Ingredients --

Hydrated silica

Chemical Formula:    SiO₂  ·  nH₂O
     SiO₂ = 1,   H₂O = 1:     H₂SiO₃
     SiO₂ = 2,   H₂O = 1:     H₂Si₂O₅
     SiO₂ = 2,   H₂O = 3:     H₆Si₂O₇
     SiO₂ = 3,   H₂O = 2:     H₄Si₃O₈
     SiO₂ = 3,   H₂O = 4:     H₈Si₃O₁₀
     SiO₂ = 4,   H₂O = 1:     H₂Si₄O₉
     SiO₂ = 4,   H₂O = 2:     H₄SiO₄ [also known as Si(OH)₄ ]

Synonyms

Silicic acid
Silica Gel
Amorphous Silicon Dioxide

Description

A transparent colloid (gel)

Uses

Hydrated silica is the abrasive used in gel toothpastes, or in the clear portion of striped toothpastes. It is often used in opaque toothpastes as well, as a secondary abrasive.

When dried in an oven, hydrated silica looses the water, and becomes a dessicant, a substance that attracts water from the air. You find little packets of "silica gel" crystals in containers whose contents will be damaged by condensing moisture, such as vitamin bottles, consumer electronics, pepperoni, or leather products.

Silica gel can be made by reacting an acid with sodium silicate (sold in drug stores as "water glass" or "egg keep", and used to paint eggs to seal them from air, preventing spoilage). Drying the resulting gel will get the dessicant, or it can be used wet in toothpastes.

You can find sodium silicate in the colorful "Magic Rocks" seen in gift shops at museums. The dry form is mixed with salts of various metals. When you drop them in water, the sodium is replaced by the metal. The resulting metallic silicate is not soluble in water, and has a color characteristic of the metal (e.g. copper is blue). The metallic silicate is also a gel, so it expands, and grows into colorful stalagmites in the water.