326 



GEOLOGY or THE COMSTOCK LODE. 



it, was preferable (see page 357). When not in use the bags were kept 

 in a glass vessel containing a zinc sulphate solution; during the obser- 

 vations, however, they were transported from place to place in jars con- 

 taining water.^ 



The electromotive force between two similar bags placed in the same 



external liquid was seldom 

 found to be greater than 0.005 

 volt, usually much less, and tol- 

 erably constant (see page 362); 

 whereas the electromotive force 

 of polarization, due to the ac- 

 tion of a Daniell under circum- 

 stances actually met with in the 

 mines, a number of data being 

 in hand, was in no case as large 

 as 0.001 volt and in the experi- 

 ments cited falls below this 

 limit. For comparison the bags 

 in a particular instance were 

 filled with water instead of zinc 

 sulphate, when an electromo- 

 tive force of polarization of 

 0.020 volt was obtained. 



LM.-Terminal in position. Wire. Gutta-pCrclia-COV- 



ered wire No. 19, of excellent quality (Tillotson & Co., New York), was 

 used almost exclusively, the whole circuit nevertheless being suspended in 

 air from threads, as in the Comstock. In the long circuit on the 600-foot 

 level it was necessary, however, to employ cotton-covered wire for part 

 of the line, the supply of the other being insufficient. This could be 

 done without disadvantage, as follows: A hollow cylinder of gutta-percha, 

 stripped from the end of a wire covered with this substance, was bent in 

 the form of a loop, Fig. 25, and kept bent by a thread passed through its 



' It was desirable during the observation to have the outside of the bag as free Irom zinc sulphate 

 solution as possible. 



