the Range of the Capillary Electrometer 



67 



It was learned by means of a series of experiments that 

 this irregular movement was in great measure caused by a dif- 

 ference in the capacity and sensitiveness of the different cells. 

 For when cells of the same capacity were adjusted to the same 

 sensitiveness and joined in series, the columns moved together 

 without seesawing. The difficulty of preparing cells of pre- 

 cisely the same capacity and of adjusting them to the same 

 sensitiveness is a serious objection to the employment of cells 

 of this kind. Hence the electrometer composed of cells in 

 which the movement of the mercury columns takes place in a 

 vertical tube seemed on the whole more advantageous. 



Several different forms were tried. One arrangement con- 

 sisted of three conical tubes each drawn to a very fine bore. 

 These were placed one above the other the capillary stem of 

 each containing mercury and dipping into the acid of the next 

 lower cell. The electrometer in this form is somewhat diffi- 

 cult to fill, and its action uncertain, owing to the formation 

 of bubbles of gas in the capillary tubes. 



To cause the movement of the mercury in all the cells to be 

 simultaneous, and of the same extent, as well as to secure 

 compactness and better insulation, the form, represented in 

 fig. 1, was finally adopted. 



A series of bulbs was blown, spaced at equal intervals along 

 a capillary tube, the diameter of the bulbs being two centime- 

 ters, that of the tube 0'6 of 

 a millimeter. Then the 

 tube was so bent, that the 

 whole contained as many U- 

 shaped parts as there were 

 cells. One arm of each U 

 was provided with a bulb 

 which was situated at a dis- 

 tance of two-thirds the 

 height of the U from the 

 base. The apparatus was 



easily filled by connecting it with an aspirator and drawing 

 in sufficient pure mercury to half fill each bulb. Then by the 

 same means dilute sulphuric acid was added until the capillary 

 tubes and the upper portion of the bulbs were filled and all air 

 bubbles excluded. Previous to the filling of the instrument, a 

 solution of pure sulphuric acid and distilled water, consisting of 

 four volumes of water to one of acid, was prepared, and allowed 

 to stand until all the bubbles of gas formed by the mixture had 

 disappeared. This was afterwards diluted, if necessary, with 

 distilled water to the proper proportion. 



The operation of filling the electrometer was greatly facili- 

 tated by having the tube which entered the upper part of the 

 last bulb of the series of much greater caliber than that of the 



