for Electrometric Measurements, 175 



element in which the circuit had been closed for only half a 

 minute. A Daniell element would have shown scarcely any 

 change under similar conditions. 



But this defect of the Latimer-Clark element may be almost 

 entirely remedied by giving to the cell so great a resistance 

 that only an insignificant current can be generated. 



A U-tube of 1 centim. diameter and legs 75 centim. long 

 was filled with the paste of mercury-sulphate and zinc-sulphate 

 solution, prepared according to the instructions, but heated so 

 much that after cooling it became hard. The paste was boiled 

 in the tube by means of a water air-pump. The zinc pole 

 was introduced into the upper end of the tube and the mer- 

 cury pole into the lower, and the openings were closed with 

 paraffin. The element is very convenient for use on the 

 laboratory-table, since the two poles may pass through holes 

 bored in the table, the whole body of the tube being protected 

 underneath the table. The internal resistance of the element 

 was 15,700 ohms*. Its electromotive force was somewhat 

 smaller than given by Latimer Clark. If, in fact, the electro- 

 motive force of a normal Daniell cell (with dilute sulphuric 

 acid) be taken as 1*195 volt, then that of my mercury element 

 was 1-442 volt (instead of 1*457 volt). When the element 

 was short-circuited, its electromotive force was as follows : — 



After 5 minutes . , 



, . 1*440 volt. 



„ 1 hour . . 



. . 1-439 „ 



„ 4 hours . . 



. . 1*439 „ 



•• 6 ;• 



. . 1-437 „ 



» 12 ,, • • 



. . 1-434 „ 



„ 48 „ . . 



. . 1-408 „ 



We see therefore that the element resists the influence of 

 polarization for a long time. Polarization could indeed only 

 be very slight, since the current which passed through the 

 element has only the intensity of 0*000091 ampere. The 

 electromotive force only diminished 2 per cent, after use for 

 48 hours, a decrease which is very small indeed compared 

 with the falling off in the usual form of the Latimer- Clark 

 element. It is easy to avoid short-circuiting the element 

 for such a length of time ; but if the element has once become 

 enfeebled, it recovers itself only slowly. Thus, after 24 hours 

 I found its strength to be 1'430 volt. 



The idea of replacing the fluid of an element by a solid 

 body may be carried out also with a Daniell element. Fine 

 alabaster plaster-of-Paris was mixed with concentrated copper- 



* The resistances were measured by my first assistant, Dr. Pfeiffer, by 

 the use of alternate currents. 



