GENERAL PHYSIOLOGY. 27 



tor; sulphuric acid, 10%; copper sulphate, saturated 

 solution; mercury. 

 2. Experiments and Observations. 



a. The Daniell cell. Present the four parts of the 

 cell. Half fill the outer receptable of the cell with the 

 saturated copper sulphate solution. Put the copper 

 plate into the cell; half fill the porous cup with the 

 dilute sulphuric acid, lower the zinc plate carefully 

 into the cup. The plate is of commercial zinc with 

 its various impurities. 



(1) Observe the vigorous chemical action in porous 

 cup. Write the reaction. It is evident that the 

 zinc will be quickly consumed if allowed to re- 

 main in the acid and this will be the case whether 

 or not the cup and zinc plate be made a part of 

 an electric cell, and whether the cell be acting or 

 resting. 



(2) The amalgamation of the zinc. [See also App. 

 A. -4.] Lift the zinc plate out of the acid, dip it 

 into the mercury. The mercury adheres to the 

 zinc, mingles with the surface layer of zinc, form- 

 ing an alloy, with a brush or an old cloth one 

 may rub the mercury over the whole surface of 

 the zinc plate the zinc is amalgamated. The 

 impurities of the zinc do not enter into the alloy. 

 In this way only the Rure zinc which forms a part 

 of the alloy is presented to the acid. Chemically 

 pure zinc is acted upon very slowly by 10% 

 sulphuric acid; join a wire to the exposed end of 

 each plate. Touch the tongue with the freed end 

 of each wire separately; touch the tongue with 

 both wires simultaneously. Record results. 



(3) Place the porous cup with the zinc plate in the 

 receptacle holding the CuSO 4 with the copper 



