onnected together to form one composite plate of the
condenser, while the other sheets were similarly connected together to
form the other plate. Obviously, in this way a very large area of
plates could be secured with a minimum degree of separation.

[Illustration: Fig. 122. Rolled Condenser]

There has been developed for use in telephony, however, and its use
has since extended into other arts requiring condensers, what is
called the _rolled condenser_. This is formed by rolling together in a
flat roll four sheets of thin bond paper, _1_, _2_, _3_, and _4_, and
two somewhat narrower strips of tinfoil, _5_ and _6_, Fig. 121. The
strips of tinfoil and paper are fed on to the roll in continuous
lengths and in such manner that two sheets of paper will lie between
the two strips of tinfoil in all cases. Thin sheet metal terminals _7_
and _8_ are rolled into the condenser as it is being wound, and as
these project beyond the edges of the paper they form convenient
terminals for the condenser after it is finished. After it is rolled,
the roll is boiled in hot paraffin so as to thoroughly impregnate it
and expel all moisture. It is then squeezed in a press and allowed to
cool while under pressure. In this way the surplus paraffin is
expelled and the plates are brought very close together. It then
appears as in Fig. 122. The condenser is now sealed in a metallic
case, usually rectangular in form, and presents the appearance shown
in Fig. 123.

[Illustration: Fig. 123. Rolled Condenser]

A later method of condenser making which has not yet been thoroughly
proven in practice, but which bids fair to produce good results,
varies from the method just described in that a paper is used which in
itself is coated with a very thin conducting material. This conducting
material is of metallic nature and in reality forms a part of the
paper. To form a condenser of this the sheets are merely rolled
together and then boiled in paraffin and compressed as before.

Sizes. The condensers ordinarily used in telephone practice range in
capacity from about 1/4 microfarad to 2 microfarads. When larger
capacities than 2 microfarads are desired, they may be obtained by
connecting several of the smaller size condensers in multiple. Table
IX gives the capacity, shape, and dimensions of a variety of
condensers selected from those regularly on the market.

TABLE IX

Condenser Data

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