ARSENIC. 71 



ARSENIC. 



Is sometimes found native, but is generally procured from the 

 native arsienuret of cobalt and nickel, by means of heat. 



Prop.— A steel-gray colour; metallic lustre; very brittle- tar 

 nishesm the air; sp. gr. 5-9; volatilizes by heat, and, if air be 

 present, is converted into arsenious acid ; its vapour has the odour of 

 garlic. Symb. As.— Eq. 76-4. It forms two well known compounds 

 with oxygen, arsemous and arsenic acids ;— -no basic compound 



Arsemous acid, white oxide of arsenic, fiy 'powder As O —is 

 always generated when arsenic is heated in the open air ; that of'iom- 

 merce is derived by roasting the native ores of cobalt. It is quite trans- 

 parent and glassy when fii;st prepared, but becomes opaque by exposure ; 

 volatile at 380 ; vapour is inodorous, and condenses on cool surfaces • 

 not very soluble in water ; reddens vegetable blues feebly; combines 

 with bases, {oYxmx^garsenites; ithas an acid tasteandis very poisonous 



Arsenic «c^^, As,0 -made by dissolving arsenious acid in strong 

 nitric acid, mixed with a little hydrochloric acid, and evaporating to 

 dryness. It is sour to the taste; much more soluble in water than 

 arsemous acid; ioxm^ arseniates-, is isomorphous with phosphoric 

 acid; when strongly heated, is converted into arsenious acid and 

 oxygen. 



There are three well known sulphurets of arsenic 



Protosulphuret or Realgar, AsS, occurs native;— may be made by 

 heatmg together sulphur and arsenious acid ; colour, ruby red 



Sesquisulphuret oxOrpiment, As,S3, is also found native ;_made 

 by transmitting sulphuretted hydrogen through a solution of ar- 

 semous acid ; colour, yellow,— called king's yellow 



Persulphuret, As,S3, made by action of sulphuretted hydrogen on 

 a solution of arsenic acid ; it resembles orpiment in colour. The 

 -sulphurets are poisonous. 



Arsenic also unites with chlorine, iodine &c 



J^~reUed hydrogen, K,^.\^ prepar'ed by adding arsenious 



acid to the materials for generating hydrogen; colourless; odour of 



garlic; sp. gr. 2-0; burns with a blue flame, generating arsenious 



Xhil V ^^"?"PP^^^^7^ combusion ; very poisonous when breathed ; 

 slightly soluble in water. ' 



Tests for arsenic— I. Ammoniacal nitrate of silver (made by 

 adding ammonia to a solution of nitrate of silver, until the oxide of 



f^lZ ""f t-" .1'°'''' ^r"" ''r^'^^ "^^ ^'''^^''^) ' arsenious acid 

 added to this, throws down the insoluble arsenite of silver of a 

 yellow colour. 



2. Ammoniacal sulphate of copper, (made by adding ammonia 



«HH ^,f ^.^^^\V"^P^'^' of copper,) throws down with arsenious 

 acid, the insoluble arsenite of copper (Scheek's green). 



