potentiometer recorder. The excitation voltage to the potentiometer was made variable to provide continuous scale expansion up to tenfold. This arrangement was used in addition to the automatic repetitive scanning mechanism to rerord repeating scans on the strip chart. This technique was used ~5 here the time course variations in the intensities of readily identifiable bands R ere of interest. Monitoring of Single Wave Length during Reaction. This method was used with t h e single c ~ l and l the strip (,hart potentiometer recorder. \There this method is used n i t h the rotating ~ 1 1 ,the regular recording facilities can be uqed since the cycle of sample clhanges provides a criterion of reaction time. PERFORMANCE
One point of interest in the mechanism of styrene-butadiene rubber oxidation is the thermal decomposition of the intermediate hydroperoxides. To study this reaction the instrument was set to scan repetitively the 5.5- to 6.5micron region of the spectrum. The polymer film was then ovidized in the single cell to the point of maximum rate in the autocatalytic reaction stage. The reaction compartment was then purged with nitrogen and the com-
partment sealed off with the front window. K i t h a slight positive pressure of nitrogen held on the reaction compartment, the scans were continued until no additional changes in the spectrum were obvious. Selected scans from this record are shown in Figure 3. As the system was not perceptibly disturbed except for the exclusion of oxygen, fine details of this reaction are obtained which may have otherwise been lost in sampling errors. Figure 4 demonstrates the use of the single cell in studying very fast reactions. I n this case the single wave length position of the 5.81-micron carbonyl band was monitored on the strip chart m-hen styrene-butadiene rubber films of varying thickness Ivere oxidized a t high temperature. The calculated results from the scale expanded runs show diffusion control of this reaction rate with these very thin films. I n studies of this nature the limiting reaction rates n-hich may be follon.ed are limited only by the response speed of the instrument. The rotating multisample cell is especially useful for comparative studies. For example, it was of interest to compare several procedures of washing the ox
