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In the R. B. Lab
241
cell being put together, the zinc element standing alongside the jar with the dilute acid solution, and the porous cup in the act of being placed in the center of the glass container. Several completed cells are shown in the photograph. When the plaster cup is placed, the zinc sheet is fitted about it, and the copper electrode placed inside of it. The sulphate solution is poured about the copper element, and a few extra sulphate crystals thrown in, which are replenished from time to time. The cell is now ready for use as soon as the few minutes elapse necessary for the plaster of paris to absorb the required amount of the solutions. It is a good idea to short-circuit this cell for several hours immediately after assembling.
The Daniell cell is a closed-circuit cell, and will give its best service when used almost constantly, day after day, four and five hours each evening. Three cells make an excellent battery for the UV-I99, while a single cell, without rheostat, may be used on the WD-i i and WD-I2.
When the zinc is practically eaten away, the internal resistance of the battery becomes very high, and it is, at last, necessary to renew the elements of the cell. New solutions and zinc should be added, at a cost of a few cents, and
FIG. 6
Assembling the cell
the cell is again ready for long and steady service.
A "SUPER" WAVE-CHANGER FROM A
THREE-CIRCUIT REGENERATIVE
RECEIVER
Recently, we've had a few hunches on the building of super-heterodyne receivers from parts such as those that the average experimenter already owns. (We refer you also to the timely and well-executed articles in the November and December, 1923, numbers by George J. Eltz, Jr.) And below we present the results of some work of our own on a home-made "super." Some of the illustrations have appeared in RADIO BROADCAST be
FIG. 7
Circuit of the set shown in Fig. 8 "2 iff is