, nor will it be contraft- 
ed by the lols of any part of its own caloric. But when 
the tendencies to expanfion'are unequal, the caloric is 
impelled from the fubftance where it had exiiled in the 
ftate of the greateft tenfion, into the fubftance where it 
had exiiled in the ftate of the leaft tenfion ; and this flaw 
of caloric continues till the forces expanding it are in 
equilibrium. When this happens, the degree of dilata¬ 
tion of the mercury, or other fluid employed in the con- 
Itruftion of the thermometer, is laid to indicate the tem¬ 
perature of the fubftance to which it is applied. 
Caloric is conllantly tending to the ftate of equilibri¬ 
um, though it pafles with different degrees cf facility 
through different fubftances. Bodies are hence laid to 
be more or lefs permeable to caloric, or to conduft calo¬ 
ric more or lefs readily. When equal quantities of wa¬ 
ter, at different temperatures, or-of any other homoge¬ 
neous fubftance fuited for fuch experiments, are mixed 
together, the caloric flows from the quantity which has 
. the higbeft temperature, and diffules itlelf through the 
quantity which has the lowed temperature, till the forces 
expanding it are in equilibrium in every part of the 
mafs; audit is thenfoundthat the temperature of the trials 
is the arithmetical mean between the temperatures of the 
two quantities that had been originally mixed together. 
When equal quantities of two different fubftances, are 
taken, and mixed together at different temperatures, the 
caloric, as in the former cafe, flows from the body which 
has the higheft temperature, and diffufes itfeif through 
the body which has the loweft temperature, tiil the ex¬ 
panding forces are in equilibrium, and confequently till 
both fubftances have acquired the fame temperature; but 
the temperature of the mixture is no longer, as in the for¬ 
mer cafe, the arithmetical mean between the temperatures 
of the two fubftances that had been originally taken. 
In every known inltance it deviates from that mean, ap¬ 
proaching more or lefs to the temperature ol one of the 
fubftances employed. An example will illuftrate this 
faft, and the conclufion to be deduced from it. When 
a pound of ice, at 32°, is mixed with a pound of the 
white oxyd of antimony by nitre (diaphoretic antimo¬ 
ny), at 27°, the uniform temperature of the mixture is 
3 i° ; the ice having loll i° of temperature, and the oxyd 
of antimony having gained 4 0 . Now, the oxyd of anti¬ 
mony receiving precilely as much caloric in this experi¬ 
ment, as is taken from the ice, it follows, that the lame 
quantity of caloric, which is capable of railing the tem- 
perature of the oxyd of antimony 4 0 , is capable of raif- 
ing the temperature of the ice only i°, fince the abftrac- 
tion of it has reduced the temperature ol the ice only i°. 
This faft is expreffed by laying, that the capacity of the 
white oxyd of antimony for caloric, is to the capacity of 
ice for caloric, as one is to four; that is, the capacities 
of bodies for caloric exprefs the relative quantities of 
caloric, 
