Tinplate, used for tin cans, roofing and kitchen utensils, is made by dipping sheet iron or steel in a bath of melted tin, thus covering it with a thin layer of tin. Tinplate is manufactured in the United States and imported from England. Tin metal is imported from England and Straits Settlements.
=Zinc= is one of the most useful metals. Germany, United States and Belgium supply most of the zinc. In this country, Missouri and Kansas lead in zinc production.
_Sphalerite_ or blend (zinc sulphide) is the chief ore. Carbonates, silicates and oxides of zinc are found. Crude zinc (_spelter_) is distilled from roasted ore.
_Brass_, _German silver_ and other alloys contain zinc. _Galvanized iron_ consists of a coating of zinc on sheet iron. _Zinc oxide_ (zinc white) resembles white lead and is used in paints.
Used in electric batteries, making hydrogen, zinc etchings, etc. The greatest amount of zinc is used in alloys and zinc compounds. Zinc and zinc ores are both imported and exported by the United States, the imports exceeding the exports. Zinc oxide is exported in larger amount than any other form.
[Illustration: =HOW AND WHERE WE GET THE SALT FOR OUR FOOD=
The United States produces one-fourth of the entire output of the world. Salt was one of the first two great articles of international commerce in the history of the world trade.]
[Illustration: =AN UNDERGROUND PASSAGE WAY THROUGH SOLID SALT=
The most wonderful salt mines in the world are those of Galicia, in Austria. In this region there is a mass of salt estimated to measure 500 miles in length, 20 miles in breadth, and 1,200 feet in thickness.]
SCIENTIFIC TERMS USED IN THE EARTH SCIENCES
=Acanthodus= (_a-kan-thō´dus_).--Fossil fish, having thorn-like fins.
=Aërodynamics= (_ā-ẽr-ō-di-nam´iks_).--The science which treats of the air and other gaseous bodies under the action of force, and of their mechanical effects.
=Aërognosy= (_ā-ẽr-ŏg´nô-sy_̆).--The science which treats of the properties of the air, and of the part it plays in nature.
=Aërolite= (_ā´ẽr-ô-līt_).--A stone, or metallic mass, which has fallen to the earth from distant space; a meteorite; a meteoric stone.
=Aërology= (_ā-ẽr-ŏl´ôjy̆_).--That department of physics which treats of the atmosphere.