And the fulphat itfelf of fifty-four parts in one hundred 
of ftrontian earth, and foifty-nx of 1 'ulphuric acid. This 
fulphat is inlipid, infoluble, very white when pure, cryf- 
tallized, and heavy. 
Charcoal decompofes fulphat of ftrontian, but the car- 
bonat of lime mult firft be feparated by an acid; nitric 
acid is commonly tiled; waflt the infoluble part in this 
acid, and treat it with charcoal as directed for fulphat of 
barytes. Thus a fulphure of ftrontian is obtained, which 
may he decompofed by the nitric acid; and then nitiat 
of ftrontian is produced. To have pure ftrontian, heat this 
nitrat in a retort, or rather in a crucible ; the nitric acid 
is decompofed and thrown off, and the ftrontian remains 
pure. This fait, when formed by art, exilts in the form of 
a white powder. It has no tafte, and very little folubility 
in water. Of one grain boiled for fome minutes in four 
ounces of diftilled water, only half a grain was dilfolved. 
The folution became turbid, by the addition of the car- 
bpnat of pot&Qi, and muriat of barytes. Sulphuric acid, 
when aided by heat, readily diffolves it. An eftufion of 
water, however, caufes the acid to part with the fulphat 
of ftrontian. 
Sulphat of Lime. —This fait exifts in large quanti¬ 
ties in nature: it is termed felenite , plafter, and gypfum ; 
but ought to be denominated, as Fourcroy remarks, cal¬ 
careous fulphat . .There are nine varieties of fulphat of 
lime d : .Laminated by that author, as follow: i. Sulphat 
of lime, or felenite in rhomboidal laminae. 2. Sulphat of 
lime, or cuneiform felenite, or of the figure of arrow¬ 
heads. It confilts of two fcalene triangles, joined in,the 
middle, each being c Graph fed of triangular laminae, ac¬ 
cording to the observation of De la Hire. It is called 
lapis fpecularis , ajj'es mirror , or talc of Mdntmcirtre . Thele 
two firft varieties are fragments of large cryitals, and are 
formed by the hand of man. They are mentioned here 
only as being fpecimens for the cabinet. 3. Sulphat of 
lime, or felenite in decahedral rhomboids. The quarries 
of Palfy afford this fort. 4. Sulphat of lime, or lelenite 
in decahedral prilins. It is formed of hexahedral prifms, 
terminated by dihedral pyramids, or by a concave angle ; 
it is found in Switzerland, &c. and refembles much the 
preceding variety. 5. Sulphat of lime, or felenite in 
cock's combs from Montmartre. It conlifts of a collec¬ 
tion of small lenticular cryitals, placed obliquely befide 
eacii other, and is formed by the union of the cryitals 
delcribed No. 2. 6. Sulphat of lime, or fiiky or ftriated 
felenite; fiiky gypfum of China. It is found in Franche 
Comte, Angoumois, See. It is formed by the union of 
flender prifms, which are molt commonly brilliant, and 
of the appearance of latin. It is very difficult to obferve 
the rhomboidal lamina:, which are found in all the other 
.varieties. 7. Sulphat of lime, or common gyplum, or 
piaftcr-ltone. This fubftance is white, more or lefs in¬ 
clining to grey, interfperfed with final! brilliant cryitals, 
eafily cut with a knife. It is found difpofed in ftrata, 
and forms molt of the mountains in the vicinity of Paris. 
We Ihall hereafter find, that it is not pure felenite, but 
owes its moft valuable property, as plafter, to the admix¬ 
ture of another kind of earth. 8. Sulphat of lime, or 
gypfeous alabafter. This is a kind of plalter-ltone, harder 
and more ancient than the foregoing, from which it dif¬ 
fers only in being femi-tranfparent, of a yellowilh grey, 
and in its laminated form or Itrudture apparently con- 
filling of final 1 plates. It is found in great plenty at 
Lagny, near Paris. This is one of the whiteft kinds; 
but it has fometimes yellowy grey, violet, or black, ipots 
or veins. 9. Sulphat of lime, or felenite, common gyp¬ 
fum, or gypfeous alabafter, varioully coloured, veined, 
fpotted, clouded, or pundiuated. This mixture of co- 
.lour fnews, that the lelenite is contaminated by fome 
foreign fubftance. The colours are almOft always occa- 
fioned by iron. Calcareous fulphat is likewile found 
dilfolved in waters, as in the well-waters of Paris; it is 
never pure*, but is always combined with fome other 
earthy fait, with bafe of lime or magnefia. This fait has 
I S T R Y. 
no apparent degree of tafte. Icdecrepitates if a fudden 
heat be applied to it; it is then of an opaque white, in 
which Hate it is called fine plafier, or plafter of Paris ; 
by this calcination it loles about twenty in one hundred. 
