LECTURE EXPERIMENTS in GENERAL CHEMISTRY*+ I. The
Rusting of Iron.
II.
Spontaneous Combustion.
III. The
Halogens
SAMUEL MORRIS AND ALVAH JOHN WASHINGTON HEADLEE West Virginia University, Morgantown, West Virginia
T
HIS is the first of a series of papers on lecture for two days without seriously impairing the results of experiments in general chemistry, which have the experiment. When ready for demonstration, the been developed for our courses and to the best of water is poured off and the bulbs of a mercury and an our knowledge are nowhere else in use. air thermometer inserted in the wool, the former to give Effective lecture experiments offer many difficulties the actual change in degrees and the latter to indicate not met with in other types of experimentation. One to the class that beat is being evolved. The battery of these is the time element. If possible, every lecture jar is wrapped with asbestos paper or cloth to prevent experiment should be begun and finished within the heat loss. A rise of 45- in 21 minutes bas been noted, lecture period. Furthermore, the ideal experiment or more than 2' per minute. A second run may be should require no more time to perform than to give made on the same iron by simply washing with hydrothe necessary explanation, for most students are prone chloric acid and rinsing with water. This second trial to watch any experiment as long as i t continues, bow- often gives a more rapid rise in temperature than the fist. ever good the lecturer mav > he. The air thermometer used in this experiment is iUusTHE OF IRON trated in Figure 1. A Dumas bulb is very convenient Usually, in the rusting of for bulb A. This is iron, the heat produced is connected by rubber conducted away so rapidly tubing to the three-way that no rise in temperature stopcock, D. The bulbs is noted. However, fine B and C are 100-ml. iron wool, t h o r o u g h l y pipets spaced so that cleaned, presents a large the top of C is on a active rusting surface and . level with the center of 300 to 500 grams of such B. C may be extended iron, in a rather compact with glass tubing to mass, surrounded by little any desired h e i g h t . or no insulation, rusts so Water, colored with rapidly that a considerable benzo-sky-blue or any rise in temperature is read- water-soluble dye, is placed in B and C to ily noted. The iron wool, in a 3-liter the heights indicated in battery jar, is covered with the figure. By means 1 N hydrochloric acid of the three-way stopuntil hydrogen is copiously cock the liquid may be evolved, whe'n the acid is re- brought to any desired moved, the iron thoroughly position on the scale. This same reaction washed, and left covered with water until needed for may be employed to demonstration. Thus pre- show that iron rapidly ~ a r e dthe , iron may remain combines with one-fifth * Contribution from the De- the volume of the enpartment of Chemistry, Division closed air. A 5-liter of Industrial Sciences, West Vir- balloon flkk is filled ginia University. t The majority of these experi- with iron wool and fitments were demonstrated before ted with a 1-hole rubber the American Chemical Society, stopper carrying a glass Division of Chemical Education, m G m E 1.-AIR THER- at Cincinnati, Ohio, September, tube 70 long' The MOMETER 1930. flask is inverted and
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clamped to a ring-stand so that the glass tube extends to the bottom of a glass vessel containing a t least 1 liter of water, as shown in Figure 2. The iron wool has been previously treated with 1 N hydrochloric acid, rinsed and kept over water as described in the preceding experiment. The water is then poured off and the flask inverted as shown in Figure 2. The water begins to rise immediately through tube A, and continues to rise until the flask is approximately one-fifth full, which usually requires about 45 minutes. If the flask is kept tightly stoppered the same steel wool may be used repeatedly for carrying out thi? znperiment. 11.
SPONTANEOUS COMBUSTION
This experiment is designed to be completed within an hour lecture period, and to use only materials similar to those commonly found around the home or other buildings. Twenty-five cc. of raw linseed oil, 5 cc. of turpentine, and 5 cc. of Japan drier, which have not been exposed to the air, are mixed and absdrbed in cotton. This mass is wrapped in more
P"
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speed increases rapidly. After the temperature has reached 200° the rate of reaction can be increased by placing the cotton in a draft of air. At 300° the temperature increases about lo0 per minute. At 350' the thermometer is removed, the ball of cotton parted to the center, and in a short time it will burst into flame. 111.
THE HALOGENS
In this experiment is shown the displacement of bromine by chlorine and iodine by the bromine. Also, if the proper conditions are maintained all three elements can be shown in the gaseous state, bromine and iodine in the liquid, and iodine in the solid state. About a third of the distauce from one end of a glass tube, which is about 4 cm. in diameter and 90 cm. long, are placed two layers of sodium bromide, held in place by glass wool as shown in Figure 3. In a similar way two layers of sodium iodide are placed about one-third of the distauce from the other end of the tube. From some easily regulated source, such as the generator shown in Figure 3, moist chlorine is passed into the end of the tube containing the sodium bromide. Bromine is displaced from the sodium bro-
F I G ~3.-THE E DISPLACEHENT OB THE HALOGENS
cotton and squeezed in order to distribute the oil evenly. The ball is fluffedup somewhat in the middle, to allow free access of air, and wrapped loosely in more cotton if the oil is near the surface. The bulb of a 360' thermometer is thrust to the middle of the mass in order to note the change in temperature. The rewtion proceeds slowly a t first but as the temperature rises the
+ .. .-,
mide and passes on to the sodium iodide, from which it displaces iodine. The sodium bromide and sodium iodide must not be too dry and the tube must be warm enough to keep the proper spaces well filled with gaseous bromine and iodine. The authors acknowledge with thanks the services of Mr. Glenn S. Watson who prepared the drawings.
CHICAGO PAPERS, DIVISION OF CHEMICAL EDUCATION 1. I. D. GARARD. "The ScientificMethod in Laboratory Work in General Chemistry" 2. I. MUSKAT.Chemist~yat A Century of Progress Exposition" 3. R. H. MCKEE. "The Chandler Museum at Columbia University"
4. FLORENCE E. WALL. ''Vocations in Chemistty" 5. S. B. ARENSON. "The Status of Broadcasting Educational Talks in the Orient" 6. K. A. KOBE."Class Exercises in the Industrial Chemistry Course" 7. R. A. BAKER."A Blast Lamp from a Bunsen Burner"
