A METHOD of TABULATING the REACTIONS of QUALITATIVE ANALYSIS STEPHEN G. SIMPSON Massachusetts Institute of Technology, Cambridge, Massachusetts
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HE following method of tabulating the reactions of qualitative analysis has been used by the writer in his classroom for a period of nearly twenty years. Although the method is not unlike
that of Hodge,' i t offers certain advantages, particularly in taking up less space and being more suitable ,HoooB, H,, ,#Animproved of re,rding the results of qualitative analysis,"J. CHEM.E ~ u c .4, , 2 4 2 4 (1927).
for blackboard demonstration. It has been found by experience to be a simple, logical way of expressing the various separations and tests, and in addition it presents graphically a bird's-eye view of the entire scheme of analysis. Without such a graphic representation, the student often becomes confused by the many procedures and fails to get a clear picture of the relationships between them. He "cannot see the woods for the trees." The method employs the following conventions. 1. A procedure within a given group analysis is ex-
6. Formulas of substances in solution are enclosed by dot-dash lines. 7. Formulas of substances which are precipitates or residues are enclosed by solid lines. 8. Formulas of gases are unenclosed. 9. Colors of precipitates and of certain solutions are denoted by appropriate abbreviations enclosed by parentheses. The accompanying figure serves merely as an illustration of the principle and covers only the analysis of the silver, copper, and tin groups according to the
pressed by a horizontal line. The operation or the essential reagent used is written above the line; the number of the procedure is written below the line. 2. The formation of a precipitate is expressed by an arrow pointing downward. 3. The formation of a gas is denoted by an arrow pointing upward. 4. The formation of a solution is denoted by an arrow pointing diagonally upward to the right. 5. The formation of a residue is denoted by an arrow pointing diagonally downward to the right.
method of A. A. Noyes. In the classroom, the instructor will find it profitable to sketch the graphic outline on the blackboard in accompaniment to the discussions of chemical principles involved. In addition, the entire qualitative scheme including the analysis of the cations, the analysis of the anions, and the preparation of the solution can be drawn on paper or cardboard even as small as sixteen by twenty inches and used as a laboratory chart. Similarly, the Noyes and Bray scheme for the common and rarer elements can be drawn on two such charts.
