Glass is the preferred material for the cell bodies because of its superior corrosion resistance. Internal metal parts are made of anodized aluminum for the same reason--corrosion resistance. We consider stainless steel and other bare metal surfaces to be less desirable than glass or anodized aluminum. The reason for this is that many of the gases to be measured in air and other media are acidic in nature and are therefore taken up in chemical reactions with the metal. It is an added benefit that glass is transparent and easy to clean.

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