carbonometer

from The Century Dictionary.

• noun An instrument for detecting the presence of carbonic acid by its action on lime-water.

from the GNU version of the Collaborative International Dictionary of English.

• noun An instrument for detecting and measuring the amount of carbon which is present, or more esp. the amount of carbon dioxide, by its action on limewater or by other means.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun obsolete ,(chemistry) an early device for measuring the concentration of carbon dioxide in a gas, by bubbling it through limewater and measuring the cloudiness