C H E M 1 
buflible bodies, generally fpeaking, which decompofe 
water, are thole which have a greater affinity, or ftronger 
attraction, for oxygen, than hydrogen has : but this at¬ 
traction is greatly affifted by the prefence of caloric, which 
has a tendency to unite with the hydrogen. A large 
quantity of caloric can even occafion the decompofition 
of water by bodies which would be incapable of decom- 
pofing it cold. To this light equally contributes. The 
combuftible bodies which will not decompofe water at 
any temperature, in confequence of their feeble attrac¬ 
tion for oxygen, which in this cafe always remains infe¬ 
rior to that which fubfhls between oxygen and hydrogen, 
muft, on the contrary, when they'have been burnt, by 
other means, be decoffipofed, or fuffer their oxygen to 
be taken from them, by hydrogen. This happens to the 
oxyds of lead, bifmuth, See. 
Hitherto the art of chemiftry has arrived at the know¬ 
ledge.of no means of decompoiing water, but by cornbuf- 
tible fubflances, which take from it its oxygen. We are 
unacquainted with any capable of attracting its hydrogen, 
and felling its oxygen free. It would ieeni, however, 
that nature has inllruments for e fie Cling this inverfe 
manner of decompofing water: the leaves of vegetables 
ltruck by ihe j ays of the fun appear to.decompofe water 
by abforbing its hydrogen, and difengaging its oxygen 
in the form of vital air. This we may prefume to be in 
part the mechanifm- of vegetation, of the formation of 
oils, and of the renovation of the atniofphere. While 
hydrogen and oxygen, each diffolved into gas by caloric 
and light, remain in contaft with each other cold, they 
do not combine ; no inflammation occurs, no water is 
formed. But if the mixture be expofed to an ignited 
body, ftrongly fpmpreffed, or affefted by any violent and 
forcible concnfficn, a combination of the two commences, 
combuflion takes place, and water is produced. A fimi- 
lar phenomenon appears to take place in the atmofphere. 
Atmofpheric detonations, claps of thunder, leem to be 
nothing more than a combuflion of hydrogen gas and 
vital air; and accordingly they are often fucceeded by a 
torrent of rain. Some llorms of rain alfo appear to be 
in like manner owing to a fudden formation of water in 
the atmofphere, from the rapid combuflion of hydrogen 
gas'and vital air, occafloned by an eleClric fpark, arifing 
from the necefiary re-eltabliflinient of an equilibrium of 
eleftikity between different clouds, or between the clouds 
and the earth. A multitude of chemical phenomena of 
nature and ait, formerly inexplicable and ranked as mi¬ 
raculous, ate now efteemed the necefiary confluences 
of the decompofition of water well underflood. Of the 
truths thus exhibited the influence on the general theory 
of chemiftry is immenfe, as will appear in our experi¬ 
ments hereafter to lucceed. From thefe data we deduce 
our knowledge of artificial refrigerations : the theory of 
the permanent ice covering the tops of mountains, and 
the neighbourhood of the poles : the varieties of atmof- 
pheTic and terreflrial waters : the art of correcting the 
bad qualities of waters : the theory of the ebullion of 
water: the difference between boiled water and water 
pregnant^with air : the diflil lation of water in the great, 
and that of fait water: the theory of fogs and dew : the 
tlieoiy of the hygrometer, and liygrometiical phenomena: 
the burning of combuflible fubflances by means of water: 
the gales difengaged from Aagnant waters : the variety 
of inflammable gafes : the colouring of fubflances by in¬ 
flammable gafes : the oxydation of metals, or rufl, pro¬ 
duced by damp air: the theory of detonations : lome 
phenomena of metallic l'olutions : fome fundamental prin¬ 
ciples of thetheoryof vegetation, the formation of oils,&c. 
THE NATURE AND ACTION OF EARTHS AND ALKALIS. 
What was formerly called earth by way of eminence, and 
confidered as an element, and the caule cf folidity, dry- 
nefs, infipidity, indifiblubilify, &c. is now conligned to 
that clafs of vague and indeterminate ideas, which the 
imagination, unlatisfied with the fuccefs of experience, 
Vol, IV. No. 186 ,' 
S T R Y. 157 
invented to fupply the place cf fafts. At prefent no ele¬ 
mentary earth is acknowledged ; and inflead of one earthy 
fubftance, we have at leafl five, all of which have an equal 
claim to be denominated elements; for each enters into 
the compofition of various bodies. Of the five earthy 
fubflances that have been difcovered, two are in fome 
meafure more earthy, dry, fufceptible of hardnefs, infipid. 
