ranges and products of decomposition and interaction, it will probably be most useful for the study of polymeric materials and natural products. It should be possible to study large repeating units rather than just the simplest ultimate pyrolysis products. Some pilot work has been done on lignin and humus, and a large number of interesting products has been detected in addition to the expected series of aromatic compounds.Because no thermal conductivity, flame ionization, or other detector is used, it is not necessary to use specific carrier gases for best results. Mechanisms and interactions can be studied in any gas or vapor system-e.g., oxygen, air, nitrogen, helium, hydrogen, carbon dioxide, or mixtures containing water vapor, acids, ammonia, etc.Collection efficiency is surprisingly good; the band of products on the plate is sharply defined. The plate must, however, be decoupled from the heat of the furnace as much as possible. Metal plates and/or efficient cooling may be necessary for operation at temperatures much higher than 500°C. The apparatus has been operated to 1000°C , but borosilicate glass plates had to be used, and it is believed that collection efficiency was appreciably reduced at the higher temperatures.
ACKNOWLEDGMENTThe author thanks M. J. Naranjo for considerable help with thin layer chromatographic work and L. E. Edwards for design of the plate holder trolley.
Accurate values of the activity coefficients of thiocyanic acid in aqueous solution have been obtained for concentrations of up to 0.1 molal at 25 "C by combining results for transference-number experiments with those for cells with transport. The transference-number experiments were done with the movingboundary method, the transference-number at infinite dilution being calculated from measured conductivities of the thiocyanic acid. For the electromotive force (e.m.f.) measurements, conventional glass electrodes were used in conjunction with a high input-impedance electrometer.The results obtained electrochemically were checked by determining activity coefficients from freezingpoint depression measurements which also extended the range of concentrations to 1 molal.The results of the two types of measurement are in good agreement.
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