esidues (of monose groups) having distinct and
opposite polarities; such a complex is essentially labile and its
configuration will change progressively under reaction. The exposition
of this view is the subject of a publication by Cross and Bevan
(_Researches on Cellulose_, ii. 1906). The main purpose is to give full
effect to the colloidal characteristics of cellulose and its
derivatives, with reference to the modern theory of the colloidal state
as involving a particular internal equilibrium of amphoteric
electrolytes.

The typical cellulose is a white fibrous substance familiar to us in the
various forms of bleached cotton. Other fibrous celluloses are equally
characteristic as to form and appearance, e.g. bleached flax, hemp,
ramie. It is hygroscopic, absorbing 6 to 7% its weight of moisture from
the air. When dry, it is an electrical insulator, and has a specific
inductive capacity of about 7: when wetted it is a conductor, and
manifests electrolytic phenomena.[1] It is insoluble in water and in the
ordinary solvents; it dissolves, however, in a 40-50% solution of zinc
chloride, and in ammoniacal solutions of copper oxide (3% CuO, 15% NH3):
from these solutions it is obtained as a highly hydrated, gelatinous
precipitate, from the former by dilution or addition of alcohol, from
the latter by acidification; these solutions have important industrial
application. Projected or drawn into a precipitating solution they may
be solidified continuously to threads of various, but controlled
dimensions: the regenerated cellulose, now amorphous, in its finer
dimensions is known as artificial silk or lustra-cellulose. These forms
of cellulose retain the general characters of the original fibrous and
"natural" celluloses. In composition they differ somewhat by combination
with water (of hydration), which they retain in the air-dry condition.
They also further combine with an increased proportion of atmospheric
moisture, viz. up to 10-11% of their weight.

_Derivatives._--Important derivatives are the esters or ethereal salts
of both inorganic and organic acids, cellulose behaving as an alcohol,
the highest esters indicating that it reacts as a trihydric alcohol of
the formula n[C6H7O2(OH)3]. The nitrates result by the action of
concentrated nitric acid, either alone or in the presence of sulphuric
acid: the normal dinitrate represents a definite stage in the series of
nitrates, and the ester at this point manifests the importan