It is not decorr.pofable by the contact of the air; it lofes, 
however, lome of its tranfparency, becomes tarnilhed 
with various colours, and fplits or feales off". Moifture 
waftes it away. It requires feventy or feVenty-two parts 
of water to dilYolve one of fulphat of lime. After the 
dilToiution, the water is heavier, of an infipid tafte, and 
heavy on the ftomach. The well-water of Paris holds 
it in folution; for, when left to fettle, fulphat of lime 
is depofited in very fmall cryitals, or in a grey pow¬ 
der. Vegetables become hard by being boiled in this 
kind of water. The experiment is eafily tried by boiling 
an equal quantity of fome vegetable, French beans for 
inftance, for an equal time, in equal quantities of water 
loaded with this fait, and of pure water. 
Charcoal decompofes fulphat of lime ; and, if the plaf¬ 
ter is not very dry, carbonated hydrogen gas is produced 
alio. Take an earthen retort; put therein one part of 
charcoal to feven of plafter; fix to the retort a bent tube, 
which is' to go under a jar in the pneumatic ciftern. The 
fulphat of lime falls to the Hate of a fulphure, which is 
found in the retort; and under the jar is obtained car¬ 
bonic acid gas, and carbonated hydrogen gas. The ful¬ 
phure of lime contains lei's fulphurated hydrogen than 
that of potafli; and it is laid, that by ufing fulphure of 
lime, initead of alkali, at the Irifh bleach-fields, on the 
fuggeftion of Dr. Higgins, there will be effe&ed a diredt 
faving to the amount of 102,653b 5s. per annum. 
To prepare hydro-fulphure of lime, temper fome lime 
with diftilled water, and impregnate it with water charged 
with fulphurated hydrogen : leparate the liquor, and fu- 
perfaturate it with fulphurated hydrogen gas. Barytes, 
ftrontian, and the fixed alkalis, have more affinity with 
the fulphuric acid than lime has: by pouring a folution 
of thele fubftances into water charged with fulphat of 
lime, a precipitate is formed. If impure fulphat of lime 
be left in digellion with muriatic acid, the fulphat is 
precipitated in cryitals, and the lime is dilfolved in the 
liquor. In calcining plafter for buildings with wood, 
the flame pafl'es, through it; at the fame time a fimali 
portion of fulphure of lime is produced; and, if water 
be poured on this frelh-burnt plafter, a ftrong fmell of 
fulphur arifes. But burnt plafter is not pure; fome quick¬ 
lime is contained in it, which, abforbing the water poured 
on it, caufes heat; this heat arifes alfo from the caloric 
of the folidified water which is difengaged during cryl- 
tallization. ■ > - 
If an acid be poured upon pure plafter, there is no ef- 
fervefcence; but with plalter-ltone there is eftervefcence, 
becaufe the carbonic acid of the carbonat of lime is there¬ 
by diflipated. Burnt plafter kept a long time, effervefees 
with an acid, becaufe the lime which it contains has had 
time to recover the carbonic acid, which it had loft by 
diftillatlon; fo that, to keep it pure, it Ihould be kept as 
much as pofiibie from contadl with the air. If calcined 
plafter be moiltened, it recovers irs water of cryftalliza- 
tion, which it folidifies. It hardens alfo, 1. Becaufe the 
fulphat of lime cryltallizes; 2. Becaufe the lime, in ab¬ 
forbing the carbonic acid, purifies itfeif; and the union 
of thele two kinds caufes folidity. 
It is the carbonat of lime which is in the plafter, that 
occafions dry plafter to decay fo quickly, when the wails 
are expofed to moifture and animal fubftances; for the 
lime then combines with the nitric acid which is formed. 
This folubility conftitutes the chief difference between 
plafter and mortar; the land in this laft, which gives fo- 
lidity, not being attacked by the water. Plafter is not, 
on this account, ufed in humid or moift places, nor in 
any works near or under water. 
Sulphat of Ammoniac. —Ammoniacal fulphat, for¬ 
merly called vitriolic ammoniacal fait, or ammoniacal vi¬ 
triol, is produced by a laturated combination of fulphu¬ 
ric 
