How did the five-bulb potash apparatus measure carbon dioxide?

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Justus, baron von Liebig Justus von Liebig, photograph by F. Hanfstaengl, 1868.

The five-bulb potash apparatus measured carbon dioxide by serving as an absorption vessel during the process of organic analysis.1

When Justus, baron von Liebig burned an organic compound with copper oxide, the resulting oxidation products included water vapour and carbon dioxide. The apparatus was filled with caustic potash, which absorbed the carbon dioxide as it passed through the bulbs. By weighing the apparatus directly after this absorption, Liebig could determine the carbon content of the compound with significantly greater precision and speed than previous methods allowed.1