tory, namely, the instability of the sulfite solution. An alternative reaction is frequently camed out for the same purpose, i. e., the exemplification of the law of "mass action," by the precipitation of arsenious sulfide from arsenite by thi~sulfate.~This clock reaction, in the opinion of the author, lacks the charm and rapidity of color change marking the termination of the induction period that is found in the iodine reaction. In 1927 Backstr6ma showed that the photochemical oxidation of sodium sulfite solntion is a chain reaction. Later Alyea and Backstrom4 reported that the action of alcohols in inhibiting the oxidation of sulfite solutions must consist in the breaking of reaction chains in the thermal as well as in the photochemical reaction. Accordingly, it seemed that the addition of a small quantity of alcohol to the sulfurous acid solution used in the above classroom experiment would effectively stabilize the solution and thereby eliminate the necessity of preparing the solution each time i t was required. This modification was camed out and very favorable results were obtained. A year-old 0.04 molar solution of sulfurous acid can still be used with considerable success. The induction period is approximately twenty per cent. longer than when, the solution is fresh, but standardization before classroom use corrects for the slow change taking place over relatively long periods. Without the inhibiting action of the alcohol on the sulfite, the solution must be prepared as required. A liter of 0.02 M potassium iodate was prepared. The second solution was prepared in the following manner. Five grams of starch were added to one bundred ml. of hot water. Aftei-cooling, this was diluted somewhat ahd 1.26 grams of sodium sulfite dissolved. Ten milliliters of alcohol and 1 gram of salicylic acid were added, and finally sufficient sulfuric acid to make the concentration 0.04 M when the solution is made up to one liter. The function of,the salicylic acid is to retard the decomposition o'f the starch. However, on long standing, the latter substance was found to be AIR JACKET A N D FREEZING-POINT TUBE rather ineffective. In a number of tests one hundred milliliters of the A completed jacket is shown in the accompanying snlfite solution are added to five hundred milliliters of diagram. water. Varying quantities of the potassium iodate Perhaps a sufficient commentary on their wearing solution (thirty-five, fifty,.seventy-five, one hundred qualities is that the students have nick-named them milliliters) are mixed with this quantity of sulfite. In "bonnceables." each case, water must be added to the iodate so that the volume of this solution is one hundred milliliters. In A MODIFIED LECTURE EXPERIMENT this manner, after mixing the sulfite and iodate, the final volume is seven hundred milliliters. The time WILLIAM J. CONWAY between the mixing and the appearance of the blue color is measured by means of a stopwatch. The Fordham University, New York City interval is found to be proportional to the concentration of the reactants. THE fundamental law underlying all reaction rates ' DANIELS, MATHEWS, AND WILLIAMS.''Experimental physical is the law of molecular concentration. Teachers of McGraw-Hill Book Co., Inc., New York City, elementary chemistry have long used for demonstration chemistry," 1934, p. 150. of this law the familiar reaction liberating iodine from Fomes, ESTILL,AND WALKER, I. Am. Ckcm. Soc., 44, 97 iodate with sulfurous acid.' There is, however, one 11922) BKCKSTROM,ibid.,49,1460 (1927). phase of this experiment which has been unsatisfac' ALYEAAND B~~CRSTROM, ibid.,51,90 (1929).
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