SIR WILLIAM CROOKES BY: Javontae Spencer Clifton Elam

ORIGIN OF CROOKES  Crookes was born in London on June 17,  Sir. William was the oldest of his six-teen bro- thers and sisters, and the son of a wealthy tailor and real estate investor.  He lived from 1832 to 1919.

ACKNOWLEDGE  Sir William is known for his discovery of the element Thallium and his studies in the Cathode-ray, otherwise known as the “Crookes- Ray.”  His researches on electrical discharges through a rarefied gas led him to observe the dark space around the cathode, which is now called the Crookes dark space.

EXPERIMENT  Particle Beams: a stream of charges or neutral particles, in many cases moving at a speed of light. 

CATHODE RAY  A vacuum tube in which a hot cathode emits electrons that are accelerated as a beam through a relatively high voltage anode, further focused or deflected electrostatically or electromagnetically, and allowed to fall on a phosphorescent screen.  A Cathode ray consists of three basic parts: the electron gun assembly, the phosphor viewing surface, and the glass envelope. The electron gun assembly consists of a heated metal cathode surrounded by a metal anode. The cathode is given a negative electrical voltage and the anode is given a positive voltage. Electrons from the cathode flow through a small hole in the anode to produce a beam of electrons. The electron gun also contains of electrical coils or plates which accelerate, focus, and deflect the electron beam to strike the phosphor viewing surface in a rapid side-to-side scanning motion starting at the top of the surface and working down. The phosphor viewing surface is a thin layer of material which emits visible light when struck by the electron beam.  The chemical composition of the phosphor can be altered to produce the colors white, blue, yellow, green, or red.

 Although the Cathode ray was previously discovered by Ferdinand Braun of Strasbourg, Crookes accidentally discovered the details involved in the Cathode ray. After his works with the Cathode, it soon led to the invention of the television somewhere in the 1920’s. A conventional television is nothing more than a cathode-ray tube.  Cathode rays were a stream of charged particles which carry a negative charge.

THALLIUM  The density of Thallium is 11,850 kg/m3 or g/cm3.  Thallium can also be deadly under certain circumstances. Along side Arsenic, it is one of the most commonly used poisons.  Thallium is in the metal classification, group thirteen, period six.  It is also a solid while stored at room temperature.  Thallium is used for insect and rat poison, special glass for the highly reflective lenses, and it is used in some medicines.  The two main oxidation states of thallium are +1 and +3. In the oxidation state most +1 compounds closely resemble the potassium or the silver compounds . For example, the water-soluble and very basic Thallium(I) hydroxide reacts with Carbon dioxide forming water-soluble Thallium Carbonate. This carbonate is the only water soluble heavy metal carbonate. The similarity with silver compounds is observed with the Halide, Oxide, and Sulfide compounds.

THE EARLY YEARS  At the age of 16, Crookes entered the Royal College of Chemistry in hopes of studying organic chemistry.  While there he became the assistant to August Wilhelm Von Hofmann. While attending a meeting Crookes met an eminent physicist named, Michael Faraday, who convinced him to change his area of concentration from chemistry to physics, and particularly to optics.  After his father's death, he received a substantial inheritance and was able to open his own laboratory and concentrate on physics. It was not long before this investment paid off.  While experimenting with spectroscopy, physics pertaining to the theory and interpretation of interactions between matter and radiation, Crookes discovered a lime green band in the spectrum of selenium, a band that belongs to no known element at that time. After several years he succeeded in isolating the element, which he named thallium ( derived from the Greek word thallos, meaning "green twig ").  In 1861 he published his discovery. While trying to determine the precise atomic weight of thallium, Crookes became interested in the use of vacuum tubes, which had recently been improved upon by Johann Heinrich Geissler.

 Crookes' was a meteorologist most of his life. In 1856 he married Ellen Humphrey and together they had three sons and daughters.

THE LATER YEARS  Crookes invented a device called a radiometer, consisting of a series of four small vanes balanced upon a pin. he two sides of each vane were painted different colors--one side black, the other silver. The entire assembly was then sealed in a vacuum bulb, when light struck the vanes the black sides would heat up, causing them to turn as the excited air molecules struck them. This device was (and still is) mostly a science toy, but it was also used by Scottish physicist James Clerk Maxwell ( ) to prove the kinetic theory of gases.  In the late 1870s the first practical cathode-ray tube was designed. It was comprised of a vacuum tube with two electrodes, a cathode and an anode, one at each end of the tube. When an electric current was introduced and the tube evacuated, a green glow would appear.  Crookes' discovered the electron. Since the Cathode Ray had previously been built, he needed to call it something else. Today it is known as the Crookes' Tube. From the tube he pulled out some objects have a negative charge when hitting the tube. It caused the objects to spin which suggested they had mass. J.J. Thomson confirmed Crookes' discovery later on.

 For some, however, his reputation is tarnished by the fact that he was a spiritualist, publishing several papers on the validity of psychic phenomena and the occult

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