T '3lU 



PHOSPHORUS, ARSENIC, ANTIMONY, BISMUTH 325 



gait. They are green, insoluble compounds used, as insecticides, 

 for spraying plants. On account of their poisonous character, 

 they are no longer employed as ingredients in paints. 



Arsenic as a Member of the Nitrogen Family. While free 

 arsenic is as different physically from phosphorus as the latter is 

 from nitrogen, the compounds have much in common. Arsenic 

 forms arsine AsH 3 (corresponding to NH 3 and PH 3 ), arsenious 

 oxide As 2 3 , arsenic oxide As 2 5 , and the acids H 3 AsO 3 and 

 H 3 As04. In these compounds it is non-metallic, and shows the 

 valences three and five. 



ANTIMONY Sb 



Preparation and Properties. Antimony is found free in 

 nature. The sulphide, stibnite SbjjSs, is also a well-known mineral. 

 When the latter is melted with iron, ferrous sulphide and free 

 antimony are formed : 



3Fe + Sb 2 S 3 - 2Sb + 3FeS. 



The molten ferrous sulphide (sp. gr. 4.8) floats upon the molten 

 antimony (sp. gr. 6.5), and the products, being mutually insoluble, 

 are easily separated. 



The metal is brilliantly silvery and non-tarnishing. It is brittle 

 and the black powder obtained by pulverizing it, " antimony 

 black," is rubbed on plaster casts to give them a dull, metallic 

 appearance. When heated, antimony volatilizes and burns in the 

 air with a brilliant white light to form the white trioxide Sb 2 3 . 



The trisulphide Sb 2 S 3 (orange-colored when precipitated) is used 

 in making matches and fireworks. 



Alloys Containing Antimony. The metal is chiefly used 

 as an ingredient in alloys. Lead, when solidifying, shrinks and 

 antimony counteracts this tendency. Hence type metal, which, 

 when cold, must fill the mould completely, is made by melting 

 together 15 to 25 per cent of antimony, 10 to 20 per cent tin, and 



i 



f 



