GENERAL SCIENCE 



DANIELL'S CELL 



copper offers no more resistance to the current than does 

 the original plate. 



177. The Daniell Cell. There are several types of 

 the Daniell cell. The two common forms are shown in 



the illustrations. The nega- 

 tive pole is zinc, which is 

 immersed in dilute sulphuric 

 acid or zinc sulphate in an 

 unglazed earthenware cup. 

 The positive pole is copper, 

 which is in a copper sulphate 

 solution. The solution is 

 kept the same strength by 

 the copper sulphate crystals dissolving as copper is taken 

 out of the solution and deposited on the copper pole. 



The chemical action which develops the current in 

 this cell is as follows: The acid acts on the zinc pole and 

 forms zinc sulphate (ZnSO 4 ) and free hydrogen is liber- 

 ated. The hydrogen atoms with their electrical charges 

 pass through the porous cup and come in contact with 

 the molecules of copper sulphate. The hydrogen dis- 

 places the copper of the copper sul- 

 phate and forms sulphuric acid (H^SCX). 

 The displaced copper atoms take the 

 electrical charges from the hydrogen 

 atqms and carry these charges to the 

 copper pole, to which the copper atoms 

 adhere when they give up their elec- 

 trical charges. No polarization can oc- 

 cur since no gas is liberated at the positive pole. Such 

 a cell has an electromotive force of about i.i volts. 



178. The 'Gravity Cell is so called because the heavy 

 solution of copper sulphate stays at the bottom and the 



GRAVITY CELL 



