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.
