The scientist Sir William
Crookes paved the way for many discoveries. He worked in his own laboratory in
London where he did all of his experiments with different types of near vacuum
tubes. A lot of Crookes tubes stood at the base of further discoveries like
the X-ray tube and the Braun tube which developed later on into our well known
TV tube. German glassblowers like Otto Pressler, Emil Gundelach and
Müller-Uri made many types of Crookes, Hittorf and Geissler tubes in the
beginning of the 20th Century. The tubes were sold to schools and universities
for classroom demonstration by companies like Max Kohl and Leybold. In WW II
the Pressler factory was bombed but they managed to go on, after the war the
name changed in VEB and produced then manly radiometers for hard western
currency. On the website of Jogis-Röhrenbude you can find
the complete Pressler story. The biography of Sir William Crookes can be
found on the website of the University of Oxford For
everyone who likes to know more about the background of this old tubes, there is
now a new book in German language. Check this website for more info.
Crookes mineral tube
Crookes Cathode Ray Deflecting tube.
Activated tube
Crookes railway or paddlewheel tube
Sir William
Crookes 1832-1919
Activated railwaytube
Crookes Maltese Cross tube
The Maltese Cross
tube is one of the most famous Crookes tubes. The tube demonstrates
that electrons go in a straight line and don't go through metal.
The cross can actually lay down and stand up (mechanical).
When the cross lies down, the glass face of the tube emits a
green glow when the electrons strike the glass wall, when it's right
up you will see the shadow of the cross. After a while the glass gets
"tired" and the glow is less strong, when the cross then falls, the
previous unexposed glass glows brighter than the surrounding glass.
The tube shown is an early Pressler tube.
The Cathode Ray
Deflecting tube demonstrates the influence of a magnetic field to
the electron beam. The visible beam appears on the aluminum
sheet covered with phosphor, will bent away from the center
when a magnet is held near the tube.
The Railway
tube demonstrates kinetic energy. The electrons bounced at
the paddles covered with a small amount of phosphor will
turn the paddlewheel to go from one to the other side
of the tube.
Mineral tubes
are real beauty's in the Crookes tube world. They glow beautiful when
the tube is activated. A nice tube can be seen at the collection of
the University of
Innsbruck. Different samples of fluorescent
minerals, shells, coral or gemstones were used. Here is a
list of some common used minerals.
Colormineral red
chalk yellow
apatite bright
green
willemite bleu scheelite brown
dolemite
violet
magnesite
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Caution. When
these tubes are activated with high voltage a small amount of soft
X-Ray's are produced ! Don't use tensions more than 5000
Volts.
The
Cathode Ray Tube site
Cross vacuum scale Picture courtesy of Alastair
Wright.
The Cross vacuum
scale demonstrates the phenomenon of discharge at different
pressures (vacuum) inside the tubes. The
pressures varies between 40 Torr (mmHg) lowest vacuum (left tube) to
0.03 Torr the highest vacuum. (right tube) In this high vacuum, used
in many Crookes tubes, X-Ray's are produced, the glass emits here a
green glow. If you click on the picture you will see a larger
model made by NARVA the successor of the Pressler
company.
Crookes radiometer
The radiometer
invented by William Crookes in 1875 stood at the base of his later
developed railway tube. The four vanes are spinning in a glass
envelope with a pressure of 1 Torr, when exposed to light the
vanes turn. Due to heating of the vanes which are black on one side
there is movement, this is called thermal creep. The black
side of the vanes are a little hotter than the silver side so the gas
molecules pushing to the black side turning the vanes.
Unknown tubes. With envelope diameters of about 6
centimeters, one with metal electrodes, the other with pyramidal shaped carbon
electrodes. One tube will light as seen in the picture left. The other one will
not light at all. The last thing I found on this is a similar tube in the
Muller-Uri catalog from 1909 called 'a tube with absolute vacuum'.
Activated tube
Crookes flower tube 30 cm in height with a paddlewheel on top, early 20th
Century. This tube can be found in the Max Kohl catalog nr.100 band III page 1015 on the site of the
Max Planck institute, The Virtual Laboratory. This was one of the most expensive tubes!
The Crookes flower
tube or bouquet tube is also a beautiful piece of
craftsmanship, these tubes were made in different sizes. The
copper flowers are covered with different phosphors, the vanes on top
are made of mica and turn when the tube is activated forming a moving
shadow on the flowers below. The stream of electrons demonstrates
kinetic energy in form of the turning vanes, and show that they travel
in straight lines which can be seen by watching the phosphors
lightning when there is no obstruction in in the way of the electrons.
The Goldstein Canal
Ray tube. This tube demonstrates that besides the cathode rays
there is another stream that travels in the opposite direction as
the electron flow. Discovered in 1886 by Eugen Goldstein
(1850- 1931) who called it "canal rays". In fact these are positively
charged protons, producing a reddish light in the upper part
of the tube while in the lower part the usual green emission of
electrons can be seen when they hit the glass wall. The
electrons in the lower part of the tube can be deflected by a magnetic
field but the canal rays almost not. Goldstein
could not explain this phenomenon, it took 12 years before Goldstein's
paper was published. An interesting pdf about the discovery of the
proton can be found here.
Goldstein Canal Ray Tube
The
perforated cathode.
Canal Rays or positive Protons (red glow)
Small chalk sample in activated tube.
Crookes vacuum tubes (Pressler 7a &
7b)
Activated 7a tube
Activated 7b tube
The Crookes vacuum
tube demonstrates the behaviour of the electron beam in different
vacuum pressures. The 7a tube has a low pressure vacuum much like a
Geissler tube, the beam inhere exists between one electrode to the
cathode via the shortest way. The 7b tube however has a high vacuum
the difference is clear to see. Radiant matter leaves the hollow
cathode in the opposite way (as X-Rays) unlike which of the three
anode's is used.