36. Q. What is the other member of the chemical family to which it may be said chlorine and bromine belong? A. Iodine.
37. Q. Where are all these three elements found? A. In sea water.
38. Q. From what source is iodine obtained? A. From sea weeds.
39. Q. To what are the chemical characteristics of iodine throughout closely allied? A. To those of chlorine and of bromine, only in general, iodine may be said to have weaker chemical affinities than either of the other two.
40. Q. What are two of the principal uses of iodine? A. In photographic processes, and as a remedial agent.
41. Q. What remarkable statement is made of fluorine? A. That is has never been known to be produced isolated, that is, in a separate or uncombined form.
42. Q. What property above all others is characteristic of fluorine? A. Its striking affinity for silicon.
43. Q. With what substance is fluorine never known to form any compound? A. With oxygen, which can be said of no other element.
44. Q. What are three considerations upon which the importance of oxygen depends? A. The surpassing abundance of the substance itself, the great number of compounds into which it enters, and the activity of its chemical powers.
45. Q. To whom is the first discovery of oxygen usually attributed? A. Dr. Joseph Priestly, an English clergyman and student of natural science.