ASTM_D_4972_-_13.pdf

Designation:D497213Standard Test Method forpH of Soils1This standard is issued under the fixed designation D4972;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method covers the measurement of the pH ofsoils for uses other than for corrosion testing.Such measure-ments are used in the agricultural,environmental,and naturalresources fields.This measurement determines the degree ofacidity or alkalinity in soil materials suspended in water and a0.01 M calcium chloride solution.Measurements in bothliquids are necessary to fully define the soils pH.This variableis useful in determining the solubility of soil minerals and themobility of ions in the soil and assessing the viability of thesoil-plant environment.A more detailed discussion of theusefulness of this parameter is not warranted here;however,itcan be found in many discussions of the subject.A few suchdiscussions are given as Refs(1-6)2at the end of the text.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 All measured and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D6026.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:3C670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction MaterialsD653 Terminology Relating to Soil,Rock,and ContainedFluidsD1193 Specification for Reagent WaterD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD6026 Practice for Using Significant Digits in GeotechnicalDataG51 Test Method for Measuring pH of Soil for Use inCorrosion Testing3.Terminology3.1 Definitions:3.1.1 For common definitions of terms used in this standard,refer to Terminology D653.4.Summary of Test Method4.1 Measurement of the pH of soils in both suspensions ofwater and a calcium chloride solution are made with either apotentiometer using a pH sensitive electrode system(MethodA),or pH sensitive paper(Method B).The potentiometer iscalibrated with buffer solutions of known pH.The pH sensitivepaper is a less accurate measurement and should only be usedfor a rough estimate of the soil pH.The electrode must be usedfor this measurement unless the pH sensitive paper is specified.NOTE1The quality of the result produced by this standard isdependent on the competence of the personnel performing it,and thesuitability of the equipment and facilities used.Agencies that meet thecriteria of Practice D3740 are generally considered capable of competentand objective testing/sampling/inspection and the like.Users of thisstandard are cautioned that compliance with Practice D3740 does not initself assure reliable results.Reliable results depend on many factors;Practice D3740 provides a means of evaluating some of those factors.5.Significance and Use5.1 The pH of the soil is a useful variable in determining thesolubility of soil minerals and the mobility of ions in the soiland assessing the viability of the soil-plant environment.5.2 pH measurements are made in both water and a calciumchloride solution because the calcium displaces some of theexchangeable aluminum.The low ionic strength counters thedilution effect on the exchange equilibrium by setting the saltconcentration of the solution closer to that expected in the soilsolution.The pH values obtained in the solution of calciumchloride are slightly lower than those measured in water due tothe release of more aluminum ions which then hydrolyses.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.22 on Soil as a Mediumfor Plant Growth.Current edition approved Nov.1,2013.Published November 2013.Originallyapproved in 1989.Last previous edition approved in 2007 as D4972 01(2007).DOI:10.1520/D4972-13.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 Therefore,both measurements are required to fully define thecharac