i6o CHE M 
and each other, are compound bodies. Such are aim oil 
all the combuftibles we meet with in nature : it is the 
province of art to feparate them from each other, and 
exhibit them pure and ifolated. When we compare the 
properties of compound combuftible bodies with thofe of 
iimple combuftibles, we perceive, that the former fome- 
times abforb oxygen with more avidity than if they were 
alone, as many metallic fulphures, and alloys ; at other 
times, on the contrary, we find them lefs ready to burn, 
on account of the ftrong attraftion they poffels for each 
other, which is the cafe in general with phofphorated 
metals. There are even fome that are long unalterable 
in the air, appearing to have loll by their intimate com¬ 
bination the property of being combuftible, which they 
exert only when ftrongly heated;, as the carbure of iron, 
which is even employed with fome l'uccefs to prevent iron 
from contrafting ruft. 
Hydrogen and carbon, very intimately united together 
in the capillary tubes of vegetables, and frequently con¬ 
taining fmall portions of earths, alkalis, acids, and elpe- 
cially oxygen, form bitumens, oils, and refins, which, 
though they have a tendency to burn and feparate, pre- 
ferve fome time the equilibrium, of their combination, 
till a rapid increafe of temperature, accompanied with 
the contaft of air or water, puts an end to this equili¬ 
brium, by il’olating their elements, and uniting them fe- 
parately with cxygen. Accordingly the produfts of thefe 
compound combuftibles are univerl'ally water and carbo¬ 
nic acid. It is the fame with alcohol, and with ether, 
formed by modifications of the principles of vegetable 
matter, which, in their ultimate analyfis, are nothing elfe 
than combinations of hydrogen and carbon with more or 
lefs oxygen and water. 
This exhibition of the different fpecies of combuftible 
bodies, and their principal cliarafteriitic properties, fhows 
the part they aft in the phenomena of the globe. It 
authoril'es us to divide almoll ail the productions of na¬ 
ture into two grand claffes, one of combuftible bodies, 
the other of bodies already burnt. In the mafl'es and ac¬ 
tion of the former we difcern the caufes of inflammable 
meteors, partial heat, volcanoes, the perpetual alterations 
of the furface of the earth. See. in the exiftence of the 
latter, we perceive the fourceof thenumberand diverfity 
of acids, laline compounds, oxyds, and metallic falts, 
which vary in a thoufand ways the appearance of ores, 
their reciprocal decompofition, and their alterations by 
the aftion of water, air, and light; in fine, we difeover 
in vegetables machines which nature has organized for 
the purpofe of intimately combining feveral of thefe fub- 
itances with each other, in order to form compounds more 
fubfervient to its grand defigns, as they are lefs durable 
and permanent. And hence we deduce the circumftan- 
tial hiftory of the combuftion of eacli combuftible :ub- 
llance in particular : the hiftory of foils impregnated 
with fulphur, and of native fulphuric acid : the pheno¬ 
mena of natural inflammable gafes in quarries, mines, 
the atinofphere, &c. the properties of earthy, alkaline, 
and metallic, fulphures: the converfion ot fulphures into 
lulphits andlulphats by the aftion of air and water: the 
properties, extraction, and combinations of phofphorus; 
.alfo metallic pholphuresthe exiftence of native metallic 
carbtires: the phenomena depending on the denfity, 
weight, duftility, and fufibility, of metals : the properties 
and ufes of alloys : the formation of fecondary ores from 
native metallic falts: volcanoes, and lulphurous and ther¬ 
mal waters: bitumens;' the companion of fulphur, car¬ 
bon and Iimple combuftible bodies, with oils, &c. 
THE FORMATION AND DECOMPOSITION OF ACIDS. 
Since all acids refemble each other in their tafte, their 
manner of giving a red colour to vegetable fubllances, 
their tendency to combine with earths, alkalis, and me¬ 
tallic oxyds, and their property of attrafting, and being 
attrafted powerfully, it was natural to prelume, as New¬ 
ton obferved, that they likewife refembled each otliev in 
I S T R Y. 
their intimate nature, and poffeffed fome homogeneal 
principle : and chemical analyfis, by the help of the new 
means it has in its power to employ, has eftablifhed this 
as a truth beyond the poffibiiity of doubt. 
