the Range of the Capillary Electrometer. 65 



surfaces of the mercury, thistle tubes of the following descrip- 

 tion were prepared. The larger part, by the head of the thistle, 

 had a diameter of about two centimeters, while the stem had 

 a capillary bore of 0*6 millimeter. The tubes were so bent, 

 that each was U-shaped. The lower portion of the tubes was 

 filled with pure mercury, and the upper part with dilute sul- 

 phuric acid. The electric connections were so made, that the 

 larger surfaces of the mercury received oxygen polarization. 



By reason of the described arrangement, a difference of 

 potential between the terminals of a cell causes the mercury 

 column in the vertical portion of the capillary tube to descend, 

 and this depression is easily measured. Hence cells thus con- 

 structed may be used singly as electrometers ; and when joined 

 in series, they form a convenient apparatus for the proposed 

 investigation. 



As a means of obtaining any desired fraction of the electro- 

 motive force of a Daniell cell, a standard box of high resist- 

 ances and a few Daniell cells were arranged in series. Then 

 the terminals of the electrometer were connected by movable 

 contact pieces to the resistance box so that, as different resist- 

 ances were inserted between the contact pieces, the electro- 

 motive force to which the electrometer was subjected was pro- 

 portionally varied. During the course of the investigation, 

 curves showing the relation between the deflection and the 

 electromotive force were carefully drawn. 



When two electrometer-cells of the form already described, 

 were placed in series, the curve deviated but slightly from a 

 straight line for electromotive forces from 0*0 to 0'9 volt. 

 However as the electromotive force is made to exceed this, the 

 deflections increase more slowly, and the entire curve when plot- 

 ted was found to be of the well known form described by Lipp- 

 mann. It is to be noted, however, if curves be drawn for a 

 single cell and for two cells in series, that although the curves 

 have the same form, the electromotive forces correspond- 

 ing to any portion of the second curve are twice as great as 

 those of the similar portion of the first curve. With three 

 cells in series, the curve did not depart greatly from a straight 

 line, until the difference of potential was about 1*35 volts, then 

 the curve rapidly flattened and reached its maximum at about 

 2-7 volts. 



These experiments show that the electromotive force is cut 

 down by each ^additional cell, and hence that a series-electrom- 

 eter may be thus constructed, which will conveniently meas- 

 ure the electromotive force of the single cells ordinarily used 

 in the laboratory. 



In order to discover how the total electromotive force, to 

 which the electrometer is subjected, divides itself among the 



Am. Jour. Sci.— Third Series, Vol. XLIV, No. 260.— July, 1892. 



