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Hi All,

I am stuck! We already have a few spectrum discharge tubes, but I am trying to find a range of tubes with either increasing or decreasing pressure (obviously each displays a different colour until you reach Faraday's dark space). This is an actual physics experiment mentioned in the HSC syllabus. Does anyone have this information (the internal pressure of each tube) or can explain to me how they do this experiment. I have spoken to the supplier and even they don't have this information, Google did not help either.

Thankyou and have a great holiday.

Sharls

Hi Sharls
We have an instrument called a Cross Vacuum Scale, consisting of 6 Geissler tubes evacuated to different pressures (approx 40,10,6,3,0.14,0.03 mm Hg), in a box-like construction.
Power is supplied to the tubes using an induction coil.

I've copied this from the instructions in with the spare tubes:

Tube A (40 mm Hg) - Discharge can be seen in violet strings.
Tube B (10 mm Hg) - Discharge can be seen in one thick violet string.
Tube C (6 mm Hg) - Reddish purple through whole tube.
Tube D (3 mm Hg) - Pink squamous pattern is seen.
Tube E (0.14 mm Hg) - Squamation becomes paler and less than above, and the tube is a little darker at the negative end.
Tube F (0.03 mm Hg) - The whole tube becomes dark, and pale green phosphorescence can be seen along the wall of the tube.

Hope this is of some help.
Carol

If you look under "Crook's tubes" you might find what you want listed

Hi Carol,
What you described is exactly what I am looking for. Do you know where you got them from and how much they cost?

Sharls

Sharls, ours are really old but Serrata sells them:

"1052047 CROOKE'S TUBES: Cross Vacuum Scale - Low pressure discharge tube set of 6 $185.00
Tubes mounted in line. The atmosphere inside varies in each tube. Electrodes at each end.
DEMONSTRATES the discharging phenomena in rarefied gas. On wood stand."

Carol

Thankyou so much Carol you have been a big help. One last question what sort of power supply do you need to run it?

Sharls

We just use the usual lab transformers,which go up to 12V, hooked up to an induction coil.
Carol

Thanks so much Carol, you are fantastic!!!

Sharls

Last year our physics teachers decided that they the old Spectrum tubes on the wooden stand did not work well enough and insisted on a new one.

We purchased the one in the Serrata catalogue. (1052047) and it is of such lousy quality that they have gone back to using the old ones. It doesn't come on a wooden stand! It's a very flimsy plastic stand and the metal "thingy" that you use didn't even have any leads. It really is very poor quality.

The only good thing is the tubes will actually fit into the old wooden stand so sometime we will swap them over.

Hope this helps,

Wendy

If you don't have an induction coil you can obtain an electric fence power unit

So I realise this thread is from quite some time ago... but are there any other suppliers of this apparatus? Any recommendations?

We brought one about a month ago from Haines. $323 inc GST. Stand alone unit, don't need an induction coil. Code is 3785001.

Depends if you want the whole set in one apparatus thingo, or a bunch of tubes to demonstrate the general principle.

We have the latter, and without a doubt the best, best, best thing to come out in recent times is the Spectrum Discharge Tube Power Supply from Scientrific! Individual tubes just slot in there. No more sparking induction coils. You can buy a set of 6 tubes to go with it. We love ours.

All I can find is the one from Serrata. The others are all different gases in the tubes but the ones we are after are the different pressures, as described by Whspa. Does anyone know if you can take the ones out of the 'frame' from serrata and use them with the spectrum discharge tube power supply?

The different pressure tubes are referred to as Crook's tubes

I tried searching for Crook, Crooke, discharge, spectrum, vacuum and still came up with only the one mentioned above from serrata... other than that, there are PLENTY of the ones for the different gasses!

The ones with the different pressures are much bigger and longer than the ones that fit into the spectrum discharge tube power supply, and therefore do not fit. They used to come in a set and a stand and hook up to the induction coil. We bought a new set years ago but put the new tubes into the old stand as the new stand was crappy. The old tubes seemed to have lost their pressures. The new tubes worked OK.

Thanks Dime. Looks like I will just go with the one from Serrata. The picture looks exactly the same as the one we currently have so I guess I won't be disappointed by the 'crappiness' of the stand. One more to cross off the list!

We're having a big clean up of equipment due to losing our store room. The Crooke's Tube Cross Vacuum set we have is very old and does not work.
Does anyone know how we can dispose of it?

Whspa wrote: ↑25 Sep 2020, 11:08 We're having a big clean up of equipment due to losing our store room. The Crooke's Tube Cross Vacuum set we have is very old and does not work.
Does anyone know how we can dispose of it?

If they are just Vacuum tubes then you can just wrap them in newspaper and dispose of them as you would an old incandescent Light bulb .

If they are gas spectrum tubes , that may be a different story ....especially if it contains Mercury