SULPHUR AND ITS COMPOUND 259 



CHIEF POINTS OF CHAPTER XVII. 



Physical Properties of Sulphur. It is a brittle, yellow solid, 

 which may easily be reduced to a fine powder. It is insoluble in 

 water, but dissolves in carbon disulphide, and also to a small extent 

 in turpentine. It melts at about 114 C. to a clear, yellow, mobile 

 liquid, which when poured into cold water solidifies to ordinary 

 yellow sulphur. On further heating the yellow liquid becomes 

 darker in colour, and more viscid, until at about 250 C. it will not run 

 out, even though the vessel containing it is inverted. At still higher 

 temperatures the liquid again becomes thin and mobile and finally 

 boils, evolving a dark orange-red vapour, which condenses either to 

 an orange liquid or to a yellow powder. If the boiling sulphur be 

 poured into cold water it solidifies to a solid resembling caoutchouc. 



Varieties of Sulphur. This elastic solid is called jrfastic sulphur. If 

 left in contact with air it returns to ordinary sulphur in a few days 

 without any change of weight. The yellow powder into which 

 sulphur vapour condenses, without passing through an intermediate 

 liquid state, is called flowers of sulphur. Ordinary commercial 

 sulphur is called roll sulphur. 



Crystalline Sulphur. The crystals left when a solution of sulphur 

 in carbon disulphide is allowed to evaporate belong to what is called 

 the rhombic system. Those obtained from melted sulphur in the 

 manner described in the chapter belong to the monoclinic system. 

 The monoclinic sulphur crystals will, if left alone, gradually change 

 back to the rhombic variety. 



Allotropy is the property some elements, like sulphur, possess of 

 existing in different forms which are known as allotropic forms. 

 The allotropic forms of sulphur are four in number, viz. , rhombic, 

 monoclinic, plastic, and amorphous. 



Oxides of Sulphur. Sulphur dioxide is formed when sulphur 

 burns in air or oxygen. It is also given off when copper is heated 

 with strong sulphuric acid. It is a gas with a pungent smell which 

 does not burn nor support combustion and has the power of bleach- 

 ing vegetable colours. It dissolves in water to form sulphurous acid. 

 When sulphurous acid is neutralised by alkalis, salts called sulphites 

 are obtained. 



Sulphur Trioxide. By suitable means sulphur dioxide can be made 

 to combine with more oxygen to form a higher oxide known as sulphur 

 trioxide. This oxide dissolves in water, with a hissing noise accom- 

 panied by the evolution of much heat, to form sulphuric acid. 



Sulphuric Acid is a heavy, oily liquid, which boils at 335 C. , giving 

 off choking, pungent, white fumes. It mixes with water in all pro- 

 portions with the evolution of much heat. It absorbs moisture very 

 readily and is consequently used for drying gases. For the same 

 reason it chars any organic substance it comes in contact with. 

 Sulphuric acid forms salts called sulphates. 



Manufacture of Sulphuric Acid. This depends upon the fact that 

 Sulphur dioxide can be made to unite with more oxygen to form 

 sulphur trioxide, which dissolves in water, to form sulphuric acid. 

 Nitrogen peroxide, which is obtained from nitric acid, easily gives 



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