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 flameAluminum               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