ARSENIC. 347 



NH 3 N 2 3 NA NC1 3 . 



PH 3 P 2 S PA H 3 P0 4 PC1 3 . 



AsH 3 As 2 O 3 As 2 O 5 H 3 AsO 4 AsCl 3 . 



SbH. SbA Sb 2 5 SbCl 3 . 



Arsenic. Found in nature sometimes in the native state, but 

 generally as sulphide or arsenide. One of the most common arsenic 

 ores is the arsenio-sulphide of iron, or mispiekel, FeSAs. Realgar is 

 the native red sulphide, As 2 S 2 , and orpiment or aurijrigment, the native 

 yellow sulphide, As 2 S 3 . Arsenides of cobalt, nickel, and other metals 

 are not infrequently met with in nature. Certain mineral waters 

 contain traces of arsenic compounds. 



Arsenic may be obtained easily by heating arsenous oxide with 

 charcoal, or by allowing vapors of arsenous oxide to pass over char- 

 coal heated to redness : 



AsA + 3C = SCO + 2As. 



In both cases the arsenic, when liberated by the reducing action of 

 the charcoal, exists in the form of vapor, which condenses in the 

 cooler part of the apparatus as a steel-gray metallic mass, which 

 when exposed to the amospheric air, loses the metallic lustre in conse- 

 quence of the formation of a film of oxide. 



Experiment 47. Eub together in a mortar a small quantity of arsenous oxide 

 and about ten times as much charcoal. Heat the mixture in a covered porce- 

 lain crucible with a small flame. After a time examine the cover for a dark 

 deposit of arsenic. 



When pure, arsenic is odorless and tasteless ; it is very brittle, and 

 volatilizes unchanged and without melting when heated to 180 C. 

 (356 F.), without access of air. Heated in air, it burns with a 

 bluish-white light, forming arsenous oxide. Although insoluble in 

 water, yet water digested with arsenic soon contains some arsenous 

 acid in solution, the oxide of arsenic being formed by oxidation of 

 the metal by the oxygen absorbed in the water. 



Arsenic is used in the metallic state as fly-poison, and in some 

 alloys, chiefly in shot, an alloy of lead and arsenic. 



The molecule of arsenic contains four atoms, and not two, like 

 most elements. It is trivalent in some compounds, quinquivalent in 

 others. 



Although arsenic is grouped with the metals in the analytical system of 

 classification, in nearly all respects it behaves like a non-metal and should prop- 

 erly be classed as such. The oxides have only acidic character, and do not form 

 salts with acids, as nitrates, sulphates, etc. The chloride, AsCl 3 , can be obtained, 



