The method of completing the cell assembly is shown in [Fig. 11]. Take the sheet of fibre with the hole cut in it and place a ⁸/₃₂ bolt 1 inch long in one of the holes. A sheet of thin clear mica is laid on the fibre and short strip of tinfoil slipped over the bolt. A nut is then run on to clamp the tinfoil and make good contact. The tinfoil should be cut off even with the edge of the opening in the fibre. Another bolt is put into the other hole and a longer strip of tinfoil clamped to it also by means of a nut.
Turn back the long strip of foil and lay the cell between the bolts with the paper wrapped end nearest the post with the short tinfoil strip. The paper will prevent contact between the plate and this post but make sure that the tinfoil strip makes contact with the gold foil. The long strip of foil is laid over the back of the plate and the other fibre strip dropped over the bolts. Nuts are then run on to clamp the whole together.
The cell is now complete and should be tested as described in the following chapter before sealing the edges with sealing wax.
CHAPTER IV
Testing and Maturing Selenium Cells
The Fritts Cell, as mentioned by the inventor, when first made has one of two states or conditions. In one the resistance is very high, in the other very low, being but a few ohms or a fraction of an ohm. In the latter state it is insensitive and possesses no definite characteristic until matured. This maturing will come about gradually if the cell is used in experimenting but can be greatly hastened by the proper treatment. By subjecting them to an alternating or pulsating current the resistance can be increased rapidly.
To facilitate the maturing and enable the resistance of the cell to be determined at various stages of the treatment the maturing and testing set shown in [Fig. 12] can be made use of. The apparatus allows of the measurement of the cell by the Wheatstone bridge and substitution methods both with the cell lighted and dark and permits the application of alternating current as desired. It consists of a base on which is conveniently mounted a closed lamp box to light the cell when necessary and the various switches and binding posts arranged for quick manipulation of the circuit.
