On 31 Mar 03 at 8:29, John Lonsdale wrote: > From memory, the pH scale is a log scale so pH 6 is ten times more > acid than pH7 ! At pH 6, the concentration of H+ ions is ten times greater than at pH 7. However, biological responses to such environmental factors are usually logarithmic rather than linear. That's the whole reason for using a logarithmic scale such as pH rather than quoting the actual acidity in millimoles of H+ per liter. Soil acidity is not the only such situation: earthquakes and star brightnesses are also measured using logarithmic scales. As the San Andreas fault, so Narcissus calcicola. -- Rodger Whitlock Victoria, British Columbia, Canada "To co-work is human, to cow-ork, bovine."