DECEMBER 15, 1940
ANALYTICAL EDITION
flask upon which the refractory material was to be plastered (Figure 1, center and right). A conduit for the terminal ends of the resistance wire (Figure 1, center) was formed by 3.75-em. (1.5-inch) lengths of 6-mm. Pyrex tubing. Refractory material-Hitempite, Quigley Co., 56 West 45th St., New York, N. Y., a plastic used for binding firebrick in furnaces-was plaqtered over the assembly in four separate layers. Time was allowed after each application for drying, and between the second and third applications 1.56-mm. (0.067-inch) braided asbestos tubing was used for reinforcing material. The total thickness of the four layers of fire clay was approximately 3.1 em. (1.25 inches). The heating unit was removed from the flask by cutting the longitudinal wires and filling the flask with hot water to melt the paraffin. The wires still in place were removed after cutting the threads attaching them to the heating coils. The assembly was then placed under a hood, and a small current passed through each heating coil to volatilize the remaining paraffin and further dry the fire clay. (Care was taken to remove any small amounts of refractorymaterial from the exposed side of the heating coils IThere
753
they had become entirely encompassed in application.) When the wax had melted away, about two thirds of the outside diameter of each turn of the heating coil was surrounded by refractory material. Thus the coils were held firmly in the heater body. A support was made for the heater from a length of 0.625cm. (0.25-inch) pipe, bent into a circle of proper diameter to fit approximately the outer circumference of the heater a t about half its horizontal height (Figure 1, center). One end was bent to extend laterally from the side of the heating unit and the pipe was cemented into place with sufficient refractory material to make it an integral part of the heater. A clamp can be used to support the heater on a ring stand. Any desired heat output can be obtained within the maximum limits of the heater. Each resistance coil draws 4.5 amperes a t 110 volts, giving approximately 500 watts maximum output per individual unit. The heating coils were arranged so that one, two, or three could be connected into a single lead. The heater also operates conveniently with a 2-liter flask. -4 Bunsen burner can be used to furnish supplementary heat through the 10-cm. (4inch) opening in the base of the heater.
Accurate Measurement of X-Rav Diffraction Films J
HAROLD P. KLUG, University of Minnesota, Minneapolis, Minn.
T
HE accurate measurement of line positions on powder and rotation photographs is a problem in all precision diffraction studies. This problem is complicated by the fact t h a t x-ray lines cannot be subjected t o high magnification, since they then tend t o fade into the background. The usual types of comparators with high magnification are therefore unsatisfactory. Xumerous devices for measuring x-ray films have been described ( 1 4 , and all of them are based on the use of a highly accurate engraved scale or an accurate micrometer screw. The chief problem is t o set the movable pointer or cross hair accurately on t h e edge or center of the line. To accomplish this some have incorporated costly auxiliary equipment such as photometers ( I ) , cathode-ray oscillographs ( 6 ) , etc. The average device for these measurements is thus very costly.
T h e instrument described involves only minor changes
in design, but it has proved t o be simple t o manipulate, sufficiently accurate, satisfactory for both powder and rotation photographs, and economical t o construct, since it requires only standard available parts and simple machine work. The design of the movable pointer, means for holding the films in place, and source of illumination are improved features.
Apparatus Figure 1 shows a line drawing of the complete measuring device. The base is a wooden case, A , with sloping front. A hinged back on the case gives ready access to the source of illumination mounted therein. The light source is a Day Brite fluorescent lamp unit (Westinghouse catalog, No. 8930) with a 2.5 X 45 cm. (1 X 18 inch), I5-watt, daylight Mazda lamp. A piece of milky glass placed between it and the film support results in a very
FIGURE1. MEASURING DEVICE
VOL. 12, KO.12
INDUSTRIAL AND ENGIREERING CHEMISTRY
754
uniform and satisfactory source of illumination. A cheaper, but less satisfactory, light source is a row of "eight in series" white Mazda Christmas-tree lamps behind the milky glass diffusing screen. Particularly with the Christmas-tree lamps, and to a less extent Tvith the fluorescent lamp, some cooling is desirable to prevent the film, scale, etc., from becoming warm and expanding during the course of a series of measurements. Such cooling is achieved by bloiving compressed air through a series of holes in a brass tube, B , running the length of the case. Air holes in the back of the case permit circulation of the cooling air. C is an aluminum alloy (17ST) plate, 46.45 X 12.5 X 0.469 em. (18.5 X 5 X 0.188 inches), attached to the wooden case a t three points. I t has a 2.5 X 35 em. (1 X 14 inch) opening directly over an illuminated slot in the wooden case. A piece of plate glass