An
amperostat delivers a constant
current of about 6—8
mA to the generator
electrodes for the titration of the solution, and a digital timer is started. A second pair of silver electrodes are used as a detector to measure the
conductance of the solution. The same constant current is known to titrate a given number of
moles (n_{Cl^-})_s of a chloride
standard solution in time t_s. Titration of the
assay solution will result in the generation of
insoluble silver chloride until the chloride ions are consumed, after which time an increase in silver ions will be detected at the detector electrodes. This time, t_u, is the titration time of the solution being measured. The concentration of chloride ions in this solution is then calculated as: :(n_{Cl^-})_u = {t_u \over t_s } \times (n_{Cl^-})_s Although the absolute quantity of silver ions (Ag^+) required to react with the chloride ions can be determined using
Faraday's laws of electrolysis, in practice calibration is required. Silver ions are generated by
oxidation at the
anode when an
electric potential is applied across the silver
electrodes. This is the anodic reaction. :Ag \rightarrow Ag^+ +e^- The silver ions enter the solution at a rate proportional to the electrical current. Because the current is constant, the rate of silver ion production is hence proportional to the time of current flow, and silver ions enter the solution at a constant rate from the silver wire anode. These ions react with the chloride ions in the titration reaction, resulting in insoluble silver chloride. :Ag^+ + Cl^- \rightarrow AgCl The
end point, which occurs when there are no more chloride ions with which silver ions may react, is detected by a pair of silver microelectrodes in the solution, which is
connected in series with a
microammeter. The increasing concentration of silver ions creates a current between the microelectrodes, activating a
switch that shuts off power to the main electrodes and the timer, terminating the measurement. The duration of the titration is the titration time t_s, which is proportional to the amount of silver ions released, and hence to the amount of chloride in the assay solution. ==Uses==