*88 C H E M 
fun, may be regarded as the true matter of fire, and that 
by admitting it as fixed in bodies, it conftitutes the 
phlogifton of Stahl, he conceives that in every infiance 
of combuftion, the pure air dilengages the light or phlo¬ 
gifton from inflammable bodies, and occupies its place; 
fo that calcination may be regarded as the precipitation 
of air, and difengagement of light. When, on the con¬ 
trary, phlogifton is reftored to neutral fubftances, the 
matter of light ferves to dilengage in its turn the air 
fixed in thole bodies, by which means they again reiutne 
the metallic ftate. In this theory, which perfectly an- 
f'wers the intention of its author, by uniting the doctrine 
of Stahl with that of the moderns, Macquer thinks that 
phlogifton can unite with bodies even in clofed vefiels, 
becaufe light, which he regards as the true phlogifton, 
paifes through glafs vefiels, as every one knows, and 
even penetrates metallic or earthen vefiels when heated 
to ignition. Scheeie has propofed a different theory, 
which alio had its adherents among the northern chemifts. 
He fuppofed that fire, heat, and light, were compounds 
of vital air and phlogifton ; that, by palling through the 
veflel, the light was decompofed, it depolited its phlo¬ 
gifton, and the vital air was difengaged as in the reduc¬ 
tion of the metallic calces or oxyds. But this ingenious 
theory, by the afiiftance of which Scheeie explained the 
influence of Tolar light and heat differently modified, in a 
great number of chemical phenomena, does not afford 
the reafon of the increafe of weight in metals, fulphur, 
phofphorus, &c. after their combuftion. 
The attention of chemifts was next drawn from the 
hypothefis of Macquer, to the very ingenious defence 
of the ddCtrine of phlogifton by Mr. Kirwan. Accord¬ 
ing to this philofopher, phlogifton, or the inflammable 
principle, may exiit in two different ftates ; ill, Combin¬ 
ed, as in all bodies fufceptible of combuftion. adly, Free 
and ifolatcd, as in inflammable air. Befides the evolution 
of light and heat, combuftion, therefore, is fuppofed to 
confift in the union of this inflammable principle with 
oxygenous gas, and in the confequent generation of car¬ 
bonic acid. A full account of this hypothefis, which the 
author has fince very candidly retraced, may be leen in 
the laft edition of Kirwan's Effay on Phlogifton. The 
hypothefis of Macquer has alfo of late been revived with 
Tome flight alterations by Richter, Gren, Lichtenberg, 
and others in Germany. Phlogifton, or the inflammable 
principle, according to the farft of thefe chemifts, is mere¬ 
ly the bafts of light united to coinbuftible bodies. In 
combuftion, this bafis is difengaged, and, uniting with 
a portion of caloric, produces the light or flame which 
ufually accompanies that procefs. The combuftion of 
any inflammable fubftance, phofphorus for inftance, is, 
therefore, to he confidered as the effeCt of a double affi¬ 
nity. The bafe of the oxygenous gas, unites with the 
pholphcrus to form phofphoric acid, while a portion of 
the caloric, difengaged from this gas, unites with the 
phlogifton, or bafis of light, to produce flame. The va¬ 
rieties which occur in the quantity of light emitted by 
different bodies, and in the colours which it exhibits, are 
fuppofed to depend on the quantity of phlogifton con¬ 
tained in thefe bodies, and on the proportions in which 
it is united to caloric. See Critique des Antiphlogifchen Syf- 
tones non J.B. Richter, Brefllau, 1793. SjJlematiches Hand- 
buck des Che?nie van F. A. C. Gren. Halle, 1794- 
Dr. Hutton has likewife publiflied a new modification 
of the phlogiftic doCtrine, together with feveral objec¬ 
tions to the French theory of combuftion. The follow¬ 
ing are his principal conclufions upon thefe fubjeCts: 
1. The caloric, which becomes free by combuftion, did 
not previoufly exift as latent caloric, either in the oxy¬ 
genous gas confumed, or in the coinbuftible body. 2. 