As every acid contains oxygen, and lofes its acidity 
exaftly in proportion as it is deprived of this principle, 
we ought to confider acids as burnt or oxygenated fub- 
ftances, which are akin to each other from the prefence 
of the acidifying principle. There are two methods of 
acquiring a knowledge of the nature of acids : one by 
forming them, by compofing them from their conftituent 
parts, in uniting with oxygen fuch lubftances as are ca¬ 
pable of becoming acid by an union with it: the other 
by decompofing them, by Unburning them, in depriving 
them of their oxygen by the aid of lubftances with which 
this principle has great affinity. Confidered in the lafl- 
mentioned viewy all known acids may be divided into 
three claffes, namely, ill, Thofe which may be both com- 
pofed and decompofed, of which our knowledge is moll 
complete : ?,dly, Thofe which we can only compofe, be¬ 
ing incapable of decompofing them; and with thefe alfo 
we are well acquainted: jdly, Thofe which have neveryet 
been either compofed, or decompofed; the nature of which 
remains altogether unknown, Since then, out of thirty 
known fpecies of acids, as there are but three, ftriftly 
fpeaking, which are in the lall predicament, or which we 
can neither compofe nor decompofe, fo that we are ne- 
ceffarily ignorant of their nature, there is no reafon why 
we fhould not regard fubllances of this kind as accurate¬ 
ly diferiminated, and contemplate their general proper¬ 
ties and compofition. 
All acids being compounds 'of oxygen with different 
fubllances, the former principle is the caufe of their re- 
femblance and common properties; the latter, being 
different in each, may ferve to charafterize each in par¬ 
ticular. For this reafon, thofe matters which are vari¬ 
able in acids are termed their radicals, or acidifiable prin¬ 
ciples. Thus all acids are combinations of radicals, or 
acidifiable lubftances, different in each fpecies, with oxy¬ 
gen, which is the fame in all: whence it follows, that 
their common properties, their charafters as acids, de¬ 
pend on oxygen ; their particular properties, their fpe- 
cific charafters, arife from their radicals. The word 
acid, indicating the general and identical nature of thefe 
fubllances, forms their generical name, while the parti¬ 
cular name of the radical contained in each may with 
propriety defignate each particular acid. Thus fulphur 
is the radical of the acid we name fulphuric, phofphorus 
that of the pkofphoric, carbon that of the carbonic , and fo 
on. Tut, though this nomenclature enjoys the advantage 
of exprefling the nature of each acid, we are unable to 
employ it for all, becaufe the radicals of fome are un¬ 
known, and thofe of others are themfelves compounded 
of feveral principles, and wmuld confequently require too 
complicated appellations. 
Acidifiable radicals may contain different quantities of 
oxygen, and under this point of view' they poffels two 
ftates of acidity. The firft is that, in which they contain 
the leaft poffible quantity of oxygen to render them acid. 
In this their acidity is commonly weak, and they adhere 
but feebly to the bales with which they are capable of 
forming falts. The modern methodical nomenclature 
defignates this ftate of combination and acidity, by giv¬ 
ing the names of thefe weak acids the-termination ousi 
Tftus we fay the lulphurous, nitrous, phofphorous, or 
acetous, acid. The fecond ftate of acids is that, in which 
they contain more oxygen, and in general are complete¬ 
ly laturated with it. In this they have all the fbrength 
and attraftion they are capaple of poffeffing as acids, and 
the modern nomenclature expreffes it by the termination 
ic. Thus we fay the fulphuric, nitric, phofphoric, or 
acetic, acid. With regard to the proportion of oxygen 
united to acidifiable radicals, Hill greater latitude may be 
given to the considerations prefented above. Each radi¬ 
cal may be contemplated in four ftates: ill, Containing 
very 
