94 SCIENTIFIC AMUSEMENTS. 



A still better way of showing the separation of lead from 

 zinc is to mould a very narrow long clay crucible (Expt. 1), 

 shaped like a test-tube, using a thick pencil rubbed with oil as a 

 "core" or mould to shape the interior by rolling and working the 

 clay round it. Such a tube should be slowly dried and fired by 

 heating in the lamp flame ; if any cracks form these should be 

 filled up with clay after cooling, and the tube heated a second 

 time, and so on until the clay test-tube is tight enough to hold the 

 molten metal. The tube is then heated in the flame of a large 

 Bunsen lamp like the pipe bowl, and the melted metals carefully 

 poured in from the crucible, and kept melted for half an hour or 

 more. Finally, after cooling, the clay is carefully broken away 

 from the long narrow ingot or rod of metal ; the lower end will 

 be soft enough to bend and hammer out flat, but the upper end 

 will be hard and rigid, and if forced by sufficient power will not 

 bend, but will break off with a "crystalline fracture," i.e., the 

 broken surfaces will show a crystalline structure (vide Expt. 18). 



Bismuth and zinc behave in exactly the same way as lead and 

 zinc when melted together, the heavier bismuth separating to the 

 bottom (dissolving some zinc in so doing), whilst the lighter zinc 

 floats up to the top (dissolving a little bismuth at the same time). 

 If equal weights of the two metals are melted and stirred together, 

 and then poured into a hot clay test-tube, and kept melted for an 

 hour, the rod of metal finally obtained after cooling will be 

 extremely brittle, and easily broken at the lower end, owing to 

 this consisting mostly of bismuth ; whilst the other end, being 

 mainly zinc, will be much harder, and less easily broken. 



The different degrees of solubility of melted metals in one 

 another are often utilised in metallurgical operations in a variety 

 of ways ; for example, certain lead ores, especially the one termed 

 " galena," contain silver, which is smelted along with the lead in the 

 process of extracting that metal from the galena, or natural 

 sulphide of lead. In order to extract the silver, a process some- 

 times used is to stir up some zinc with the melted lead ; the zinc 

 rises to the top, being mostly undissolved by the lead, and carries 

 a great part of the silver with it, because molten zinc dissolves 

 silver more freely than does melted lead. By skimming off the 

 melted zinc from the top, and then heating it strongly, the silver 

 is ultimately obtained (mixed with a little lead), the zinc being 

 volatilised and driven off by the heat. 



Bromine is a liquid element of a most intolerable odour ; it will 

 dissolve in water to a slight extent, forming a brownish-orange 

 solution. If a weak solution of bromine in water be shaken up 

 with a little chloroform or bisulphide of carbon, the latter will 



