Dilute solution. A  dilute solution formed by the addition polymerization of two molecules of a monomer.

Dimethylamine. (CH₃)₂NH. A colourless gas with an ammonical smell. It is used in dehairing hides and as a rubber accelerator.

N.N.-Dimethylaniline. C₈H₁₁N, PhNMe₂.Colourless oil of characteristic smell; b.p. 193°C.
Prepared by heating aniline with methanol and a little sulphuric acid at 215°C. Used as solvent and as a second component in a few azo-dyes

Diol. (dihydric alcohol) An alcohol containing two hydroxyl groups per molecule.

Diorite. A widely distributed igneous rock composed of plagioclase

Dioxane.
It is a good solvent for cellulose acetate resins, rubber, mineral and vegetable oils.

Dipole moment. In a heteronuclear diatomic molecule, because of the difference in electronegativities of the two atoms, one atom acquires a small positive charge (q+), the other a negative charge (q-). The molecule is then said to have a dipole moment whose magnitude m - qd, where d is the distance of separation of the charges. Wit polyatomic molecules the net dipole moment is the vector sum of the dipole moments of the individuals bonds within the molecule. Thus symmetrical molecules, e.g. CCl₄, may contain polar bonds but possess no net dipole moment. Measurements of dipole moments may be used to give information about the structure of complex molecules.