•210 
-CHEMISTRY. 
invifible medium, which never had been feen before, 
and which mod probably had never been fufpecled. It 
leemed to follow as an obvious conclulion from thefe 
phenomena, that caloric cannot be propagated down¬ 
wards in water while the particles of that fluid continue 
to be condcnfed by cold; but the truth of fo Angular a 
conclufion required to be confirmed by Hill more decifive 
experiments, the refult of which led the count to decide 
“ that water is a perfect nonconduftor of heat, and that 
heat is propagated in it only in conl'equence of the mo¬ 
tions which the heat occafions in the inlulated and foli- 
tary particles of that fluid.” See Count Rumford's Expe¬ 
rimental Ejfays. 
We cannot help thinking this conclufion by far too 
general. The experiments related undoubtedly prove 
that caloric is communicated very {lowly from one par¬ 
ticle of water to another: but it would require more nu¬ 
merous and diverfified experiments to eltablilh the fact 
that no communication whatever occurs. 
CARBONIC ACID GAS. 
We have (hewn that carbon has the property of de- 
Compofmg oxygen gas, and of taking the bale from ca¬ 
loric ; but the acid which refults from this combultion 
does not condenfe into the degree of prelfureand tempe¬ 
rature in which we live : it remains in the ftate of gas, 
and requires a great quantity of water to abforb it. Car¬ 
bon united with oxygen forms therefore carbonic acid. 
Of all the known acids, the carbonic is the moll abun¬ 
dant in nature. It is found under three forms: i. In 
gas. 2. As a mixture. 3. In combination. There are 
divers artificial methods of forming it. i. By oxygen gas 
and charcoal. —The combuftion of the charcoal may be 
performed, like that of phofphorus, under a bell-glafs 
filled with oxygen gas, inverted in mercury; but, as 
the heat of red-hot iron would not be lufiicient to light 
it, a little bic of tinder and a morfel of phofphorus mull 
be laid on the charcoal: the phofphorus is eafily fet in 
combuftion by a red-hot wire ; the flame communicates 
to the tinder, and then to the charcoal. Lavoifier fays 
it requires feventy-two parts by weight of oxygen to ia- 
turate twenty-eight parts of charcoal. 
2. Extruded from marble by fire. —Reduce marble to 
powder, put it in a gun-barrel, which lay acrofs a fur¬ 
nace ; adapt a tube which is to be bent at the lower end, 
and carried under ajar in the pneumatic chemical appa¬ 
ratus : urge the fire fo as to make the gun-barrel red-hot, 
and the carbonic acid gas is difengaged at that tempe¬ 
ra tu ret 
3. Extruded from carbonat of lime by an acid. —-When 
carbonic acid gas is in a ftate of combination, as in chalk, 
■&c. it is eafily obtained by the afilion of other acids. 
Sulphuric, nitric, and muriatic, acids, may be ufed in¬ 
differently; but they mull be exhibited in water; fix 
times its volume of water ftiould be mixed with the ful- 
phiiric acid. 
The apparatus for thefe experiments may be varied in 
infinitum. The moft Ample when we wi(h to obtain it 
without the pneumatic apparatus, is exhibited in the 
Chemiftry Plate III. fig. 6. Take a large long-necked 
matrafs, perforated at the lower part for adjufting a tube 
which is to ferve the office of a cock. By the fide of this 
place a jar with two necks, commonly called a Woulfe’s 
bottle; which mull contain a weakened acid; in one of 
the openings fix a perforated cork, and through the hole 
introduce a glafs tube about three-tenths of an inch in 
diameter, terminated by a funnel; the other end of the 
tube mull be drawn to a point, that it may the more ea- 
iily enter the cork; introduce a fmaller tube within this, 
with lorae hemp or cotton at the end of it, that it may 
ferve as a piiton. From the other neck or mouth of the 
bottle goes another tube, which is adapted to the large 
matrdfs. The apparatus being thus difpofed, l'oak the 
chalk in water; pour the diluted chalk into the tube, 
and fet the pifton to work, As foosn as the chalk comes 
in contact with the acid, a brilk effervefeence is produC-* 
ed, and the carbonic acid gas is difengaged': this is to 
be received into a jar, through the tube or cock placed 
in the lower part of the matrafs for that purpole. As 
this acid gas may be decanted or drawn off, it is fafe and 
eafy to receive it into jars; this arifes from its different 
denfity from atmofpherical air. The gas may alfo be 
drawn off through the cock of a lamp for inflammable 
gas. If you wilh to colled it under jars-in the pneuma¬ 
tic apparatus, a fmall matrafs is then to be ufed, or a 
doubly-tubulated bottle, to which two tubes are adjuft- 
ed, one for receiving the diluted chalk, the other for car¬ 
rying the gas under the jars. 
