Demonstration Notes Many useful and interest,ing items are submitted as modifications or additions to previously published demonstrations. These may be attached to the respect.ive demonstrations or filed separately if desired. Spontaneous Combustion
Joseplr E. Joh,nson, Eastern District High School, Broolilyn, New York, 11211, finds the following very simple demonstration to be quite effective. [See "Spontaneous Combust,ion," GEOGHEGAN, JOHN'T., AND SHEERS, EDWARDH., J. CHEM.EDUC.,46, A429 (1968)l. Rlix 20 ml of boiled linseed oil, 5 ml of turpent,ine, and 5 ml of Japan drier and thoroughly work into a 6-in. square piece of cotton from a roll. Shredding helps. Ii'orm into a ball and wrap it in a fresh layer of cotton and place on a t,ripod. Run a pencil or dowel stick through the ball and suspend a laboratory thermometer with the bulb halfway through the hole. When the temperature starts to rise rapidly the thermometer should be removed. The mass should start to burn in 30 to 45 min. Keep windows open and use tongs to place t,he ball in water after action has been demonstrated. NOTE: Keep all unburned cotton under water overnight after disposing of it to prevent spontaneous combustmion. Diffusion of Gases
An improvement in the demonstration by C. N. IlcCarthy ["Tested Demonstrations in Chemistry," Chemical Education Publishing Co., Easton, Pennsylvania, (6th Ed.), 1965, p. 1601 is suggested by Joseph E. Johnston (address above). Two hydrometer jars, one with a solid rubber stopper and the other with a one-hole stopper fitted with a glass stopcock are
provided. An ampuh of bmnii~w (:lbout 0.5 ml) is placed in each and the jars str~ppcrcd. The second jar is then evacuated and closed with the stopcock. With a jar in each hand, a quick snap of the wrist d l break the ampules and the jars may be set on the table. The diffusion of the bromine in the jar of air will be slow but almost instantaneous in the evacuated jar. The ampules may be easily blown from small diameter glass tubing or may be purchased from a supply house. Patriotic Colors Based on Cobalt Complexes
Philip S. Chen, At,lantic Union College, South Lancaster, Massachusetts 01561 has adopted the follo\ving demonstration from "Dem 312-Cobalt Ion and Complex" [BARNARD, R., J . CHEM.EDUC.,43, A540 (1966) 1. Grind 2 g each of dry CoC12.6H20and KSCiY together in a mortar and extract the resulting blue cobalt complex with 30 ml ether. Place 10 ml of the ether extract in each of the two large test tubes. To each tube now add 10 ml of water which will form the bottom layer and will gradually turn pink as it extracts the Co2+ from the ether layer above. Gently tap the tubes a few times until a good pink is obtained. NOT\add 10 ml of carbon tetrachloride to one tube and 10 ml of benzene to the other, using a 20-ml pipet that is filled to the mark. The organic solvent is allowed to flow out only after the tip of the pipet has reached the bottom of the water layer. This is done to avoid mixing of the ether layer with the added solvent, in which it is soluble. The pipet is withdrawn after about 10 ml of the solvent has been delivered. The reason for not using a 10-ml pipet is that the hydrostatic pressure is great enough to prevent the pipet from emptying all its contents. The colors in the carbon tetrachloride tube from the bottom up are colorless, red (pink), and blue while those in the benzene tube are red, white, and blue.
Volume 47, Number 6, June 1970
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A439
