248 S. P. Sharpies on some forms of the Galvanic Battery. 



used were those manufactured by Chester of New York for 

 ordinary medical batteries and had a section of about a square 

 inch. The exciting liquid was a mixture of sulpharic acid with 

 nine times its volume of water ; this was found to be without 

 action on the zincs when the battery was not running. The 

 zincs were kept well amalgamated. 



The electro-motive force was determined by Wheatstone's 

 method,* as follows : One of the cells was thrown into the cir- 

 cuit; the rheostat was then adjusted until the needle stou; 

 4S)° ; the resistance was then decreased, until the needle i- 

 oO ; the length of wire removed was noted. The second cii 

 then placed by the side of the first and the resistance inci- 

 until the needle again stood at 50°, and the added leiiL' 

 wire noted. While both cells were connected the needle 



brought agam to 40 , by „ ^ 



length was also noted; it should correspond exactly t^ 

 first length. One of the cells was then removed and the r 

 ance again adjusted; the wire removed should exactly e4U|^. 

 the second length noted above. The second cell was now sub- 

 stituted for the first, and if the needle still remained at a 

 constant point, the measure was considered satisfiictory n 

 there was any discrepancy in the measurements, or if the needle 

 stood at a difi-erent point with one cell, from what it did with 

 the other, the connections were all examined and the measure- 

 ments repeated. It was rarely found necessary to make more 

 than one trial . > 



The formulas used were those given by Wheatstone (loc. cit). 



as follows : For electro- motive force - ,^,- = -y— ^^ which 

 the electro-motive force of a standard battery, and e the leiigt!| 

 of wire necessary to reduce the needle of the^ galvanometei 

 from one given point to another given point B'= the elec 

 motive force of the battery to be determined, and / the leng^" 

 of wire which was required to be removed to change the neeai 

 from one of the given points to the other. . , -^.j^ 



For the internal resistance of the battery, B=2/, m 

 formula E= the internal resistance, and 1= the length oi 

 which must be added when a second cell is Placed by tne- 

 to bring the needle to the same point where it stood wben i 

 one cell was in circuit After making one series of measuremei ^j 

 the needle was brought to 40°, and allowed to remain ai^^^ 

 point for twelve hours if the battery remained constant lo 

 length of time ; the measurements were then repeated, anot^^ 

 pared with those of a Bun sen cell made under the same c 



