C H E M I S T R Y. 
264 
We {hall prefently fee how all thefe falts may be pre¬ 
pared, by difeftly combining the arfenical acid with thefe 
fame bales. We may alfo prepare thefe kinds of falts, by 
pouring the mixture by degrees into a heated crucible. 
JBy this means, particularly with care, the fwelling up 
may be prevented ; but there is one very great inconve¬ 
nience, which is, that, when the arfenical acid is without 
a bale, then it corrodes the earth or clay of the crucible ; 
but, for the decompofition or the nitrat of potalh and of 
loda, thefe may be eafily performed in iron-crucibles, ef- 
pecially if we do not with to preferve the nitric acid: in that 
cafe, by folutions and filtrations,. we deprive them of ar- 
ienical fait with an argillaceous bale. 
Arsenical Acid. —Scheele gives two precedes for 
obtaining this acid: one by means of the oxygenated 
muriatic acid ; the other by nitric acid. This acid may 
alfo be obtained by decompoling the arfeniat of potafh 
with fulphuric acid: Take arfeniat of potalh, well dried, 
and mix it with half the quantity of fulphuric acid. Put 
this mixture into a luted retort, and bring it by degrees 
to a red heat: a white mafs remains in the retort, which 
ftrongiy draws the humidity of the air. When the matter 
is quite liquefied, there remains a white powder, which, 
when well-walhed, is no longer arfeniat of potalh, but 
•fulphat of potalh. The fame procefs will anfwer for de- 
compofing arfeniat of l'oda. 
Thefe experiments prove the polfibility of oxygenating 
arlenic, and of converting the arfenious acid into arl'e- 
nical acid. Hence we may underhand, alfo, why the ar¬ 
fenious acid, previous to being laturated with oxygen, 
produces no arfeniats ; and why it cannot conttitute thole 
falts, but after having been previoufly treated by the 
acids it decompofes, and from wdiicli it extrafts oxygen 
. by means of heat. This acid, in its concrete form, draw¬ 
ing the humidity of the air, has a lironger favour than the 
arfenious acid : it turns the blue vegetable colours red. 
If arfenical acid be put into a glais retort, and expofed 
to a fire that will make it red-hot, it comes out tranf- 
parent, but grows dull in cooling. If the heat be in- 
crealed till the retort begins to melt, the acid rifes in 
ebullition, and is fubiimed in the neck of the retort. If, 
inltead of a retort, a covered crucible be ufed, and ex¬ 
pofed to a ftrong heat, the acid boils violently, and be¬ 
gins to fmoke in a quarter of an hour. If the crucible 
be placed under a bell-glafs, while the acid linokes, it 
will be found covered within with a white dult, which is 
arfenious acid, not arfenical acid. In the crucible remains 
a little tranfparent glafs, difficult to meit, which is fpread 
over the fides of the crucible : this is arfeniat of Illumine. 
Pure charcoal, or carbon, decompofes this acid. For 
this purpofe, in a mixture of arfenical acid, there iliould 
be about one-haif of charcoal: Put the mixture into a 
glafs retort, luted with earth, and on a matrafs : put the 
retort into a reverberating furnace, and heat it by de¬ 
grees till the bottom is red-hot; then the whole mafs 
burns violently, the acid is reduced, and rifes into the 
neck of the retort in a metallic form,'mixed with a little 
oxyd and charcoal-dufc: l'ome drops of an infipid liquor 
are ufuaily found in the receiver. 
With fulphur, different effects are produced. By di- 
gefting a mixture of fix parts of arfenical acid and one 
of puiverifed fulphur, it undergoes no change; but, by 
evaporating to drynefs, and diddling in a glafs retort, 
with a receiver, a violent combination is produced, as 
foon as the mixture is hot enough to melt the fulphur. 
The mafs rifes almoft all at once, and forms a red fubii- 
mate. Sulphureous acid then paftes into the receiver. 
Pelletier direfts another method : Take equal parts of 
arfenical acid (in the vitreous form) and fulphur; put 
the mixture into a matrafs, and keep it over the fire an 
hour; a very ftrong fulphureous acid will be dilengaged: 
when this acid is no longer perceived, take the matrafs 
off the fire and break it: a very beautiful fubiimed real¬ 
gar will be the refult. 
