C H E M I 
or any other acid, be added, which has no aflion on hy¬ 
drogen, fulphyraired hydrogen gas will be dil'engaged, 
without any depofition of fulphur; but, if the hydro-ful- 
phure has become coloured, a depofition of fulphur will 
take place in proportion to the changes which the lul- 
phurated hydrogen has already Undergone. It is the hy¬ 
drogen, therefore, which is firlt diminifhed in the decom- 
pofition of lulphurated hydrogen. In combining with 
the oxygen of the atmofphere to form water, it quits the 
fulphur, but a portion of the fulphur is loon changed 
into an acid ; and when the fulphurated hydrogen has 
been reduced to a certain point, the oxygen a&s equally 
in decompofing it upon the hydrogen and the fulphur. 
If an hydrogenated fulphure be expofed to the a&ion 
of the air, it abforbs oxygen, which a£fs on the hydrogen 
and fulphur. In proportion as hydrogenated fulphur is 
decompofed, there is a depofition of fulphur produced ; 
but in the decompofition of a hydro-fulphure, no depo- 
fition whatever takes place. It is the fulphuric and not 
the fulphureous acid which is formed, when water is de¬ 
compofed, to produce fulphurated hydrogen, but it is the 
fulphureous acid which is formed by the fpontaneous ab- 
forption of oxygen from the atmofphere. In the former 
cafe the oxygen is more completely deprived of its calo¬ 
ric, and confequently difpoled to enter into a clofer union. 
Sulphureous acid, in contact with fulphurated hydro¬ 
gen, yields its oxygen to the hydrogen ; and the fulphur 
contained in the fulphureous acid, as well as that in the 
fulphurated hydrogen, is precipitated. Nitric acid alfo 
decompofes fulphurated hydrogen, by yielding its oxygen 
to the hydrogen. But this adtion of the nitric acid is 
dedroyed, or, at lead, greatly weakened, by diluting it 
with water. Ann. de Chem. tom.xxv. p. 233. 
Of METALS. 
Metals are a peculiar clafs of combuftible bodies. Me¬ 
tallic oxyds are nothing more than combinations of me¬ 
tals with oxygen. Some of thefe oxyds even pafs into 
the acid date ; fuch are, arfenic, tungden, molybdena, 
and chrome. A certain quantity of oxygen deprives 
metals for a time of their metallic brightnefs; a larger 
quantity dedroys that brightnefs entirely ; and the pro¬ 
portion of oxygen may be increafed fo as to give the 
oxyds a complete earthy appearance. 
Metals have not the fame elective attraction for oxy¬ 
gen. In a general view they may be divided into two 
claffes, acidifiable metals, as arfenic. See. and oxydable 
metals, as copper, tin, &c. 
Metallic acids may be obtained in two different dates, 
namely, arfenious acid, and arfenical acid. There are 
alfo different dates of oxydation in metals, as, grey oxyd 
of zink, and white oxyd of zink. Metals prelent alfo 
two forts of combudion, the flow and the rapid: zink 
may furnifh an example of each, the dow being perform¬ 
ed by fufion in an iron fpoon with air, the rapid by in¬ 
flammation in a crucible. The peculiar properties of 
metals will be hereafter deferibed. 
Of WATER. 
Water is to be confidered as prefenting itfelf, in three 
forms ; the lolid, as ice ; the liquid, as common water; 
and the gafeous, as fleam or vapoxir. 
Ice, or solid Water. —Ice feems to be water in its 
natural date; for the natural date of a body, chemically con- 
fidered, is that in which it has the Arongeflpoflible aggre¬ 
gation. But, as water is mod abundantly found in the li¬ 
quid date, this lad has been condantly regarded as the na¬ 
tural date of water. The formation of ice is attended with 
feveral concomitant circumdances, which well deferve to 
be confidered. A heat of fome degrees of Reaumur’s ther¬ 
mometer is produced in the water by the adt of free zing, 
as is always the cafe when a liquid body is changed into 
a folid. This thermometer, plunged into the water be¬ 
ginning to freeze, will indicate a temperature fome de¬ 
grees above zero; though another thermometer, placed 
Vol. IV. No. 190. 
