I was sealing some red P in a glass tube by fusing the end closed. I had gently heated the whole tube first and when I applied the flame the the end
to fuse it I noticed a faint thin disc of greenish glow very slowly move down the tube. Presumable a very slow combustion front. I will try to get an
image and perhaps a video of it though I doubt it is bright enough.ave369 - 19-6-2019 at 21:08
That was obviously white phosphorus in trace amounts. Heating red P causes white P to form. It reacts with the oxygen in the tube with a glow.
[Edited on 20-6-2019 by ave369]j_sum1 - 19-6-2019 at 23:09
Ave! Good to see you!
I concur: white P. I wonder if this could be done in a more controlled fashion as a demo...wg48temp9 - 19-6-2019 at 23:30
That was obviously white phosphorus in trace amounts. Heating red P causes white P to form. It reacts with the oxygen in the tube with a glow.
[Edited on 20-6-2019 by ave369]
I would expect that too. More specifically I thought any vapor of 4P would spontaneously ignite with oxygen in the tube while the whole tube was
heated (probably to more than 50C, too hot to hold).
When I tried to repeat the effect I heated the tube too strongly. The red P at the closed end ignited briefly and brightly followed by a luminous
disc that moved towards the open end but then extinguished about 10mm from the red P leaving a white smoke behind. The luminous disc was brightest in
the center. The original disc appeared to be brightest at the surface of the glass almost a ring and less luminous. Perhaps it was a diffusion limited
flame.
wg48temp9 - 20-6-2019 at 07:34
I have a theory of what happened.
When I gently heated most of the tube, P vapor was generated that combined with the oxygen possibly generating a glow though I did not notice it.
Eventual the phosphorus vapor and the now mostly nitrogen reached the tube end being fused if there was a glow at that position it would not be
noticeable due to the flame from the torch when I removed the flame to crimp the tube end most of the tube was now cooling so the P vapor and nitrogen
contracted so the interface (the luminous disc) between the vapor and the ambient air moved in to the tube and down it..
Note when sealing a tube its useful to have the majority of the tube cooling so when the end does fuse closed the pressure in the tube is negative so
the molten glass will not form a bulb and the fused section will collapse to a good joint.
