C H E M I 
*>erty of loading Itfelfwith a greater quantity of fulphuric 
acid than is neceflary to conflitute a fulphat. If ful¬ 
phuric acid be diddled, and concentrated over fulphat 
of potath, this 1 all is impregnated with the acid, and ac¬ 
quires frelh properties. It reddens tindlure of violets ; 
it cryftallizes climbing up the lides of the vellels in 
needles; it has been laid that they always creep towards 
the enlightened fide of the vellels. Its tafte is very lharp, 
pungent, and bitter. It makes aneffervefcence with al¬ 
kalis faturated with carbonic acid. It melts by fire much 
eafier than fulphat of potalh ; and produces a kind of 
glafs, or white opaque enamel, of a very acid flavour. 
It is much more foluble in water than neutral fulphat of 
potafh : by adding fugar to the folution, an imitation of 
a kind of laxative lemonade is produced. 
Sulphat of Soda.— This fait is more abundant in 
nature than fulphat of potafh; it is found plentifully in 
fea-water, in fait fprings, and in feveral mineral waters 
in Lorraine. It has been till now named Glauber's fait , 
from the name of a German chemifl who difeovered it. 
To obtain it very pure, put cryllals of foda or carbonat 
of foda into a flone veflel: diffolve it in a fufficient quan¬ 
tity of warm water; pour into the folution, by little and 
little, weakened fulphuric acid a brilk effervefcence is 
produced, which arifes from the difengagement of the 
carbonic acid; continue to pour on the acid till the ef¬ 
fervefcence ceafes, and till the mixture is perfedlly fatu¬ 
rated as remarked under fulphat of potafh. Strain the 
liquor, and evaporate. When left to cool, it affords 
cryllals fo much the more beautiful in proportion as the 
quantity of matter is larger, and the cooling more (low 
and gradual. When the operation is performed in the 
large way, fix-fided flriated prifms are often obtained, of 
feveral inches in length, terminated by a dihedral pyra¬ 
mid or roof. In the formation of its cryllals, this fait 
admits more than one half its weight of water. It has a 
bitter faltifh tafte. 
Fonrcroy diftinguifhes two kinds of fufion of which fa- 
line matters are capable. The firft, called the aqueous 
fufion, is produced by the water which enters into the 
formation of their cryllals. It obtains only in fetch lalts 
as are more foluble in hot than in cold water ; whence it 
follows, as a confequence, that the water, which enters 
into the formation of the cryllals, by being fo heated, is 
rendered capable of diffolving the faline matter. The 
aqueous fufion is therefore merely a folution in hot wa¬ 
ter. The fulphat of foda, therefore, after this fufion, 
affumes a concrete form by cooling; but, if the heat be 
urged, it becomes dry and white, and another fufion en- 
fues, which is called the igneous fufion, becaufe produced 
merely by the fire. Sulphat of potafh appears to be as 
difficult to melt as fulphat of foda; and, like that fait, 
is volatilized by a violent heat, without fuffering any al¬ 
teration in its principles. 
After the ef'eape of the large quantity of water con¬ 
tained in the cryllals of fulphat of potafh, it becomes 
converted into a fine white powder by expofure to the air. 
This phenomenon is termed efflorefcence, becaufe the pul¬ 
verulent down of the cryllals refembles, in whitenefsand 
form, thole matters which are obtained in chemiflry un¬ 
der the improper name of flowers. As this fait falls into 
powder when in contadlwith air, merely from thelofs of 
its water of cryllallization, the efflorefcence proceeds 
more rapidly when the air is very dry, and confequently 
greedy of moiflure. The phenomenon of efflorefcence is 
therefore very analogous to the drying of this fait by 
heat, both depending fimply on the evaporation of the 
water, which is a eonllituent part of the cryllals. But, 
as the water which enters into the cryllals of fulphat of 
foda, and, in general, of every other efflorefeent fait, is 
truly combined, the efflorefcence appears to take place by 
virtue of a kind of eledtive attradlion between air and wa¬ 
ter, which is greater than between water and the faline 
matter. The fulphat of foda lofes near half its weight 
by efflorefcence, but its properties may all be rellored, 
Vol. IV. No. 152. 
