complete transfer of electrons, but a decrease in electron density of the atom oxidized. (4) Covalent bond formation in which there is an increase in electron density of the atom oxidized. The reader is referred to C. A. VANDERWERF, J. CAEM.EDUC., 25, 547 (1948) for a lucid and rational explanation of the role of electrons in redox reactions, and for examples of oxidation by each of the four means listed above. In this excellent article mill also he found examples of increase or decrease in electron density, without redox. Item 188 has no correct answer listed in the possible T o the Editor: choices. Ions of a salt are not "united" either in water On page 375 of the July, 1951, issue of the JOURNAL solution or in the dry crystalline solid. Therefore item OF CHEMICAL EDUCATION, Engelhart exhibits a fine ex- 188 is not correctly answered by response C, but reample of one of the most common pitfalls encountered quires a fifth choice, F, "none of the above," or "nonin constructing a so-called "objective" examination. sense." It is stated that each item is to have one correct answer, Why should a 1951 publication adhere to an 1890 but only one. In three items listed (187, 188, 189) two concept of "molecules" of a salt in which ions are items have two possible answers, and one item has no "united"? correct matching answer listed. "Ionize" obviously means to form ions. Therefore if a neutral atom gains electrons, it has formed an ion, in addition to its being reduced. Therefore item 187 may be answered correctly by either B (ionization) or E (reduction). To the Editor: For the same reason, a neutral atom which loses one The use of ferroxyl gels to demonstrate the corrosion or more electrons has formed an ion (ionized) in addi- of iron has been given by Meldrum' and by Orr and tion to being oxidized. Therefore item 189 can be Stafford.= The gels may also be used to show that rust correctly answered by two of the listed answers, B is a secondary product of corrosion and that it is formed (ionization) as vell as by D (reduction). in the superficial layer of moisture and not directly on The statement of these two items indicates that the the surface of the iron. The gels are left until rust is author has employed the very common, but nonetheless seen, which is not until a day or so after the Prussian fallacious, definition that all oxidations are loss of elec- blue precipitate has shown that iron has been passing trons. Loss of one or more electrons is certainly oxida- into solution in the ferrous state. When the gel is tion, but such a reaction is only one of several means by split and the nail taken out the nail will be found to be which a substance may be oxidized. Oxidation may quite clean, the rust remaining in the gel. take place by four different means: (1) Loss of electrons by complete transfer (electrovalent bond formation). (2) Mutual sharing of electrons (covalent bond formation) in which there is no transfer of electrons. ' IMELDRUM,W. B., J. CHEM. EDUC., 25.254 (1948). (3) Covalent bond formation in which there is no PO^^, W. L., AND H. A. STAFFORD, {bid., 27,202 (1950).
