Barium hydroxide lime turns yellow after desiccation.

Ethyl violet is added to carbon dioxide absorbents and normally serves as an indicator of absorbent exhaustion. During the course of several prior studies of anesthetic breakdown, we noted (but did not publish) that barium hydroxide lime (BL), but not soda lime, turns yellow upon desiccation. We hypothesize that ethyl violet undergoes chemical reaction to produce a yellow colorant in desiccated BL. We qualitatively studied the time course of yellow color development during desiccation of these absorbents with dry oxygen. The yellow colorant was extracted from desiccated absorbent with diethyl ether, separated with chromatography, and analyzed with proton nuclear magnetic resonance and combined gas chromatography and mass spectrometry. The yellow color develops after BL has reached nearly complete desiccation. We successfully identified that ethyl violet decomposes into the yellow colorant 4,4'-bis(diethylamino)benzophenone upon desiccation of BL. The color is not intense, is not useful for identifying low levels of absorbent desiccation, and may be difficult to see through tinted canisters. It may be possible for BL to be sufficiently desiccated to allow chemical breakdown of anesthetics, but not yet show yellow coloration. However, if yellow coloration exists, one should assume that it has become desiccated.