1396 the sintered-glass frit on the mercury valve [see ( I )for details of this valve] is loosened on the half-joint, so that carbon dioxide sweeps briefly through the lower part of the apparatus. D is closed, the chamber is transferred to the position shown in the lower part of the diagram, and E is opened. The mercury in the valve is thus sucked up against the sintered-glass frit in the mercury valve, reserving t h e vacuum in the chamber. ?n the meantime, the sample flask, containing 2 to 30 mg. of sample and a spatula tip full of potassium iodate (Baker's Analyzed c.P.), has been
ANALYTICAL CHEMISTRY :
C..ll._
r.*Eliii.,.
: :
r.5:::,.:..L--,
1
..-.T'..T"..>
I
L.rTJ
Z I:
I :
I
,
trap (this greatly extends the usable period of the mercury valve frit); increased flexibility provided by the use of ball joints; an improved form for traps, pressure regulators, and bubble counters which eliminates the possibility of sucking back of the trap liquids; and a more compact and rugged arrangement of parts. The radioactivity in the ion chamber is measured as described by Raaen and Ropp ( 3 ) . ACKNOWLEDGMENT
The apparatus described has evolved from the work and suggestions of a large number of people. These include 0. K. Seville, 8. R. Jones, G. A. Ropp, A. J. Weinberger, D. N. Hess, V. F. Raaen, C. J. Collins, W. A. Bonner (Stanford Cniversity), K.G. Brown, Davis (University of Chicago), and H. \I7, (Vniversity of South Carolina). LITERATURE CITED
5 1 A N O A R O 200-1
(1) Serille, 0. K., J . Am. Chem. SOC.,70, 3501 (1948). ( 2 ) Xiederl, J. B., and Niederl, V., "Micromethods of Quantitative Organic Analysis,'' p. 106, Sew York, John Wley &
Sons, 1942. (3) Raaen, V. F., and Ropp, G. 8 . ,dsir.. CHEM., 25, 174 (1953).
.PASS
Two-Point Converter for Single-Point Recorder. Ernst P. Hal: and William L. Nelson, M d o n Institute of Industrial Research, Pittsburgh 13, Pa.
k verting - .
Y I V E X P E S S I ~ E device
for externally cona curve-drawing thermoelectric recorder from single-point t o two-point recording has been developed and used t o record two temperatures on the same iecorder chart. Two-point operation is achieved by a system of automatically switching from one thermocouple pair t o another on a timed cycle, identifying each thermocouple pair by the length of line on the recorder chart (dotdash for a two-point recorder). 1
affixed to the ball joint and clamped. About 15 ml. of Van Slyke solution are then added through stoucock C. The formulation used was '25 grams of chromium trioxide, 5 grams of potassium iodate, 167 ml. of 85% phosphoric acid to which sufficient phosphorus pentoxide had been added to bring i t up to about 100% phosphoric acid, and 333 ml. of 20% oleum. (The vacuum in the ion chamber draws in the liquid.) With stopcocks C and D closed, the sample flask is heated with a free flame until the freely boiling mixture stops foaming and the bubbles become dark and coarse. T h e burner is removed and the mixture allowed to stop boiling. Stopcock C is then opened completely and a vigorous stream of carbon dioxide is admitted through B and C until the ion chamber is a t atmospheric pressure as shown by the level of the mercury in the side arm of the valve. Stopcock E on the ion chamber is then closed, and ion chamber is removed from the valve. T h e sample flask is immediately removed (with gloved hands), and the contents are poured into running water. The flask is rinsed with water and dried with acetone and air; it is then ready for another sample. Corrosion of the mercury in the valve and subsequent clogging of the frit are largely prevented by filling one arm of the U-tube in the lower part of the drawing with stannous chloride dihydrate (3). Samples very high in nitrogen (like dinitrophenylhy Irazones) form an excessive amount of nitric acid upon combustion; this acid may be removed if a standard lead dioxide mortar ( 2 ) is inserted in the system just following the stannous chloride trap. The advantages of this apparatus over Keville's earlier one lie in provision for an easily removable frit in the mercury valve; the use of stannous chloride dihydrate in the combustion line
The converter is constlxcted as shown in Figure 1 by mounting the blades of a double pole-double throw knife saitch on an insulating block, so that they short between the two sets of light spring brass contacts as they move from one pair of contacts t o the other. T h e solenoid (Guardian 4ilC1, 110 volts) and return spring are mounted so that the switch will be moved from position A to position B by energizing the solenoid, and returned t o position A by the return spring when the solenoid is deenergized. The solenoid is controlled by a timer-operated microswitch. A war surplus 4 r.p.h. timer motor (similar to Synchron No. BH 889) is fitted with a brass disk or cam and the microswitch is attached so that a notch cut in the periphery of the cam will permit the micros%-itch to open as the timer motor rotates the notch past the microswitch plunger. T h e over-all operation is shown by Figure 1 . -4s the timer rotates cam section A (cutout) past the microsT\+tch, the solenoid circuit is opened and the return spring pulls the switch blades to contacts A , connecting thermocouple A to the recorder. Tyhen cam section B is rotated past the micros%-itch, the solenold is energized, pulling the switch blades alvay from contacts A (momentarily shorting contacts A with contacts B ) to contacts B , connecting thermocouple pair B to the recorder. I n this manner the temperatures indicated by thermocouples d and B are alternately recorded on the recorder chart. A means of identifying the switch position on the recorder chart is usually necessary, and this may easily be accomplished by varying the lengths of cam segments -4 and B. As shorn,
1397
V O L U M E 2 6 , NO. 8, A U G U S T 1 9 5 4
purity. It may be operated continuously for long periods without attention. Its advantage over commercially available types is most pronounced when refractometric measurements are made a t irregular intervals, for no time need be wasted in preliminary manipulations before the arc is struck. These tubes have been used successfully for several years in this laboratory as a source of illumination for the routine measurement of dispersion. CONSTRUCTION OF TUBE
scale &an iiig of the tube is a h o ~ v nin Figure I . I t is constructed entirely of borosilicate glass and is about 8 inches long A\
Figure 1
t h r recording cycle of 7 . 5 minutes (txVo cycles per timer cain revolution) is divided 2.5 minutes on thermocouple -4 and 5 minutes on thermocouple B , resulting in a n identifiable dotted line for temperature A and a dashed line for temperature B on the recorder chart. I n some cases where sudden changes or rapid cycling in temperatures are t'o be recorded, the ovrr-all lengtli of the recording cycle may be objectionable. Shortening t!ic c\.cle (by using a motor of higher revolutions per hour or cutting a different cam) will minimize this objectional feature; howevei,, for a strip chart speed of 1 inch per hour on the average recorder. it is recommended that the shortest time interval or dot be about 1 minute and t h a t the dash be at, least twice as long as the dot.
