Museum help needed

[jmoss]

Hi,

I am working on a museum exhibit and have a light bulb that I would like help identifying.  On the glass it has the GE logo and says "Edison Mazda" on the bulb.  It is 22 cm (8.6") tall and a diameter of 11.5 cm (4.5")  The base has 2 patented dates, which are on your wonderful patent portion of this website, but that still doesn't help me, as I have no idea how long this patent was used.  What I make out on the base (it's not real clear and my eyes are bad) is 300 W, 123 V.  Hand written on the glass piece on the interior of the bulb is "C2    300"

I am also wondering why there is a tip at the top of the glass.  All early light bulbs seem to have this, and I (as well as everyone I have asked) am assuming that this is a result of the manufacturing process, but I want to be sure, as I've read on your site that both hand and machine methods were used.

Thank you so much for your help,

JIM

[Straick]

The tip on the top of the bulb is where they used to pull the vacuum that is inside the bulb at. That vacuum is needed to prevent the filament from oxidizing as soon as the bulb is turned on. Newer bulbs are now purged with an inert gas though the base during manufacture.
Good luck on identifying the bulb.

[jmoss]

Thank-you!  That was my guess, but I couldn't prove it.  Everyone else seemed to think it was from blowing the glass.

[Mónico González]

This one seems to be one of the early Mazda gasfilled lamps, using the classic pear-shaped bulb. As jmoss have said, the tip on the top of the bulb is for air extraction (to make the vacuum within the globe) and further gas filling. This one seems to be a street lighting lamp because its relatively high power rating (300 watts), intended for parallel connection.
Note the coiled structure of its filament. Gasfilled lamps needs to fit coiled filaments to concentrate the heat preventing the cooling of it due to thermal conduction of filling gas that happens when the straight wire surface is widely exposed to gas contact.
So, lamps with drawn tungsten wire only can work properly at high vacuum, like classic "cage" lamps does.
Regards.