422 Prof. R. Bunsen's Spectral- Analytical Researches. 



the action of the mercury used for amalgamating on the chromic 

 acid. 



The constants of the battery were determined with a tangent- 

 galvanometer on which one minute could be accurately read off. 

 The current-intensity was determined, according to. Gauss's 

 measurement, by help of the formula 



T _ RT sinw . . 



~~ 2tt ' cos (u + x)' ' ^ ' 



where u = the angle described by the needle measured from zero 

 of the circle, 

 jK = the radius of the galvanometer-ring in millimetres, 

 T = the horizontal components of the earth's magnetism 

 in Gauss's measure, 

 and x = the deviation of the zero-point of the needle from the 

 plane of the coil. 



In order to arrive at the value of x, the angle u through which 

 the needle is turned from its zero-point by a constant current, as 

 also the angle v described by the needle under the influence of 

 the same current reversed, must be determined; the equation 

 then becomes 



tan x—\ (cot v — cot u) . 



From the observations / 



u 10 45, 

 v 10 35, 

 u 10 41, 

 v 10 31, 

 u 10 37, 



the value 1° 58' was found for x ; R was equal to 201 '6 millims.; 

 T was determined for a position not free from iron, by the de- 

 composition of water, with help of the electrochemical equivalent 

 of water, from the equation 



rp 2tt cos (u—x) G 

 li sm u at 



where « = 0009421 milligrm., the electrochemical equivalent 

 of water, G the amount of water (expressed in milligrammes) 

 decomposed during the flow of the current for t seconds, and u 

 the average deviation-angle" of the needle during the water-de- 

 composition. Two experiments gave the following values : — 



t 1382"-0 1320"-0, 



G 300-8 milligrms. 299-9 milligram., 



u 20° 35' 21° 27'. 



From these observations the value 1*939 (mean of 1*941 and 



