418 MM. F. Kohlrausch and 0. Grotrian on the Electric 



city-conducting power of which almost nothing was known. 

 Observations have been made on it in seven proportions of solu- 

 tion ; and thereby a sufficient knowledge for all purposes has 

 been gained. 



The method used for measuring the resistances was the one 

 first described in the Nachrichten (1869, Nov. 14) — that of 

 quickly alternating currents, which, with some subsequent im- 

 provements (namely, the production of a convenient induction- 

 coil for the alternating currents, the application of Wheatstone's 

 bridge to the dynamometer, and the introduction of platinized 

 electrodes*), in simplicity and accuracy leaves nothing to be 

 desired. Indeed the determination of the temperature of the 

 liquid under experiment now presents greater difficulties than 

 the measurement of the resistance, if the same degree of accu- 

 racy is demanded for both. 



We have been most careful to make sure of the sensibly com- 

 plete exclusion of polarization of the electrodes, which, when 

 constant currents were used, hindered the exact measurement of 

 the work of the current in decomposable conductors. To mention 

 one of the tests applied in this direction, we experimented upon 

 a solution of sulphate of zinc, first between electrodes of amalga- 

 mated zinc (which generally give no polarization), and then be- 

 tween the platinized platinum electrodes of 2000 square millims. 

 surface which were employed for all the subsequent measure- 

 ments. The greatest difference between the resistances found 

 corresponded to a temperature-error of about ^ of a degree. 

 With the zinc electrodes, constant as well as alternating currents 

 were used; and at the same time, by the accordance between 

 the results, it was established that the work of the alternating 

 currents follows the same laws as that of a constant current. 



From the commencement onward, the materials for observa- 

 tion were so arranged as to facilitate comparison when put toge- 

 ther in Tables. The solutions contained approximately 5, 10, 

 . . . (or, in the case of nitric acid, 6*2, 12*4, . . .) per cent. ; and 

 the temperatures were near 0°, 18°, and 40°; so that reduction 

 to exactly these proportions was attended with no risk of error. 



Our thanks are due to Professor Biichner, Dr. Heumann, 

 and Dr. Rbssler for the preparation and analysis of the most 

 concentrated solutions of each substance. The other solutions 

 were prepared from these by weight. 



The specific gravities (at 18°; water at 4° equal 1) present a 

 second definition, independent of the analysis, of each solution. 



The electric conducting-powers k, given below, are all referred 

 to that of mercury at 0° as unity. Siemens's standards no. 1135 

 and no. 1143, which were made use of for the reduction of th 

 * Pogg. Ann. Jubelband, p. 290, vol. cli. p. 378. 



