Invented many lecture-room and laboratory appliances (Bunsen burner); invented the spectroscope and with it discovered rubidium and caesium; greatly perfected methods of electrolysis, inventing a new battery; made many investigations among metallic and organic substances] CHAPTER XXIV THE ALKALINE-EARTH FAMILY =========================================================================== | | | | | | | | | MILLIGRAMS SOL- | | | | | UBLE IN 1 L. | | | | | OF WATER AT 18 deg. | | SYMBOL | ATOMIC | DENSITY |__________________| CARBONATE | | WEIGHT | | | | DECOMPOSES | | | | SULPHATE| HYDROX-| | | | | | IDE | __________|________|________|_________|_________|________|_________________ | | | | | | Calcium | Ca | 40.1 | 1.54 | 2070.00 | 1670. | At dull red heat Strontium | Sr | 87.6 | 2.50 | 170.00 | 7460. | At white heat Barium | Ba | 137.4 | 3.75 | 2.29 | 36300. | Scarcely at all =========================================================================== ~The family.~ The alkaline-earth family consists of the very abundant element calcium and the much rarer elements strontium and barium. They are called the alkaline-earth metals because their properties are between those of the alkali metals and the earth metals. The earth metals will be discussed in a later chapter. The family is also frequently called the calcium family. 1. _Occurrence._ These elements do not occur free in nature. Their most abundant compounds are the carbonates and sulphates; calcium also occurs in large quantities as the phosphate and silicate. 2. _Preparation._ The metals were first prepared by Davy in 1808 by electrolysis. This method has again come into use in recent years. Strontium and barium have as yet been obtained only in small quantities and in the impure state, and many of their physical properties, such as their densities and melting points, are therefore imperfectly known. 3. _Properties._ The three metals resemble each other very closely. They are silvery-white in color and are about as hard as lead. Their densities increase with their atomic weights, as is shown in the table on opposite page. Like the alkali metals they have a strong affinity for oxygen, tarnishing in the air through oxidation. They decompose water at ordinary temperatures, forming hydroxides and liberating hydrogen. When ignited in the air they burn with brilliancy, forming oxides of the general formula MO. These oxides readily combine with water, according to the equation MO + H_{2}O = M(OH)_{2}. Each of the elements has a characteristic spectrum, and the presence of the metals can easily be detected by the spectroscope.