1394
ANALYTICAL CHEMISTRY
105 (1936)I. A cell (Richards, I,. hl., M.A. dissertation, Cniversity of California a t Los Angeles, p. 20, 1938) previously developed in this laboratory had the disadvantages of requiring several drops of liquid and of allowing rapid evaporation of low boiling materials. A new design has been developed which remedies the faults of the previous cell and has proved satisfactory for use with liquids having refractive indices in the ranges I .30 to 1.48 and 1.54 to 1.70. Values in the intermediate range may not be determined with this cell, because the refractive index of the glass interferes. For determining refractive indices over the entire range of the refractometer, the cell must be constructed from special glass having a refrartive index greater than 1.70, as was the case in the first cell.
the new lamp incorporates a convenient means for charging a i 1 h hydrogen, based on the f:wt that this gas can pass through palladium a t red heat. Available hydrogen lamps anti othcr lamps described iii the literat,ure ( I - d ) , producc a point murcc of light suit,able for Ppwtroscopic ~ v 0 r . k . IIou-ever, in nieasuriiig rpfractive dispersion of hydrocarbon liquids, the hydrogen light must be intense anti rover thc entire face of the refractometer prism; this is particularly required when samples are slight,ly colored. To obtain strong lines from a hydrogen lamp, a high rurrcint density must exist in the discharge section of the lamp whieh, together with the high voltage necessary to st'art and maintain the current, means that corisiderahle heat must be dissipated iluring operation. Howevrr, with conventional air-cooled units, the current cannot be inrreased to give t'he rather strong radiation required to measure refratative dispersion of hydrocarbon mixtures, because of limitations in heat dissipation. By providing the lamp with a water-cooled jacket it was possible t'o increaw the current and thus the intensity of radiation appreciably. The operating current is supplied by a ll5/9000-volt, 60-ma. luininous-t,ubc t,ransfornirr wit,h the primary winding connected t,hrough
,Pollodium
Tube
,Silvered
Reflector
i
Water Oullel
Refractometer Cell
Lapping Tool 'An
The new cell as constructed f i om a corrosion-resistant microscope slide and two square cover glasses. The microscope slide was cut to len t h (40 mm.), and the edges were polished with the aid of 400-mesf1 Carborundum. A square cover glass of thickness Yo. 1 (0.005 inch) was cemented t o a fourth piece of glass with hpiezon wax, and the unit was mounted upon the stage of a drill press. -4hole (15 mm.) was lapped through the cover glass using the brass lapping tool, A , and 150-mesh Carborundum The assembly was then removed from the drill press and washed with water. After drying, the unit was placed in an oven (100" C.) t o soften the thermoplastic wax, and the drilled cover glass separated from its glass support. After being washed with benzene, the drilled cover glass was coated on one side with sodium silicate and then placed upon the previously cut and polished microscope slide. The two components were pressed together, and the excess silicate was removed with a cellulose cleansing tissue. The cell was placed between t a o large rubber stoppers and allowed to dry under pressure. After drying, any excesc silicate was removed with the aid of a razor blade. In using the cell, 2 drops of liquid were placed in the depression and a cover glass was placed over the cell. The covered rcll unit was then attached to the refractometer with 1-bromonaphthalene in the same manner as a calibrating prism. The reading observed while using the cell was identical with the one obtained hy placing the liquid directly upon the refractometer prisms. This cell may be constructed nith about 0.5 houi of actual labor, and the material cost is negligible. WORKmade possible h y research grant
fioiii
General Laboratories, U S
Rubber Co
Improved Hydrogen Discharge Lamp. Vincent A. Campanile and Vernon Lantz', Shrll Development Co., Emeryvillc, Calif. HE increase iu the use of refractive dispersioii for the analysi. T o f hydrocarbon mistures has created a need for a strong, convenient source of the hydrogen F and C spectral lines commonly employed for the measurement of this physical property. Commercially available hydrogen discharge lamps are fragile, give weak lines, and have a short useful life. A hydrogen lamp has been developed in this laboratory which represents a rorisiderable degree of improvement in each of these rpspects. I n addition,
Deceased
Kwor Tube,
4
,,Hydrogen Dirchofge Section
jacket ~
\j
Electrodes
Window
water l n t e t 2
Figure 1.
Improbed 1IFtlrogen Discharge Lamp
a rctlay cont,rolled by a puP1ihuttai snitch. In this iiianiic'r, the lamp need be energized only u.hcn making measurementi. T ~ U S reducing the electrical shock hazard to a minimum and at itling :ippreciably to the life of thr unit,. The lamp (Rankin Glassblowing Co., 3990 Franklin C a i i ~ ~ oRoad, n Martinez, C:ilif. ) ip convenient to use with either the Zeiys Pulfrich or R:i11wh ancl 1,onih prccipion refractometcrP. COYSTRUCTlOh~OF L 4 M Y
-1 sketch of the lamp is given in Figure 1, and Figure 2 s h o w t,he unit attached to t'he Bausch Pr Lomb instrument. The lamp consists of t'wo electrode chambers, containing aluminiim electrodes, and a reservoir connected with a 400- to 500-mm. length of 2-mm. inside diameter by 4-mni. outside diametrr horoqilicate glass tubing arranged in the form of a helix having a n inside diameter of 10 mm. The helix is located within a Drwartypc rdletrtor, which is rvacuated and sealed after silvering. The cllectrode chamber and the h e l i d radiator are sealed into a water jacaket constructed of 57-mm. outside diameter borosilicate glaw tubing. The end of the jacket' sealed to the reflector is made flat arid smooth to form a clear window to permit passage of light. The palladium tube for charging the lamp is made from a short length of 2-mm. out,side dianieter material of 0.016-inch wall t,hicskness,flame-sealed on one end. The open end is butt-\T-elded fa1ectrir:tlly t,o Kovar metal t,ubing of the same diameter. the Kovar tubing is sealed into Corning glass tubing No. 705-2. and hi^ entire assembly is then fitted oiito the evacuating tuhe. The c*ompleted lamp is evacuated to a pressure of less than 10 - 3 mm. OT mercury finti baked 24 to 1s hours firfore sealing. OPER.AlION
To charge the lamp with hydrogen, circulation of cooling water is started and the palladium tube is heated to redness with a small hydrogen flame, being certain that no voltage is impressed on the electrodes. When thr tube rearhes red heat, the flame is extinguished, and n *ni:dl stretiin of hydrogen is direct,ed a t the
V O L U M E 26, NO. 8, A U G U S T 1 9 5 4
1395
wide filled tape; with
range of flows. I n operation the liquid reservoir is first and the bottom chamher is inverted to seat the standardjoint. The flowmeter is next placed in position for use stopcock D in position 1-3, 80 that it is a t atmospheric
IarG coil, A , YnTnio {he system. When the' liauid in-the hott'om
outer tub;.
This level will remain esseutiallv unch&ed
until
2 to 6 hours. The s&e of theca&arv'o&l suitable far the desired ~~~~~~~
~
chambcr were 35,'18, and 8 mm., rcspeet
