Chemical Affinity in terms of Electromotive Force. 277 



Similarly with voltameter no. 4, containing acid of which 

 100 cubic centims. contained 27*0 grammes H 2 S0 4 , the 

 averages of two similar series of daily observations, near the 

 beginning and end respectively of a lengthened period of 

 time during which the curve-values were being determined, 

 were as follows : — 



Current in e in 

 inicrowebers. volts. 



General average from early series 4*70 2*334 



„ „ „ later „ 4-85 2-337 



Mean 4-77 2*3355 



and so on in dozens of other analogous cases. 



87. The following tables give the final averages deduced 

 from four lengthened series of daily morning observations 

 made with voltameters nos. 1, 2, 3, and 4 above mentioned (§ 80), 

 containing acid of such strength that 100 cub. centims. con- 

 tained 27*0 grammes of H 2 S0 4 . The average temperature of 

 the different series of experiments was in each case not far 

 from 18°, near to which temperature the specific resistance of 

 dilute sulphuric acid was found to be as follows by Kohlrausch 

 and Nippoldt (Pogg. Ann. cxxxviii. p. 379, 1869): — 



Sp. gr. 

 of acid. 



1-1431 

 1-2045 



Percentage of 

 H 2 S0 4 . 



20-2 



28-0 



H 2 SC>4per 1- 

 100 cubic cen- 

 timetres. Mercury =1. 



Specific resistance at 22 c 



grammes. 

 23-1 

 33-7 



14990 

 13133 



Absolute 

 (C.GKS. system). 



1-424 Xl0 9 

 1-247 Xl0 9 



the numbers in the last column being deduced from those in 

 the preceding one by taking the specific resistance of mercury 

 on the C.G.S. system as being 0'000095 x 10 9 , I e. 0-000095 

 ohm per column of 1 square centim. in section and 1 centim. 

 long ; whence, by interpolation, the specific resistance of acid 

 containing 27 # grammes H 2 S0 4 per 100 cub. centims. is, at 22°, 

 1*31 x 10 9 . The numbers obtained by Kohlrausch (Pogg. Ann. 

 Ergbd. viii. p. 1, and clix. p. 233, 1876) yield a slightly dif- 

 ferent value, about 12 per cent, higher. 



Sp. gr. 

 of acid. 



Percentage of! H 2 S0 4 per 



H SO 



100 cubic cen- 

 timetres. 



1-1414 i 

 1-1807 



20 



25 



grammes. 

 22-8 

 29-5 



Conductivity 



at 18°. 

 Mercury = 1. 



Specific re- 

 sistance at 

 18° (C.G.S. 

 system). 



•0000(5108 

 •00000700 



1*556 xlO 9 



1-417 XlO 9 



Phil. Mag. S. 5. Vol. 11. No. 68. April 1881. 



X 



