In the discussion of the composition of hydrochloric acid it was stated that one volume of hydrogen combines with one volume of chlorine to form two volumes of hydrochloric acid. With bromine and iodine similar combining ratios hold good. These facts recall the simple volume relations already noted in the study of the composition of steam and ammonia. These relations may be represented graphically in the following way: +---+ +----+ +------+ +------+ | H | + | Cl | = | H Cl | + | H Cl | +---+ +----+ +------+ +------+ +---+ +---+ +---+ +--------+ +--------+ | H | | H | + | O | = | H_{2}O | + | H_{2}O | +---+ +---+ +---+ +--------+ +--------+ +---+ +---+ +---+ +---+ +--------+ +--------+ | H | | H | | H | + | N | = | NH_{3} | + | NH_{3} | +---+ +---+ +---+ +---+ +--------+ +--------+ In the early part of the past century Gay-Lussac, a distinguished French chemist, studied the volume relations of many combining gases, and concluded that similar relations always hold. His observations are summed up in the following law: _When two gases combine chemically there is always a simple ratio between their volumes, and between the volume of either one of them and that of the product, provided it is a gas._ By a simple ratio is meant of course the ratio of small whole numbers, as 1 : 2, 2 : 3. EXERCISES 1. How do we account for the fact that liquid hydrofluoric acid is not an electrolyte? 2. Why does sulphuric acid liberate hydrofluoric acid from its salts? 3. In the preparation of chlorine, what advantages are there in treating manganese dioxide with a mixture of sodium chloride and sulphuric acid rather than with hydrochloric acid? 4. Why must chlorine water be kept in the dark? 5. What is the derivation of the word nascent? 6. What substances studied are used as bleaching agents? To what is the bleaching action due in each case? 7. What substances studied are used as disinfecting agents? 8. What is meant by the statement that hydrochloric acid is one of the strongest acids? 9. What is the meaning of the phrase _aqua regia_? 10. Cl_{2}O is the anhydride of what acid? 11. A solution of hydriodic acid on standing turns brown. How is this accounted for? 12. How can bromine vapor and nitrogen peroxide be distinguished from each other? 13. Write the equations for the reaction taking place when hydriodic acid is prepared from iodine, phosphorus, and water. 14. From their behavior toward sulphuric acid, to what class of agents do hydrobromic and hydriodic acids belong? 15. Give the derivation of the names of the elements of the chlorine family. 16. Write the names and formulas for the binary acids of the group in the order of the stability of the acids. 17. What is formed when a metal dissolves in each of the following? nitric acid; dilute sulphuric acid; concentrated sulphuric acid; hydrochloric acid; aqua regia.