EXPERIMENT STATION BULLETINS. 



567 



It has also been objected that the necessarily strong current in the coils 

 to produce the greatest sensitivity would in turn produce such a load 

 on the electrolytic solution as to exert a deleterious lieating effect. This 

 objection is not valid. Such a trouble can be obviated by introducing a 

 variable resistance in the bridge circuit to control the amount of current 

 to any strength desired. This heating effect is sometimes quite appre- 

 ciable, and causes a very considerable error. It takes place in the more 



c: 





r^ 



Fig. 5. 



Diagram of connections when using an clcctrodynaniomctcr. 

 rhysical I'apcrs, Figs. 10 and 14, page 302. 



From Henry A. Rowlancrs 



concentrated solutions. To determine the resistance of such solutions 

 only a small amount of current is necessary. Cutting down the current 

 does not decrease the sensitivity when working with such solutions. A 

 paragraph from the works of Professor Rowland concerning the sensi- 

 tivity of an electrodynamometer is quoted here: — "An electrodynamo- 

 meter can be made to detect .0001 ampere without making the self induct- 

 ance of the suspended coil more than .0007 henrys or that of ,tlie station- 

 ary coils more than .0000 lienrys, tlie latter readily sustaining a current 

 of 1/10 amperes without much heating." The point of balance is exact. 