4. By fermentation, in the manner defcribed under 
that head. 
5. By the decompofition of metallic oxyds. The ufual pro¬ 
portion is one part of the red oxyd of lead, and three of 
black flux. For this purpofe we ufe a Hone retort, to 
which a bent tube is adapted, which goes into a Woulfe’s 
bottle with two necks ; from the other neck paffes ano¬ 
ther tube, whole extremity goes under a jar in the pneu¬ 
matic apparatus. The lead is quickly reduced to its me¬ 
tallic ftate, and carbonic acid gas is obtained. This gas 
may be produced alfo by decompofing nitrat of potaftt 
with dry charcoal; but it is a dangerous experiment. 
Its properties .—It is invifible, elaitic, inodorous, heavier 
than atmofpherical air; .it is the weakeft of acids; it is 
not altered by light; caloric dilates it, but makes no 
change in it, not even if put into porcelain tubes made 
red hot. 
This aeriform fluid is truly an acid perfe. The proofs 
are thefe : 1. It is always the fame, whether difengaged 
by acids, or by any other means. 2. It turns tinfture of 
turnfole ot a purplilh red, not entirely red like other 
acids; and what is remarkable, the red colour produced 
by this acid paffes of itielf into blue pr violet, which is 
a Unking charafteriftic to know this acid from any other 
which may be in the colouring liquor. 3. It diffolves in 
air, of which it conftitntes a fmall part, namely one in 
four. It will mix alfo with oxygen gas, one part in three. 
This gas is not proper to maintain combuftion. Take 
three glafs tubes ; rill the firft with atmofpherical air, the 
fecond with carbonic acid gas, the third with oxygen 
gas. Introduce fucceffively and quickly a lighted taper 
into each tube, in the order we have named them. In. 
the tube filled with atmofpherical air, the taper burns as 
ufual; it is prelently extinguiftied in the tube filled with 
carbonic acid gas; but takes fire afrefh in the tube con¬ 
taining the oxygen gas, and exhibits a dazzling bright- 
nefs. This experiment confirms a truth already eftablifh- 
ed, namely, that oxygen gas is much more favourable 
to combuftion than atmofpherical air ; and is a complete 
proof that inflammable bodies cannot burn in carbonic 
acid gas. 
This gas is hurtful to refpiration. The epiglottis and 
trachea arteria of animals are ftrongly clofed by it, refpi¬ 
ration is flopped, and the animal dies. The Grotto del 
Cane at Naples is filled with this aeriform fluid, whence 
the danger of exploring it. 
This gas is hurtful to vegetation. Roots put in water 
impregnated with carbonic acid, foon perifh. Senebier 
has obierved, that plants which are made to grow in wa¬ 
ter (lightly acidulated with this, gas, tranfpire much more 
oxygen gas, becaufe in that cafe this acid is decompofed; 
and the carbonic principle is combined and fixed in the 
plant, while, the oxygen is driven out. 
It diffolves in water, but (lowly ; the colder the water, 
the more it diffolves : Bergman calls this aerated water * 
There is an apparatus foreffe6ling this purpofe, invented 
by Dr. Nooth, and improved by Parker and Magellan; 
but its price, and frangibility, have occafioned it to be 
little ufed. We have given a view of it, at fig. 7, in the 
preceding plate. It is conltruifted of three gla(s veffels, 
formed purpofely for this ufe. The lower part, or bell- 
glafs C, contains the effervefcent materials 3 it has a (mall 
orifice 
