1. Henderson-Hasselbach equation:
   i. pH = pKa + log [HCO3-] / .03 * pCO2
   ii. (.03 = Bunsen's coefficient = solubility of CO2 in plasma)
   iii. (pKa for HCO3- = 6.10)
   iv. alternative form:  [H+] = Ka * .03 * pCO2 / [HCO3-]   (Ka = 800
      nm/l).
2. Henderson Equation:   [H+] = 24 * pCO2 / [HCO3-]  ("pH = respiratory
   over metabolic").
3. Total CO2 = [dissolved CO2] + [HCO3-] + [H2CO3] ~= .03 pCO2 + [HCO3-
   ] ~= 1.2 + [HCO3-].