MICHIGAN ACADEMY OF SCIENCE. 49 



A SIMPLIFIED APPAKATIJS FOR MEASriRING THE 

 CONDUCTIVITY OF ELECTROLYTES. 



BY R. P. HIBBARD. 



(Abstract.) 



During the study of certain problems in plant physiology it 

 became necessary to measure the concentration changes in cultui;e 

 solutions. The Wheatstone Bridge apparatus seemed fitted for this 

 kind of work but it was later observed that there were many 

 sources of error in the usual set up and the attempt was made to 

 eliminate these as far as possible. As a result of our studies, we 

 have not only simplified the method but increased its accuracy to 

 a considerable extent. The modifications suggested also make the 

 apparatus mudi easier to operate, thus eliminating to a great ex- 

 tent the '^personal error." The correct bridge setting is made by 

 the aid of the eye instead of the ear. The important changes sug- 

 gested are as follows : ( 1 ) The induction coil is abandoned for a 

 60 cycle rotary converter on a current of constant potential. The 

 Vreeland Oscillator is to be preferred to this but when this work 

 was done the Vreeland Oscillator was not on the market. It has 

 been shown that in assuming polarization at 60 cycles we are as- 

 suming something neither apparent nor real. We have used the 

 frequency for a period of two years, and have had no trouble, from 

 polarization but what could be eliminated. (2) The Curtis Resist- 

 ance Coils, wound for the annulment of capacity and inductance 

 take the place of the ordinary resistances. (3) An alternating 

 current galvanometer is put in the place of the telephone and in 

 many ways is superior to the telephone tuned to any definite 

 frequency. (4) The roller type of bridge with the "extended'^ 

 wire should be used. The possible error from the use of the bridge 

 thus modified would not be more than .002 of 1 per cent. (5) 

 The construction, and the correct selection of suitable electrolytic 

 cells for the different solutions necessitates more attention than 

 is usually given. A, preliminary report was published in the 15th 

 Annual Report of the Michigan Academy of Science, 1913. The 

 completed work has appeared as Technical Bulletin No. 23, of 

 the Michigan Agricultural College Experiment Station. 



Michigan Agricultural College Experiment Staticfn, East Lan- 

 sing, Michigan. 

 7 



