394 



TENTH ANNUAL REPORT OF 



urements only after the current had been passing for some hours 

 throufljh the voltameter. 



Metal plates with rough surfaces appeared from his measurement to 

 be polarized less than polished ones, which accords well with Pog- 

 gendorff 's observation, that the polarization on platinum plates is less 

 than on naked ones. The polarization of polished copper plates by 

 hydrogen, Svanberg found in the ratio of 12 to 8 less when they were 

 made rough with a file, or still better when rendered granular by 

 galvanic precipitated coi3per. 



§3*7. Bvff' s researclies on galvanic polarization. — Single results of 

 these researches have been already mentioned above, but we must 

 here present a few more extracts from Buff's Memoir. (Pogg. Ann., 

 LXXIII, 497.) 



He found that a deflection of 45 degrees in his tangent compass 

 corresponded to a development of hydrogen of 21.08 cubic centime- 

 tres per minute, (reduced to the temperature of 0° and 760 milli- 

 tres pressure?), which is equivalent to a development of explosive 

 gas of 31.6 centimetres ; hence the strength of the current was re- 

 duced to chemical measure by multiplying the tangent of the angle 

 of deflection by 31.6. 



In the course of this investigation. Buff found the electro-motive 

 force of a Danieil element equal to 4.20*7. Since, in establishing our 

 unit we have taken the electromotive force of this element at 470, 

 Buff's data of electro-motive force, as well as his value of polariza- 



. . . 470 



tion, must be multiplied by ^^ =: 111 to make the results compar- 

 able with ours. Buff's comparison of the strength of current and 

 magnitude of polarization in a voltameter with naked platinum plates, 

 (referred to our unit), gave the following results : 



In those experiments the platinum electrodes formed the opposite 

 sides of a trough ; the above numbers relate to the case where the 

 trough was filled to a height of 45 millimetres. 



Filled to a height of 10 millimetres, the following respective values 

 of strength of current and polarization were obtained : 



