CHEMICAL CHANGE AND THE METHODS OF STUDYING IT 13 



It is very difficult to melt it (m.-p. over 1500 C.). It does 

 not dissolve in any common liquids at ordinary temperatures. 

 It crystal izes in cubes, and is attracted strongly by a magnet. 



Study of the Mixture, before Combination. Now, it 

 some iron filings and pulverized sulphur are stirred together in a 

 mortar, the result is a mixture. True, the color is not that of 

 either substance, but with a lens particles of both substances can 

 be seen. Passing a magnet over the mixture will 

 easily remove a part of the iron, and with the 

 help of a lens and a needle the mixture could be 

 picked apart particle by particle, completely. 

 We can separate the components of the mixture 

 more expeditiously, however, by using manipula- 

 tions based upon other more suitable properties. 

 Thus, sulphur dissolves in carbon disulphide while 

 iron does not. If, therefore, a part of the mix- 

 ture is placed in a dry test-tube along with some 

 carbon disulphide (Fig. 8), and is shaken, the liquid dissolves 

 the sulphur and leaves the iron. To complete the separation, the 

 iron must be removed from the liquid by 

 filtration, and the sulphur recovered by 

 evaporation of the carbon disulphide. 



Filtration. Iron, or any solid, when 

 it is mixed with a liquid or with a solu- 

 tion (like the solution of sulphur in car- 

 bon disulphide) is said to be suspended 

 in the liquid. If the solid is one that 

 settles rapidly, the liquid may be sep- 

 arated from the solid, in a rough way, by 

 pouring off as much of the clear, super- 

 natant liquid as possible. This is called decantation. 

 A complete separation is effected by pouring the mixture on to a 



FIG. 8 



FIG. 9 



