Charcoal, activation decolorising with

Aminophenol [95-55-6] M 109.1, m 175-176 , pKj 4.65, pKj 9.75. Purified by soln in hot water, decolorised with activated charcoal, filtered and cooled to induce crystn. Maintain an atmosphere of N2 over the hot phenol soln to prevent its oxidation [Charles and Preiser J Am Chem Soc 74 1385 7952]. Can also be crystd from EtOH. 

Potassium hydrogen malate [4675-64-3] M 172.2. A saturated aqueous solution at 60° was decolorised with activated charcoal, and filtered. The filtrate was cooled in water-ice bath and the salt was ppted by addition of EtOH. After being crystallised five times from ethanol-water mixtures, it was dried overnight at 130° in zir [Edenand Bales J Res Nat Bur Stand 62 161 1959],... 

The polyacrylamide is added to flocculate any clay which is dispersed by the presence of sodium and a high pH, so that when the suspension is filtered a clear solution is obtained. Some soils release soluble organic matter during shaking which colours the solution and could interfere with the measurement of phosphate. So, to decolorise the extracts, activated charcoal is added during the extraction procedure. 

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