1254
ANALYTICAL CHEMISTRY
water outlet, and the anode oompartment and sulfuric acid rcservoir. The various components are held by spring clips arranged on a suitable stand above a tray. The stand and tray are canveniently built into the same unit, Where possible, connections are glass to glass, covered by polyethylene or polyvinyl chloride tubing. The dimensions are shown in Figure 1. Modifications of Design. The sample holder and mercury cathode are surrounded by a cooling jacket, from which water passes to the mercury lift pump. A sufficient flow of water through this jacket to prevent overheating in the oathode chamber is thus ensured, and higher current densities can he employed if required. The design of the mode compartment has been modified so that the thermometer is in a more convenient position, no air locks are possible, and the rate of flaw of the anolyte (1% v./v. sulfuric acid 8s suggested by Dent) is clearly visible. The cellophane sheet membrane used in earlier designs is r e placed with Visking cellophane tubing (standard siee 24/32, 2.9 em. wide when flat) which is knotted a t one end, turned inside out, and threaded over the shaped end of the anode compartment. It is secured by two rubber bands wound tightly around the glass tubing. Leakage and pinhole formation are considerably reduced in this design and one membrane will survive a t least two desal6 ing runs, after which it should be replaced. Connection of B direct current power supply of about 200 volts to the terminals indicated in Figure 1 is made through a variable resistance (400 to 600 watts, 100 ohms), a voltmeter, and an ammeter.
In a trial run, 10 ml. a i 1% sodium chloride was desalted in 65 minutes. The temperature of the anolyte did not exceed 28.5' C. At the start the potential difference was 24 volt8 and the current flowing was 0.45 ampere (resistance 53 ohms). After 65 minutes the solution failed to produce a precipitate with silver nitrate, the potential difference had increased to 122 volts, and the current flowing remained steady a t 0.20 ampere (resistance 610 ohms).
rapid by using z set a i transparencies made from the Bsird Associates Colthup transposition. Rather than a single transparency corresponding to each of the three sheets provided, a single transparency for each of the major functional groups such as alkane, aromatic, and keto has been used. The frequency scale is exactly the same as that of the spectrogram, hut the width of each of the group divisions hits been enlarged so that i t is the same as that of the chart paper. I n use then, onc aftor another of thcse transparencies is placed over the spectrogram and the possible functional groups are noted. When these have been compiled, a possible structure or structures are assigned and'the spcctragram is compared directly to spectrograms of similar compounds which are in the literature or in the lihrarv.
Demoun B. M. Mitener xatory, Deparir and S ment or Lnemiswy, uxumma umversny, and Department of Chemistry, New York University, New York, 3. Y.
occasionally arises for an infrared gas absorption cell Tthatneed . vacuum tight, yet may be easily dismounted and reHE
is
assembled-e.g., t o permit the insertion or removal of solid specimens. The cell illustrated is particularly useful in these respects. It is made from a 50/50 standard-taper joint, with the ends cut and ground perpendicular t o the joint axis. This size of joint produces a cell with internal diameter larger than the light beam in commercial spectrometers. The salt plates are cemented an with a beeswax-rosin mixture. If the joint is even without. lightly greased, the cell length - is very. reDroducible . the use of glass hcmks and springs to hold the joint together.
LITERATURE CITED (1)
Astrup, T..
Stage, A,.
and Olsen, E., Acta Chen. Scad., 5, 1343
(1951). (2) Blook, R. J.. and Bolling, D., "The Amino Aoid Composition of Proteins and Foods." 2nd ed., P. 429, Sprinpfield, Ohm, C. C
Thoma-,m,
l'nr' i.YI.
(3) Consden, R., Gordon, A. H., and Martin, A. J. P.. Biocha m. J . , 41, 59Cl(1947). (4) Dent, C. E., in "Recent
Advances in Clinical Pathology." edited bv6.C:. Dyke. 2nd ed., P. 252, London, J. &A. Churchill, 1952.
Transparent Colthup Infrared Chart. Bernard Manning, dtomic Warfare Directorate, Air Force Cambridge Research Center, Cambridge 39, Mass.
rr
HE table of infrared frequencies normally associated with atomic groupings compiled by Calthup [J. Opt. Soe. Amer., 40, 397 (1950)] is of vduable assistance in the identification of unknown compounds or mixtures from their infrared absorption spectra. Baird Associates, 33 University Road, Cambridge, Mass., for u8e in conjunction with the spectra obtainable from the sodium chloride prism infrared spectrometer which they manufacture, have made ssailable a transposition of the Colthup tabulation on chart paper of the same dimensions and v a v e length calibration 8 8 are used with their instrument. I n practice, the absorption spectrum of the unknown is determined and a tentative structure arrived a t by mtching the ahsorption bands of the unknown with the frequencies assigned to a particular functional grouping. This task is made simpler through the use of the Baird Associates Colthup charts, as the frequencies of the unknown can be matched by placing the Colthup chart and the spectrogram adjacent to one another on a flat surface with their wavelength scales touching and then matching the absorption bands with those of the Colthup chart. This mat,ehing procedure has been made lesa tedious and more
i n oraer t o maKe a cell 01 s n m e r iengtn man IU cm., IC IS necessary to cut off some of the tapered portion of the female joint, and to mount the stopcock in the tapered portion of the male joint. It requires considerable skill to do this without d i e torting the joint and losing its vacuum tightness. This technique is not recommended for cell lengths less than 5 em. This cell has been used in studies of the interaction of vapors with solid surfaces by mounting a. sheet of the solid in the male joint perpendicular to the axis of the joint, and examining the absorption spectrum before and after introducing the gas of interest. This cell has the additional advantage that the salt plstes can he repolished without demounting them. The external surfaces are treated in the usual manner, and the internal surfaces can be readily polished by means of a suitable buffer pad mounted on the chuck of a drill press. The authors are indebted to Karl Schuman, Columbia Department of Chemistry glassblower, for the glass work involved in t,he fabrication of the cell.