The arfenical acid lofes its acidifiable property, if put 
in cent a ft with hydrogen gas. Take pure arfenical acid; 
mix it with a little diitilled water ; the folution is tranf¬ 
parent. Introduce a certain quantity of hydrogen gas, 
dilengaged by the aftion of fulphuric acid upon iron ; 
tlie liquor grows thick ; a muriat is precipitated, which, 
when well waflied with diitilled water, exhibits all the 
phenomena of arfenic. The oxygen of the acid has united 
with the hydrogen, and formed water, while the arfenical 
acid came over : therefore the refult is arfenic, and fome- 
times a dark-grey oxyd of arfenic. If, inltead of hydro¬ 
gen gas, fulphurated hydrogen gas be ufed, the refult 
is water and a fdphure of arfenic. With phofphorus, 
phofpboric acid is obtained. The arfenical acid may 
alio be diffolved in two parts of water. How this acid 
afts with other acids, is not yet known. According to 
Scheele, barytes, lime, magneiia, and alumine, form ialts 
with this acid ; but they are very little known, and rare¬ 
ly employed. 
The combinations of this acid with alkalis, is better 
known. By combining arfenical acid with potafh, the 
true neutral arfenical fait of Macquer, arfeniat of potafh, 
is produced. With foda, a fait is formed fimilar to that 
obtained by decompofing nitrat of ioda with arfenious 
acid. To obtain arfeniat of ammoniac, combine the ar- 
lenical acid with the ammoniac to the point of faturation. 
A ftrong effervefcence is brought on; then evaporate the 
liquor in a gentle heat, and let it cryftallize. Very re¬ 
gular cryftals are obtained, of a rhomboidal figure, which 
at firft fight refemble nitrat of potafh, but they differ in 
this : if expoled to the aftion of fire in a retort, they 
firft iofe the water of diftiljation ; then the ammoniac ; 
and a vitreous mafs remains in the retort, which ftrongiy 
attrafts the humidity of the air, and is nothing butverypure 
arfenical acid. Ail the alkaline arfeniats ate decompofed 
by lime; and it appears that lime and barytes have more 
affinities with this acid than alkalis have. Of the neutral 
falts, only fulphat of potafh and of foda, nitrat of pot¬ 
afh, muriat of foda, and muriat of ammoniac, are de¬ 
compofed by the arfenical acid ; but this decompofition 
requires the aid of caloric, or heat. 
Arfenic is ufed in many of the arts; in wafhes for 
whitening of metals; in glafs-houfes, for melting; and 
in mining ; it alfo enters into the compofition of fome 
kinds of varnifh. Orpine and realgar are much ufid in 
painting; but, in general, arfenic is one of thofe pro¬ 
ductions whole advantages hardly compenlate for its de¬ 
leterious effefts : this metal, efpecially in the oxyd ltate, 
or in that of arfenious acid, is well known to be a ftrong 
and fatal poifon. To thofe who may be unfortunately 
poifoned by arfenic in the ftate of a white oxyd, fulpbure 
of potafh, formerly called liver of fulphur, diffolved in 
water, may be given with effeft, as this decompofes the 
arfenious acid; then try fulphureous mineral waters, or 
milk; but never (what is commonly, though very eiTO- 
neoufly, the firft thing adminiftered) oil. 
Of TUNGSTEN. 
There are two fpecies of mineral which have the gene¬ 
ric name of tungften. The one is called tungfen by the 
Swedes, and lapis ponderofus, ponderous ftone; and by 
the chemifts, lungjlat of lime. The other is called wol¬ 
fram, or tungftat of iron. Some lay the German word 
wolfram fignifies wolf's foam, becaufe the Germans, when 
they put it in their furnaces, only oxyaated and lcorified 
metals inftead of reducing them : others derive it from 
wolf, and ram, or rba.m, • loot. When we come to ex¬ 
amine the tungftats of lime and iron, we fliall defetibe 
the manner of obtaining tungften, and the tungftic acid. 
This metal, when pure, is of a light brown colour, 
extremely hard, very brittle, and cryftallizable : it is 
hardly to be touched by a file, and the magnet has no 
effeft upon it. If a little metallic tungften be boiled 
with muriatic acid, no hydrogen gas is difengaged, nor 
does the metal feem to undergo any change. If nitro- 
mur-iatic acid be boiled over the fame metal, it will be a 
little 
