Coulometer:

You have looked which in electrogravimetry, an analyte is weighed as a deposit on the one of the electrodes. Instead, the coulometric methods are based upon the measurements of quantity of electricity. Alternatively, the quantity of electricity required to finish the electrolysis serves as a measure of the amount of analyte present in the solution.

A coulometer is a device used for measuring the quantity of electricity needed to bring about a chemical change of the analyte. It is common practice in coulometry to substitute the ammeter (that measures the current in electrical experiments) along with a coulometer.

Every coulometer is a second electrolytic cell, in that anode and cathode might be in the similar compartment or in separate compartments, supposed to proceed at 100 percent current competence. It is put in series along with the electrolytic cell so in which the similar quantity of electricity passes by both the cells. Several categories of coulometers viz. Gravimetric coulometers - silver coulometers - Titrimetric coulometers - Iodine coulometers, Gasometric coulometers - Hydrogen-oxygen coulometer,  etc. are used.