decolorimetern.

/dɪˌkʌləˈrɪmɪtə/Etymology: < Latin dēcolōr-em deprived of colour + -meter comb. form2.
1864 H. Watts II. 308 Decolorimeter, an instrument invented by Payen for estimating the decolorising power of charcoal.
This entry has not yet been fully updated (first published 1894; most recently modified version published online March 2018).