The long-standing model of pigment cell origins is implicitly based upon a progressive fate restriction model of neural crest development and postulates the existence of a partially restricted progenitor common to all pigment cell types (i.e., a chromatoblast) [38] .
Sodium is the fourth most abundant element on earth, comprising about 2.6% of the earth's crust; it is the most abundant of the alkali group of metals. It is now obtained commercially by the electrolysis of absolutely dry fused sodium chloride.
Sodium: the essentials. Sodium is a Group 1 element (or IA in older labelling styles). Group 1 elements are often referred to as the alkali metals. The chemistry of sodium is dominated by the +1 ion Na + .Sodium salts impart a characteristic orange/yellow colour to flames and orange street lighting is orange because of the presence of sodium in the lamp. Soap is generally a sodium salt of fatty acids.roup 1 elements are often referred to as the alkali metals. The chemistry of sodium is dominated by the +1 ion Na + . Sodium salts impart a characteristic orange/yellow colour to flames and orange street lighting is orange because of the presence of sodium in the lamp.