AMMONIUM COMPOUNDS.
248. Read the chapter on NH3. Also, review the experiments on bases. Examine NH4Cl, NH4NO3, (NH4)2SO4, (NH4)2CO3.
Ammonium, NH4, is too unstable to exist alone, but it forms salts similar to those of K and Na. NH3 dissolved in water forms NH4OH.
The food of plants, as well as that of animals, must contain N. It has not yet been shown that they can make use of that contained in the air, but they do absorb its compounds from the soil. All fertilizers and manures contain a soluble compound of NH4. All NH4 compounds are now obtained either from coal, in making illuminating-gas, or from bones, by distillation.
Suppose the product obtained from the gas-house to be NH4OH, how would NH4Cl be made? (NH4)2SO4? NH4NO3? Write the reactions. (NH4)2CO3 is made by heating NH4Cl with CaCO3. Give the reaction.
Chapter XLVI.
CALCIUM COMPOUNDS.
Examine CaCO3—marble, limestone, chalk, not crayon,—CaSO4 — gypsum or selenite—CaCl2, CaO.
249. Occurrence.—The above are the chief compounds of Ca. The element itself is not found uncombined, is very difficult to reduce (page 141), is a yellow metal, and has no use. Its most abundant compound is CaCO3. Shells of oysters, clams, snails, etc., are mainly CaCO3, and coral reefs, sometimes extending thousands of miles in the ocean, are the same. CaCO3 dissolves in water holding CO2, and thence these marine animals obtain it and therefrom secrete their bony framework. All mountains were first laid down on the sea bottom layer by layer, and afterwards lifted up by pressure. Rocks and mountains of CaCO3 were formed by marine animals, and all large masses of CaCO3 are thought to have been at one time the framework of animals. Marble is crystallized, transformed limestone. The process, called metamorphism, took place in the depths of the earth, where the heat is greater than at the surface.
250. Lime.—If CaCO3 be roasted with C, CO2 escapes and CaO is left. CaCO3 - CO2 = ? This is called burning lime, and is a large industry in limestone countries. CaO is unslaked lime, quicklime or calcium oxide. It may be slaked either by exposure to the air, air-slaking, when it gradually takes up H2O and CO2; or by mixing with H2O, water-slaking. Ca0 + H2O = Ca(OH)2.