EXAMINATION OF COMMON SUBSTANCES 105 



liquid. Pour a little of the boiling liquid into cold water. Examine the 

 cooled sulphur ; it is plastic and not unlike india-rubber. 



(c) Notice that a yellow deposit has been formed on the cold, upper part 

 of the test-tube in which the sulphur was heated. This is the result of the 

 condensation of sulphur vapour. The deposit is known as flowers of sulphur. 



iii. Plastic variety of sulphur. After examining the plastic solid which 

 results from suddenly cooling boiling sulphur, weigh a lump of it and 

 place it on one side for a few days. After this interval examine it again 

 and weigh it. There is no alteration in weight, but the lump has changed 

 again to the ordinary kind of sulphur. 



iv. Crystalline varieties of sulphur. (a) Dissolve some powdered roll- 

 sulphur in carbon bisulphide. The solution must be made entirely by 

 shaking, for the carbon bisulphide must on no account be heated. When the 

 sulphur has all dissolved, pour the solution into an evaporating basin, 

 and put it into a draught cupboard free from dust to evaporate slowly. 

 Examine the basin after an hour or so. Observe the crystals which have 

 formed. Take the largest and most perfect and sketch its form. This 

 kind of crystalline sulphur is known as the octahedral variety (Fig. 82). 



(6) Place some powdered roll-sulphur in a clean, dry, evaporating basin 

 and heat gently on a piece of iron wire gauze. When it has all melted 

 remove the flame and allow it to cool. As soon as a solid film has formed 

 on the top of the liquid, pierce two holes in it and quickly pour out the 

 remaining liquid sulphur through one of the holes. Remove the film of 

 solid sulphur and examine the yellow needle-shaped crystals on the sides 

 of the basin. This kind of crystalline sulphur is known as the prismatic 

 variety (Fig. 83). 



Examine the crystals after a few days. Observe they are now opaque. 

 The prismatic sulphur has changed back again to ordinary sulphur. 



How sulphur is found in nature. Sulphur is found naturally 

 both alone that is, in an uncombined condition and also united with 

 other substances in the form of chemical compounds. The uncombined 

 or native sulphur is rarely pure. It is found most abundantly in the 

 neighbourhood of volcanoes as, for example, hi Sicily from which 

 island a large part of the brimstone, as sulphur is commonly called, of 

 commerce is obtained. Before being placed on the market the sulphur 

 is purified, or separated from the earthy impurities by distillation, in 

 suitable retorts connected with large cool chambers, in which the sulphur 

 vapour, driven off by heating, is condensed. In the first stages of the 

 first process the sulphur condenses as " flowers of sulphur," but later, 

 when the condensing chambers have become heated, as a liquid on the 

 floor. This liquid is cast into the familiar " roll-sulphur " or brim- 

 stone which is well known to most people. 



In recent years the centre of the world's sulphur supply has been 

 transferred from Sicily to the United States, where large underground 

 deposits are melted by superheated steam and forced to the surface 

 in a liquid state, being afterwards led to large bins where the sulphur 

 is allowed to cool. 



