ottle of ammonia, as a little sprinkled about the chemical room soon
disinfects it of all iodine or bromine vapor, and also tends to
facilitate the operation in the camera.

IODINE.

History of Iodine.--This is one of the simple chemical bodies which was
discovered in 1812 by M. Courtois, of Paris, a manufacturer of
saltpetre, who found it in the mother-water of that salt. Its
properties were first studied into by M. Gay Lussac. It partakes much
of the nature of chlorine and bromine. Its affinity for other
substances is so powerful as to prevent it from existing in an isolated
state. It occurs combined with potassium and sodium in many mineral
waters, such as the brine spring of Ashby-de-la-Zouche, and other
strongly saline springs. This combination exists sparingly in
sea-water, abundantly in many species of fucus or sea-weed, and in the
kelp made from them. It is an ingredient in the Salt Licks, saline,
and brine springs of this country, especially of those in the valley of
the Mississippi. It is sparingly found in fresh-water plants, as well
also in coal, and in combination with numerous other bodies.

Fermented liquors contain iodine; wine, cider, and perry are more
iodureted than the average of fresh waters. Milk is richer in iodine
than wine; independently of the soil, with which it varies, the
proportion of iodine in milk is in the inverse ratio of the abundance
of that secretion. Eggs (not the shell) contain much iodine. A fowl's
egg weighing 50 gr. contains more iodine than a quart of cow's milk.
Iodine exists in arable land. It is abundant in sulphur, iron, and
manganese ores, and sulphuret of mercury: but rare in gypsum, chalk,
calcareous and silicious earths. Any attempt to extract iodine
economically should be made with the plants of the ferro-iodureted
fresh waters. Most of the bodies regarded by the therapeutists as
pectoral and anti-scrofulous are rich in iodine.

It is probably to the application of this body that we owe the
discovery of the daguerreotype. There is no record of the precise date
when Daguerre commenced experimenting with iodine, but by the published
correspondence between him and M. Neipce, his partner, it was previous
to 1833. There is no doubt, however, that the first successful
application was made in 1838, as the discovery was reported to the
world early in January, 1839.

Preparation.--Iodine is mostly prepared from kelp, or the half
vitrified ashes of seawee