W – Salt Water 

Potentiometers are used to measure electromotive force (EMF) by balancing it with a known EMF. Leeds & Northrup, the creator of the potentiometer, was formed in 1903 by a partnership between Morris E. Leeds and Dr. Edwin F. Northrup. By 1920, the company was the leading manufacturer of precision measuring instruments in the country.  

Dr. James L. Gamble’s specialty was the physiology and pathology of extracellular fluid of the body in health and disease. His studies of the electrolyte composition of blood plasma and digestive fluids of the gastrointestinal tract facilitated the understanding of salt metabolism in children.  Gamble also worked with the U.S. Navy in WWII to determine the water ration requirements for survival of personnel forced down at sea or sailors who were adrift at sea.