The immediate effect of combuftion is the di/engage¬ 
ment of light, and this light produces free caloric, by 
its aCtion, in the bodies upon which it is incident. To 
ufe .Dr. Hutton’s own words, “it is not heat which is 
the.caufe of light in fire, but it is the light of fire which 
a 
I S T R Y. 
is then the caufe of heat.” 3. The light which is difen¬ 
gaged during combuftion previoufly exifted in the burn¬ 
ing body in the ftate of phlogifton. This phlogifton is 
a peculiar modification of the folar fubftance, exifting 
in combultible bodies, and diftinCtfrom any modification 
of heat. It neither adds to the weight of bodies, nor 
does it feem, like latent caloric, to impair their weight. 
It communicates duCtility and fplendour to the metals. 
It is feparated from its union with gravitating matter 
during combuftion, and appears in the form of light. It 
is formed in plants during the procefs of vegetation, and 
may be transferred from one body to another. See Dif- 
fertaiions on Different Subjeds in Natural Phi/ofophy, and 
Dffmtations upon the Philosophy of Light, Heat, and Fire, 
b/jamesglutton, M.D. 
It would be an endlefs, as well as ufelefs talk, to enu¬ 
merate ail the,different modifications of phlogifton which 
have been propofed by the partizans of that doCtrine, 
fince Lavoifier firft ventured to queftion its exiftence. 
Thofe readers who will take the trouble to perufe all the 
different writings on this controverfy, will immediately 
perceive that no two -chemifts are agreed with regard to 
the precile nature and properties of this principle, and 
that it is merely for the name, and not for the thing, 
that plilogiftians fo eagerly contend. It would be eafy 
to illuftrate the truth of this remark, by a reference to 
the writings of Prieftley; Kirwan, Wiegleb, La Methrie, 
Macquer, Richter, Gren, &c. but this reference is un- 
neceflary. Stahl is univerfally allowed to have been ig¬ 
norant of the principal phenomenon that occurs in every 
inftance of combuftion; and does it not feem ftrange, 
that we fhouid adhere tenaceoufiy to the theory which 
he invented to explain that procefs, and continue to ufe 
the language of a fyftem now fo avowedly defective? 
The theory of Lavoifier, if we may to give it that name, 
is merely a fimple relation of faffs. Unable to difcover 
the fource from which the light is derived in combuftion, 
that philofopher, in his Elements of Chemiftry, has taken 
care not to mix any hypothefis concerning it with the 
faffs he had fully aiccrtained by experiment. Whether 
future dif'coveries flia.Il ftiow, that heat and light are mo¬ 
difications of the fitme fubftance, or that they are cflen- 
tially different from each other; whether the whole of 
the light difengaged in combuftion (hall be found to 
come from the oxygenous gas, or from the coinbuftible 
body, or partly from both, the theory of combuftion, as 
eftabliflied by Lavoifier, will remain unalterably the fame. 
Difcoveries with regard to the origin and nature of light, 
can only tend to widen and toftrengthen its bafis. 
It now remains that we inveftigate the properties of 
heat as a chemical agent, employed in the proceffes of 
decompofing and of combining.natural produflions. The 
firft circumllance to be attended to, is the meafure of the 
degrees of heat neceflary to effeft the changes of which 
the matters under examination are fufceptible. The de¬ 
grees of heat are generally confidered under two princi¬ 
pal divifions ; one comprehending thole under the tem¬ 
perature of boiling water, and the other fuch as are above 
that temperature. The fcale of the thermometer ferves 
to diftinguifh the former; the latter, for the greateft 
part, can be eftimated only from the fufibility of diffe¬ 
rent fubftances. 
The firft divition of heat below the boiling water point, 
extends from 45° to 6o° of Fahrenheit. This tempera¬ 
ture favours putrefaction, vegetation, flow evaporation, 
&c. It is not commonly ufed in chemiftry, becaufe not 
confiderable enough ; except in certain macerations made 
during winter, or for the cryftallization of laline mix¬ 
tures, after due evaporation, placed in caves, or other 
fituations of this temperature. The fecond divifion ex¬ 
tending from about 68’ to 8o°, continues to promote pu¬ 
trefaction. It excites the f'pirituous fermentation in fac- 
charine liquors, and facilitates evaporation, and the flow 
cryftallization which follows. This is the ordinary heat 
of temperate climates. It is ufed for digeftion, f’aline 
l'olutions 
