1383
V O L U M E 2 4 , NO. 8, A U G U S T 1 9 5 2
1 Figure 2.
One 3Iethod of Fabricating and Using Condenser
up tliflicrilty is experienced with condensation of \vatu from t h e air. The selected distillate, xvhich has drained into the lip, C’, is withdrawn with a pipct m:ide from small-diameter plws tubing (Figure 2). In work described eli;~tn.here( 2 ) , the dircctionnl contlen*ers have been used for long runs at loiv temperatures. Vlien used for rat,e determinations at low rates, the end errors for start,ing and stopping represent only a fraction of a per cent of the t,ime factor. The condensers are rhus precision instruments for high-vacuum t’eiisimetry,particularly because t’hearea of the receiring entrnnce c z n b~ accurat,elT-detrrminctl. LITER.ATURE CITED
(1) Qrisif. 11. L., and Harris, P. L., I s n . ESG.C m x . , ~ ~ N . L E Lu . . , 18, 7 0 i (1946). ( 2 ) Trevoy, D. J., and Hickman, IC. C . D., I d . Eng. Cheni., 44, 1182-1911 (1952). (3) TI-nshburn,E. W., Brunn, J. H., ancl IIicks, .\I. SI.,Bur. Standards J . Research, 2,467 (1929). Co.\!>IcxIc.4.rIoN 1416 f r o m the Kodak Research Laboratories
Simple Peak Current Recorder for Pen Recording Polarograph. B. E. Gordon, Shell Oil Co., Martinez, Calif.
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advantages of recording peak current value.* i n quantitative polarography have been discussed [Liiigane, ,J. J., XXAL. CHEM.,21, 45 (1949); Schulman, J. H., Batt,ery, H. E., and Jelatis, D. G., Rev. S c i . Ins2rzimentsJ 18, 226 (1‘34T)].The?. become greater in the analysis of difficultly reducible compounds such as the polynuclear aromatics. Very rarely do capillaries perform well enough to yield a smooth, easily evaluated curve at these potentials. In such cases plotting the maximum points of this erratic diffusion current usually results in better precision than plotting the complete curve, because at high negative potentials (ca. -2.7 volts PS. S.C.E.)the surface tension a t the mercurysolution interface is so low that erratic drops frequently fall immediately after a normal drop. Because the second drop doe;: not acquire its full size, and because the pen, having a finite response time, does not immediately return t o the full value of the diffusion current, a lox current value results. After this, a succession of normal drops is necessary to enable the recording circuit to reach the diffusion current again. When this cffect is so ’HE
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I
I
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I
NORMAL
RECOPDIN
1
P AK REC RDING
Figure 1. Polarograns
pronounced that the diffusion current cannot be reached, the capillary needs replacement. Usually, however, this effect of a fast small secondary drop is sporadic, allowing for partial attainment of the diffusion current, yet resulting in a curve (see Figure 1)of poor appearance. h simple mechanical peak current recorder, installed in a Sargent Model XXI polarograph, plots a smooth polarogram of the maximum current values only. This has been accomplished by installing a pen carriage (purchased from the Brown Instrument Co.) and recording pen on the upscale side of the regular pen carriage, and removing the regular pen. The extra carriage with the recording pen is pushed upscale by the regular carriage, and thus records only maximum values, as it does not follow downward movements of the regular carriage. The result, two polarograms of the same system, shown in Figure 1, is a smooth curve easily interpreted by inexTerienced personnel, and in a form more presentable in reports. The presence of maxima will, of course, completely distort the appearance of a wave made in this way and therefore this technique is not advocated for exploratory polarography where half-wave potentials and the presence of maxima are of interest. Ilon-ever, when a method has been thoroughly established and is being applied routinely, the modification map well prove useful. Where high sensitivity is required in conjunction with large t values, resulting in a small step composed of large oscillations, the peak recorder n-ill simplify the appearancc of the record.
Method of Adding Sample to Closed Systems. hlartha J. Bergin (present address, Sylvania Electric Products, Inc., Salem, Mass.) and &no H. A. Hegn, Boston Universit.p, Boston, Mass. ~ S I X P L Eand direct method for increasing the concentration of - solutions in closed systems by the addition of k n o w amounts of nonvolatile solutes has been developed. The standard procedures of breaking bulbs containing the samples (Sanderson, R . S., “Vacuum Manipulation of Volatile Compounds,” S e w York, John Wilep & Sons, 1948) or of titrating a measured amount of concentrated solution into t,he solution from a thermostated buret [Watt, G. W., and Keenan, C. W., J . Am. Chem. SOC.,71, 3833 (1949)], require complex equipment, the operation of which is both tinieconsuming and erratic. The equipment required for the simplified method de.mibed below is generally available and easily constructed. This method of addition has been found to be as accurate as previous procedures and may be used over a wide range of sample sizes.
A series of boats containing weighed amounts of the desired nonvolatile solute is lowered one by one into a well stirred solution. I n the schematic diagram of the apparatus A is a ground-glass plug with reduced glass tube, B is a glass bobbin, C is a glass fiber thread, D is a sample boat, and E is a borosilicate glass weight. The apparatus consists of a head made of borosilicate glass uitli two standard-taper joints a t right angles to each other. The size of the joints may be varied to fit the needs of the equipment. Into one of the joints a standard-taper plug with reduced glass tube is inserted. The end of the glass tube contains a bobbinlike arrangement consisting of two glass ridges 0.25 inch apart and a small hole between the ridges. Borosilicate glass fiber thread, which can be obtained from any laboratory supply house, is knot’ted a t one end and threaded through the hole. The knot serves to hold one end of the fiber tight, Rotntion of the plug will wind or unwind the thread.
