CHEMISTRY. 
acid yields its oxygen to gold, when it is mixed with mu¬ 
riatic acid; though, if alone, it does nor part with any, 
becaufe the affinity of the nitric acid for the oxyd ot gold 
is not lufficient to produce the decoinpofition of a part of 
the acid. Itistherefore the pre-exilling affinity of theoxyd 
of gold for the muriatic acid, which is very ltrong, that fa¬ 
vours the oxydation of that metal. It is all'o in this manner 
in confequence of the greater affinity which alkaline and 
earthy bales have for the lulphuric and phofphoric acids, 
that thele bafes folicit, as it were, the fulphits and phof- 
phits to abl'orb a freffi quantity of oxygen, in order to 
unite with their acids more clolely or completely. But 
as the lulphuric acid has a much ltronger affinity for al¬ 
kaline fubftances than the phofphoric, the combuftion 
of the fulphits mult be more rapid than that of the pliof- 
phits. In addition to this, there feems to be a greater 
difference between the affinity of the fulphuric and fu'l- 
phurous acid for the fame fubftances, than between that 
of the phofphoric and phofphorous; the pholphoms in the 
phofphorous acid being in a (late of much more complete 
combuftion than the iulphur in the fulphurous acid ; fo 
that, being furrounded by a great number of particles of 
oxygen, its affinity for this principle is proportionally 
diminiflied, and confequently the combuftion.of thephol- 
phits is rendered lefs energetic. 
Of F.LUATS. 
Tliefe have in general two properties: fome have but 
little tafte, and are hardly foluble; others have more 
tafte, and are more foluble. Some cryftallize; others 
not. The ftronger acids decompofe them all; fo does 
lime. Heat alio decompofes the greater part of them. 
Fluat of Lime. —This fluat is found native in the 
neighbourhood of mines, and in the ores of lead, filver, 
cobalt, copper, &c. There are ten varieties partaking 
of different colours, as blue, green, white, red, &c. 
This diverlity of colours arifes from the prefence and 
ftate of the iron, which affumes various hues, according 
to the quantity of oxygen it contains. The molt beau¬ 
tiful fluor fpar, and the rarelt yet known, is the white ; 
the green is the moft common, and next to that the ame- 
thyftine. It is neither denfe, hard, nor fulceptible of a 
line polilh ; it has commonly a lamellated appearance, 
and is mingled with quartz. That which is called white, 
has always a caft of yellow. It is called fluor fpar', vi¬ 
treous fpar, fpath fluor, phofphorous fpar, and calcareous 
fluat. Tliefe fiuats are in general one and the fame faline 
fubftanqe, that is to lay,' the combination of the fluoric 
acid with lime. This fpecies of fait is three times the 
weight of diftiiled water. Harvey difcovered that its cryf- 
tal was a perfeft octahedron, which afterwards diminiflied 
into a cube. 
The calcareous fluat, broken in pieces, and heated in 
a red-hot {hovel, gives out a violet phofphoric light; but 
it is only the coloured fpar which does this, fo that it ap¬ 
pears the light is due only to the colouring lubftance. 
Scheele made fome experiments on this fubjeft; and he 
has demonftrated, that, when this fpar has once been 
expofed to a red heat, it cannot be made phofphoric again 
by a lecond calcination. Scheele fuppoled alfo that the 
phofphoric property was due to the combuftion ; but the 
matter is phofphoric in vacuo : fo that the caule of the 
phenomenon is not yet known. 
