V O L U M E 25, NO. 8, A U G U S T 1 9 5 3
1285
I
I Figure 2.
Oscilloscope I'attern for 5 to 1 Frequency vision
within 5% of nominal and due caution should be observed to protect components from exeefisive heat insoldering. A heavy brass clamp applied to the lead wire between the component and the soldering terminal is conveniont for the latter precaution. ACKNOWLEDGMENT
This circuit was developed a6 part of a project aided financially by the Research Council of Canads.
chemieah, being attacked only by molten alkali metals. It is unaffected by temperature up to about 225' C. The stirrer blade shown on the right is patterned after a glass stirrer blade commercially available (Trubore stirrer blade, Ace Glass, Inc., Vineland, N. J.). The two stirrers shown on the left are reminiscent of the wire stirrer described by Hershberg [TND.ENG.CHEM.,ANAL.ED., 8, 313 (193611. These stirrer blade8 are cut from '/,sinch or '/&ch sheets of Teflon. They are readily fashioned using a Isboratoiy cork borer and a sharp knife. The segments of one type of stirrer are gently twisted, and will maintain their shape in most laboratory reactions. The two blades shown on the left are snapped onto the stirrer Ehaft loou throueh a cut in the center seement of the blade, This arrangement, which has withstood much wear, permits the interchangeable use of a variety of sizes of blades on the same shaft. The Teflon stirrer blades are superior to their glass or wire counterparts, being readily con8tructed and virtually indestivcb ible. These blades are easily cleaned, as few things adhere t o i do the the smooth plastic. They do not scratch I glass or wire blades. I
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Precise Speedy Pipet. C. H. Whitnah, Ktr~w,rmmt. College, Manhattan, Kan.
s
workers have studied the speed, accuracy, and precimon of pipets ( 1 , 3, 4). The pipet described was built ( d ) to measure pyridine sulfate dihromide reagent for iodine numbers by a modified Rosenmund and Kuhnhenn method ( 6 ) . It wm desired to measure two blanks and four duplicate determinations so quickly and precisely that the density and concentration of the reagent could be considered constant during these ten measurements. The pipet (Figure 1) may be considered to be a modified Koch buret. EYERAL
LITERATURE CITE1 (1) Craig, R. 8.. Satterthuwsite, C. B.. and CHEM., 20,555(1948). (2) Cruft Laboratory Staff, "Electronic CirLrlvr XXIV, New York, McGraw-Hill Book Co., 1947. (3) Tibbetts, D. R., E'lecfonies, 14.35 (October 1941).
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ALL.
-hap.
Plastic Stirrer Blades. Verne11 R. Shellman and Barney J. Magerlein, Research Laboratories, The Upjohn Co., Kalamazoo, Mich.
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Closing the suudv bulb with a calcium chloride tube urevented
wo types of laboratory stirrer blades made of Teflon (E. I.
Tdu Pant de Nemours & Co. Inc., polymers of tetrafluoroethyl
ene) have been satisfactorily used in this laboratory for several months. This plastic is noted for its outstanding resistance t o
A mirror'was~~laced~back of this tube, and scratches on this
and could be partly filled with Gater from a leveling &lb with stopcock. A stopcock, near the top of the reservoir, could be ._._. 1 . 2 : . . -
..... ~~. :~~ 1 1 ~
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adjusted, increased pressure would stop flow of reagent into the measuring tube just above the upper scratch, and decreased pressure would stop flow out of the tip just below the lower scratch. These pressure changes also hastened the initial flow rate of cach filling and emptying, and slowed down the find rates. The slow h a 1 rates greatly sided in adjusting the level of the meniscus and its image exactly to the scratches. The volume of air in the resrrvoir must be increased as the level of reagent in the supply bulb is lowered. It was adjusted so that the measuring tube would just fill and just empty when the supply bulb was full. The lowest reagent level, after each of 8everd definite increases of air volume, was then determined. A
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50
10
3.5
Figure 1
60 13.5
4.5
0,002
0.04
0.002
0.04
0.006
0.10
