CHE M 
much grcaterabundance than that produced by the cauftic 
potaffi. Monnet took notice of this phenomenon, and 
has with juftice attributed it to the gas which is difen- 
gaged. The folution of iron, by fixed alkali, is called 
the martial alkaline tinSlure of Stahl, and ot a very beau¬ 
tiful red. This martial alkaline tin£ture lofes its colour 
at the end of a certain time, and depofits the oxyd of 
iron it contains; it may be decompofed by the addition 
of an acid. The nitric acid feparates from the tinSlure 
an oxyd of a brick-duft colour, which is foiuble in acids, 
and is called Stahl's aperitive faffron of Mars. 
The muriatic acid, diluted with water, difl'olves iron 
■with rapidity, and difengages a large quantity of hydro¬ 
gen gas, produced by the decompofition of the water, as 
happens when this metal is dilfolved in fulphuric acid. 
'The folution of iron by the muriatic acid is attended 
with much heat, which continues with the lame force 
till the acid isfaturated ; a proportion of the iron is pre¬ 
cipitated in a true jEthiops, as happens in all other folu- 
tions. After filtration, this folution is of a green colour, 
inclining to yellow; when preferred in a well-ltopped 
phial, it does not depofit oxyd of iron ; but if, on the 
contrary, it be expoled to the air, almoft all the iron it 
contains is precipitated in a few weeks, and this preci¬ 
pitate is of a lighter colour, in proportion as the accefs 
of air is the eaiier. It is now proved that this precipi¬ 
tation, which takes place equally in all the other folu- 
tions of iron, is produced by the oxygen of the atmof- 
phere, abforbed by the metal, which becomes oxydated 
more and more. This (alt is of a green colour, with an 
aftringent tafte. The folution of iron by the muriatic 
acid does does not cryftallize regularly by evaporation. 
Monnet has obferved, that if it be fuffered to cool when 
it has acquired the confiftence of fyrup, it forms a kind 
of magma, in which may be feen needle-form flat cryl- 
tals, which are very deliquefcent. This magma melts 
by a very gentle heat; a greater heat decompofes it, 
though lefs readily than the nitrat of iron, and it afiumes 
the colour of reft when it is dry; the muriatic acid is 
diiengaged from it, and may be obtained by diftillation ; 
it carries up with it a fmall quantity of oxyd of iron, ac¬ 
cording to the oblervation of Brandt. The duke cl’Ayen, 
in one of the four excellent memoirs he communicated to 
the Royal Academy reipebting the combination of acids 
with metals, has very minutely examined what paffes in 
this decompofition of the muriat of iron. The operation 
afforded very Angular produfts : a mild heat diiengaged 
a phlegm (lightly acid; the muriatic acid then became 
concentrated, and its gas, which is much more volatile 
than water, was-partly fixed by the iron: a much ftronger 
heat railed a portion of this acid with a fmall quantity 
of iron, and cryftals were formed in the receiver, which 
were not deliquefcent; very tranfparent cryftals in the 
form of blades of razors, which decompofed the light in 
the manner of the beft prifms, and exhibited very beau¬ 
tiful tinges of red, yellow, green, and blue, were at the fame 
time fublimed to the upper part of the retort; at the bottom 
there remained a ftyptic and deliquefcent fait, of a bril¬ 
liant colour, and foliated texture, which perfebtly re- 
fembled that kind of talc, in large plates, which is im¬ 
properly called Mufcovy glafs. This laffc (ait, expofed 
to a violent heat in a (tone-ware retort, was decompofed, 
and afforded a fublimation (till more aftonifhing than the 
former products ; it was an opake matter truly metallic, 
which, when examined by the microfcope, exhibited re¬ 
gular cryftals, or fections of hexagonal prifms, which the 
duke d’Ayen compares to the pieces inlaid in floors : 
thefe cryftals were as brilliant as the molt highly poliihed 
fteel, and were ftrongly attrafted by the loadllohe. They 
confided therefore of iron reduced in part and fublimed. 
