Intelligence and Miscellaneous Articles. 543 



the aqueous vapour. Iu order to be able to shake the distilling 

 apparatus with its water briskly, the connexion with the mercurial 

 air-pump was made in the manner described by Kundt, that is by 

 means of long bent glass tubes. The supply-tube already men- 

 tioned was hermetically sealed. Mr. Otto Wiegand, of Wurz- 

 burg. the glass-blower, who had also constructed the double vessel, 

 gave his experienced help in these operations. 



The vacuum thus obtained I estimate at 0-01 mm. pressure at most. 



There is so much water in the apparatus, that when it is brought 

 into the larger vessel it is two-thirds full. By using a moderately 

 warm hot-air bath of 30° to 45°, and a cooling bath between 0° 

 and — 8°, there being no freezing on account of the heat of con- 

 densation, the requisite quantity of 6 to 8 c. c. was distilled over 

 into the resistance vessel. This took from 8 to 15 minutes, 

 according to circumstances. 



The capacity of the two apparatus was only about 0*00002 Sie- 

 mens unit. The water had up to a resistance of 80,000 units. 

 From the small delicacy of the dynamometer or of the telephone 

 under these circumstances, alternating currents were not used, but 

 short separate throws with an extremely sensitive rapidly vibrating 

 galvanometer in the bridge. Two Smee's elements produced the 

 current. "With careful treatment great electrolytic resistances of 

 this kind may be determined with sufficient accuracy. The current 

 is so weak that the polarization requires a few tenths of a second. 

 By using a varying number of elements, by occasionally reversing 

 the current, and by varying the duration, an accuracy of one to 

 two per cent, could be obtained. 



Even in a vacuum the resistance of a distillate was not constant, 

 but diminished with the time. In one of the vessels this decrease 

 was even considerable, so that the resistance of a distillate, which 

 5 minutes after ending the distillation was" 660,000 ohms, sank 

 after 10 minutes to 337,000, in 1 hour to 236,000, in 3 hours to 

 84,000, and in 15 hours to 26,400, that is -^ of the first value. 

 The initial increase of conductivity is almost uniform. Whether 

 this action is due to the sides of the glass vessel or to the platinum 

 electrodes, I cannot at present say. In the other vessel the resist- 

 ance decreased more slowly. 



In any case it is necessary to hasten with the measurement of 

 resistance after the distillation is complete, so that the temperature, 

 whether judged by the feel or by using a bath, is only approximately 

 determined. 



Eight different distillations gave the following conducting powers 

 as compared with mercury, to which are prefixed the temperature 

 and the number of minutes that have elapsed since the end of the 

 distillation. 





Vessel I. 





Vessel II. 



o 



Min. 



o 



Min. 



20 



3 29-10" 12 



16 



3 29-10 



12 



2 25 „ 



18 



4 28 , 



20 



3 32 „ 



20 



3 27 , 



8 



2 25 „ 



20 



4 31 , 



