A Coal Gas Indicator
An old Short’s coal gas indicator & leather case.
Made from brass and leather. Size 5″ x 3″ inches.
Dated to the 1900’s but I am unsure of the exact date. This instrument was made by Short’s, I have also seen indicators like this made by Short & Mason. I don’t know which makers predates each other?
This indicator was used to test the percentage of coal gas in areas where there may have been a build up wherever coal was burned or stored in confined places or coal gas escapes. It worked on the same principle as a barometer, there is a thin metal diaphragm inside the body to which a small rod is connected and attached to a spring which in turn is connected to the dial hand. The slightest imbalance in the atmospheric pressure bends the diaphragm which imparts a strain on the rod and spring, which results in the dial hand moving and giving a reading.
There were many uses for this indicator apart from the colliery use, it was used in coke works, coal gas works, coal bunkers and also on board cargo ships that transported coal around the world. In the ephemera section on this site there is a coal shipment receipt from the Powell’s Coal Company for a cargo of coal transported on the Sister Ann ship. There is a warning printed on the bottom of the receipt which states “A caution to Captains and Officers of Vessels loading Coal – not to close the hatches immediately after loading coal so that the explosive gas can escape and no light be permitted in the hold until a free circulation of air has been established” These indicators had a wide range of uses.