EXPERIMENT STATION BULLETINS. 571 



not suitable for work of precision and must be replaced by the Curtis 

 Coils which are wound to avoid inductance and capacity. The resistance 

 cups must be selected according to certain necessary conditions. A con- 

 denser must be used across the resistance to balance out the capacity in 

 the electrolytic cell. In the following pages we describe the apparatus 

 we have been using and then add the results of a few tests to show the 

 precision which this method attains. 



3. THE SIMPLIFIED RESISTANCE MEASURING APPARATUS. 



When working with electrical instruments, or a resistance measuring 

 network like the Wheatstone Bridge it is a good plan, on general princi- 

 ples, to select the apparatus so that its various parts are in conformity. 

 It is therefore necessary to know the various pieces and to be able to 

 judge as to the relative value of things. It is obviously wrong to use a 

 poor grade low resistance and a moderately sensitive detector if one de- 

 sires to measure conductivity water. There are other arrangements 

 which should be condemned, but yet are not so apparently wrong as in the 

 above illustration. Each part should be selected and arranged to con- 

 form to certain demands in other parts. In the usual method the station- 

 ary coils and the swing-ing coils of the dynamometer have been connected 

 in series. The better way and one in which the sensibility is increased 

 nearly 1,000 times is to connect the swinging coils across the bridge and 

 place the stationary coils in the main circuit. We believe, after working 

 for some time with all the old and the most recent devices for measuring 

 the conductivity of electrolytes, that we have now brought together a 

 simplified, accurate and efficient apparatus. Fig. 6 shows the arrange- 

 ment and scheme of connections for the new apparatus. Fig. 7 represents 

 the apparatus all assembled ready for a measurement. 



