C H E M : 
fifatrafs, and place it in, a fand-bath; then proceed to 
fiiblimation, firft with a gentle heat, in order to warm 
the veflels, and diflipate damp vapours. Increafe the fire 
by degrees, fo as to make the bottom of the veffel red -hot. 
In the upper part of the matrafs a fubftance almoft black 
will be fublimed. Break the matrafs, and feparate the 
fublimed matter: this is metallic arfenic, or regulus. 
This reduction may alfo be obtained by fufion: Mix 
one part of oxyd of arfenic with, two parts of foft foap, 
and one and a half of potalh. Melt the mixture quickly 
in a crucible: as foon as melted, pour it into an iron- 
mortar fomewhat heated and greafed; then cover it up; 
when the matter is quite cold, feparate the arfenic, which 
occupies the lower part, from the fcoria. 
Oxyd of arfenic has a very ftrong and cauftic tafte. If 
placed upon burning coals, it flies off in vapour with a 
itrong fmell of garlic. In doled veflels, it is volatilized, 
and vitrifies in a ftrong heat; and hence ariles a tranf- 
parent glafs, fufceptible of cryftallization into four-fided 
pieces with truncated angles. This glafs eafily tarnilhes 
or grows dim in the air, and becomes la&eous, undergo¬ 
ing a fort of efflorefcence. This oxyd unites very well 
with fulphur : hence arifes a femi-tranfparent mafs, very 
heavy, of a yellow or red colour, according to the pro¬ 
portion of lulphur. Take two parts of arfeniat'of potalh 
and one of fulphur ; put the whole into a fmall matrafs, 
and expofe it to a fire that will make the bottom red- 
hot ; take it off in an hour, and break it: it will produce 
orpiment and a fine fublimed realgar. The bottom of 
the matrafs contains a little arfeniated fulphure of pot- 
afh, and l'ulphat of potalh. When red, it is called realgal, 
realgar, factitious risigal, or red arfenic ; but, according 
to the modem nomenclature, oxyd of red fulpburated arfe¬ 
nic. When yellow, it is called orpinum , or factitious or¬ 
piment, or oxyd of yellow fulpburated arfenic. But, as many 
of thefe fubltances are found in commerce, it is not now 
ufual in laboratories to work at fuch combinations. 
Thefe oxyds of fulphurated arfenic are decompofed by 
lime and alkalis, which have more affinity with fulphur 
than oxyd of arfenic has. The oxyd of white arfenic may 
be reduced by hydrogen gas, becaufe this gas has more 
affinity with the oxygen than the arfenic. The oxyd of 
arfenic is eafily diffolved in water: it requires but fifteen 
parts of boiling water, and eighty parts of cold water, to 
diffolve one. By evaporation and cooling, we obtain it 
cryftallized in eight-fided prifms, but oftentimes under 
various indeterminate Ihapes. 
The oxyd of arfenic, then, participates in the proper¬ 
ties of faline fubftances, and differs from other metallic 
oxyds, i. In being foluble. 2. As the metallic oxyds are 
inodorous and fixed. 3. As the other oxyds form no 
union with metals. 4. It unites with alkalis, whence 
arife the falts we are now to examine. All thefe pro¬ 
perties, therefore, ferve to clal's this oxyd in the rank of 
acids per fe. In this rank they are placed by Fourcroy, 
who calls this oxyd arfenious acid ; a name which we 
fhall preferve in fpeaking of it in this treatile. 
Arsen ious Acid is an excellent folvent of earthy mat¬ 
ters in general; it fixes with moft of thefe earths, and 
promotes their vitrification : but every kind of glafs, in 
the composition of which it enters, has the fault of foon 
tarnifhing in the air. Arfenious acid combines with pot- 
ath to the point of faturation ; with foda the fame. Am¬ 
moniac diffolves this acid alfo, and is obtained in a cryf¬ 
tallized ftate : if heated a little, the ammoniac is decom¬ 
pofed, the azotic gas is difengaged, the hydrogen unites 
with a portion of the oxygen of the acid, and forms wa¬ 
ter. But thefe combinations have not yet been made 
with fufficient care to eftablifh the properties of thefe 
falts, which fhould be called arfeniats. 
