A method for measuring the total number of negative or positive charges liberated in large silver halide single crystals by shallowly absorbed radiation is described. The use of thin samples allows all the photocharges to be displaced the full thickness of the crystal and induce a certain amount of charge on a series capacitor, whose potential is measured with an oscilloscope. Data at room temperature are obtainable by the use of pulse techniques. Details are given of apparatus used for these experiments and earlier photographic experiments. Repetitive, well formed square pulses up to 500 V and 1 msec or 5000 V and 3 &mgr;sec are obtained. Synchronization with light flashes can be controlled to within a fraction of a microsecond.