battery, and no part of his work requires greater skill
than the work on the covers. The manufacturers have developed special
constructions, their aims being to design the cover so as to
facilitate the escape of gas which accumulates in the upper part of a
cell during charge, to provide space for expansion of the electrolyte
as it becomes heated, to simplify inspection and filling with pure
water, to make leak proof joints between the cover and the jar and
between the cover and the lead posts which project through it, and to
simplify the work of making repairs.

Single and Double Covers. Modern types of batteries have a single
piece cover, the edges of which are made so as to form a slot or
channel with the inside of the jar, into which is poured sealing
compound to form a leak proof joint. This construction is illustrated.
in Exide, Fig. 1.5; Vesta, Fig. 264; Philadelphia Diamond Grid, Fig.
256; U. S. L., Figs. 11 and 244; and Prest-0-Lite, Fig. 247,
batteries. Exide batteries are also made with a double flange cover,
in which the top of the jar fits between the two flanges. In single
covers, a comparatively small amount of sealing compound is used, and
repair work is greatly simplified.

In the Eveready battery, Fig. 262, compound is poured over the entire
cover instead of around the edges. This method requires a considerable
amount of sealing compound.

The use of double covers is not as common as it was some years ago.
This construction makes use of two flat pieces of hard rubber. In such
batteries a considerable amount of sealing compound is used. This
compound is poured on top of the lower cover to seal the battery, the
top cover serving to cover up the compound and brace the posts. Fig.
10 illustrates this construction.

[Fig. 10 Cross-section of Gould double cover battery]

Sealing Around the Posts. Much variety is shown in the methods used to
secure a leak proof joint between the posts and the cover. Several
methods are used. One of these uses the sealing compound to make a
tight joint. Another has lead bushings which are screwed up into the
cover or moulded in the cover, the bushings being burned together with
the post and cell connector. Another method has a threaded post, and
uses a lead alloy nut with a rubber washer to make a tight joint.
Still another method forces a lead collar down over the post, and
presses the cover down on a soft rubber gasket.

Using Sealing Compound. Some of the batteries