Page:On the various forces of nature and their relations to each other.djvu/201

Rh is formed, which, on the further addition of the iodide, changes into the brilliant scarlet biniodide of mercury. If too much iodide of potassium is added, the scarlet precipitate disappears, and a colourless solution is left.

($9$) 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.

($10$) Page 59. "Prince Rupert's Drops."—These are made by pouring drops of melted green glass into cold water. They were not, as is commonly supposed, invented by Prince Rupert, but were first brought to England by him, in 1660. They excited a great deal of curiosity, and were considered "a kind of miracle in nature."

($11$) Page 60. Thick Glass Vessels.—They are called Proofs or Bologna phials.

($12$) Page 61. Mica..—A silicate of alumina and magnesia. It has a bright metallic lustre—hence its name, from mico, to shine.

($13$) Page 62. Common salt, or chloride of sodium, crystallises in the form of solid cubes, which, aggregates together, form a mass, which may be broken up into the separate cubes.