The spectra of the known elements have been carefully studied, and any element which imparts a characteristic color to a flame, or has a spectrum of its own, can be identified even when other elements are present. Through the spectroscopic examination of certain minerals a number of elements have been discovered by the observation of lines which did not belong to any known element. A study of the substance then brought to light the new element. Rubidium and caesium were discovered in this way, rubidium having bright red lines and caesium a very intense blue line. Lithium colors the flame deep red, and has a bright red line in its spectrum. EXERCISES 1. What is an alkali? Can a metal itself be an alkali? 2. Write equations showing how the following changes may be brought about, giving the general principle involved in each change: NaCl --> Na_{2}SO_{3}, Na_{2}SO_{3} --> NaCl, NaCl --> NaBr, Na_{2}SO_{4} --> NaNO_{3}, NaNO_{3} --> NaHCO_{3}. 3. What carbonates are soluble? 4. State the conditions under which the reaction represented by the following equation can be made to go in either direction: Na_{2}CO_{3} + H_{2}O + CO_{2} <--> 2 NaHCO_{3}. 5. Account for the fact that solutions of sodium carbonate and potassium carbonate are alkaline. 6. What non-metallic element is obtained from the deposits of Chili saltpeter? 7. Supposing concentrated hydrochloric acid (den. = 1.2) to be worth six cents a pound, what is the value of the acid generated in the preparation of 1 ton of sodium carbonate by the Le Blanc process? 8. What weight of sodium carbonate crystals will 1 kg. of the anhydrous salt yield? 9. Write equations for the preparation of potassium hydroxide by three different methods. 10. What would take place if a bit of potassium hydroxide were left exposed to the air? 11. Write the equations for the reactions between sodium hydroxide and bromine; between potassium hydroxide and iodine. 12. Write equations for the preparation of potassium sulphate; of potassium acid carbonate. 13. What weight of carnallite would be necessary in the preparation of 1 ton of potassium carbonate? 14. Write the equations showing how ammonium chloride, ammonium sulphate, ammonium carbonate, and ammonium nitrate may be prepared from ammonium hydroxide. 15. Write an equation to represent the reaction involved in the preparation of ammonia from ammonium chloride. 16. What substances already studied are prepared from the following compounds? ammonium chloride; ammonium nitrate; ammonium nitrite; sodium nitrate; sodium chloride. 17. How could you prove that the water in crystals of common salt is not water of crystallization? 18. How could you distinguish between potassium chloride and potassium iodide? between sodium chloride and ammonium chloride? between sodium nitrate and potassium nitrate? [Illustration: ROBERT WILHELM BUNSEN (German) (1811-1899)