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.
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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
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DETAIL A
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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
ANALYTICAL CHEMISTRY
1398 of a 9000-volt, 60-ma. transformer. A lavender light is produced, which may be easily adjusted t o maximum intensity by manipulation of the screw clamps. T h e vacuum pump runs continuously while the tube is in use. It'hen operated in this manner, the lamp is capable of producing illumination of a little over 2 candlepower.
CLAMP
SCREW
II I/
VACUUM PUMP HYDROGEN CYLINDER
Figure 2. Arrangement of Accessories for Operating Lamp
The tube described has been used for several years for precise measurements of refractive index using a hollow prism spectrometer, the Bausch & Lonib precirion refractometer, and the Zeiss Pulfrich instrument. I n use with refractometers, the lamp should b e placed in such n position that the spiral discharge section is perpendicular to the face of the illuminating prism or to the axis of the mirror used on the refractometers. When desired, Corning filter No. 2404 may be used to isolate the hydrogen red line a t 657 mH, and Wratten filter No. 45 will serve t o isolate the blue line a t 486 mp.
partly or fully by withdrawing B a smaller or greater distance, such that the triangular ports are partly or totally to the right of the rightmost O-ring. Assuming t h a t the vessel is evacuated and the valve is suddenly opened, the flow of air will be from the outside through the angular space between the solid portion of B and the cylinder walls of A . The gas flow then is through the triangular ports of B into the tubular section and through the tubular section into the vessel. The operation of valve b is made easier by a screw arrangement which permits fine adjustment of piston B into cylinder A . T h r left set of O-rings effects a seal between the vessel and the branch arm. The right set effects a seal between the branch arm and the atmosphere. Construction. The simplest valve t o construct is shown in Figure 1, a. Cylinder A is made of a section of borosilicate glass tubing joined betw-een two pieces of tubing of smaller diameter. Thc inside diameter of the larger tube minus the outside diameter of the inner tube may be chosen 1 mm. less than twice the diameter of the 0 part of the O-ring for the desirable seals. The tubing of larger diameter is made roughly 0.5 to 0.75 inch long to contain two to three O-rings. Two-part glass spacers may be used to reduce the number of O-rings or to maintain alignment. The O-rings can be slipped into place conveniently through the shorter sect,ion of the smaller tubing. Piston B is made from tubing and rod having an outside diameter 0.5 t o 1 mm. smaller than the inside diameter of cylinder A . I t is fabricated by joining a short section of tubing to the rod. Four V-notches are cut into the open end of the tubing, then a desired length of the same tubing is sealed to the open ends of the V-notches. Care must be taken to make good coaxial seals. The sharp edges of the S'-not,ches are carefully fire-polished. Circular ports may be carefully blown or drilled into the open tube of t>hepiston, if the careful throttling action of the V-ports is not required. Hooks are provided for springs for operation a t pressures above 1 atmosphere. A
LITERATURE CITED (1) I m o l d , G. B., and Donn, L., ANAL.CHEY.,19, 666 (1947). (2) Campanile, V. A , , and Lanta, V., Ibid., 26, 1394 (1954). (3) Hogness, T. R., Sidwell,-4. E., and Zscheile, F. P., J . Phys. C l i e n i . , 41, 379 (1937). (4) Munch, R. H., J . -4m.C i w n . SOC.,57, 1863 (1935).
Glass and 0-Ring Vacuum Valves. George W. Preckshot and Jlernon E. Denny, Department of Chemical Engineering, University of Minnesota, Minneapolis, Minn.
b
n:
for apparatus clcarilinees prompted the design of :I glass O-ring typc of value suitable for use under pressures ranging from high vacuum to about 1 atmosphere. Thc value is particularly useful r h r r c liquids arc also present and whcre metals and stopcock and valve greases interfere with ouperimental results. The O-ring is selected for the known cnnditions of operation and may be made of rubber, neoprene, silicoiic. rubber, or Teflon. These valves are leakproof, lubricant-free, rapid-operating, of large bore, and particularly adapted for vacuum work. Operation. Pictured in Figure 1 are tw-o types of these valves, connected t o a vessel and shown in cross section, disassembled. EED
a is the simplest type of discharge valve. b is a closure valve used between vessels or as a discharge valve where recovery of the liquid is necessary. Operation of the valves is identical. 1-aive a consists of a cylinder, A , containing O-rings in its largrr section and a piston, B , containing the open tubulation and triangular ports on the left half. The wtlve is assembled by inserting the open end of piston B into el-linder A through the 'O-rings until the spring hooks on the pieton rest against the open end of A. This puts the trittngular poTts to the left of the leftmost O-ring and closes the valve. The valve may he opened
Figure 1.
Vacuum Valves
The more complicated typc of valve is shown in Figure 1, b. The c!-linder section, A, contains t x o such sections of O-rings, between n-hich ia attached the discharge tube. Beyond the rightmost of these O-ring sections is a coaxial brass tube fastened to A with a gasketed split flange. T h e tube contains 0.75 to 1 inch of thread to accommodate the male valve operating wheel attached to B. The construction of B is similar to that described in the previous paragraph. The knurled operating wheel slips over the open end of B and engages against the lrft side of the slightly raised shoulder. Two screws through the hand wheel secure a follower which bears on the right side of the glass shoulder and permits the rotation of the piston within the valve handle but does not allow it to slip off. This arrangement permits more careful movement of the piston in its cylinder and thus facilitates better valve operation.
