Note 9 — LECTURE II. GRAVITATION—COHESION.
Reading edition
Page 57. Paper Coated with Scarlet Biniodide of Mercury.—In order to fix the biniodide on paper, it must be mixed with a little weak gum water, and then spread over the paper, which must be dried without heat.
Biniodide of Mercury is said to be dimorphous; that is, is able to assume two different forms.