borax-bead test

 

 

A preliminary test in qualitative inorganic analysis that can be a guide to the presence of certain metals. A small loop is made in the end of a platinum or Nichrome wire and heated in a Bunsen flame until red hot. It is then dipped into powdered borax, and the adhering solid is held in the hottest part of the flame where it swells up as it loses its water of crystallization and then shrinks, forming a colorless, transparent glass-like bead .
A minute sample to be tested is introduced into the bead and the color observed in in the lower, reducing, part of the flame, allowed to cool, and the color observed. It is then heated in the upper, oxidizing, part of the flame, allowed to cool, and the color observed again. The color is also noted when the bead is cold.
Characteristic colored beads are produced with salts of copper, iron, chromium, manganese, cobalt and nickel. After the test, the bead is removed by heating it to fusion point, and plunging it into a vessel of water.

Metal                     Oxidizing flame                                       Reducing flame

Aluminum             colorless (hot and cold), opaque              colorless, opaque

Antimony              colorless, yellow or brown (hot)              gray and opaque

Barium                   colorless

Bismuth                 colorless, yellow or brownish (hot)         gray and opaque

Cadmium               colorless                                                  gray and opaque

Calcium                 colorless

Cerium                  red (hot)                                                  colorless (hot and cold)

Copper                 sky blue (hot and cold),                           opaque red, opaque

Iron                      yellow (hot and cold), opaque                  bottle-green, opaque

Manganese          pink (hot and cold), opaque                      colorless, opaque

Cobalt                 deep blue (hot and cold), opaque              deep blue, opaque

Nickel                  yellow-brown (hot and cold), opaque      grey, opaque

Silver                  colourless (hot and cold), opaque             grey, opaque

Vanadium           colourless(hot and cold), opaque              green, opaque

Uranium             yellow-brown (hot and cold), opaqu       green, opaque

Chromium         green (hot and cold), opaque                   green, opaque

Platinum            colourless(hot and cold), opaque            grey, opaque

Gold                  yellow-brown (hot and cold), opaque       grey, opaque

Tin                     colourless(hot and cold), opaque              colourless, opaque

Titanium            colourless (hot and cold), opaque            yellow, opaque (hot) violet (cold)

Tungsten            colourless(hot and cold), opaque              brown, opaque

Magnesium        colourless(hot and cold), opaque             colourless, opaque

Molybdenum      colourless(hot and cold), opaque             yellow or brown, opaque

Strontium           colourless(hot and cold), opaque              colourless, opaque

Thorium             colourless(hot and cold), opaque               colourless, opaque

Yttrium              colourless(hot and cold), opaque               colourless, opaque

Neodymium       colourless(hot and cold), opaque               colourless, opaque

Praseodymium  colourless(hot and cold), opaque                colourless, opaque

Silicon              colourless(hot and cold), opaque                colourless, opaque

Germanium      colourless(hot and cold), opaque                colourless, opaque

 

 

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