86 NON-METALS AND THEIR COMBINATIONS. 



earthy impurities. Melted sulphur poured into round moulds, 

 is known as roll-sulphur. 



Sublimed sulphur, Sulphur sublimatum (Flowers of sulphur}. 

 Obtained by heating sulphur in suitable vessels to the boiling- 

 point, and passing the vapor into large chambers, where it de- 

 posits in the form of a powder, composed of small crystals. 



Washed sulphur, Sulphur lotum, is sublimed sulphur washed 

 with a very dilute ammonia water, and then with pure water; 

 the object of this treatment being to free the sulphur from all 

 adhering sulphurous and sulphuric acid. 



Precipitated sulphur, Sulphur praecipitatum (Milk of sulphur}. 

 Made by boiling hydrate of calcium with sulphur and water, 

 filtering the solution, adding to it dilute hydrochloric acid until 

 nearly neutral, washing and drying the precipitated sulphur. 



By the action of sulphur on calcium hydrate are formed poly- 

 sulphide of calcium, hyposulphite of calcium, and water: 



3(Ca2HO) + 12S == 2CaS 5 -f CaS 2 O 3 + 3H 2 0. 



Hydrate Sulphur. Polysulphide Hyposulphite Water, 



of calcium. of calcium. of calcium. 



On adding hydrochloric acid to the solution, both substances 

 are decomposed and sulphur is liberated: 



2CaS 5 + CaS 2 3 + 6HC1 = 3CaCl 2 + 3H 2 + 12S. 



Precipitated sulphur differs from sublimed sulphur by being 

 in a more finely divided state, and by having a much paler 

 yellow, almost white color. 



Sulphur dioxide, S0 2 = 64. (Sulphurous anhydride, improperly 

 also called sulphurous acid}. 



Two combinations of sulphur and oxygen are known; they 

 are sulphur dioxide, S0 2 , and sulphur trioxide, S0 3 . 



Sulphur dioxide is always formed when sulphur or substances 

 containing it in a combustible form (H 2 S, CS 2 , etc.) burn in air. 

 It is also formed by the action of strong sulphuric acid on many 

 metals (Cu, Hg, Ag, etc.), or on charcoal: 



2H 2 S0 4 + Cu = CuSO 4 + 2H 2 O + SO 2 



Copper. Cupric Water, 



sulphate. 



2H 2 S0 4 + C = C0 2 -f 2H 2 O + 2SO 2 . 



Sulphuric Copper. Cupric Water. Sulphur 



acid. sulphate. dioxide. 



