forces arising from the working together of ancient and modern methods. Greece needs more of science and less of politics, yet the teaching of the former is very difficult. The situation is not hopeless by any means but i t will take many years of careful training on the part of American educators in the Near East. The Greek Orthodox Church has many teachings which keep her adherents slightly aloof from ideas such as science gives, but this angle of the situation is not the most inaccessible. The climatic and geographic conditions in Greece have kept her behind other countries in accepting modern ideas and methods. If we can train, for a few generations, the youth of Greece, he will be able to conduct the affairs of his nation quite well. The present legislators are a little slow in realizing certain of the needs of their country but as soon as they do, Greece will quickly regain her former prominent position among nations. It is the purpose of our college to instill in our 200 boys, the idea of thinking for themselves and through the branches of study that come under the science department, I hope to stress this point with greater force than can he done through other courses. With the thoughts of adding chemistry to the course of study I am elated in that it will make our school the foremost of technical and liberal arts schools in the city. I feel confident in launching upon this new project and I am deeply indebted to many of the contributors to THISJOURNAL for interesting and valuable articles on such subjects as relate to the teaching of chemistry. H. BICELOW MAURICE AMERICAN COLLEGE, SALONICA, GREECE EQUATIONS REPRESENTING OXIDATION-REDUCTION REACTIONS In a previous paper1 the writer discussed the method in use in this University, in the courses in general chemistry, for the application of the electron concept to a consideration of valence and of oxidation-reduction phenomena. The method described in the above-mentioned paper has been slightly modified to meet the difficulty which the student encounters in balancing the equations for those reactions in which the same substance serves the double function of oxidizing agent and source of anions, or of reducing agent and source of anions. In deriving the equation for the reaction of cupric sulfide with nitric acid, i t is noted that the oxidation-reduction ratio is 3CuS for 2HN03. The tendency of the average student is, without further reflection, to fill in these numbers in the skeleton equation. When he then tries to complete the balancing of the equation by inspection, he finds that he has Tms JOURNAL, 2, 576-81 (July. 1925).
to change the numher of molecules of nitric acid from 2 to 8 in order to account for the 6N03- required for the 3Cu++. Making this change in the number of the molecules of the oxidizing agent tends to destroy his confidence in the method, because he is inclined to think that i t is legitimate to make such changes in all equations for oxidation-reduction reactions, and he does not see that contribution is made to the work by deriving the proper electronic ratio. The better students do not run into this difficulty; hut the average student, early in his work, fails to distinguish between substances which serve a double function and those which serve as the oxidizing agent or reducing agent only. By the use of the electron change ratio to establish the numbers of the molecules of the products of such reactions, instead of the ratio of the molecules of the initial substances, the above-mentioned difficulty is avoided. In the case of the reaction of cupric sulfide with nitric acid, the steps involved in representing the number of electrons gained and lost may be written in the manner previously described.
+
+ +
+
HNOs CuS +NO S Cu(NOsjr HnO. HNOs -+ NO; N S +--+ NP+; Chin 3 (-); X 2 2 6 (-1. CuS -+ S ; ss- --+ so;Lass 2 (-); X 3
Equalizing the electron changes shows that the ratio of the oxidationreduction products is 2NO E 3s; and these numbers are entered in the ahove equation so that i t becomes, HNOa
+ CuS +2NO + 3S + Cu(N0J2 + H20.
Since no other valence changes occur under the ahove conditions, the final equation is obtained by completing the balancing through inspection, leaving until last the substance which serves the double function-in this case HN03. Since there are 3S, there must he 3CuS and ~ C U ( N O ~ ) ~ . There are now represented 8 atoms of nitrogen in the products of the reaction and hence 8HN03 must be represented. This calls for 4H20 and the final equation becomes, 3CuS
+ 8HNOn +2NO + 35 + 3Cu(NOsjl + 4H20
It is obvious that i t is not necessary to write the equation in this partial form three different times; but that the proper coefficients may be entered in the original skeleton equation as soon as they are determined. The student must remember that the numbers of the molecules established by a consideration of the electronic changes are fixed points in the equation and are not to he changed in the inspection balancing; but that the other coefficients must be such as to accord with these fixed points. In the beginning of the work, this fact may he emphasized by placing a check mark over the numbers of the molecules of the oxidation-reduction products determined from a consideration of the numbers of electrons gained and lost.
