through the polaroids when samples of high opticai activity are used. EFFECT
OF SLIT WIDTH
The data in the uqable range were obtained I Q rising ii spectrophotometer slit n idth of 0 1 to 0.2 mm. and with full sensitivity of the multiplier phototube. Outsick that range larger slit widths nere in most cases necessary. This inc rmses the spectral band width and a b ~ ii~~fluences tho reading-e.g., when 3 iiiciose sample was measured at 625 nid r( t d i n g ~of 1002' P(IUd1 t o 90.2, 90.4, 90.': 90 A and 90.1 n e r e obtained for a z i i t LT iiltli oC 0.6>0 5 0 4 0.3, and 0.2 r i m , rwpectivelj TI114 effect may be aiiot1lt.r ~rqtrictionon the accuracy of i e m t - ohrninable CONCLUSIONS r)E
~ m v length e and
of tile paiaroid disks b y u::it a i i j presumably also ~.mausi:of 100% polarization protiui'tti iq-thch Sic01 prisms. The increaseti ic.ngth oi the unit due to such ,i
1
.
a change should not involve serious technical problems, but because a large aperture is required it may be costly. The higher transmittance of Nicol prisms would permit the use of smaller slit widths. The slit width of 0.2 mm. a t 500 mp necessary with the current unit corresponds to a half-intensity band width of 4 mp for the light entering the sample. The rotatory dispersion curve for the sucrose solution can be considered only approximately linear within that band width. So calibration of the instrument-e.g., with sucrose-will be accurate only to a degree which depends in a complicated way on the monochromaticity of the light used. As for ordinary optical rotation measurements, the instrument may be considered a valuable analytical tool. It is especially useful when working with colored substances, where visual polarimetry causes considerable strain on the eye or may even be impossible. The precision of approximately 2% is considered goo& for small rotations (-0.3") but the visual polarimeters are superior a t iarger values of rotation when the ~n1u:ic~nsare not too highly colored. It is r;nfa-tunate that technical problcis appear t o impose some limitations tne use of the ingenious 0'7
principle upon which the Keston at tachment is based. ACKNOWLEDGMENT
The author thanks C. S. Garner for his interest in this investigation and for valuable discussions. Financial support from the U. S. Atomic Energy Commission under Contract AT( 11-1)-34, Project 12, is gratefully acknowledged. LITERATURE CITED
(1) Gallop, P. M., Rev. Sci. Instr, 28
209 (1957).
(2) Gibbs, R J., Agricultural Research Service, U. S. Department of Agricul-
ture, Beltsville, Md., private communication, October 28, 1959. (3) Gibbs, R..J., Fryar, A. J., Abstracts. 132nd Meeting. ACS. New York, X . Y., September 19g?, p. 32C. (4) Grabau, & J. I. Opt. , SOC.Am. 27, 420 (1937). (5) Keston, A. S., Abstracts, 12ith hfeeting, ACS, Cincinnati, Ohio, April 1953, p. 18C. (G),Keston, A. S., Lospalluto, J , Federat z o n Proc. 12, 229 (1953). (7) Lowry, T. M., Richards, E. 31. J . Chem. SOC.125,2523 (1924). (8) Standard Polarimeter Co., Kew Tork, S . Y.,,,BuIl. 2 and "Calibration Procedure. RECEIVEDfor review July 15, 1989. Accepted December 31, 1959.
Determination of Sulfur in Petroleum Products by Hydrogenation E. C. SCHLUTER, Jr., E. P. PARRY, and GEORGE MATSUYAMA' Ilnior! Oil Co. of California, Union Research Center, Breo, Calif. F A i a p i d method for the determination of sulfur throughout a wide concentratior range i s described. The sample i s heated in a hydrogen stream ana passed over a nickel catalyst at 1 2 W C Sulfur is converted to hydrogen sulfide and absorbed in a dilute sodium hydroxide solution. The absorbed hydrogen sulfide i s titrated ainperametrically with standard mercuric chloride solution if the sulfur conBelow centrotior i s above 0.1%. 0.1 ";b sulfur the methylene blue method I S usea to determine as little as 5 p.p.m. of sulfur in a 0.2-gram sample. as littie as p . ~ . r n OX sulfur may be aetermined because no Siank is detectabie unaer normal operating conditions. The accuracy for iow sulfur concentrations is equal to or better than the lamp method below 1OC p.p.ni. Average recovery OR a variety of sulfur types was 99%. With petroleum samples, comparisons with referee methods showed recoveries of
97 to 100%.
With the sample introduction system described, recovery of sulfur decreases as the amount of heavy suifur-containing material in the sample increases. Halogens, nitrogen, phosphorus, and arsenic d o not interfere at concentrations normally found in petroleum. The method requires a high temperature furnace, but otherwise the equipment is simple. Depending on the character of the sample, av analysis requires 30 to 45 minutes.
BRIOUR combustion iiicthods are used ior the determination of total sulfur ir. petroleum products. The choice of method depends on the nature of thP samplc, Put in all, the sulfur is oxidized to either sulfur dioxide or sulfur trioxide, which is then deter1 Present address, Beckman Instruments, Inc., Fulierton, Calif.
niined titrimetrically, gravimetrically or colorimetrically. The combustion approach gives good results but has some limitations. Halogens, nitrogen, and phosphorus interfere by forming acids in the lamp, induction furnace, and alkalimetric finish methods (1, 2 ) . Gravimetric methods are not subject to this interference, but are slow and insensitive. Gaseous and volatile samples cannot be analyzed by the bomb or induction furnace methods; these methods are also limited to small amounts of sample. Sample size limitation is overcome a t the expense of long Combustion time in the iamp method, but materials n hich burn with a smoky fiame or contain elemental sulfur give unsatisfactory results ourids werc :m sent The amount of cuivature was more pronounced the greater the amount of nitrogen, and very large amount? cf n i t r o p n may cause uncertainty in :he t-rd point. The end point of the titration wa. obtained by extrapolating the straight-line portion of the anodic current until it intersected
Colorimetric Determinafion of Sulfur in Naphthas
API Gravity, 60" F.
3
0.178 0.181 1 67 1 70 0.49 0.50 1.42 1.43 1.24 1.18 1.19 3.53 3.51
1.59 0 50 0 51 1 48
P5roxide bomb
%antaXaria crude
Hydrogenation yo Results, Sulfur
52.5
47.6
ANALYTICAL CHEMISTRY
Results, P.P.N. Sulfur ASTM ilydroI3 1266 genation
Absorption Volume, M1.
740 760 500 530
670 710 430 440
75 75
440
140 120
140
75 75 75 75 '7 5 75 75 75 75 75
70 70