S T R Y. 229 
together with its cryflalline form, by the addition of the 
water it had loft. Though no medical author has attend¬ 
ed to this circumftance, it is certainly of confequence to 
-afeertain the quantity of water which the fulphat of l'oda 
lofes by efflorefcence, that the dofe of the fait preferibed 
may be alwavs of the fame ftrength. It fhould be given 
with a dedudli'on of about one third of its weight when 
in efflorefcence, compared with the fame weight in tine 
tranfparent cryllals. 
The lulphat of foda may be decompofed by charcoal, 
phofphorus, &c. in the fame manner as fulphat of potafh: 
but: it mull be underflood that this decompofition takes 
place, not becaufe thefe Jubilances take away the fulphu¬ 
ric acid, but becaufe they feize upon the oxygen of the 
bafe ; now, as oxygen is a diftant principle, while the 
foda and the acid are the intimate principles: thu,s the 
combuftibles a< 5 l only upon one of the diftant principles, 
and a l'ulphure is obtained. If then we decompofe this 
lulphure by the aid of carbonic acid, a fait is produced, 
which, being calcined, gives pure foda. This is the 
mode which has been propofed for diffolving fulphat of 
foda; but charcoal alone is not fufficient; a calcareous 
carbonat mull be added; in this cafe the lime abforbs 
the fulphur : 1000 parts of fulphat of foda, 500 of char¬ 
coal, and 1000 of calcareous carbonat, will be fufficient; 
Sulphure of lime and carbonat of foda are produced, 
which may be feparated by ley-wafhirig. Scbeele ob- 
ferved, that, by mixing quicklime in a folution of foda, 
and leaving the mixture expofed to the air, carbonat of 
foda was formed, which cryftalljzed creeping up the fide* 
of the veflel. The lame effedl takes place with muriat 
of foda. 
Sulphat of foda quickly diffolves in water, and makes 
it colder; this arifes from the fulphat abforbing a quan¬ 
tity of caloric before it will liquefy. At 10° of heat, 
water diffolves but one-fifth of its weight; but boiling- 
water will diffolve almoft its own weight of this fait. 
Mixed with twice its weight of ice, it produces 2 0 of 
cold, the temperature being at the freezing point. 
The fulphat of foda has no more action on liliceous 
and aluminous earths, than fulphat of potafh, and does 
not enter into the formation of glafs. Barytes is the only 
earth which decompofes this fait; but the falino-terref- 
trial matters have no adtion whatever upon it. Pure and 
cauftic potafh, mixed with a folution of fulphat of foda, 
decompofes it, becaufe of the flronger affinity of that 
alkali to the fulphuric acid. To fhew this fail, cauitic 
potafh mult be poured into a hot and faturated folution 
of fulphat of foda. This folution, which would have af¬ 
forded cryllals of this latter fait by cooling, affords oniy 
fulphat of potafh by evaporation, and the mother-water 
contains the cauftic foda. All the properties in which 
fulphat of foda,differs front fulphat of potafh, fhew that 
the two fixed alkalis, which perfedtly refemble each other 
when confidered in a Irate of purity, are certainly dif¬ 
ferent, fince they form very different falts with the fame 
acids. The proportion of the component principles is 
likewife very different in the two falts we have compared 
together, a centenary of fulphat of foda containing, as 
Bergman finds, fifteen parts of foda, twenty-feven parts 
of lulphuric acid, and fifty-eight of water. This fait is 
not employed in the arts, but is much ufed-in medicine ; 
it is given as a cathartic medicine, from half a drachm 
to an ounce and a half, according to circumftaiices. Its 
effedls are more confiderable and fpeedy than thole of 
fulphat of potafh, becaufe it is more foluble in the fluids’ 
of the animal economy, and becaufe its tafte is more 
penetrating. 
Sulphat of Strontian.— This fulphat has been 
but lately known ; the flrontian was found in the (fate 
of an earthy carbonat in the. places mentioned under 
Jlrontiav, along with a vein of lead-ore. From the ex¬ 
periments of Vauqueiin, native fulphat of flrontian is 
compoled of ten parts of carbonat of lime, five of water, 
and eighty-five of fulphat of flrontian, in one hundred. 
3 N And 
