ELECTKICAL ACTIVITY OF OHK I'.ODllOS. 



325 



the well-known fact of the excellence of amalgamated zinc in a zinc, sul- 

 phate solution, for the purpose in question, was tinall}- adopted. 



Into a large cork (/,' Fig. 23 (longitudinal section), is in.serted a strip 

 of amalgamated zinc, c/J about one-half inch 

 broad, to the \o\) of which, c, a gutta-percha- 

 covered copper wire, hik, is .soldered. Through- 

 out the greater jiart of its length it rests against 

 a stick of wood, cd, cylindrical above at c, which 

 end is to be thrust through a perforation in the 

 cork a, but wedge-shaped below, d At i the 

 wire and stick are firmly tied together. A 

 smaller cork, b, secures the lower end of both 

 zinc and stick. The whole is surrounded by a 

 piece of beef-gut, gy (free from salt), tied to the 

 corks « and h, as shown in the cut. 



Into the bag (6 to 10 inches long) thus 

 formed is poured a solution of zinc sulphate, 

 the wooden plug I being for this purpose re- 

 moved and a small funnel inserted. On replac- 

 ing the plug the terminal is ready for use. The 

 object of the stick is to obviate accidents due 

 to breakage of the zinc, thi.s material becoming- 

 very brittle by amalgamation. stftiini. 



Fig. 24 represents the terminal in place. A suitable hole, 6 to !• inches 

 deep and 1 to IJ inches in diameter, is drilled into the rock or vein, at an 

 angle of about 30° with the vertical, and filled with a solution of sodic sul- 

 phate or water; whereupon the bag is introduced as shown in the figure. 

 The dotted Hne nin indicates the level of the outer liquid.- Solution of sodic 

 sulphate was at first used, because it increases the conductivity and is not 

 acted upon appreciably by the rock (limestone). It was found, however, 

 that ordinary water, which had previously been placed in contact with zinc 

 for some time, so as to precipitate all dissolved matter which might act upon 



ric. -JH.— TiTiiiiual, loiinitiuliiial 



' 1 to H inches in diameter. 



■Till! Huliition poured into tilt- hole will be referred to throUKlidiit tlii 



deMcriplion as the "outer 



li(iMid." 



