March 15, 1941
203
ANALYTICAL EDITION
mm. oil-immersion fluorite objective in a short (metallographic) mount. The objective must be specially selected for freedom from birefringence. An analyzer is used in the microscope for visual examination, and the stage is rotated in order to observe reflection dichroism. For microspectrographic work, the Wollaston prism serves as an analyzer. The vertical illuminator is used without a polarizer for this work. This particular aspect of the optics of strongly absorbing crystals is worthy of further study by the chemical microscopist, as the surface color of such crystals is independent of their thickness.
Acknowledgments I n conclusion the author wishes to thank H. D. Babcock for the gift of a speculum grating, J. L. Houghton and Max Wiedling for valuable assistance in the constmotion of the microspectrograph, Fred Lee for the gift of a specially worked
sapphire disk, and L. G . S. Brooker and Frances M. Hamer for many splendid specimens of strongly absorbing crystals.
Literature Cited
(1) Chamot,
e. M., and Mason, C. W., “Handbook of Chemioal
Microscopy”, 2nd ed.. Vol. I. pp. 183-6,N e w York, John Wiley & Sons, 1938. (2) Jelley, E. E., J . Roy. Mieroscop. Soc., 54, 234 (1934). (3) Ibid.. 56, 101 (1936). (4) Jelley, E. E., Nature, 136,335 (1935). (5) Jelley. E. E., Phot. J., 74, 514 (1934). (6) Kuns, A. H., and Spulnik, J., IND. ENQ.Cmaa., Anal. Ed., 8. 485 (1936). (7) Spedding, F. H., J . C h m . Phys., 5, 160 (1937); Phys. Ra., 50. 574 (1936). (8) Wooster, W. A., “Crystal Physics”, Cambridge, England. Cambridge University Press, 1938. P n s s s ~ before ~ ~ o the Division of Mieraohemistry at the 100th Meeting of the American Chemical Society, Detroit. Mich. Communication 781 from the Kodak Researoh Laboratories.
An Electric Heating Mortar For Use in Carbon and Hydrogen Microcombustions G. FREDERICK SMITH AND WM. H. TAYWR
University of Illinois, Urbana, Ill.
T
H E heating mortar usually employed in carbon and hydrogen microcombustion analyses has not proved entirely satisfactory, as this glass heating device containing boiling cymene with an air-cooled reflux condenser and gas microburner is both fragile and cumbersome. Another disadvantage is insufficient variability of temperature adjustment. This type of heating mortar has been improved upon by Schneider and Van Mater (2), who use electrical heating with thermostatic control. A second improved electrically heated and thermostatically controlled heating mortar, known as the “micro thermostatic sleeve”, is now commercially availahle (f). The present discussion bas for its object the description of an electric heating mortar, thermostatically controlled, which is compact, simple in construction and operation, and
FIQUEE 1. HEATING MORTAB
at the same time provides constant temperature control over a comparatively wide range of temperatures. For the most part standard units of laboratory equipment are used. The construction of the remaining parts involves simple machine
tool manipulations. InFimre 1theheatinemortarwith thermometerwell.thermam-
bridae. Mass.). shown at D, may be replaced by
a suitable lamp
The mart&-sectioned diagram (Firmre 2) shows details of the
The b&d of the h e a t h mortar is gem. long with the screw w p .&own at The It,fr full\ extended nnd is 48 mm. in outside cli3mrter. The 1,oIe nt e k l i end nnd through thr griphire disk* nre II mm. in hruerrr. Tlie rleetrienl rontdctd for ntruciinreiit of the thermostatic control switch are 4.5 mm. in diameter and extend approximately 15 nun.from the body of the heating mortar, with a 1-cm. space between. The casing of the heating mortar serves as one electrical contact, and the brass shoulder at the left of the Transite disk insulating ring at the exit end serves a8 the other electric contact. The side N& of the barrel of the heating mortar are insulated by use of a Transite tube &s shown. The electrical circuit is thus through the easing (using the right-hand lug which is insulated from the casing) into the resistors and out through the right-hand “Anyheat control” lug. (According to the assembly as described, if the electrical contacts of B are not checked a short circuit may n m l t between the operator and a ground connection. This point should be checked, using a voltmeter, and reversing the contacts either at the power supply line or the thermostatic control switch from the transformer, so that no short circuit will he possible.) The carbon disks (Figure 2) are 37.5 mm. in diameter and 1.5 nun. thick (Allen-Bradley Co., Milwaukee, Wis., Type E2910 rheostat uaphite disks). A sufficient number are slotted as shown, to-provide for an opening below the thermometer tube. The Nichrome resi8tors we 37.5 mm. in diameter and are made from 3-nun. wire cut from asuitable wound helix.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