S T R Y. 205 
in the furrounding atmofphere, fufficiently cold to freeze 
water, will remain at this point, or even fink below it. 
It follows, therefore, that a portion of the heat which 
was fixed in the liquid water is dil'engaged when it be¬ 
comes converted into a folid; and accordingly we find 
the fpecific heat of ice inferior to that of water. The 
lame heat is obfervabte in the crydallization of falts. 
The accefs of air favours the production of ice. Water 
in a well-clofed vefiel freezes very flowly ; but if the vef- 
fel be opened, it freezes much more quickly, and fiome- 
times in the inflant of expofure to the contact of the air. 
This phenomenon is fimilarto that which happens in the 
crydallization of falts. Solutions of frdts in doled 
veflels frequently exhibit a fudden crydallization when 
uncovered, and expofed to the contact of air. A flight 
degree of agitation likewife accelerates this formation ; 
in which refpeft, alfo, we find a fimilitude between this 
and the crydallization of falts. By agitating certain fa- 
line folutions which do not ufually afford crydals, it is 
fometimes found that they are by that means produced. 
We have often feen this in folutions of calcareous ni- 
trats and muriats. Thefe analogies between the for¬ 
mation of ice and of faline crydals prove tbit the former 
is obtained by a true crydallization. 
Ice feems to have a greater bulk than the water had be¬ 
fore it was frozen, and even breaks, by its expanfion, 
the veflels in which it is formed. This expanfion of wa¬ 
ter, while converting into ice, is fo great, as to be al- 
mofi incredible. Several philofophers have endeavoured 
to mealure the degree of this force; and from their com¬ 
putations it would appear, that the expanfion of a cubic 
inch of water, during its converfion into ice, isfuflicient 
to raife a weight of 27001b. The knowledge of this fait 
affords a ready explanation of the hunher in which trees 
are often fplit, and even the harded'rocks rent al'under, 
during intenfe froff. Fourcroy fays, it is not the water 
which acquires a greater expanfion in this cafe ; but the 
air, which is feparated from the water during congela¬ 
tion, that is the true caufe of the increafe of bulk. But 
this explanation is by no means adequate to account for 
the phenomenon. The force with which the ice expands 
is greater than what can poflibly arife from the fucceflive 
difengagements of fmall portions of fo comprefiible a 
fluid as air ; and befides, it is known that the volume of 
a given quantity of water, deprived completely of its 
air by boiling, or by means of the air-pump, is very fen- 
fibly increafed during its converfion into ice. We are, 
therefore, inclined to aferibe, with M. Mairan, this in- 
creale of bulk to the new, regular, and cryflallized, ar¬ 
rangement which the particles of water affume in freezing. 
Properties of ice. —1. When flowly formed, its crydals 
have the figure of needles, eroding each other at an angle 
of 60 or of 120 degrees. Sometimes its crydallization 
takes a determinate and regular form. M. Pelletier ob- 
ferved, in a piece of fidulous ice, crydals in the form of 
flat quadrangular prifins, terminated at the ends by di¬ 
hedral pyramids, though with great varieties. If, on 
the contrary, water, in a confiderable mafs, be frozen 
fuddenly, it forms only an irregular folid, in the fame 
manner as happens when fidine liquids are too much eva¬ 
porated, and cooled fuddenly. 2. Its confidence is fuch, 
that it may be reduced to dud. In very cold climates 
the ice is lb hard, that it is cut like flones, and has been 
employed in the conflrudtion of edifices. We are allur¬ 
ed, that even cannons have been bored out of ice, 
which have been charged with powder, and difeharged 
feveral times before they melted. 3. Its eladicity is very 
flrong, and much more remarkable than that of fluid 
water. A ball of ice, thrown on a hard lurface, rebounds 
in the lame manner as other folids. 4. It has a lively 
taffe, approaching to caudicity. The imprelfion of ice 
on the ienfe of feeling is univerfally known. Phyficians 
employ it as a tonic or difeutient, &c. 5. Its fpecific 
gravity being lei's than that of water, it fwims on the 
lurface. The fpecific gravity of ice is faid to be about 
v, 3 G i-toth 
