384 



TENTH ANNUAL REfORT OP 



« i 



The apparatus represented in Fig. 20 Avas used hj 

 Becquerel for measuring the resistance of licjuids (Ann. 

 de chim. et de phys, 3 series, XVII, 242.) Its construction 

 hardly requires any further explanation. The metal 

 plate a is movable up and down in a glass tube, at the 

 lower end of which the plate b is placed ; thus the cur- 

 rent has to traverse the liquid column between a and h. 

 The conducting wires of the plates a and h are enclosed 

 in glass tubes to prevent lateral currents. 



Becquerel applies the differential galvanometer here 

 also; in each of the two closing circuits is inserted an 

 apparatus like that of Fig. 26. In order that he might 

 raise or lower the plate a in one of them, lie arranged so 

 that tlie multiplier needle came to rest at 0. 



A spiral wire of knov/n resistance having been inserted 

 ;n one of the closing arcs, tlie needle deviated and the 

 liquid column of tlu^t circuit had to be shortened to re- 

 store the needle to 0. In this manner 't was found how 

 i long the liquid column should be, to exert the same 

 resistance as the inserted spiral wire. Ifc is understood, 

 of course, that there were contrivances for measuring t' e exact eleva- 

 tion or descent of the plate a; but of these, it is not necessary to 

 give the description. 



By this method Becquerel found the following values for the specific 

 resistances of different liquids, silver being taken as 1 : 



Saturated solution of sulphate of copper 18,450,000 



Do common salt 3,173,000 



Do nitrate of copper 11,120,000 



Do sulphate of zine '. 17,330,000 



Dilute sulphuric acid (220 c. c. water -!- 20 c. c. 



sulphuric acid with 1 atom of water) 1,128,000 



Commercial nitric acid of 36° B 1,606,000 



With reference to the influence which the degree of concentration 

 had upon the solution, Becquerel found the following results : 



Liquid. 



Resistance. 



Sulphate of copper, sn.turated solution - . 

 " " diluted to 2 volumes 



" " diluted to 4 volumes 



Common salt, satui'ated solution - 



' ' diluted to 2 volumes 



" diluted to 3 volumes 



" diluted to 4 volumes 



18,450,000 

 28,820,000 

 48,080,000 

 3,173,000 

 4, 333, 000 

 5,721,004 

 7, .864, 000 



§32*. Computation of strength of current by means of an inserted 

 voltameter. — When the resistance of the liquid and the approximate 

 quantity of galvanic polarization are known, it is easy to compute 

 the strength of current of a given combination. Suppose, for example, 

 a voltameter, whose plates have a surface (on each side) of 25 square 



