252 ARSENIC.

tapped, to cause the small globules of antimony tounite, and form one button at the bottom.

The crucible is broken as soon as it gets cold, andthe metallic button at the bottom carefully freedfrom adhering matter, by gently tapping it with thehammer, brushing off dust or other adhering matter,and weighed. Unless great delicacy of manipulationbe observed when detaching the slag, portions of themetal will be removed on account of the brittlenessof the antimony rendering it liable to the detach-ment of small particles, which, of course, would beso muen loss.

Those ores which consist principally of trioxide ofantimony, but which contain small quantities of sul-phur, may be analyzed by the foregoing method; foras the sulphide yields to the black flux just half itscombined antimony, a very small portion only canbe retained in the slag.

Ores of the second class offer more difficulties thanthose just described. Their assay may be performedeither by first roasting the sulphide, and subsequentlyfusing the oxide produced with black flux, or bydirectly treating the mineral, reduced to an impal-pable powder, with finely-divided metallic iron oriron scales, and a little black flux, at an elevatedtemperature.

As the grey sulphide of antimony is very fusibleand volatile, it requires much care and attention toroast it thoroughly, in order to expel the sulphur,and form the trioxide of the metal; to be successful,the temperature should be moderate, and the masskept stirred with an iron rod or wire as long as anysulphurous acid is given off. It is then fused with3 parts of black flux in the usual way, and a buttonof antimony is obtained.

The results of the dry assay of antimony ores areso very fallacious, that the process is now butseldom used.

ARSENIC. — Arsenic, French ; arsenik, arsen, scher-bcnkobalt,jliegenrjift, napclienkobalt, German; arsenicum,reguhis arsenici, Latin ; ugritvixw, Greek. Symbol, As;atomic weight, 75.

Arsenic is mentioned by Dioscorides and otherauthors who lived about the commencement of theChristian era. In their works the word was used tosignify a reddish mineral composed of arsenic and sul-phur, which was used as a medicine and in painting.

Arsenic is found native, but more often in com-bination with other metals and sulphur.

The distinct metallic characters of arsenic werediscovered by Brandt in 1773, who gives the firstaccurate process for procuring it. He mixed whiteoxide (arsenious oxide or arsenious acid (As„O g ) withpotassium hydrate and ammonium chloride, andfused the mixture in a well-luted crucible. Its pro-perties were further investigated by Macquer in174G, by Mcnnet in 1773, and by Bergmann in1777 ; but the latter took many of his facts fromBrandt’s paper.

Arsenic forms two native compounds with oxygen,namely, arsenious and arsenic acid. Orpiment andrealgar, two of its sulphides, are also met with in themineral kingdom. It has been discovered in minute

quantity in a largo number of mineral waters. Smallquantities of arsenic are always found with iron ores,and frequently influence their quality. It is oftenfound in combination with metallic sulphides, espe-cially with the sulphide of iron, constituting arsenicalpyrites (FeAs + FeS 2 ) ; and two kinds of arsenicaliron are found, having the compositions FeAs andFe 4 As g respectively.

Arsenic is obtained as a bye-product from arseni-cal cobalt, cobalt glance, bismuth cobalt ore, nickelochre, polybasite, red silver, arseniate of copper (ofwhich several varieties are known), from euchroite,kupferscliaum, erinite, scorodite, smaltine, cloanthite,nickel glance, copper nickel, arsenical nickel, arseni-cal fald ores, &c.

The principal mines are those of Freiberg, Anna-berg, Marienberg , and Schneeberg; Joachimsthal inBohemia, Andreasberg in the Harz , Oravicza inHungary, Kongsberg in Norway, Zmeoff in Siberia ,where native arsenic is found in large masses, andat St. Marie-aux-Mines in Alsace .

The metal is readily prepared in the laboratoryby mixing 1 part of pure arsenious acid with 3 ofcharcoal, or a mixture of charcoal and sodium car-bonate in a crucible, on which another of a similarshape is inverted as a head, and applying a moderateheat, either in a furnace or over a lamp. By keep-ing the cover as cool as possible the metal will befound in the course of a short time to have sublimed,and to be adhering to the interior of the crucible inthe shape of a brilliant metallic coating.

Arsenic is of a bluish-white colour, approachingsteel grey, and has a crystalline structure. It is themost volatile of all metallic bodies, being completelyvaporized without fusion at 3C5° Fahr. (185° C.). Itis so brittle that it may be easily reduced to a finepowder by trituration in a mortar. Kept in water itsuffers no alteration; but when exposed to the airit soon loses its lustre, becomes black, and falls topowder. When exposed to a moderate heat in freecontact with air it sublimes in the form of a whitepowder, and at the same time emits its characteristicalliaceous odour, and is wholly converted into arseni-ous acid (As 9 0 8 ). With limited access of air metallicarsenic is deposited in a compact brown mass, havinga strong metallic lustre. If air be excluded and thetemperature be high, the arsenic is deposited as anearly white crystalline mass, which docs not oxidizein the air even when heated to 80° C. The otherforms readily pass into arsenious oxide by exposureto air.

Arsenic burns in air or oxygen with a pale blueflame into arsenious oxide (As 2 O g ).

Orfila states that metallic arsenic, when swal-lowed, acts as a powerful poison, probably by beingoxidized into arsenious acid.

The specific gravity of arsenic is between 5'62 and6'96, its vapour density is 10-3995, air being unity:or 150, hydrogen being 1.

Heated with chlorine, arsenic ignites spontaneously,producing a brilliant white flame and forming arseni-ous chloride (AsCl g ). It is soluble in nitric acid andin aqua regia, and is converted by this treatment into