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DRY CELL BATTERIES FOR RECORDING AND PROJECTING
W. B. SCHULTE*
FROM inquiries received from sound-picture engineers and sound studios, we know that dvj cell batteries are being used to a certain extent in recording and projecting. The details of why and how these batteries are used are not always available, probably, because the art is still experimental and perhaps also because some of the methods are being held secret. At any rate the interest in dry batteries indicates that they -are becoming a standard part of the equipment. This being the case, a few words concerning dry cell batteries and their characteristics might be of interest to the motion picture engineers.
A dry cell battery is an electro-chemical unit which produces electrical energy from chemical reactions that take place within itself. It cannot be recharged similarly to a storage battery. A dry cell consists of a zinc container into which is packed a carbon rod surrounded by an oxygen carrying compound, a manganese dioxide ore, called a depolarizer. This depolarizer tends to maintain the current at a maximum value and aids the cell to recuperate and quickly recover its normal condition after periods of work. The open circuit voltage of a dry cell is about II/2 volts, irrespective of its size. The momentarj^ current that a dry cell can fill depends upon its resistance, and ranges from 5 ampere for this very small cell, the size of a thumb, to as much as 50 amperes for the large 2l^ inch by 6 inch size which is used on door bells, or as the Radio ''A" battery.
The electrical capacity of a cell is more than proportional to its size. The larger the cell the greater the ampere-hour capacity ; likewise, the cost increases with size, but not at as rapid a rate. Where high voltages are necessary a number of cells are soldered together in series to produce the required value. If large cells are used the bulk will be great, and the electrical capacity and cost high. With smaller cells the same voltage can be obtained in a smaller volume but with a lower electrical capacity and smaller cost. It is
* Burgess Battery Co., New York, N.Y.
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