Art appears here to imitate nature, which fublimes the 
black oxyd of iron by volcanic fires, in the form of bril¬ 
liant and well-polifhed laminae, refembling fteel; fuch at 
leaft appears to be the origin of the fpecular iron ore, 
and of that of Volvic, which, according to the valuable 
s T R y. 303 
obfervations of de l’Arbre, is always found in the clefts 
of lavas. From thefe details we may perceive how rich 
the fcience of cbemiftry is in curious phenomena, and 
what a fund of difcovery is held forth to fuch as perform 
experiments with all the accuracy the importance of the 
fubjeft requires. We mull not forget to obferve, that 
this reduction of iron favours the dobhine of gafes, and 
that we may perhaps obtain fimilar refults from many 
other metallic folutions treated in the lame way. 
The muriatic folution of iron, like all other martial 
folutions, is decompofed by lime and alkalis; but the 
precipitates are lefs altered, and may be eafily reduced, 
especially fuch as are produced by the addition of cauftic 
alkalis. Alkaline fulphures, fulphurated hydrogen gas, 
and aftringents, decompofe it like the others. Pruftian 
alkalis, or the alkaline Prufllats, precipitate a beautiful 
blue powder. 
Vauquelin, who analyzed pieces of iron continually 
wetted with urine, found thefe to be a true phofphat of 
iron. This iron is of a yellow brown without, dark 
brown within, and may be broken by the hand. In its 
internal frabture, its grain is lamellated, fhining, and, 
as it were, fpathofe; its external cavities are filled with 
a quantity of fmall brilliant cryftals. Heated in a forge- 
furnace in a crucible, lined with charcoal in powder, it 
melts, readily, and gives a very homogeneous button, 
fragile, of a very clofe brittle grain, of a bright metallic 
grey colour, exhibiting with the blow-pipe and with 
acids, all the properties of phofphure of iron. Its fur- 
face is covered with a kind of rough enamel, of a green- 
ilh grey colour, which Vauquelin difcovered to be phof¬ 
phat of lime. Iron altered and rufted by urine, is there¬ 
fore true phofphat of iron mingled with phofphat of 
lime, and with fome other faline principles from the 
urine. In this experiment, the charcoal, at a high tem¬ 
perature, converts the oxyd of iron into metal, and the 
phcfphoric acid into phofphorus. 
Liquid phofphoric acid difl’olves iron in the heat with 
violence. During the folution an inflammable gas is dis¬ 
engaged , which burns, like pholphorus, with a blue flame. 
If the acid be not fully faturated with iron, the folution 
(hoots into cryftals, which remain unchanged, in.the'air, 
but which melt in the fire into a garnet-coloured glafs. 
When the acid is fully faturated with iron, a white pre¬ 
cipitate is inftantly formed, which is extremely infoluble 
even in boiling water: this is the fyderit of Bergman and 
other chemifts. The neutral phofphat of iron is infoluble, 
but it may be difl’olved when it contains an excefs of its 
own acid. This pnolpbat is decompofed by cauftic alka¬ 
lis, by muriatic acid, but not by fulphuric acid. 
Water charged with carbonic acid eafily difl'olves iron: 
to form this combination, nothing more need be done 
than to add iron filings to the acid, and leave the mixture in 
liquid digeftion for fometime; this fluid, when filtered, has 
a penetrating and father ftyptic tafte. Bergman, who calls 
this combination aerated iron , affirms, that when expof¬ 
ed to the air, it becomes covered wdth a pellicle of rain¬ 
bow* colours; that it is dehompofed by the pure alkalis, 
but that thefe falts, when faturated with the acid, do not 
produce the fame eft'ebt. This folution converts the fy¬ 
rup of violets to green, and affords very brilliant Pruf- 
( 5 an blue with the calcareous Prufllats; it precipitates 
the brown oxyd of j.ron when left expofed to the air, or 
when heated .- this combination is now named carbonat of 
iron. Iron Iras a (Irong tendency to unite with the carbo¬ 
nic acid, arid nature very frequently prefents it in this 
ftate. The muddy iron ores and lpathofe iron appear to 
be in a great meafure formed by this combination ; fer¬ 
ruginous mineral waters often contain this metal in the 
ftate of carbonat of iron. This fait, feparated from the 
water and dried, is fcarcely foiuble in that fluid, but it 
difl'olves in a large proportion in the liquid carbonic acid, 
from which it is precipitated in proportion as the acid is 
volatilized. 
Fluoric acid attacks the metal as well as the oxyd of 
iron. 
