Abstract: A vented plug for a storage battery, has a cap portion with a threaded stem depending therefrom for threaded engagement in the threaded fill opening of the storage battery, the interengaged threads of the stem and fill opening defining a helical space or labyrinth passage for escape of gases originating inside the battery, and providing an extensive area for condensation of liquid particles carried with the gas. Vent openings extend from the threaded area to outside the cap portion for venting the gases to atmosphere, while the condensed liquid flows back into the battery.

Abstract: An apparatus for continuously measuring the density of a liquid within prespecified limits, utilizing the law of refraction, particularly an apparatus for measuring the acid density of a motor vehicle storage battery for the purpose of determining its state of charge. The apparatus has an optical system with a photosensitive element and a light transmissive body with a measuring surface which is in contact with the liquid, and with a light source which illuminates the measuring surface.The light source has an illuminated surface with a non-directional transmission.The illuminated surface facing the measuring surface is spaced therefrom.The illuminating surface together with said measuring surface define an open container filled with the said liquid. A frosted glass disc illuminated by a lamp forms the illuminated surface.The optical system contains a convergent lens whose main plane, together with the measuring surface encloses a precisely defined acute angle.

Abstract: An apparatus for continuous measurement of the density of a liquid within prespecified limits, by utilization of the law of refraction,particularly for the continuous measurement of acid density of a storage battery of a motor vehicle for the purpose of determining the state of charge of the battery.The apparatus is equipped with a photoconductive rod, a light source which radiates a pencil of parallel or nearly parallel rays into the rod toward a measuring surface, located at the end of the rod immersed in the liquid. The surface is struck by the pencil of rays at an angle with respect to the surface that equals at most the total reflection angle occurring at the lower limit of liquid density. A photosensitive element is located in the path of the ray pencil opposite a surface deflecting the pencil of rays, which is refracted by the measuring surface into the liquid.