Materials: Bismuth, dry ice, small porcelain crucible, hot-plate, forceps, 2-inch Alnico horseshoe magnet), a thin broom-straw, very fine thread, H-3.

Procedu7e: fiIclt a small mass of Bi in the crucible, pour out onto dry ice: crystals of Bi form. Tie a broom-straw to the thread, and 3 in. lower tie a crystal of Bi. Hang from H-3 and project, with the Bi lower- most and the straw projecting as a pointer which nl- tates when the thread is twisted. Now insert thc magnet so thc crystal is betwccn its polcs. Rotate the magnet.

Obsevvations: When the magnet is rotated, the Bi crystal (as shown by the motion of the pointcr) rotates with i t ; the crystal always remains across the magnetic field.

Reference: TAYLOR, E. A,, J. CHEM EDUC., 27, 457 (1950).

Dem. 547-Hydrolysis of BiCla

To shozc.: The hydrolysis of bismuth chloride to form bismuthyl chloride.

Materials: C-4, BiC13-aq, conc. HC1, medicine drop- pers.

Procedure: Project C-4 with all cells half-filled with BiCla-aq. (a ) Add H1O dropmise to cells 2,5,4 until precipitate just forms. (b) Sow add conc. HC1 drop- wise to cclls 3 and 4 until precipitate just dissolves. (c) Finally add H 2 0 dropwise, until precipitate re- forms.

Observations: The results are explained by the follow- ing shifting of equilibrium:

RiCls + HsO F? BiOCll + 2 HCl clear white

F. Analytical Dem. 548-Identification of As, Sb, Bi

To shozc: Analytical procedures for As, Sb, and Bi in routine qualitative analysis.

Materials: AsC13-aq, ShCla-aq, BiCls-aq, HzS-aq, or NaS-aq, culture tubes, filter paper, funnels, C-3, H-3, (NH4),S,, HC1-aq.

Procedure: Project culture tubes half full of water. Add about five drops of As+' to one, of Sb+3 to the second, and of Bi+3 to the third. Regulate acidity to about 0.3 N H+. Add HpS-aq or bubble in HzS gas. Filter off the three precipitates and place in C-3 and pro- ject. Fill each cell one-quarter full of (NHa)&, and stir. Finally make acid with HCI-aq.

Observations: Sulfides Biz&, (brown), As& (yellow), and Sb2S3 (orange) form. Thc Bi2S3 is insoluble in (NH4)&, but the arsenic and arlt,imony sulfides dissolve forming thio compounds. See Dems. 539 and 544. The As& and SbzSs reappear when the solution is acidi- fied.

Note: I luch of the above, particularly the colors, must hc shown macro. The actual yellow of the arsenic sulfide and orange of thc antimony sulfide may he sccn only if very dilute reagents are employed.

GROUP VI. THE SULFUR FAMILY

Members: S, Se, Te

Elemental Sulfur Dem. 549-Sulfur from H2S + SO2

T o show: The formation of sulfur as i t occurs in a volcano.

Reacticn: 2H2S + SO2+ 2H20 + 35 (yellow).

Materials: Two 2-02. wide-mouth, stoppered, square clear-glass bottles; H a , SO2.

Procedure: Fill the bottles with H,S and SOz respec- tively, put a few drops of water into each and stopper. Project the H2S bottle on the vertical stage.

Suddenly remove both stoppers and bring the mouth of the SOz bottle, inverted, to the mouth of the HzS bottle.

Observations: I n half a minute the walls of the bottles become coated with sulfur. Pass around class. Query to class: Why is the SO2 put on top (consider molecular weights, c.g. densities)?

Dem. 550--Rhombi Sulfur

Experiment developed by Crosby U . Rogers

T o show: Formation of rhombic sulfur.

Materials: Clear saturated solution of flowers of sulfur in CS2in dropper bottle; 3-in. watch glass, 10 ml beaker.

Procedure: (a ) Rapid growth,. Put the watchglass and the beaker on the horizontal stage. P u t 10 drops of solution into each. Let stand. ( b ) Slow growth. P u t 1 ml of solution in the 10-ml beaker; cdver with the watchglass and let stand for a week. Project results.

Observations: (a ) With rapid evaporation only small rhombic crystals are formed, rapidly. (b) I n a week, large crystals are formed, slowly. Project and exhibit them macro.

Dem. 551-Pr;smatic Sulfur

Experiment developed by Crosby U . Rogevs

T o show: Formation of prismatic needles of sulfur

Materials: Flowers of sulfur, H-3, 4 mm glass tubing with 1-ft length of rubber tubing attached.

Procedure: Heat 2 g of sulfur in the culture tube in H-3 until very hot and molten. Project. Now blow in air to cool it until i t soldifies. Both project and show macro.

Observations: The sulfur melts to an amber liquid. Upon cooling i t rapidly, by blowing air through it, it. solidifies to a lighter color. Especially, spikes or needles (prismatic sulfur) can bc seen upon projection.

A836 / journal of Chemical Education