Heat melts this fait, but does not decompofe it: it be- 
comse a fort of enamel; when fuddeniy heated, it decrepi¬ 
tates almoft as ftrongly as muriat of foda. By the help of the 
blow-pipe, it may ferve as a lblvent for ores. It is not 
altered in the air, nor foluble in water, yet it will dilfolve 
and cryftallize of itfeif. Sulphuric, nitric, and muriatic, 
acids, decompofe the fluat of lime. The refldues are fait 
with a bafe of lime, contrary-to what is aft'erted by Mon- 
net; and the acid obtained is of a peculiar nature, no¬ 
thing like the acids employed, as we have already (hewn, 
in the examination of the fluoric acid. When this de- 
compolidon is made, the acids muft be diluted with wa¬ 
255 
ter, that the falts which are formed may find water for 
their folution ; they feize on it quickly. Without this 
precaution, the imall quantity of water which the con¬ 
centrated acid contains is prefently abforbed, which clogs 
up the mixture, hinders the point of contaft, and may 
even flop the operation. The calcareous fluat is not 
however decompofed by any alkaline or earthy matter; 
but, if alkalis in the ftate of carbonats be tiled, then the 
double affinity is excited, and a double decompoiition 
takes place. For this purpofe, one part of this fluat be¬ 
ing fufed with four parts of carbonat of potaffi, and 
poured hot into water, a precipitate of chalk, formed 
by the carbonic acid united to the lime of the calcareous 
fluat, is obtained; and the fluid holds in lolution fluat 
of potafti, which may be obtained, by evaporation, in 
the form of a jelly. When the experiment is repeated 
with carbonat of foda, chalk and fluat of foda are in like 
manner obtained ; aifo a cryftallized fait. 
Calcareous fluat is of no ufe excepting in fome mineral 
countries, where it is uled as a very good flux. It might 
be applied to the fame purpofe in allays. 
Fluat of Barytes. —The fluoric acid poured on a 
folution of nitrat or muriat of barytes, occafions a pre¬ 
cipitate; and this precipitate effervefces with the fulphu¬ 
ric acid, which dilengages the fluoric acid. This expe¬ 
riment proves, that Monnet was wrong in ftating, what 
he has repeated in his very laft work, that the fulphuric 
and fluoric acids were fimilar. This fluat is decompofed 
only by lime, and the alkalis in a carbonaceous ftate. 
Fluat of Strontian. —This la It has as yet been 
but little invelligated. If fluoric acid be added to a lo¬ 
lution of ftrontian in water, or in the nitric or muriatic 
acids, the refillt will be fimilar to that of fluat of barytes. 
This fait is decompofable by lime and barytes. 
Fluat of Potash. —When an alkaline fluat is pre¬ 
pared with filiceous fluoric acid, the filex will never be 
all precipitated ; part of it remains as a triple fait, which 
however may be decompofed by continuing the heat 
fomewliat longer, and then the fllex comes away like a 
jelly. If, on the other hand, w'e work with pure fluoric 
acid, the fluat of potafh is then obtained in duftile platp, 
but with the acid prepared in veflels of earth it will be 
in a jelly: this circumftance led the celebrated Scheele 
into an error, for he never could obtain it in cryftals. 
Fire difengages the fluoric acid, and leaves the alkali 
only in the veflel; if the experiment be not made in me¬ 
tal retorts, a triple fait, in a gelatinous form, would be 
produced. It is foluble in water. The fulphuric, nitric, 
and muriatic, acids, feparate the fluoric acid: heavy white 
vapours are immediately perceived, which are filiceous 
from the beginning if veflels of glafs are ufed in the ope¬ 
ration. This fluat is decompofed alfo by lime, barytes, 
and ftrontian; according to Scheele, the calcarean mu¬ 
riat, and the magnefian fulphat, decompofe this lalt. 
Some of the metallic lolutions, as tfiofe of filver, mer¬ 
cury, and lead, are decompofed by double affinity. 
Fluat of Soda. —The true nature of this fait is lefs 
known than that of the preceding. Boullanger, who ex¬ 
amined all the products of the fluoric acid, lays, that it 
cryftalliz.es in the cubical form; Scheele fays it does not 
cryftallize at all. In general, it afts nearly the fame as 
fluat of potafh when heated. It is decompofed by lime, 
barytes, ftrontian, and potafh : barytes even diflolved in 
water decompofes it, and the fluat of barytes which is 
formed, fhews clearly a direft affinity, for no double affi¬ 
nity can take place here. The carbonats and the muriat 
of lime decompofe it alfo. By double affinity, it is de¬ 
compofed by folutions of filver, mercury, lead, &c. for, 
the fluoric acid alone would occafion no precipitation, 
did not the foda attraft the acid, while the fluoric acid 
attrafts the metal. 
Fluat of Ammoniac. —This may be prepared from 
cryftallized carbonat of ammoniac, or by faturating li¬ 
quid ammoniac with fluoric acid. It cryltallizes in little 
grains, if the fluoric acid be very pure ; for, if it contains 
filexj 
