Gallium


1871 Dmitrii Ivanovich Mendelev predicts the existance and properties of the
element after zinc in the periodic table. He Gives it the name "eka aluminium".

1875 Paul Emile Lecoq de Boisbaudran discovers gallium. Its properties closely
match those predicted by Mendelev.


     Gallium, atomic number 31, is very similar to aluminum in its chemical
properties. It does not dissolve in nitric acid because of the protective film
of gallium oxide that is formed over the surface by the action of the acid.
Gallium does however dissolve in other acids, and alkalies.

     Gallium was discovered (1875) by Paul Emile Lecoq de Boisbaudran, who
observed its principal spectral lines while examining material seperated from
zinc blende. Soon after he isolated the metal studied its properties, which
coincided those that Dmitrii Ivanovich Mendelev had predicted a few years
earlier for eka-aluminium, the then undiscovered element lying between aluminum
and indium in his periodic table.

     Though widely distributed at the Earth's surface, gallium does not occor
free or concentrated in independant minerals, except for gallite. It is
extracted as a by-product from zinc blende, iron pyrites, bauxite, and
germanite.

     Silvery white and soft enough to be cut with a knife, gallium takes on a
bluish tinge because of superficial oxidation. Unusual for its low melting
point ( about 30 degrees C, 86 degrees F ), gallium also expands upon
solidification and supercools readily, remaining a liquid at temperatures as
low as 0 degrees C ( 32 degrees F ).

     Gallium has the longest usefull liquid range of any element. The liquid
metal clings to glass and similar surfaces. The crystal structure of gallium
is orthorhombic. Natural gallium consists of a mixture of two stable isotopes:
gallium-69 ( 60.4 percent ) and gallium-71 (39.6 percent ).

     Somewhat similar to aluminum chemically, gallium slowly oxidizes in
moist air until a protective film forms, and it becomes passive in cold nitric
acid.

     Gallium has been considered as a possible heat-exchange medium in
nuclear reactors, although it has a high neutron cross section. Radioactive
gallium-72 shows some promise in the study of bone cancer; a compound of this
isotope is absorbed by the cancerous portion of the bone.

     The most common use of gallium is in a gallium scan. Gallium scans are
often used to diagnose and follow the progression of tumors or infections.
Gallium scans can also be used to evaluate the heart, lungs, or any other organ
that may be involved with inflammatory disease.

     A gallium scan usually requires two visits to the Nuclear Medicine
Department. On the first day you recieve an injection in a vein in your arm,
you will then be scheduled to return beetween 2 and 5 days later, depending on
your diagnosis. Your initial scan can take several hours, while you lay on a
stretcher, or imaging table, and a camera is positioned above you or below you,
taking pictures as it moves slowely along the length of your body. No special
preperation must be taken before the scan, and the gallium is usually excreted
through the bowel.