with its upper surface flush with the surface of C fills this opening, and serves as a support for 2.5 X 32.5 em. (1 X 13 inch) powder films which are temporarily held in place by the spring clips D, a t each end. E is a similar aluminum alloy plate, 46.45 X 8.75 cm. (18.5 X 3.5 inches), hinged to C a t the upper edge. A 1.25 X 35 em. (0.5 X 14 inch) beveled slot in it is centered over the opening in C. E is lifted up for insertion of a film and returned to position. When the film has finally been adjusted to the exact position for measurement it is clamped tightly in position between plates C and E by the removable thumbscrews, 111,which are threaded into C. Plates C and E must be flat and have good surfaces. To ensure this it is well to specify that they be cut by sawing rather than by shearing. The scale, F , is a 60-em. vernier caliper (KO. 122 ?vl, L. S. Starrett Co., Athol, Mass.) graduated in 0.5-mm. divisions and provided with a vernier reading to 0.02 mm. I t is clamped in position 1.875 cm. (0.75 inch) above plate E by the slotted blocks, G, fastened to E. Clamped to the movable jaw is a 2.5-em. (1-inch) 4 X magnifying lens, in a tubular focusing mount, H , for readin the vernier. The vernier is illuminated by a 2.5-volt flashli&t bulb in tube J . One contact is made at the end of J by a flexible wire, K , and the other through the metal parts
of the instrument. A toggle switch on the left end of the case controls the light whose current source can be two dry cells or a small transformer. 9 rectangular lens would give a slightly better field in reading the vernier. The movable jaw was also drilled at L and provided Ivith setscrem for holding a pointer, P , in place. In Figure 1 is shown a detail of P , which is used in the horizontal position. The angle of the point should not be too sharp nor too broad-approximately 15' has been found satisfactory. The tip of the pointer should not end in too sharp a point but should be slightly dull. The pointer is adjusted to be just the thickness of a thin sheet of paper above the film, thereby preventing parallax errors. With this type of pointer and a low-power reading glass it is possible to set on the edge or center of a line x i t h ease and accuracy. For example, in determining the position of the undeviated beam image on a powder film a single setting was made on the center of each of five pairs of lines symmetrically situated xyith respect to the exit beam. These measurements gave for the position of the beam image 36.308, 36.308, 36.306, 36.305, and 36.307; average, 36.306. Rotation films are inserted in the device and shifted to bring successive layer lines into position for measuring.
Acknowledgment The author takes pleasure in acknowledging the helpful auggestions and excellent workmanship of Floyd 0. Grapp, instrument maker, in the construction of this instrument.
Literature Cited (1) Jette and Foote, J . Chem. Phys.,3,605 (1935).
( 2 ) Owen and Pickup, Proc.R o y . SOC.(London),137, 397 (1932). (3) Schlossberger, 2. Krist., 98, 259 (1937). (4) Straumanis and Mellis, 2. Physik,94, 184 (1936). (5) Tatel and Hultgren, Rea. Sci. Instruments, 9, 47 (1938).
A Centrifuge Cooling Unit H. L. WUNDERLY A X D L. s. SMELO Renziehausen Diabetic Foundation, Children's Hospital, Pittsburgh, Penna.
S
OMETIMES it is desirable to keep liquids 5" to 10" below room tem-
perature during centrifuging. For those lacking a refrigerating unit a n attachable cooling unit utilizing solid carbon dioxide may prove satisfactory, Such a unit was devised in this laboratory for the centrifuge (International Equipment Company, size 1, type SB centrifuge). The unit (Figure 1) consists of a metal container, 9 inches in diameter and 2.5 inches deep, within which is a short copper coil (gas stove copper connection) the open ends of which project through the centers of the top and bottom of the container. The coil is held in place by solder where it is inserted through the bottom of t,he container. The unit is packed with solid carbon dioxide by removing the lid. Then it is assembled and adjusted to t,he underside of the lid of the centrifuge by the threaded end of the copper coil, which projects through both the lid of the container and the lid of the centrifuge and is held firmly by means of a metal nut. Sufficient clearance must exist between the cooling unit and the head so that there is no possibility of the centrifuge tubes coming in contact x-ith the cooling unit. A metal brace to fit around the container gives support to the unit. If the lid of the centrifuge does not fit firmly on the protecting case when enclosed, insulating with adhesive tape adds to the efficiency of the cooling process.
The temperature attained in the centrifuge is dependent on the quantity of solid carbon dioxide placed in the container and the temperature of the laboratory. OF COOLIXG GXIT TABLE I. EFFECTIVENESS
(During 10-minute periods of centrifuging water initially cooled t o 20') F i n a l Temperature of Water F i t h cooling unit a t Without cooling unit a t room temperature of room temperature R. p. m. 28' C of 29' C.
FIGURE 1. COOLING UXIT Above. Below.
Adjusted t o centrifuge lid Disasaembled
1100 1800 2400 2800
28.0 29.0 30.0 32.0
20.5 20.0 21.5 21.5
