,ooo
Figure 3. graph
I N D E X LINE
Example of folded nomo-
The device appears to have certain operating advantages over the nomograph compasses described by Van Nes
and Van Westen ( 3 ) . Essentially, their guide consists of two opaque straightedges connected by a n open-center hinge fitted with a transparent windon-, which has cross hairs that mark the intersection of extensions of the two index lines, regardless of the angle subtended. Simultaneous setting of the first arm upon three values is requiredthe straightedge passes through the proper values, in the present example, of n D and d, while the intersection of the cross hairs must fall upon the y axis. Once this first arm is properly placed, it is held in position while the second arm is rotated until its edge crosses the proper value of 111; the corresponding value of per cent C E is then read. After the nomograph compass has been placed in its final position, a check reading on all five axes is possible. The present device is trans-
parent, and the initial setting is made on only two points rather than three simultaneously. If one is willing to forego the latter convenience, the spool can be fitted into a closely fitting circular hole rather than the slot, simplifying the machine work required for construction. LITERATURE CITED
(1) Allcock, H. J., Jones, R. J., “The Nomograph,” 3rd ed., p. 40, Sir Isaac Pitman &- Sons, London, 1946.
(2) Davis, D. S., “Empirical Equations and ,h;omography,” p. 125, hlcGrawHill, New York, 1943. (3) Tan Nes, K., Van Westen, H. A,, “Aspects of the Constitution of Rlinera1 Oils,” p. 347, Elsevier, Amsterdam, 1951.
PUBLICATION 159, Exploration and Production Research Division, Shell Dewlopment Co., Houston. Tex.
Machine for Preparing Phosphors for the Fluorometric Determination of Uranium R. E. Stevens, W. H. Wood, K. G. Goetz, and C. A. Horr, U. S. Geological Survey, Denver, Colo.
of uranium are S usually determined by measuring the fluorescence of a sodium or lithium M ~ L L QUASTITIES
fluoride-uranium phosphor. A serious handicap has been the difficulty of preparing the phosphors. When the flux is melted by manually holding a container of platinum or gold over a n open flame, conditions of heating and cooling cannot be readily duplicated and fluorescence may vary widely. Sadowski and Gentry ( 5 ) describe a fusion rack which prepares one phosphor a t a time over a flame. Racks for preparing a large number of phosphors at one time have been used (1, 4, 7 , 8 ) . The equipment consists of a single large burner over which 20 small dishes ( i/le-inch internal diameter) containing uranium and flux can be heated at once. There is no adequate provision for stirring the melt. Variations in heat over different parts of the burner and in cooling rate from outside to inside positions are compensated by random arrangement of the unknowns, standards, and blanks. Although these racks are suitable for use with small dishes, they are not practical for supporting a large number of the larger dishes used by many laboratories. Thatcher has designed a support for preparing three phosphors at a time in a muffle furnace (6). The melts are swirled by a n externally mounted motor, which swings the support for the dishes in the furnace. Preparation of the phosphors in a muffle furnace is not completely satisfactory, however. because of the greater solubility of the platinum in the flux in the oxidizing 962
ANALYTICAL CHEMISTRY
atmosphere of the furnace, with consequent variability of results, as recognized by most users of the fluorometric method for uranium. Recently Michelson ( 3 ) described a device for dran-ing the dish through a n electric tube furnace or burner a t a repeatable rate. The machine described here was designed for use in the procedures described by Grimaldi, May, and Fletcher (2), in which 2 grams of flux (45.5 parts by weight of sodium carbonate, 45.5 parts by weight of potassium carbonate, and 9 parts by weight of
sodium fluoride) are used for making the phosphor, with platinum dishes of 38mm. inside diameter. The 4-mm. flat lip around each dish holds the dish in a horizontal position in the mountings provided in the machine. Phosphors prepared a t one time in the machine show good reproducibility and separate runs show good agreement, \There precise values are wanted, each run can be standardized by including blanks and phosphors of known uranium content. The machine eliminates the tedious hand preparation of phosphors
-
1
Figure 1.
Cutaway drawing of machine in inclined position
Showing motor, mounting of dishes, inclining lever, etc., but only parts of dishes and mounting rods
and makes possible a significant increase in the number of samples run per unit of time by the method. Operation requires little skill. Preparation of phosphors with the machine is more than three times as rapid as preparing them one a t a time by hand. Results are generally free from gross errors arising in the fusion process. DESCRIPTION OF MACHINE
The essential feature of the machine is a metal plate which revolves above the ring burner a t a fixed height and speed, with fused-silica rods mounted at the edge of the plate to support the platinum dishes. The upper and lo\Ter base plates are 201/2 X 201/2 X l / 4 inch aluminum, hinged together as shown in Figure 1. Ten-inch ventilating holes are cut in the upper and lower base plates, with an uncut segment in the upper base plate for mounting the motor. A lever, pivoted a t A , running to a stop, R, inclines the machine during the fusion period. The dish-mounting plate is machined from an aluminum casting to 83/4-in~h diameter, with a 11/4 X 23/4.inch hub for attachment to an electric motor. A zo-hp., 110-volt alternating current motor rotates the dish-mounting plate, by means of a gear box, a t 10.8 r.p.m. X inch, are atCable clamps, tached to the upper surface of the plate for clamping the fused-silica mounting rods for the dishes. The ring burner is formed from standard 'j2-inch nater pipe in a circle 11 inches in diameter, and the ends are nelded. Slots, 25 Inch wide, '4 inch deep, and spaced 1 inch apart, are cut on the upper surface of the ring. The valve assembly from a Fiqher burner is n elded to an opening on the bottom of the ring burner. The burner is held ', 8 inch belon the dish-mounting plate and centered by adjustable amounts. TIYOgas inlets are provided (Figure I), one with unrestricted f l o ~for initial melting of the flux and the other n i t h an adjustable needle valve for heating the flux a t or near its melting point. The gas is diverted to the latter inlet by means of the valve handle a t the front of the machine. The machine is encased in a metal box extending 2 inches above the ring burner, with a 161/2-inch diameter opening in the top. A cover prevents contamination when not in use. If the gas pressure is too low. an estra gas inlet is added. The manner of fastening the 3-mm. fused-silica mounting rods to the dishmounting plate is shown in Figure 1. The long arm of one L-shaped rod (3 inches long with a right-angle 1-inch arm) is placed under a cable clamp, the rod parallel with the radius of the dishmounting plate and extending out so that the center of a dish, when mounted, is centered over the ring burner. It is securely fastened with the short arm
HAND PREPARED
I.'
