Again, it might be important to know whether a certain pulp or
composition contained flax in combination with cotton. The composition
might be of such a well-digested character as to destroy all appearance
of normal form, that is to say, the "twisted ribbon" character of cotton,
as well as that of the cylindrical and jointed characteristic of flax,
might be lost to ordinary view. In this case make a watery solution of
the pulp, spread it out thinly on a glass slide 3 inches by one, draw off
any superfluous water, then add one or two drops of a strong solution of
chromic acid to the preparation, and place over it a glass cover; when
viewed by the microscope, any portion of the flax joints present will
appear of a dark brown color; a solution of iodine has a similar effect.
The brown portions of the joints are nitrogenous in character; cotton
fibers are devoid of nitrogen.
[Illustration: Figs. 1, 2, 3, 4, 5.]