ANALYTICAL CHEMISTRY
742 very sensitive in the proper concentration region. Titrations may be easily and speedily performed with it. Using the differential procedure, many titrations may be carried out with no plotting and little manipulation. Although the instrument must be carefully constructed, it is simple and easy to maintain. The one serious difficulty with this titrimeter is the low concentration range necessary for adequate sensitivity. This p r o p erty severely restricts its use in many reactions. From the mechanism of the loading effect, it is apparent that an instrumant of higher frequency must be used to overcome this difficulty. The construction and properties of such instruments are the subject of the next section of this paper. T H E 360-Mc. TITRIMETER
Exploratory Work at 100 Mc. It waa considered necessary t o go t o higher frequency in order to carry out titrations in a higher concentration range than is possible with the 30-Mc.per-second titrimeter. Theoretically it is possible to extend the Clapp circuit (6) to 100 Mc. per second. Such a unit was built, but it did not oscillate under load. A fairly successful 100 Mc. per second unit was then constructed according to a conventional tuned plate design (IS). The stability of this titrimeter was not sufficient for use as a satisfactory instrument. However, a few titrations were performed with it and data were obtained which showed that maximum sensitivity occurred a t a salt concentration around 0.05 N , in accord with calculations using the empirical formula of Forman and Crisp (9). It is believed that a stable lOO-Mc.-per-second titrimeter could have been built, had sufficient time been spent in that direction. This appears to be close to the upper frequency limit for stable vacuum tube oscillators using conventional circuit components. Because i t was desired eventually to have an oscillator operating a t 300 to 500 Mc. per second, and because the lOO-Mc.-per-second instrument did not seem capable of extension to this region even if it could be stabilized, work on this instrument was abandoned. Exploratory Work on 360-Mc. Titrimeter. A survey of the electronics literature for very stable and simple oscillators operating a t about 400 Mc. per second was not encouraging. A quarter-wave-length concentric line oscillator seemed the best of several kinds described (Is), even though it was stated to possess a frequency stability of only 1 to 109 However, it appeared possible to improve this stability with better mechanical construction and by beating two such oscillators together, using the same filament and plate supplies, so that frequency drift would be reduced. Two such identical oscill&ors were built, with the lines of such a design that they could be loaded with titration vessels. The outputs were fed into a crystal mixer, and the beat frequency was meamred with the same frequency meter that was used with the 30-Mc.-per-second titrimeter. The beat frequency showed fluctuations of the order of 50 cycles per second representing a relative stability of 2 to lo’ which was beyond expectations. Application of this titrimeter to chemical systems is now under way. Preliminary data have shown that maximum sensitivity occurs a t a salt concentration around 0.2 MIclosely in accord with calculations using the empirical formula of Forman and Crisp (9). The sensitivity a t present appears to be of the same order as that for the 30-Mc.-per-second instrument, with the possibility that it may be increased manyfold. The 360-Mc.-per-second titrimeter haa promise of becoming a good analytical instrument. ACKNOWLEDGMENT
The authors wish to express their thanks to V. C. Rideout and Han Chang, of the Electrical Engineering Department, for their
invaluable advice and help with this work. This work was also aided by grants from the Wisconsin Alumni Research F O U d 5 tion. The authors also thank Wilbur J. Larson for providing photographs of the equipment. LITERATURE CITED
(1) Anderson, Kermit, Bettis, E. S., and Revinson, D., ANAL. CHEM.,22,743(1950). (2) Arditti, R., and Heitzmann, P., Compt. rend., 229, 44 (1949). (3) Bever. R. J.. Crouthamel, C. E., and Diehl, H., Iava State Coll. J . Sci., 23, 289 (1949). Blake, G. G., Australian J . Sci., 11, 59 (1948). Charterjee, S. K., and Breekantan, B. V., Indian J. Phys., 22, 229,325(1948). Clapp, J. K.,Proc. Inst. Radio Engrs., 361,356 (1948). Daniels, F., “Outlines of Physical Chemistry,” p. 417, New York, John Wile:,& Sons, 1948;, Falkenhagen, H., Electrolytes, p. 213, London, Oxford University Press, 1934. Forman, J., and Crisp, D., Trans. Faraday Soc., 42A, 186 (1946). Jensen, F.W.,and Parrack, A. L., IND. ENC.CHEM.,ANAL.ED., 18,595(1946). Kolthoff, I. M.,and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis.” p. 550, New York, Macmillan Co.. 19461
Malmstadt, H. V., “A High Frequency Titrimeter,” thesis, University of Wisconsin, 1948. Massachusetts Institute of Technology, Electrical Engineering Staff, “Applied Electronics,” p. 603, New York, John Wiley & Sons, 1947. Radio Corp. of America, Harrison, N. J., “RCA Receiving Tube Manual,” p. 42, 1947. Radio Corp. of America, Harrison, N. J., “RCA Reviews,” pp. 352,531,1948.
Richards, W. T., and Loomis, A. L., Proc. Natl. Acad. Sci.,
U.S.,15,587(1929). Roberts, I., IND. ENG.CHEM.,ANAL.ED.,8, 365 (1936). Solley, B. J., Wireless World, 51, 170 (1945). West, P. W.,Burkhalter, T. S., and Broussard, L., ANAL. CHEM.,22,469(1950). RECBIVED January 11, 1950.
Corrections The following corrections are submitted to take care of errors in the review on “Paper Chromatography” [ANAL.CHEM.,22,48-59 (1950) 1. The legend for Figure 2, page 50, should be “Apparatus for One- and Two-Dimensional Paper Chromatograms.” Figures 2 and 8 were accidentally interchanged, and therefore all remarks concerning Figure 2 should be referred to Figure 8, and vice versa. Reference (81) should be: Gordon, Martin, and Synge, Biochem. J. Proc., 37,xiii (1943). This refers to the firat reference to (81) on page 48. All other references numbered (81) should be (39). DORIS L. CLEGG I n the article on “Automatic Operations in Quantitative Analysis” [Patterson, G. D., Jr., with Mellon, M. G., ANAL. CHEM.,22, 136 (1950)], an error waa made on page 143, second column, where the last paragraph should have read: Transmissimetry. The process complementary to emission of radiant energy is transmission, and it is in this field that perhaps the largest number of applications of automatic methods exist. Tremendous advantages inherent in radiant energy transmission measurements make them especially adaptable for continuous automatic analyses. Of particular importance are the facts that the sample being tested is usually undamaged in the methods used and that the photoelectric or thermal response to changes in transmission (and thus concentration) is practically instantaneous. From the standpoint of automatization, the simplest caaes, of course, are those where the desired constituent itself absorbs radiant energy of a particular wave-length band where there is negligible interfering absorption by other substances present.
