14 



cone of filter paper supported in a glass funnel (Fig. 9) . The liquid, 

 together with anything that may be dissolved in it, runs through 

 the pores of the paper and down the hollow stem of the funnel. 

 The liquid is then called the filtrate. The particles of the sus- 

 pended solid are too large to pass through the pores, and so col- 

 lect on the surface of the filter paper. This operation, like every- 

 thing the chemist does, takes advantage of differences in the 

 specific properties of the various materials. 



The material remaining on the paper (the residue), when dry, 

 is wholly attracted by a magnet and shows all the other properties 

 of iron. 



Evaporation. To recover the sulphur, the solution in carbon 

 disulphide the filtrate is poured into a porcelain evaporat- 

 ing dish. (Carbon disulphide is very in- 

 flammable! Keep flames away). When 

 the vessel is set aside, the liquid grad- 

 ually passes off in vapor (e-vapor-ates). 

 Sulphur, however, does not evaporate 

 at room temperature and remains as a 

 residue, in the form of crystals of rhombic outline in the bottom 

 of the dish (Fig. 10). Here, again, differences in specific properties 

 have been utilized. 



Since the physical properties of two substances are not changed 

 by mixing, we have thus used the properties of the iron and sul- 

 phur so as to separate them once more. The iron is on the paper; 

 the sulphur is in the dish. 



Combination of Iron and Sulphur. But iron and sulphur 

 are capable of combining to form a new substance, if we alter 

 the conditions by raising the temperature. When we place some 

 of the original mixture of iron and sulphur into a clean test-tube 

 and warm it, we soon notice a rather violent development of heat 

 taking place, the contents begin to glow, and what appears to 



