Construction

The apparatus consists of an intake valve which feeds into a calibrated water or glycerin jacketed gas burette, this burette is then connected by tubing to two or more absorption pipettes containing chemical solutions that absorb the gases it is being used to measure. The intake and each of the absorption pipettes are valved with stopcocks to allow the movement of gas through the apparatus to be precisely controlled. For safety and portability, the apparatus is usually encased in a wooden box with a handle.

The most common absorbents are:

• Potassium hydroxide (caustic potash) for carbon dioxide
• Pyrogallol (pyrogallic acid) for oxygen
• Copper(I) chloride (ammoniacal Cuprous chloride) for carbon monoxide

Any left-over gas is assumed to be nitrogen, though other absorbents or vessels can be used to isolate additional gases. Platinum on asbestos for example can be used to determine the hydrogen content of a sample, and the Fischer-type Orsat gas analyser for example uses a platinum electrode to explode the remaining gases with hydrogen.

The base of the gas burette is connected to a leveling bottle which typically contains slightly acidulated water with a trace of chemical indicator (typically methyl orange) for colouration. The small amount of acid added to the water reduces the solubility of carbon dioxide. The leveling bottle can be lifted and lowered to enable readings to be taken at constant pressure and to transfer the gas to and from the pipettes containing the different absorption media. The movement of gas through the apparatus is entirely controlled using the leveling bottle and the various stopcocks.