Sulphuric acid, concentrated and boiling, diffolves ar¬ 
fenious acid ; but, when the folution is cold, the arfe- 
nicus acid is precipitated, and the fulphuric acid feems 
no longer to retain it. Nitric acid concentrated attacks 
the arfenious acid more effectually: Pour fix parts of ni- 
s T £ Y. 263 
trie acid upon one of concrete arfenious acid, and make 
the experiment in clofed veflels, with the pneumatic che¬ 
mical apparatus, and with the help of caloric a nitrous 
gas will be obtained. In the retort will remain a white 
concrete matter, of properties entirely different from ar- 
lenious acid : this is called arfenical acid. This method 
may be employed to obtain it: When the muriatic acid 
is much concentrated, it diffolves by ebullition a third 
of its weight of arfenious acid ; and, in cooling, a great 
part is fpontaneoufly feparated, but faturated with that 
acid. With the oxygenated muriated acid, a complete 
acidification of the arfenious acid may be obtained, as 
with nitric acid. 
The adtion of the other acids is not known. Becker, 
Stahl, Kunkel, and Macquer, have particularly examined 
the adlion of the arfenious acid upon the nitrat of pot- 
afh. The "1 aft in particular repeated the experiments of 
preceding chemifts; he examined the refiduum,of which 
thofe chemifts had not fpoken, and he clifcovered that it 
was a particular neutral fait, -which he calls neutral ar¬ 
fenical fait. 
To decompofer nitrat of potafh by means of arfenious 
acid, mix equal parts of both, and put it into a retort 
much larger than the proportions of the mixture, to al¬ 
low for the fwelling which follows: place it in a fand- 
bath ; adapt a cap with two apertures, one large, to re*- 
ceive the mouth of the retort; the other, lefs wide, but 
to be fo lengthened and narrowed, as to be received into 
a tube, which in its bending is much leffened in diame¬ 
ter, and plunged into a bottle containing a quantity of 
water, more or lefs, in proportion as the nitric acid is 
required to be more or lefs concentrated. The appara¬ 
tus being thus prepared, lute up the joinings, and diftil 
with a gentle heat. As the nitrous vapour is thrown off, 
it pafl'es through the.tube, and is diffolved in the water; 
fome nitrous gas alfo efcapes, which may be gathered 
under a bell-glafs : the water imbibes a blue colour. The 
refiduum is the neutral arfenical fait of Macquer, or ar- 
feniat of potajh. Let this faline mafs be diffolved in a 
fufficient quantity of boiling water; filter the liquor; 
and, in cooling, very regular cryftals are obtained, in 
four-fided prifms, terminated by pyramids of four equal 
faces; much variation is alfo oblerved in the figures of 
the cryftals. 
Nitrat of foda is alfo decompofed by the arfenious acid. 
For this purpofe the fame precautions muft be taken as 
in the preceding operation; the fame phenomena take 
place; and the fame apparatus may be ufed. The refi¬ 
duum furnifhes not the fame fait: it cryftallizes into 
hexagonal prifms, terminated by planes perpendicular to 
their axis : this is arfeniat of foda. 
Nitrat of ammoniac may in the fame manner be de¬ 
compofed by arfenious acid ; but the phenomena are dif¬ 
ferent. The operation formerly required great precau¬ 
tion ; but Pelletier has proved that it may be performed 
without danger. This is his method : When the mix¬ 
ture has been made, in the proportions above-direfted, 
it is put Into a pretty large retort of glafs, luted, and 
placed in a reverberatory furnace with a balloon for a 
receiver. Begin with a flight degree of heat; for the 
decompofition is fo rapid, and the nitrous vapour flies off 
with fuch force, that they may carry away a portion of 
the arfenic not decompofed; but, by proceeding gently, 
the decompofition is more gradual. Firft, fome nitrous 
acid paffes off; and, if the fire be increafed or continued, 
fome ammoniac is difengaged ; laftly, if the fire be made 
ftill ftronger, a portion of oxyd of arfenic is fublimed, in 
the form of a white powder, and a. vitreous mafs remains 
in the retort, which attacks the retort very violently, and 
eats into it: this is arfenical acid. When the experiment 
has been conduced with the precautions recommended, 
there remains in the retort a faline mafs, which is to be 
diffolved in boiling water; filter the liquor, and let the 
air evaporate: it furnifhes cryftals. This is arfeniat of 
ammoniac. 
We 
