CHROMOTOCRAPHY Submitted b ~ :Professor J . M . Saurer, 41 Rue P.-Jolissaint, St. Immier, Switzerland. Chrrked b?/: Roger Wheaton, Michigan State University, East Lansing, Michiga~l
PREPARATION
Provide sticks of soft white chalk (the hard-pressed chalk found in many American classroomswill not work. Number 320 white chalk made by Binney and Smith, Inc. and sold at S. S. Kresge Co. Stores is suitable), 0.1 41 solutions of Cd(iXO& and Pb(N03), a source of H2S,a beaker, and three test tubes. DEMONSTRATION
Show the color of cadmium sulfide by adding Hi3 to
cadmium nitrate in a test tube. Show similarly the color of lead sulfide, and the color of the mixed sulfides formed by adding H2Sto a 1: 1 mixture of the two salts. Place some of the mixture in the bottom of the beaker; stand a piece of white chalk on end in the solution. After 15-20 min, expose the chalk to HzS, and observe at the bottom of the piece of chalk a dark brown zone and above that a long yellow zone.
SOlVAY PROCESSES Submitted by: Robert J. Johns, Academy of the Xew Church College, Bryn Athyn, Pennsylvania. C h e c l d by: Roger Wheaton, Michigan State University, East Lansing, Michigan. PREPARATION
Provide a large balloon filled with carbondioxide, 100 ml concentrated ammonia solution saturated with NaC1, a bottle, a one-hole stopper, and a rubber tube connected to the balloon.
Laboratory Manual," Houghton-Mifflin Co., Boston, 1950. The small chips of dry ice are dropped into a bottle containing brine, which is then enclosed nith a onehole rubber stopper carrying a Bunsen valve, as shown in B.
DEMONSTRATION
Flush the air out of the top of the bottle with the carbon dioxide. Attach the balloon to the bottle with the rubher tube, as shown in A , and shake the bottle. Observe the solution of carbon dioxide and eventually (20-30 minutes) the formation of a precipitate of NaHCOa. Depending on its size, it may be necessary to refill the balloon. REMARKS
An alternate procedure makes use of dry ice as a source of carbon dioxide, as described by BOYK,S., GANTZ,E. ST. C., AND RICE,C. N., "General Chemistry Journal 01 Chemical Edueofion
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July 296.5
