208 METALS AND THEIR COMBINATIONS. 



Liquor sodii arsenatis is a 1 per cent, solution of sodium arsenate 

 in water. 



Hydrogen arsenide, AsH 3 (Arsine, Arsenetted or arseniuretted 

 hydrogen). This compound is formed always when either arsenous 

 or arsenic oxides or acids, or any of their salts, are brought in con- 

 tact with nascent hydrogen, for instance, with zinc and diluted 

 sulphuric acid, which evolve hydrogen : 



As 2 3 -f 12H = 2AsH 3 -f 3H 2 O. 

 As 2 5 + 16H = 2AsII 3 + 5H 2 O. 

 AsCl 3 + 6H = AsH 3 + 3HC1. 



Hydrogen arsenide is a colorless, highly poisonous gas, having a 

 strong garlic odor. Ignited, it burns with a bluish flame, giving off 

 white clouds of arsenous oxide : 



2AsH 3 + 6O = As 2 O 3 + 3H 2 O. 



When a cold plate (porcelain answers best) is held in the flame of 

 arsenetted hydrogen, a dark deposit of metallic arsenic (arsenic spots) 

 is produced upon the plate (in a similar manner as a deposit of 

 carbon is produced by a common luminous flame). The formation of 

 this metallic deposit may be explained by the fact that the heat of the 

 flame decomposes the gas, and that, furthermore, of the two liberated 

 elements, arsenic and hydrogen, the latter has the greater affinity for 

 oxygen. In the centre of the flame, to which but a limited amount 

 of oxygen penetrates, the latter is taken up by the hydrogen, arsenic 

 being present in the metallic state until it burns in the outer cone of 

 the flame. It is this liberated arsenic which is deposited upon a cold 

 substance held in the flame. 



Arsenetted hydrogen, when heated to redness, is decomposed into 

 its elements ; by passing the gas through a glass tube heated to red- 

 ness, the liberated arsenic is deposited in the cooler part of the tube, 

 forming a bright metallic ring. 



Sulphides of arsenic. Two sulphides of arsenic are known and 

 iiave been mentioned above as the native disulphide or realgar, As 2 S 2 , 

 and the trisulphide or orpiment, As 2 S 3 . Disulphide of arsenic is an 

 orange-red, fusible, and volatile substance, used as a pigment ; it 

 may be made by fusing together the elements in the proper propor- 

 tions. Trisulphide is a golden-yellow, fusible, and volatile substance, 

 which also may be obtained by fusing the elements, or by precipitating 

 an arsenic solution by hydrogen sulphide (Plate V., 1). Both sul- 

 phides of arsenic are sulpho-acids, uniting with other metallic sul- 



