exchHions-2 Copyright Jürgen Prenzel 2001 The program is licenced through the GPL (see LICENCE) A program to calculate exchangeable H-ions from pH and Al concentrations in salt extracts of soil samples. Theory ====== The calculation is based on the idea that exchangeable H-ions acidify the extract solution. But part of the observed acidification may stem from hydrolysis of exchangeable Al-ions. The program tries to figure out the correction for the latter effect. For this purpose the hydrolysis of Al is calculated according to the stability constants as given in the book by Baes and Mesmer. The calculation is done by numeric iteration. This theory has obvios shortcomings. The most important is that organic complexing of Al is not included. An other is that all Al in the extract is assumed to stem from 3-valent Al at the exchange complex. Due to the shortcomings the correction term may be greater than the amount of H-ions present, in this case a negative value for exchangeable H results. Usage ===== This is a C subroutine: int akeh(double ph0, double ph1, double ctal, double str, double* exh); where: pH0 = pH of extractant pH1 = pH of extract ctal = Al in extract [µmol/L] str = ionic strength of extract [mol] *exh = H-ions from exchange complex [µmol/L] return values: 0 = o.k. 1 = illegal arguments 2 = no convergence of iteration Note ==== This program is equivalent to an older FORTRAN program, exchHions-1.