Other Experiments Using the Standard Technique

Nassau et al.,21 using an elaborate U-tube arrangement, experimented with copper iodate and found six different forms of copper iodate in different locations in the gel. The largest of these were Cu(I03)2 -2H20, which grew to 2 mm. 

Lead and zinc sulfides have been produced by the standard technique in gels. The lead compounds are toxic and should be handled with care. For lead sulfide,25 26 the gel is prepared by mixing sodium metasilicate (sp gr 1.05) with 2.26 N HC1 to reach a pH of 6. A few drops of lead acetate or chloride solution are added to the gel before it is allowed to set. Setting requires about 1 week. The solution is then covered with a 1 M solution of thioacetamide. The thio-acetamide slowly releases hydrogen sulfide into the solution according to the 

The sulfide ion then reacts with the lead ion in the gel to precipitate lead sulfide. Crystals up to a millimeter in length can be produced in 2 weeks. Temperatures range from room temperature to 35°, with best results reported at the higher temperature. The same sulfide source is used for the growth of zinc sulfide crystals.25,27 The crystals grow to a size of 3-4 mm in 2 months. It should be mentioned that a modified U-tube system has been used to produce this size crystal and it is expected that smaller crystals will be produced if a simple U-tube is employed. 

Lead iodide and lead hydroxide iodide3,28 29 are popular experimental systems. The lead iodide is best prepared at 45°, but room temperature can also be used. Thin hexagonal platelets of Pbl2 up to 8 mm in diameter have been grown in 3 weeks at 45°. Lower temperatures produce smaller, but thicker, crystals. Lead hydroxide iodide (PblOH) is formed in a basic gel in a test tube.30 If the gel is not alkaline, some Pbl2 crystals are also formed. 

Other crystals grown by this technique include lead molybdate,31 barium and strontium tungstate,32 silver acetate,33 potassium perchlorate,34 and copper(I) iodide.35 

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