of iodine gradually in portions of ten grms., and agitating between each fresh addition, until the alcohol becomes colorless again.

After the addition of the last 4 grms.

the alcohol remains colored, the whole of the mercury having become converted into iodide.

The resulting preparation is washed with alcohol; it is crystalline and of a hyacinth color.
Iodide of Silver .-- This compound is formed upon every plate upon which a Daguerreotype is produced.

The vapor of iodine coming in contact with the silver surface, forms an iodide which is peculiarly sensitive to light.
The various colors produced are owing to the thickness of the coating, and the maximum sensibility of the coating, as generally adopted, is when it assumes a deep yellow, or slightly tinged with rose color.
This compound is largely employed in most photographic processes on paper, and may be easily prepared by the following formula: By adding iodide of potassium to a solution of nitrate of silver, a yellowish-white precipitate of iodide of silver is obtained, which is insoluble in water, slightly soluble in nitric acid, and soluble in a small degree in ammonia, which properties seem easily to distinguish it from the chloride and bromide of silver.