Very odd mercury lamp

[Chris Kocsis]

Hi everybody, I wonder if anyone has any information on this mercury
lamp I recently found in England, on eBay.

The entire assembly stands 9-1/4" high. The fixture is decorative and
well made:


 

From the cloth-covered cord I would guess it was made in the 1940s or
1950s. The mercury lamp sits on top, under a screw-down retaining ring.
Here it is removed from the "vase":



You can see that the glass envelope (which is 2" in diameter and rises
3/4" above the metal flange the lamp is clamped in) has a cone-shaped
dip, almost like an inverted tip, in the center. The amount of mercury
in it is very substantial, maybe a tablespoon (15 cc). You can also see
a hollow cylindrical glass tube rising into the envelope from the bottom
of the lamp. Inside this tube is an electrode (just a straight wire)
that rises about half an inch into the cylinder. There is another
electrode outside the cylinder, about the same length. Here are some
pictures of the base (or cap), showing two lead-in wires plus a third
knobby protrusion that merely seems to be filled with mercury (and it
vents to the space outside the inner cylinder):


 

[Message continued below]

[Chris Kocsis]

The metal holder the lamp is in has two contact points on the bottom -
actually these are just threaded hollow rods that rise about 3/4" into
the bottom of the holder. Inside the fixture, the supply wires end in
long wire loops that can be wedged into the rods. Clearly the lead-in
wires were once soldered to these rods; now one is unconnected and the
other has a thin insulated wire clumsily soldered to it as you can see
above.


 

Finally, through the bottom of the fixture you can see a DC bayonet
socket mounted upside-down, clearly intended for a lamp or resistance
that functions as a ballast. The socket is wired in series with one side
of the mains:



Any ideas what/when/why? Why so much mercury? Why this elaborate
decorative fixture? It's not what I would design for a therapeutic
skin-contact device. Plus the ballast would probably make the fixture
too hot to hold.

Cheers,

Chris

[Mónico González]

Please, don't let us so...!
We want more info!
It's an enigmatic device.
Best regards,
M. Gonz?lez

P.S.
(my website are temporarily out of service)

[Chris Kocsis]

Aha!  Progress.  I believe this to be an ozone generator/?air cleaner? lamp made by Pressler under the Lumitra brand, similar to (and probably earlier than) that shown in marvelous detail at the bottom of the following page:
 http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/Glimmroehren/UV-Lampen/UV-La   mp.htm

There is also a blurry photo of a similar-looking bulb at Stan Slabyhoudka?s web site (this is where I got the name Lumitra):
 http://muzeum.pre.cz/aplikace/galerie/spec_zdroje.php?th=0&obr=16

Going by the pictures on the first site, perhaps a 2K-ohm resistor would suffice as a ballast.  Because of the DC bayonet socket on mine, I assume a lamp went there ? that?s a pretty high resistance for a light bulb, isn?t it?  What sort of bulb would have that high a resistance without getting too hot in that space?  However, note that there are vent holes at the bottom of the fixture as well as at the top.

Going by the text under Stan's picture, this sort of lamp seems to have been patented in 1925.  Unfortunately I haven't found a free online translator that will give me an English translation of his text that makes any sense.

Further thoughts, anyone?

Chris



[This message has been edited by Chris Kocsis (edited September 13, 2004).]

[Max]

Hi Chris,

Thank you for sharing the pictures of your very interesting (and odd, indeed) mercury lamp.

This source is definitely an early ultraviolet lamp. My opinion is that it was a UV-C germicidal lamp, because the cone-shaped bulb seems to be close to the electrodes, and hence would help the mercury resonnance radiation to escape from the discharge before it was re-absorbed by the surrounding metal vapor.

A large ammount of mercury was a common feature of early lamps of this type, firstly because mercury pools were used as electrodes. This made the efficiency of the lamps rather low, but critically avoided any rapid blackening of the bulb as it was the case when solid electrod rods were employed.
The second reason was that the liquid metal was used to start the lamp when no high-voltage step-up transformer was employed. Simply put, tilting (or moving) your lamp results in the electrical connection between the electrodes by a channel of mercury. From this point on, a current circulates in the circuit. The lamp was then tilted back, which broke out the mercury channel, and ignited an arc (or a discharge) between the electrodes. This was a very common procedure of ignitions in Cooper-Hewitt and Kurt-Retschinsky-like lamps.

About the ballast, it was a general rule for early mercury lamps to connect them with resistive elements that would regulate the arc/discharge current, as it was a cheap and easy-to-use solution. In some cases, this ballast was embodied by filament lamps providing heat for therapeutical applications, or emitting extra red-orange light (which is still the case is some UV lamps for sun-tanning applications, and more generally in blended light lamps). The second possibility being the use of baretters, a form of incandescent lamps used as high-power resitors.
Personnaly, I think that it made sense to place the resistive ballast beneath the mercury lamp, as the former would provide extra energy to heat up the mercury pool and raise the vapor pressure inside the bulb. As opposed to modern mercury lamps, early sources did not employ a rare gas as a buffer - mercury vapor was by itself the buffer. So for low-power lamps, it was certainly needed to raise the mercury vapor pressure in order to have a sizable current circulating in the discharge.

Your fourth and fifth pictures show a very primitive form of quartz-metal seal, akin to Kuch and Retschinsky original lamp. This is my opinion that your lamp was therefore made in the early 1930's or before, because the first viable quartz-tungsten seals were invented in 1935 (Philips - graded seals) and 1937 (GE - moly foils). Before this date, the electrode lead-in wires were mecanically locked in quartz tubes with cone-shaped metal corks, or in this precise case, by vacuum-shrunk quartz around wires, and using tar (or something else) as a sealant.

Beside this, I don't know anything further about this precise lamp. You really have a neat example of an early mercury lamp, and know that we came a very long way since then!


Max

[Chris Kocsis]

Thank you, Max, for all that information.

I was going to ascertain if the envelope is quartz by attempting to pass short-wave UV through it, but I'll just take that as a given.

I was also going to try to power the lamp through a resistor.  However the wires that emerge from the seals are so thin and fragile that I would probably have to grind away a small length of quartz before getting enough sturdy wire to make a good connection.  Given the early nature of this lamp, I'll just leave it alone and imagine the glow.

All the best,

Chris

[Max]

Hi Chris,

No problem for the information. If you really want to light this lamp up without damaging the feed-through, then you can use a high-frequency HV generator (several kV at 10kHz+), and connect its leads capacitively to your lamp.
What you have to do is simply wind the HV live wire around one lamp feedthrough (that is, a shrunk quartz tube containing an electrode wire), and an earthed wire around the next feedthrough. The high frequency of the HV supply will allow a sizable current to flow in your lamp electrodes, and hence help create and maintain a discharge in the mercury vapor (if the HV level is hiogh enough). Be careful though that the mercury radiation can cause you severe skin and eye burns.
As for the HV generator, you can use either a small Tesla coil, or a transformer circuit of a "plasma" sphere.

Regards.

Max