What change in color do you note (R)? Add potassium hydroxide to this solution. Is the color change reversed (R)? Write the equation for the transformation of a chromate to a dichromate as a reversible reaction. Why does the addition of acid throw it one way, while bases throw it the other? b. To a solution of a chromate add a solution of a soluble salt of lead (R). Repeat, using a salt of barium (R). Repeat these experiments, using a solution of a dichromate instead of a solution of a chromate (R). c. Pour 2 or 3 cc. of concentrated hydrochloric acid upon a few crystals of a chromate (R). Repeat, using potassium dichromate (R). d. Place three or four crystals of potassium dichromate in a test tube and add 2 cc. of concentrated sulfuric acid. The deep-red crystals are chromic anhydride (CrO2) (R). Pour the mixture into cold water. Do the crystals dissolve? What do they form (R)? APPENDIX DATA FOR CALCULATION OF GAS VOLUMES The relation between the volume of a gas under standard conditions, V., and its volume V when measured over water at a pressure P, an absolute temperature T, and an aqueous tension a is expressed by the equation. In comparing the pressure exerted by a column of water with that exerted by a column of mercury, it must be remembered that the density of mercury is 13.56. TENSION OF AQUEOUS VAPOR AT VARIOUS TEMPERATURES EXPRESSED IN MILLIMETERS OF MERCURY WEIGHT IN GRAMS OF 1 LITER OF VARIOUS GASES UNDER STANDARD CONDITIONS, AND BOILING POINTS UNDER PRES SURE OF 760 MILLIMETERS 2 Bunsen burners. 1 burner, wing-top. 1 burette clamp. 1 screw clamp. A. ARTICLES RETURNABLE 1 set cork borers, Nos. 1-3. 1 hemispherical iron dish, 75-mm. 1 lead dish. 1 pair forceps. 1 pinchcock. 1 deflagrating-spoon. 1 test-tube holder. 1 test-tube rack. 1 mortar and pestle, 75-mm. 1 piece platinum wire. 1 porcelain spatula, 130-mm. 1 casserole, 75-mm. i porcelain crucible and lid, No. 00. 1 porcelain dish, No. 0. 2 beakers, 60-cc. 2 beakers, 100-cc. 2 beakers, 150-cc. 1 towel. 1 clay triangle. 1 test-tube brush. 1 sponge. 50 splints. 1 box matches. 2 beakers, 225-cc. 2 beakers, 325-cc. 1 bottle, narrow-mouthed, 1000-cc. 1 bottle, wide-mouthed, 1000-cc. 4 bottles, wide-mouthed, 250-cc. 2 bottles, wide-mouthed, 60-cc. 1 drying-tube, straight. 1 flask, Erlenmeyer, 120-cc. 1 flask, Florence, 120-cc. 1 flask, Florence, 250-cc. 1 flask, Florence, 500-cc. 2 funnels, 65-mm. 3 glass plates, 75-mm. x 75-mm. 12 test tubes, 130-mm. 2 test tubes, hard-glass, 150-mm. 1 test tube, graduated, 30-cc. 1 funnel tube. 1 glass retort, 200 cc. 1 U-tube, Marchand, 100-mm. 1 watch glass, 78-mm. 1 Sargent lock and 2 keys. B. ARTICLES NOT RETURNABLE 2 bottles litmus paper. 1 hard-glass tube, 500-mm. × 7-mm. 1 hard-glass tube, 300-mm. × 10-mm. 1 pkg. filter paper, 110-mm., No. 595. 2 oz. of glass tubing, 6-mm. 1 oz. of light-weight glass rod. 1 cake soap. 3 ft. of rubber tubing, 4-mm., No. 22. 6 ft. of rubber tubing, 6-mm., No. 22. 2 rubber stoppers, two-hole, No. 6. 1 rubber stopper, one-hole, No. 5. 1 rubber stopper, one-hole, No. 4. 1 file, triangular. 1 file, round. 1 wire gauze. APPARATUS TO BE AVAILABLE WHEN CALLED FOR Burette, 50-cc. Cylinder, graduated, 150-cc. 1 for every 8 students 1 for every 8 students Cylinder, plain, 2500-cc. (for collecting gases in tubes) 1 for every 8 students 1 for every 4 students 1 for every 6 students 1 for every 4 students 1 for every 4 students 1 for every 10 students 1 for every 10 students 1 for every 4 students 1 for every 4 students 1 for every 8 students 2 or 3 sets APPARATUS PROVIDED FOR GENERAL USE Balance and weights (see note to § 7, p. 148). Barometer, mercurial. Blast lamp. Pneumatic trough (see note to § 12, p. 148). If locker space permits, the pneumatic trough should form a part of each outfit. Ring stands. If movable ring stands are used, one should be in each outfit. It is better to provide the laboratory with permanent ring stands on each desk. These are easily made by screwing an iron rod into a flat disk that in turn is screwed to the desk top. Local workmen can make them. LIST OF CHEMICALS FOR A CLASS OF TEN STUDENTS In the following list will be found an estimate of the actual quantities of reagents required for a class of ten students. In many cases these quantities are less than the smallest commercial package, and no supply house would want to furnish such small quantities. In the second column will be found the smallest commercial package that will be sufficient, the figures having been supplied through the kindness of the Kauffman-Lattimer Co. Columbus, Ohio. It will be noticed that in ordering for classes of large size it will not in all cases be necessary to multiply the number of commercial packages by the number of pupils in the class. |