Introduce a given quantity of standard sodium tetraphenylboron solution to the prepared sample solution to precipitate potassium, and the excess reagent is then titrated by a standard solution of ammonium chloride using Nessler's reagent as an outside indicator.Carbonate ions interfere. But this interference can be eliminated by acidifying the sample solution previously. Ferric and manganous,ions form colored precipitates with the Nessler's reagent. Theyshould be precipitated in slightly alkaline solution after oxidation.The modified procedure of tetraphenylboron is suggested for the determination of total potassium of soils following Na₂CO₃ decomposition.