Electrical noise from synthetic membranes

Voltage fluctuations were measured across collodion membranes acting as a constraint between two identical aqueous salt solutions, in the presence of an applied electrical potential difference. Membranes with d-c resistance between 1 and 20 MΩ cm(2) were studied, in solutions of KCl between 0.01 and 1.0 moles per liter.The steady-state d-c currents passed were between 1 and 1,000 namps/cm(2) of membrane. The noise was measured in the frequency range between 8 and 5,000 Hz. The spectral density of the noise power, in excess of that measured at equilibrium, was found to be proportional to the mean power being dissipated in the membrane, and inversely proportional to frequency. The d-c conductance of membrane, and the excess noise, are discussed in terms of the frictional interaction between the ions and the membrane.