The difference between Method 19B1 and Method 19B2, both of which are only moderately quantitative (e.g. Nelson 1982), is that the former relies on the direct measurement of CO2 pressure (≈80–100 mm Hg) via a manometer (or similar), whereas Method 19B2 uses a corrosion resistant gas pressure transducer with an electrical output in volts direct current (Vdc). Method 19B2 is the more attractive, as it avoids the need to use a manometer containing liquid Hg, which (including its vapour) is a toxic heavy metal.
The methods demand close attention to operator safety associated with the use of strong acid and potentially high gas pressures, particularly when analysing soils of high carbonate content. Also, operators need to be vigilant to ensure there is no leakage of CO2 and to ensure there is only minimum contact with reaction vessels to avoid the possibility of temperature changes that affect gas pressure. Incomplete chemical reaction between acid and solid-phase carbonates is a potential source of error (low results), while positive errors can occur: (i) should sulfides and sulfites form gaseous hydrogen sulfide and sulfur dioxide in the presence of acid and heat, and (ii) should the decarboxylation of organic compounds produce CO2 (Nelson 1982).