Comm., Rept. AECD-2738,138 (August
(15) Walter, J. L., Freiser, H., ANAL. CHEM.24, 984-6 (195"). (16) Wilkinson, G., Grummitt, W. E., Nucleonics 9 (KO. 3), 52-62 (1951).
1949). (7) Nordling, W. D., Chemist Analyst 45, 44-5 (1956). (8) Rulfs, C. L., Przbylowicz, E. P.,
RECEIVED for review- February 12, 1959. Accepted June 19, 1959. Division of Analvtical Chemistrv. 134th Meetinn. ACS; Chicago, Ill.," ' September 195i: Work supported in part by the U. S. Atomic Energy Commission.
Skinner, C. E., ANAL.CHEM.26, 408 (1954). (9) Salteman, B. E., Ibid., 25,493 (1953). (10) Sandell, E. B., IND.ENG.CHEM., ANAL.ED. 11, 364 (1934).
Melting Point Apparatus for Simultant,,, of Samples in Transmitted and Reflecl H. E. UNGNADE, E. A. IGEL, and 6. B. BRIXNER University of Cofifornia, 10s Afamos Scientific Laboratory, Los mIuIIIyJ,
b A melting point apparatus utilizes an electrically heated copper block and an optical system which projects both transmitted and reflected images of the sample side b y side on a rear projection screen. It is particularly suitable for use with explosive materiols.
T . .
copper block . apparatus for determining capillary melting points has been used extensively since its introduction in 1927 ( I ) . Various suggestions have been made for optical systems t o facilitate observation of the sample (3-4). The use of light sources, lenses, screens, etc., has made it possible to observe enlarged images of the sample either in transmitted or in reflected light. It is often desirable, however, to observe both transmitted and reflected images simultaneously for a complete study of the phase transition during or prior to melting. The apparatus described below was constructed for this purpose. HE
Figure 1.
Melting point appc
Copper block pulled out and resting on 3plit-ring top of lamp housing removed
1432
-
ANALYTICAL CHEMISTRY
,",
APPAR L
U
~ucw
ULUULL~
pumb apparaiuv
shown in Figure 1 consists of an electrically heated copper block insulated by a Transite housing, a 200-watt light source, and an optical system which permits the 1OX enlarged images of the melting point tubes to be viewed on a 5 X 6 inch screen with normal room illumination. It is portable and self-contained. All power units for heating and lighting, as well as their controls, are found in and on a single aluminum housing. The melting point block is a stepped copper cylinder, 3 inches long by 2'/$ inches in diameter, which has a '/rinch long indexing flange. The periphery of this flange contains a '/16-inch wide X %&nch deep slot into which fits a '/,Anch diameter index nin t o alien
mis nange, m e diameter of the block is 2l/4 inches for a length of 23/, inches. A 3/r-inch diameter hole (the optical cavity) was drilled through the block, perpendicular to the axis of the cylinder and 3 / n inch from the bottom-i.e., the end away from the index flange. The optical cavity is sealed by I-mm. thick quartz windom, locked into position by snap rings. On the axis a t the bottom of the block there is a 24 hole tapped through to the optical cavity. A 3/s-24 bolt is fitted into the tapped hole and affords an adjustable base or platform on which the melting point tubes rest. Two '/&ch diameter X Z8/,inch long holes were drilled from the bottom of the block to accommodate two stainless steelsheathed Chromalox heaters (Edwin I,. Wieemtl C n ) ~Cnt.nlnp No m2-c
housing, to allow precise focusing of the discrete particles within the melting point tubes. The beam splitter is chosen so as to reduce the illumination of the transmitted images to the level found on the reflected image side of the screen. This beam splitter as well as the melting point block windows, Ti-hich are tilted a t an angle of 7" to the optical axis, minimize undesirable background illumination and flare spots a t the reflected image side of the projection screen. These precautions help to give a clean pictorial presentation on the screen as shown in Figure 3. DISCUSSION
Figure 3. 1OX images of melting point tubes on projection screen with solid, liquid, and two-phose samples eitch
