500 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



In using the cell in comparative conductivity in this labora- 

 tory several taps are provided. At each is a lamp socket so 

 that the direct lighting current may be cut down with lamps 

 of various resistances. The glow of the lamp itself gives a rough 

 quantitative measurement of the strength of current transmitted 

 by the cell, but in addition it is better to introduce ammeters 

 reading as low as one one-hundredth of an ampere. In each 

 test the cell is filled to the same height as indicated by some 

 suitable mark, such as gummed paper. Tenth noinnal solutions 

 are made up in quantity for general use. The following have 

 been found instructive : hydrochloric acid, sodium chloride, acetic 

 acid, sodium acetate, ammonia, sodium hydroxide, distilled and 

 ordinary tap water. . 



The experiment offers a good opportunity for the review of 

 electrical terms and relations. Knowing the wattage of the 

 lamp and the electromotive force of the current the resistance of 

 the lamp may be calculated. The current transmitted by the 

 lamp alone may ibe calculated and the result verified by the am- 

 meter. From the current transmitted by both lamp and cell the 

 resistance and conductivity of the solution in the cell may be 

 calculated. 



Department of Chemistry, 

 Grinnell College. 



