Carbon as Reference for Normalizing Infrared Photoacoustic Spectra

Photoacoustic spectra of solids1 are usually “source compensated,” i. e., normalized for differences in source emission at different wavelengths, and such compensation is done by comparing the photoacoustic spectrum of a sample to the emission spectrum of the source measured directly with, say, a photocell,2 power meter,3 or photodiode,4 or to the photoacoustic spectrum of “carbon” recorded under the same conditions as that of the sample. A variety of carbons has been used for this purpose, including carbon black on silica,5 soot from a gas torch,6 and acatylene-sooted bakelite,7 such a reference substance being assumed to be a flat black absorber. That assumption appears to be valid, as indicated by the close