JULY 15, 1936
ANALYTICAL EDITIOK
second layer of asbestos is put on in a similar manner and the remaining 60 em. (2 feet) of wire are wound back with wide spacing so that both leads come out on the same side. Finally a top layer of asbestos is put on. Connections are made to brass clamps shown in Figure 2. The current is controlled by a 200ohm rheostat of 3-ampere capacity or by an auto-transformer. Capillary melting point tubes are of conventional size and sufficiently long t o extend at least 0.93 em. (0.375 inch) below the top of the sleeve. They are supported by small steel clips of a type commonly used for display purposes, clamped t o short lengths of 0.3-em. (0.125-inch)thin-wall rubber tubing. The tube is slipped in one of the holes in the cap and guided through a platinum loop. The thermometer is supported by a narrow rubber band fastened near the tor, and rests on the central tube of cap F . INTERNAL HEATING.For this Dumose 180 em. (6 feet) of No. 32 B. and S. gage wire with a resihaice of 0.33 ohm per'cm. (10 ohms per foot) are wound into a spiral, annealed at red heat, and inserted in the curved portion so that one lead comes out the tube at the back (shown in Figure 2, but not in Figure 1) and the other comes out at the lip under cap F. In this case about 200 watts are ample for heating the tube and the same controls may be employed as above.
Operation The apparatus described is suitable for the conventional short Anschdtz enclosed-scale thermometers, but the over-all dimensions are not critical and may be varied over considerable limits. Sulfuric acid is added to a point level with the top of the upper horizontal connecting tube and the stirrer operates a t a speed just below the point a t which cavitation occurs. Using two identical thermometers and a special sleeve without platinum loops, the temperature difference between points 0.62 cm. (0.25 inch) from the top and bottom of the sleeve was measured a t equilibrium conditions and was found to be approximately +0.025" C., or within the limits of accuracy of the thermometer reading. There was no observable lateral deviation from the center of the tube to the sleeve wall. Without the sleeve, however, the vertical deviation was about 0.2" and the lateral deviation from the center of the tube to the wall was considerably greater, depending on the closeness of the outer thermometer to the wall of tube
A. With external heating the bath rose from 40" to 200' C. in 7 minutes and t o 280" in 14 minutes. If the tube was externally heated a t the maximum rate and the current shut off atj loo", the temperature rose 7", while a t 250" it rose about 1". With internal heating a much smaller amount of power raised the temperature over the same interval in about 12 minutes and the maximum overshoot was only about 1' or 2". The highest temperature reached with concentrated sulfuric acid was about 295" C. and a t this point smooth, steady ebullition took place without bumping. With Nujol paraffin oil as the bath fluid and heating internally with a 200-watt element, the temperature rose to about 310" C. Unfortunately the oil darkened rapidly and other organic fluids behaved similarly. The rheostat was calibrated for the equilibrium temperatures reached after about 0.5 hour a t a setting and this greatly facilitates subsequent determinations. The rate of rise may be readily controlled by setting the rheostat a t a pwdetermined number of degrees above the thermometer temperature, while maintaining this difference by continually decreasing the resistance. Gas heating also gave satisfactory results. I n this case the tube was heated a t the curved portion, E , after first winding on a single layer of No. 22 B. and S. gage copper wire.
Aclrnowledgment The author is indebted to L. F. Fieser and M. S. Newman for helpful suggestions and criticisms.
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Literature Cited (1) Awry, IND.ENQ.CHEM.,20, 570 (1928). (2) Conte, Ibid., Anal. Ed., 2, 200 (1930). (3) Dennis, J. IND.ENQ.CHEM.,12, 366 (1920). (4) Markley, Ibid., Anal. Ed., 6, 475 (1934). (5) Meyer, Hans, "Analyse und Konstitutions-Ermittlung organischer Verbindungen," 5th ed., pp. 41-60, Berlin, Julius Springer, 1931. (6) Pratt, J. IXD.ENG.CHEM., 4, 47 (1912). (7) Sando, Ibid., Anal. Ed., 3, 65 (1931). (8) Thiele, B e y . , 40, 996 (1907). RECEIVED Apiil 15, 1936
A New Type of Laboratory Stirrer EMANUEL B. HERSHBERG Converse Memorial Laboratory, Harvard University, Cambridge, Mass.
T
HE stirrers shown in the photograph have proved very satisfactory for stirring mixtures thick with solid where the propeller type of stirrer is ordinarily useless. I n such instances as condensation reactions with sodium, the preparation of benzalacetophenone, the Blanc reaction, and some Friedel-Crafts reactions the stirrers shown have performed good service where other types failed. Unlike propellers, these stirrers can be made much larger than the mouth of the flask and the wires swung sufficiently to permit insertion as shown in the upper left-hand example. Once inside, they follow the contours of the flask without s c r a t c hi n g and are even more easily removed. Various alloy wires of No. 18 B. and S. gage may be used, depending on the type of reaction. I n particular, NEW TYPE OF LABORATORY STIRRER c 1-1 r o m i u m - n i c k e 1 a n d copper-silver alloys h a v e been found to be very resistant to attack and have the requisite stiffness and resilience. Stirrers of all types run more smoothly and for longer periods of time with a minimum of attention if ball bearings are used as guides. I n general two sets spaced a few inches apart are necessary and are best fastened by inserting a piece of rubber tubing with the inside well moistened with glycerol and then slipping the whole on the glass tubing as shown in the lower center of the photograph. Ordinary commercial unground ball-bearing assemblies 2.2 cm. (0.875 inch) in outside diameter and having a 0.94-cm. (0.375-inch) hole used in conjunction with 6.5- to 7-mm. glass tubing have proved a very satisfactory and inexpensive combination for general use. An occasional drop of oil is all the lubricationnecessary. RECEIYED April 9, 1936.