Sec. while the other three poffefs faline properties, which 
; render them fomewhat akin to the fubflances denominat¬ 
ed alkalis. Tliefe three, which have in confequence been 
termed lalino-earthy, faline earths, alkaline earths, and 
earthy alkalis, are baryt, magnefia, and lime. 'I'he other 
two are filex and alumin. The generical characters com¬ 
mon to all thefe are drynefs, unalterablenefs in the fire, 
infufibility, and the quality of being infufeeptibie of de¬ 
compofition, and aiding as Ample and indeftruftible fub¬ 
flances in combination. Belides thefe, each has fpecific 
characters by which it is diftinguilhed. 
Silex, which has been named filiceous earth, quartzofe 
earth, and vitrifiable earth, is rough to the touch ; it 
feratehes and wears away metals ;'it is infufible, incom- 
buflible, infoiuble in water and mofl acids, foluble by 
alkalis in a flrong fire, and forming glafs with thefe fairs. 
It is found in abundance in land, quartz, flint, agate, 
jafper, fandflone, and ail flones that llrike tire, of which 
it conflitutcs the balls. It has neither been analyfed, nor 
imitated by fynthefis. Some have confidered it as the 
mofl Ample of tire earths, the terreous element, the ori¬ 
gin of all the other earths j but experience has not fup- 
ported their affections. It is employed for various pur- 
pofes, particularly for miil-fiones, and making glafs, ce¬ 
ments, earthen-ware, &c. 
Alumin, fo named becaufe it conflitutes the bafis of 
alum, the fame which fome authors have called argil, is 
foft to the touch, and adheiiveto the tongue ; it hardens 
in the fire, makes a palte with water, unites with mofl 
acids, dries in flakes, acquires great hardnefs when mixed 
with water and filex, and is contained in a large propor¬ 
tion in clays, fchifls, (leatites, &c. It is employed for 
various purpofes of art, from its aptitude for moulding 
into different forms, and retaining them, audits quali¬ 
ties of hardening in the fire, and holding water. By 
fome it has been erroneoufly confidered as Alex changed, 
attenuated, and rotted, by the aftion of air and water ; 
but with its intimate nature, or principles, we are totally 
unacquainted. 
Baryt, or hea-uy earth, is remarkable for its extreme 
ponderoAty. This is never found alone in nature, but 
always united with the fulphuric or carbonic acid. In 
the Are, and in contact with the Alex or alumin ot the 
crucible, it affumes a blue or green colour : it is fblubie 
in nine hundred times its weight of water, changes fyrup 
of violets green, has a ftronger affinity even than alkalis 
for mofl: acids, and will any where deleft the prefence of 
fulphuric acid, and indicate its quantity. Its principles are 
unknown, though it is fulpefted of being a metallic oxyd. 
Magnefia, is very fine, very white, unalterable in the 
fire, loft, and light. It refembles vegetable fecuke, re¬ 
quires near two thoufand parts of water to dilfolve it, 
very flightly greens the tinfture of violets and mallow 
flowers, forms with acids extremely foluble falts, and is 
lefs retentive of acids than lime, which attrafts them 
from ic, having nearly the fame affinity for them as am¬ 
moniac, with which and acids it forms falts with two 
bafes, or a clafs of triple falts. Il exills in conliderable 
quantity in lerpentines, mica, flates, and amianthus ; is 
equally incapable of analyfis with the preceding earths ; 
and, like theirs, its compofition is unknown. 
Lime is the mofl alkaline of earths, and the only one 
that poffelfes an acrid, burning, almoil cauflic, difagree- 
able, and urinous, tafte. It is very powerful in convert¬ 
ing the fyrup of violets to a green colour ; attrafts water 
from the atmofphere when flacked in it; heats greatly 
with water, and becomes foli'd with it; gives out a large 
quantity of caloric when flacked dry; diffolves in lefs 
S f " tl>an 
