294 Messrs. Wright and Thompson on the Determination of 



Valuation of scale : a normal Daniell cell (set up with amal- 

 gamated zinc, electro-copper, and zinc- and copper-sulphate 

 solutions of equal strength) gave 125*7 scale-degrees as mean 

 reading when 200100 ohms were in circuit, the yoo shunt 



being used, whence 1 scale-division = 100x2001 qo xl25 - 7 



ampere = '000443 microampere = 443 elassoamperes. 



Readings before exchanging plates. After exchanging plates. 



Average scale-reading (no 



shunt used) \ 484*25 467-0 



Currrent passing, in micro- 

 amperes* -2145 -2069 



Total resistance in circuit, in 



ohms 207400 207400 



B.M.F., in millivolts 44*5 42'9 



Mean of the two results 43*7 millivolts. 



Maximum departure between ditto . 1*6 millivolt. 

 Difference from mean + # 8 „ 



In the same kind of way other similar experiments gave 

 means ranging from 41*6 to 44*4 millivolts, the final average 

 being 43*3, with a probable error of ±'34 millivolt. 



153. The following tables give, in millivolts, the results 

 obtained with various kinds of metals, natures of plate-surfaces, 

 and descriptions of saline solutions : — 



I. Variations of Potential due to Variations of Strength in 

 Zinc-sulphate Solution. 

 lc Amalgamated Zinc Plates. 

 A. Observations with the Electrometer. 

 Probable error of each value cited not exceeding ±1'0 mil- 

 livolt. The numbers represent the difference of potential set 

 up when one solution is m ZnS0 4 100 H 2 0, and the other 

 n ZnS0 4 100 H 2 0. 



Value of m. 



Value of n. 



42 



30 2-1 



ri 



•55 



•167 



51 

 4*2 

 30 

 2-1 

 11 

 •55 



4 



12 



8 



16 



12 



4 



23 

 19 

 11 



7 



28 

 24 

 16 

 12 

 5 



37 

 33 

 25 

 21 

 14 

 9 



* Representing a current-density of about *045 microampere per square 

 centimetre. 



