CH. xii CONSTRUCTION OF SIMPLE VOLTAIC CELLS 185 



EXPT. 180. Now tilt the pieces of metal towards one another 

 until they touch outside the liquid, or connect them with a 

 wire as in Fig. 94. Observe that bubbles of gas appear on 

 the copper plate. 



EXPT. 181. Take the pieces of 

 copper and zinc in the last experi- 

 ment out of the acid, wash them 

 under the tap, and carefully dry them 

 on clean blotting paper. Weigh both 

 pieces of metal and record their 

 weights thus : 



Weight of rod of pure zinc grams. 

 Weight of strip of copper - grams. 



Now replace them in the dilute acid 



and make them touch outside the liquid, or connect them by 

 a piece of copper wire, and allow the action which ensues to 

 continue for ten or fifteen minutes. Then remove them from 

 the acid and wash, dry and weigh them as before. Record 

 your result beneath the last entry thus : 



After 15 minutes' action. 



Weight of zinc rod grams. 



Weight of copper strip grams. 



Notice that while the zinc has diminished in weight the weight 

 of the copper has remained unaltered. 



EXPT. 182. Prepare a plate of amalgamated zinc by dipping 

 a plate of ordinary commercial zinc into dilute sulphuric acid, 

 and after it has been acted upon for a minute or two rub some 

 mercury completely over its surface with a piece of cloth. 

 Repeat Expt. 178, and observe that amalgamated zinc behaves 

 just like pure zinc. 



Properties of the Wire connecting the Plates of Copper 

 and Zinc. EXPT. 183. Into some dilute sulphuric acid con- 

 tained in a beaker plunge a plate of amalgamated zinc and one 

 of copper, to each of which a copper wire is attached by a 

 suitable binding screw. There is no chemical action until the 

 free ends of the wires are joined, when, as before, bubbles of 

 gas are seen to collect on the copper plate. 



EXPT. 184. Procure an ordinary compass needle, which 

 consists of a light magnet, suitably supported at its middle 

 point, so that it can move freely in a horizontal plane. Bring 



