machine-prepared phosphors showed better precision than those prepared b y hand, and the two runs with the machine are essentially in agreement. ACKNOWLEDGMENT
The authors thank Charles G. Bay and Leonard B. Riley for suggestions in the building of the phosphor-making machine, and A. G. King, Wayne Mountjoy, Irving Frost, and John C. Antweiler for confirmatory experiments establishing its usefulness.
LITERATURE CITED
(1) Centanni, F. A., Ross, A. M., De Sesa, M. A., ANAL.CHEM.28,1651 (1956). (2) Grimaldi, F. S., May, Irving, Fletcher, M. H., U. S. Geol. Survey, Circ. 199 (1952). (3) Michelson, C. E., U. S. Atomic Energy Comm., HW-36831 (1955). (4) Price, G. R., Ferretti, R. J., Schwsrtz, Samuel, ANAL.CHEM.25, 322 (1953). (5) Sadowski, G. S., Gentry, J. R.,
Hemphill, H. L., Clinton National Laboratory, CNL-23 (1947). (6) Thatcher, Leland, U. S. Geological Survey, oral communication.
( 7 ) Zimmerman, J. B., Canada Dept. Mines Tech. Surveys, Mines Branch, Memo. Series 114 (1951). (8) Zimmerman, J. B., Rabbits, F. T., Kornelsen, E. D., Canada Dept. Mines Tech. Surveys, Mines Branch, Radioactivity Div., Topical Rept. TR-122/53 (1953).
PITTSBURGH Conference on Analytical Chemistry and Applied Spectroscopy, February 28 to March 2, 1956. Publication authorized by director, U. S. Geological Survey. Part of investigations undertaken by the Geological Survey on behalf of the Division of Raw Materials, U. S. Atomic Energy Commission.
Protein Determination for large Numbers of Samples Gail Lorenz Miller, The Pioneering Research Division, Quartermaster Research and Engineering Center, Natick, Mass.
Rosebrough, Farr, and RanL dall's procedure for colorimetric determination of protein [J.Biol. Chem.
samples and reagents a t 50" C. accelerates development, reducing the time to minutes.
193, 265 (1951)] is particularly convenient when only a few samples are deter.2 mined at one time. Two modifications in procedure make it possible to determine large numbers of samples. Use of a comparatively smaller volume of more concentrated alkaline copper reagent and a larger volume of more dilute Folin phenol reagent permits introduction of a proportionately larger volume of phenol reagent with sufficient force to ensure adequate preliminary mixing, and final mixing can be postponed until after the reagent has been added to all the samples. Heating the final mixtures of
One-milliliter aliquots of alkaline copper reagent composed of 10 parts of 10% sodium carbonate in 0.5N sodium hydroxide and 1 part of 0.5% copper sulfate in 1% potassium tartrate are added to I-ml. aliquots of protein solution in colorimeter tubes 14 mm. in outside diameter. After the mixtures have stood for 10 minutes, 3-ml. aliquots of a 1 to 11 dilution of Folin phenol reagent are added to the samples as forcibly as practicable. The mixtures of samples and reagents are heated for 10 minutes a t 50" C. in a constant temperature water bath. After the mixtures are cooled to room temperature, absorbance is read at wave lengths of 540 to 750
OWRY,
mp, depending on the sensitivity required. For addition of the alkaline copper reagent and the Folin phenol reagent, hand-operated plunger-type pipets or motor-driven automatic pipets are very useful. With automatic pipets, glass instead of stainless steel valves are required when the phenol reagent is used, because of the problem of corrosion. Entirely analogous results were obtained with bovine serum albumin and with gelatin, although, as expected, the color with gelatin was about half that with bovine serum albumin. The reproducibility of analyses over the range of 0.04 to 0.20 mg. of protein in the modified test is, on the average, to 2%, essentially the same as in the original test.
Automatic Multistage Semimicro Zone Melting Apparatus A. P. Ronald, Chemistry Section, Fisheries Research Board of Canada, Technological Station, Vancouver, 8. C.
technique of zone melting, the mathematics (1, 9) and principles (8) of which have been adequately described, is not entirely new in metallurgical purification (8, 9, I S ) , b u t is relatively new in organic chemistry. Rock (11) has purified benzene; Hesse and Schildknecht (6),fatty alcohols; and Handley and Herington (S), benzoic acid, pyrene, anthracene, and crysene. The limited success of chromatographic techniques in the sterol field suggested that a suitable apparatus might make zone melting applicable to problems in this laboratory. This method for purifying organic compounds requires that a narrow molten band travel slowly down a vertical column of the solid substance in a glass tube; impurities are separated and normally concentrated a t the bottom of the column. A horizontal THE
964
ANALYTICAL CHEMISTRY
tube may be used in metallurgy (b), but in organic separations when the molten zone passes and the material crystallizes the solid drains away from the side of the tube and seeps back. No available apparatus (3-7, 11, 1.2) was entirely suitable for the purpose. An automatic macromodel (6) was investigated, b u t the disengagement of the drive motor b y the system of pawl and ratchet was not clearly understood, and i t did not appear suitable for adaptation to a micro scale. A zone melting apparatus could have been modified b y changing the heater carriage to a sample carriage and building a bank of heaters through which the sample tubes could pass, b u t the apparatus described here was completed before the advertisement appeared (10). An apparatus ( 7 ) apparently similar to the commercial one has been described, but
the mechanical operations are different. The apparatus described here is cheaper, smaller, and self-contained. PRINCIPLE
OF OPERATION
The apparatus (Figure 1) consists of a drive motor which raises a platform
that supports four tubes containing the material to be purified. As the platform rises, the tubes pass through a heater which creates a well defined molten zone of material. The molten zone passes slowly down the column to the bottom. The platform reverses, travels quickly to its starting position, and again commences its slow ascent. The slow drive speed for raising the platform is attained b y a synchronous motor with a drive shaft speed of 120 revolutions per hour. This is reduced by external gears to 20 revolutions per hour. The last reduction is b y a bevel gear with a n internally threaded hub