of 75-watt capacity. Three holes, 0.U78-inch diameter, were drilled from the top of the block to the optical cavity. These holes are on 0.100-inch centers and accommodate three 1-nun. diameter melting point tubes. Also at the top of the melting point block is a precision thermometer m l l extending Z a / 4 inches deep and 2 thermocouple wells, one of which extends la/,inches deep, and the other, drilled at 30" to the axis of the block, opens into the optical cavity to allow a thermocouple to he placed in contact with the melting uoint tubes at the center of the ontical cavity. The entire block can be lifted out of its Transite housing by the attached loop handle and set on a split-ring support for cooling or cleaning, Upon replacement, the block is indexed for optical alignment, and in this position the optical cavity is parallel to the viewing screen and thus affords maximum protection to the viewer. This block may be heated to a maximum temperature of 300" C. by the two Chromalox heaters which are powered from a Standard Electric Time Co. variable transformer (0-135 volts alternating current, 3-ampere maximum), thus enabling t he user to control the derivative of the block's tempera ture-time function
by setscrews which lock into the lamp base. This housing is soldered to a Z'/,-inch diameter tube which acoommodates the projectioh optics. The entire uroiection svstem is bolted to the
variable transformer (0-135 volts alternating current, 3-ampere maximum) and by forced-air cooling supplied by a 120-volt alternating current 25-watt bloner. This blower is operated off the lamp transformer and is mounted directly on top of the lamp housing (not shown in Figure 1). The optical system (Figure 2) is designed to avoid excessive waste of light and unequal magnification of the images. The melting point tubes a x illuminated by a large aperture condenser system, comprising the light source, a $/,inch focal length by 2inch diameter reflector, two 3.3-inch focal length by 2-inch diameter condensing lenses, and a Corning No. 4600 low infrared transmission filter (Corning Glass Works). The converging cones of light from the condenser are reflected into the optical cavity of the block and on t o the melting point tubes by a mirror a t 45" to the principal ray of the projection and condenser system. The filament of the projection lamp is imaged on the projection lens, a Zinch focal length f/3.5 anastigmatic trip1let. ' The light reflected from the melting point tubes returns to the mirror a ippasses through the umilvered, ell'nd tical, central section in an f/5 be;&m which is then picked up hy the proj ect,d tion lens. The light transmiti._ through the melting point tubes is picked up by the other projection lens after passing through the beam splitter a t 45" to the principal ray of the projection system. The images from both projection lenses are folded by mirrors which in turn relay the images onto a 5 X 6 inch Kodak black rear-projection screen (Eastman Kodak Co.). The enlarging lenses are coupled by gears and shafts to knobs, located on the sides of the melting point apparatus
Temperatures in the melting point block and in the optical cavity have been determined with an iron-constantan thermocouple encased in a thinwalled borosilicate glass capillary. Over the range of 30' to 300" C. these temperatures did not differ by more than 1" C. It is concluded that local radiation heating of the melting point tubes by the projection system is trivial. For the determination of melting p0int.s a total-immersion thermometer was used and the apparatus was calibrated hy determining the melting points of a series of Kofler hot-stage melting point standards. The corrections were 0' at 149" C., -2" at 40" C., and $2' at 310" C., and most of the experimental points from a large number of determinations could be fitted to a straight line. The apparatus has performed satisfactorily for several months, and none of the optical and electrical components have shown any deterioration after having be, peratures ACKNOWLEDGMENT
The authors acknowledge the expert technical assistance of W. T. Wynne for the mechanical fabrication of this instrument, of T. E. Deem for the fabrication and assembly of optical componente, and of C. C . Cummings and C. A. Lehman for the preparation of drawings and illustrations. LITERATURE CITED
Bed, E., Kullmann, A,, Ber. 60B, W., Bioehem. Z . 209, 65 n, C. F., Chem. Fabrik 7, I.
RECEIVED for review February 27, 1959. Accepted April 17, 1959. Work carried out under the auspices of the U.S. Atomic Energy Ca
VOL. 3 1, t.
