The action of this detector is based upon the fact that only the tip of a platinum wire a few hundred-thousandths of an inch in diameter is immersed in an electrolyte solution, and a small D.C. voltage bias is applied to the cell thus formed. Platinum is used because other metals are too quickly dissolved in the acid. The applied bias current decomposes the solution by electrolysis into tiny gas bubbles that cling to the metal point insulating the metal tip from the solution thus reducing the bias current.