Hydrometer vent cap

Claim 1

A VENT CAP FOR THE VENT OPENING OF THE CELL OF AN ELECTRIC STORAGE BATTERY HAVING LIQUID ELECTROLYTE THEREIN TO BE MAINTAINED AT A NORMAL LEVEL HAVING A PORTION SEALINGLY ENGAGEABLE WITH SAID VENT OPENING AND ADAPTED TO HOLD SAID VENT CAP IN PLACE IN SAID VENT OPENING AND PREVENT LOSS OF ELECTROYTE THEREBETWEEN, A VENT WITH AN OPENING BELOW AND ABOVE SAID PORTION TO PROVIDE MEANS FOR VENTING THE CELL AND PREVENTING ABNORMAL ACCUMULATION OF PRESSURE THEREIN, A TRANSPARENT RESERVOIR ABOVE SAID PORTION ADAPTED TO TEMPORARILY RECEIVE ELECTROLYTE FROM THE CELL, A TUBE WITH AN UPWARDLY OPENING CONICAL PORTION CONNECTED TO SAID RESERVOIR AND A LOWER END CONSTITUTING AN INLET TO BE POSITIONED BELOW THE NORMAL LEVEL FOR THE ELECTROLYTE IN THE CELL, AN IMPERFORAATE PLUNGER OPERABLE WITHIN SAID RESERVOIR HAVING A DOWNWARDLY FACING CONICAL PORTION OPENING TOWARD SAID TUBE AND PROVIDED WITH MANUALLY ENGAGEABLE MEANS EXTENDING EXTERIORLY OF SAID RESERVOIR FOR RAISING AND LOWERING SAID PLUNGER TO DRAW ELECTROLYTE FROM THE CELL INTO SAID RESERVOIR AND EXPEL IT FROM SAID RESERVOIR BACK INTO THE CELL WITHOUT REMOVING THE VENT CAP FROM ITS PROPER POSITION IN SAID VENT OPENING, AND SPECIFIC GRAVITY INDICATING MEANS WITHIN SAID TRANSPARENT REDERVOIR COOPERABLE WITH LIQUID DRAWN INTO SAID RESERVOIR TO INDICATE WHETHER THE SPECIFIC DENSITY IS ABOVE OR BELOW NORMAL.