function henry(coc,temp,tempunits)
{
//***********************************************************************
//*
//* Function  henry - computes dimensionless Henry's law constant at user-defined temperature
//*
//* Language:  JavaScript1.1
//*
//* Inputs:
//*   object   form object
//*
//* Returns:
//*   returns Henry's Law Constant (H) 
//*
//* Limitations:
//*   
//*   
//*
//* Author:
//*  Dr. Fred Tillman
//*  National Research Council Research Associate
//*  Regulatory Support Branch
//*  Ecosystems Research Division
//*  National Exposure Research Laboratory
//*  United States Environmental Protection Agency
//*  960 College Station Road
//*  Athens, Georgia 30605
//*  tillman.fred@epa.gov
//* 
//*
//* Reference:
//*  Flanagan, D., 1997, JavaScript: The Definitive Guide, 2ed, O'Reilly and Associates
//*
//* Created: 6-22-2004
//* Updated: 
//*
//* Note:  data from OERR-J&E spreadsheets, Conversion relationship from pg. 12 of OERR manual
//*
//* 
//* Required functions: contable.js
//*
//* Required scripts: none
//*
//***********************************************************************
   var f = document.vaporsite;
   var Rc = 1.9872;
   var R = 8.205E-5;

//* Get required contaminant parameter values
//* Contaminant data taken from VLOOKUP Table of OERR-issued J&E spreadsheets
//* Contaminant parameter values in contable.js function
//* coc = contaminant CAS value, delHv = enthalpy of vaporization at normal boiling point (cal/mol), Tref = Henry's law const. reference temp (K)
//* Hr = Henry's law constant at reference temp (atm-m3/mol), Tb = normal boiling point (K), Tc = critical temp (K)

    var delHv = cont(coc,'delHv');
    var Tref = cont(coc,'Tref');
    var Href = cont(coc,'Href');
    var Tb = cont(coc,'Tb');
    var Tc = cont(coc,'Tc');

//* Convert temperature to units of Kelvin
    var Ts = '';
    if (tempunits == 'F') { temp = ((5/9)*(temp-32))+273.15;}
    if (tempunits == 'C') { temp = temp + 273.15;}
    Tref = Tref + 273.15;

//* Calculate value for "n" exponent (pg. 13)
    var n = '';
    if ((Tb/Tc) < 0.57)   {n=0.30;} 
    else if ((Tb/Tc)>0.71) {n=0.41;}               
    else    {n=0.74*(Tb/Tc)-0.116;}               

//* Calculate delHvT
     var delHvT = ((1-temp/Tc)/(1-Tb/Tc)); 
     delHvT = Math.pow(delHvT,n);
     delHvT = delHvT*delHv;

//* Calculate Henry's Law Constant at system temperature using Clapeyron equation:
     var H = -1*(delHvT/Rc)*(1/temp - 1/Tref);
     H = Math.exp(H);
     H = H * Href/(R*temp);
     

     f.H.value = Num2String(H,7,-10,10,-7,7);

       
}