S o difficulties have been encountered from contact re or contact potential a t the converter sn-itch. The center shorting feature of the converter switch is necessary to prevent the I('corder from "wandering free" in the brief time interval het\veeri contacts. The substitution of a ratchet-driven rotary switrh (shorting type) with appropriate timer and cam changes should permit recording three or more temperat,ures with a recordfir drrign(9ii for single temperature recording. COSTRIBUTIOK from the Coal 'Taste Fellowship sponsored by t h e Wrzltcrn Pennsylvania Coal Operators Bssociation.
:rnd 2.25 inches in diameter. I t consists of two electrode chambers connected by a length of tubing 2 mm. in inside diameter, arranged in the form of a spiral, the entire assembly being inserted in a water jacket. T h e electrodes are fabricated of pure aluniiiium sheet as shown in A , Figure 1. T h e aluminum blank is first, rriniped t o a piece of tungsten wire and then bent into cylindrical hapr. The external contacts for the power supply are contructed as sho1T.n in B (Figure l ) , and are sealed in place with de Khotinsky cement. During assembly of the lamp, it is important that the lon-er end of the discharge section be placed as close as possible to the flat \\-indo\? a t the end of the water jacket. T h e external surface of the jacket is silvered to the dashed line in order to increaw the intensity of the illumination, and the entire tube, with the esception of the windon- and electrode terminals, is given a coat of flat 1)l:ick lacquer.
-
HYDROGEN
SOFT SOLDER
ELECTRODE CHAMBER
DETAIL
B
SPIRAL DISCHARGE L SECTiON
Figure 1.
Improved Hydrogen Discharge Lamp for Use in Refractometry. R. W. King and A . E. Hirschler, Research and Development Department, Sun Oil Co., ?;orwood, Pa. EFRACTIVE dispersion is a physical property frequc'iltl?. used in the petroleum industry for hydrocarbon-type analysis.
R.
It is usually defined as the difference between the refractive inlies of the sample for the blue ( F ) line of the hydrogen spectrum an I thcl refractive index for the red (C) line. For many years such refractive dispersions were measured using a conventional Abbc refractometer with Amici compensating prisms and white light. the compensator orientation a t total achromatizatiori being :i measure of dispersion. However, the Zeiss Pulfrich a n d the recently introduced Bausch B: Lomb precision refractometera, if provided with a suitable source of illumination for the C' an I F lines of the hydrogen spectrum, can be used for more accurate‘ dispersion measurements than those obtained by the method of compensator readings. The principles of the hvdrogen discharge tube are so well knon-n (3,4) t h a t the description of another model \\-auld be superfluous if i t did not offer certain advantages over other types. The lamp described combines a simplification of the design of Campanile and Lantz ( 2 ) with a continuous-flow method of operation described by Arnold and Donn ( 1 ) . It uses a relative1)low current source, is R-ater cooled, exceptionally rugged and easily constructed, and produces a hydrogen spectrum of high
-
DETAIL A
-
0
102050
SCALE-mrn
IIyIrogen Discharge Lamp
In construction of the tube, care must be exercised to prevent foreign particles from adhering to the inside of it or to the electrodes, as such impurities affect the quality of light obtained from the finished lamp. OPERATIOY AND U S E
The useful life of any sealed discharge tube of rmsonable arily short because of absorption of the hydrogen hy the electro !e.?. Consequently, such tubes must frequentlhbe rwharged. T o avoid this inconvenience, a slow stream of hydrogrn is p:issed continuously through the tube a t about 3 mm. of mei.curp pressure. T h e arrangement of the accessories for operating the Limp in such a manner is shown in Figure 2. T h e hydrogen is supplied b y a pressure cylinder fitted with a conventional regulator and needle valve. T h e three-nayystopcock permits the vacuum on the pump to be broken without affecting that in the tuhe. The hydrogen and vacuum lines are lengths of Tygon tubing. Tygon was found to be superior to rubber tubing for this purpose, a n d imparts more flexibility than ~ o u l dbe obtainable with an all-glass system. T o eliminate any possiblity of electrical shock, it is advisable to ground the hydrogen cylinder and vacuum pump thoroughly. Details of the operation of such an arrangement have been described ( 1 j. I n brief, screw clamps 9and B are adjusted to give the desired pressure and rate of flow of hydrogen, and the lamp electrotles are energized by connecting them across the secondary