MACKINE PREPARED-2
n
:h I
65
70 75 FLUOROMETER SCALE READINQ
80
Figure 2. Reproducibility with handand machine-prepared phosphors
extending to the right in the same plane as the surface of the plate. A straight 3-inch rod is then clamped to the right of the L-shaped rod, so that the bowl of the platinum dish fits the opening b e h e e n the rods with a slight amount of play. The lips of the dish rest on the fused-silica rods. The remaining pairs of rods are similarly clamped in position, with equal spacing around the circumference of the dish-mounting plate, and all dishes equidistant from it. (For each dish to fit all positions precisely, the dishes should be shaped frequently to exact size with a wooden shaping mold .) ADJUSTMENT OF FLAME
The high and low flames of the burner are first adjusted to the proper height; no further adjustment is normally needed. With the machine in the horizontal position, 18 dishes, each containing 2 grams of flux (discarded phosphors can be used) are mounted in the machine. Tlie'niotor is turned on. The flame indicator a t the front of the box is turned to the high position, the aperture on the right of the box opened, the ring burner lighted, and the aperture closed. After the flux has sintered, the machine is put in the inclined position. The Fisher burner valve under the ring burner is adjusted so that the flux in the dishes melts completely in 1 to 2 minutes. The flame indicator is then turned to the low position, and the low adjustment screw, at the left of the box, is adjusted until there is a continuous small cloud of crystals in the molten flux. OPERATING PROCEDURE
Place the 18 platinum dishes, each containing 2 grams of flux and uranium to be measured, over the ring burner with the machine in the horizontal position. Turn the motor on to rotate the dishes around the ring burner. Open the door a t the right side of the
box, turn the flame indicator t o the high position, light the burner, and close the side door. Note the time. Continue heating in the horizontal position until the flux is \Tell sintered, then place the machine in the inclined position by pulling the positioning lever a t the right of the box until the stop is reached Continue heating a t full heat until most of the flux in the dishes has melted. Turn the flame indicator to the low position and continue heating until 5 minutes have elapsed from the time the flame was lighted. (Operating a t the full heat of the ring burner during the entire heating period gave someivliat more erratic results.) Turn the flame adjustment to high. Immediately return the machine to the horizontal position with the positioning lever, and turn off the flame. Continue rotation of the dishes over the ring burner during a 10-minute cooling period. Remove the dishes and read the fluorescence of the phosphors with a fluorometer. ADAPTATION TO DISHES OF DIFFERENT DEPTH
K i t h the dish described by Grimaldi, May, and FlQcher ( 2 ) and with 2 grams of flux, the molten flux reaches nearly to the edge of the dish and covers the center when the machine is in the inclined position. This allows the molten flux to reach all surfaces in the dish, as the dishes revolve n-ith the machine inclined. This is not so with deeper dishes, and design of the machine has to be changed for complete solution of the uranium in the dish into the molten flux. ii second lever gives a steeper angle of inclination to the machine, so that the molten flux can reach nearly to the edge of the deeper dishes. -1. suggested routine n i t h a machine modified for deeper dishes, following preliminary melting of the flux, would be to heat for 1 minute in the lower inclined position with the molten flux reaching the center of the dish, heat for 1 minute in the higher inclined position n ith the flux reaching nearly to the edge of the dish, heat another minute in the lower inclined position, raise the flame to full heat, put thP machine in the horizontal position, turn off the gas, and cool. COMPARISON OF PRECISION OF HANDFUSED AND MACHINE-FUSED PHOSPHORS
Comparisons of hand fusion and machine fusion, made by a number of laboratory n orkers, showed a definite improvement in repeatability when a machine n as used. Figure 2 compares results after hand preparation and machine preparation of phosphors. These represent runs made in sequence, each of 18 phosphors (three blanks in each run are not shown), to illustrate repeatability of each method of preparation of phosphors containing 0.05 y of uranium. The VOL. 31, NO. 5, MAY 1959
963
machine-prepared phosphors showed better precision than those prepared by 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
O ~ Y ,
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.
T"" 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 ) , but 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
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, but the disengagement of the drive motor by the system of pawl and ratchet was not clearly understood, and it did not appear suitable for adaptation to a micro scale. A zone melting apparatus could have been modified by changing the heater carriage to a sample carriage and building a bank of heaters through which the sample tubes could pass, but 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 by 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 by a bevel gear with a n internally threaded hub
