15 октября, 2015 
Pokraskin Pumice is broken up into pieces about 3 mm. in size and screened, using a sieve that retains the 3-mm. pieces. The more uniform the pieces are, the better. This pumice is placed in a hot solution of ammonium vanadate which is as concentrated as possible. When the pumice is thoroughly impregnated, it is removed from the solution and dried in a porcelain dish on a water bath. About 3 grams of vanadium are taken up by 200 grams of pumice. The dried mass is now heated to 400°C. until the grains have a reddish brown color. It is important that the
54 Wohl, Ger. Pat. 347,610 (1921) and 379,822 (1923) [Frdl, 14, 836, 450 (1921-1925)1. See also Chowdhury and Choudhury, /. Indian Chem. Soc., 11, І85 (1934), and Chowdhury and Saboor, ibid, 14, 638 (1937′).
catalyst is not heated above the temperature at which it is to be used later, a precaution to be observed in many catalytic reactions.
Rule: A catalyst should not be heated above the reaction temperature.
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