80 LABOR A TOR Y G UID E IN PH YSIOL OGY. 



electric energy liberated in the foregoing experi- 

 ments is the latent chemical energy represented in 

 the plates and liquids of the cell. 



Under the conditions produced in the working 

 galvanic cell the latent chemical energy is trans- 

 formed, and at the same time liberated as electric 

 energy. This liberated electric energy may make 

 itself manifest in the contact spark, in moving the 

 detector needle or in lifting the armature of a mag- 

 net. In the last case mentioned it would not be 

 difficult to determine the amount of work done, 

 though it might be somewhat difficult to determine 

 the amount of work which a cell is capable of per- 



FIG 5. 

 FIG. 5. Pohl's commutator. For description and uses see III=c. 



forming in a given time. If one were to weigh the 

 copper plate before and after using the cell, one 

 would find that it had increased in weight. This 

 increase in weight is an index of the amount of 

 chemical action in the cell of the latent chemical 

 energy which has been transformed into electric 

 energy. It must be, then, at least an approximate 

 index of the electric energy liberated. An exact 

 index of the amount of current is afforded by the 

 amount of electrolysis. For example, if the nega 

 tive pole of a cell be attached to a silver or platinum 



