Class 7. Tungsten class: molybdenum, tungsten, vanadium.
Class 8. Arsenic class: antimony, arsenic, bismuth.
Class 9. Lead class: lead, thallium.
Class 10. Silver class: copper, mercury, silver.
Class 11. Gold class: gold, iridium, osmium, palladium, platinum, rhodium, ruthenium.
POTASSIUM.
Potassium was discovered by Sir H. Davy in the beginning of the present century, while acting upon potash with the enormous galvanic battery of the Royal Institution, consisting of 2,000 pairs of 4-inch plates. It is a brilliant white metal, so soft as to be easily cut with a penknife, and so light as to swim upon water, on which it acts with great energy, uniting with the oxygen, and liberating the hydrogen, which takes fire as it escapes.
EXPERIMENT.
Trace some continuous lines on paper with a camel’s-hair brush dipped in water, and place a piece of potassium about the size of a pea on one of the lines, and it will follow the course of the pencil, taking fire as it runs, and burning with a purplish light. The paper will be found covered with a solution of ordinary potash. If turmeric paper be used, the course of the potassium will be marked with a deep brown colour.—Corollary. Hence, if you touch potassium with wet fingers you will burn them!
If a small piece of the metal be placed on a piece of ice, it will instantly take fire, and form a deep hole, which will be found to contain a solution of potash.