204
setscrew as shown, for adjustments in height. All soldered connections are made with silver. The carbon disk resistors in the middle portion of the mortar provide for the production of less heat energy than that from the Nichrome rings at either end, which brings about an equal heat distribution not attainable if all heatin elements are either the whole mortar is graphite or Nichrome. The resistance diminished or increased in proportion to the tension applied by adjustment of the screw cap. The "make" and "break" of B may be adjusted by altering the position of the adjusting knob to higher or lower temperatures. The Variac control is powered by the regular 110-volt laboratory power source. It is used over the voltage range 5 to 15 volts and supplies the third heat control. The thermometer is an Anschdtz type having a range of 150" to 220' C. Temperatures at the thermometer well in the middle of the heating mortar can be readily adjusted at any point between 150" and 220" C. and maintained constant within 1' to 2". variation from center to extreme ends can be kept belowTht 5 temperature gradient.
07
ll
Carbon D k k
FIGURE 2. DETAILS OF CONSTRUCTION The thermometer tube is 18 mm. long, 1 cm. in outside diameter, and of 6-mm. bore. The tripod upright is 55 mm. long, and of 6-mm. diameter to provide a slip joint with 55 mm. of the same tubing as that used for the insertion of the thermometer. The heating mortar is supported in contact with it by means of a
The heating mortar described has been used for 6 months in the authors' microchemical laboratory a t the University of Illinois with perfectly satisfactory results and its life span should be practically endless, without need for further adjustments. The temperature at which it is operated does not alter the carbon-to-Xichrome resistance contact in a measurable degree. The heating mortar has been operated continuously for 30 days with no change required in its three temperature-adjusting variables; during this period there was no change in temperature that could not be attributed t o changes in room temperature.
Literature Cited (1) Fisher Scientific Co., Laboratory, 10, KO.4, 68 (1939). (2) Schneider and Van M a t e r , IXD. EXG.CHEM.,-4nal. Ed., 9, 295 (1937).
Volumetric Flasks for Microanalysis EARLE R. CALEY Frick Chemical Laboratory, Princeton University, Princeton, N. J .
W
HEN solutions are mixed in small volumetric flasks of the
usual design, the error caused by the trapping of pure solvent or partly mixed solution in the ground glass at the stoppered end of the flask is proportionately much greater than that caused by the same source of error in large flasks. Moreover, thorough mixing of solutions in conventional flasks of 5- or 10-ml. capacity is difficult to accomplish rapidly. Both this source of error and this lack of convenience in mixing are avoided by the use of flasks of the design shown in the figure. I n such a flask the upper part has a capacity about five times that of the calibrated part, so that after the solution is made up to the mark it may be passed into the upper part by tipping the flask on its side. Then by righting the flask and at the same time giving it a slight circular motion the liquid is caused to swirl as it passes back into the lower part. By repeating this about three times the solution is thoroughly mixed. The sides of the calibrated lower part should slope more than in flasks of the usual design, in order that the liquid may be entirely, or almost entirely, transferred to the upper part without coming into contact with the upper neck. The neck of the calibrated part may be made slightly smaller in diameter than the neck of conventional flasks, with a corresponding gain in accuracy of measurement. For use with aqueous
-
This disadvantage is of no significance if such a flask is habitu-
