:ind eliminat,ion of the ion exchange with its necessary rinses. The total volume titrated can thus be kept down to 15 nil., making possible the use of 0.0023f barium perchlorate and replicate titrations with a standard deviation of 0.6 pg. of sulfur. The use of the methylene blue in the mixed thorin indicator helps the eye to distinguish slight changes in color at the end point. This internal color filter was essential !\-hen titrations were performed on the Sargent-Malmstadt automatic spectrometric titrator. ‘I’his unit gave about the same accuracy as the best visual results obtainable, iising 0.005.1l bariuni perchlorate, which was added a t a rate of 3 nil. per minute. standard deviat’ion of 0.6 pg. of sulfur might, be expected to give the accuracy tabulated beloiv-, provided the combustion absorption steps introduced 110 wrors. Standard deviations :tpproaching these values are obtained in the extreme low range. (Also see Table I1 ‘i Grams Sample Burned 10 c50 100
Expected Standard Deviation 60 p.p.b. 12 p.p.b. 6 p.p.b.
Sulfur recovery on k n o m blends of a ?vide r a n g of sulfur content averaged about 987& which indicates the completeness of the combustion and absorp-
Table II.
Analyses of Synthetic Aromatic Blends Containing Sulfur in Parts per Billion Range by Richfield Trace Sulfur Method
Materiala Benzene Blend 75 -4 (Benzene & Thiophene) Blend 711 A Toluene (Toluene & Thiophene) a
b c
Sulfur, P.P.B. Present Found 69, 80, 58, 46 383b 391, 385, 382, 488, 330
790c
530, 320, 540, 620 830, 820, 780, 770, 810, 760
Recovery, AV.
%
63 395
103
470 780
Std. Dev., P.P.B. 15 57 134
98
30
Burned 50-mi. samples. Includes 63 p.p.b. sulfur in benzene. Includes 470 p.p.b. sulfur in toluene.
tion. This is much better than the 85 to 95% recovery we had obtained with the Wickbold apparatus. No loss of sulfur occurred during the evaporation step as long as the solution was slightly alkaline and was not boiled dry with resultant splattering. ACKNOWLEDGMENT
The authors acknodedge the help of
J. C. Marantette, J. A. Sandefur, and K. A. Heath in developing the appatatus, and the useful criticism of G. R. Meador in preparation of this paper. They also thank the management of Richfield Oil Corp. for permission to publish this paper.
LITERATURE CITED
(1) Am. Soc. Testing Materials “Standards for Petroleum Products and Lubricants,” p. 1337, Sovember 1949. ( 2 ) Ibad., D-1266, “Procedure for C o y ; bustion of Liquified Petroleum Gases, p. 655, October 1960. (3) Ibid., Appendix I, “Method of Test for Trace Quantities of Sulfur,” p. 658, October 1960. (4) Fritz, J. S., Yamamura, S. S., A4N.4L. CHEM.27, 1461 (1955). (5) Granatelli, L., Ibzd., 27, 266 (1955). (6) Houghton, S . IT’., Ibzd., 29, 1513 (Oct. 1957). (7) Hudy, J. A., ITair, R. D., I b a d , 27, 802 (1955). (8) Wickbold, R., Angew. Chem. 69, 530 (1957). RECEIVED for review January 29, 1962. Accepted May 15, 1962.
A N e w Type of Rotating Disk Electrode SIR: The theoretical treatment of mass tr:tnsfer in the rotating disk system ,specifies a lamina, of infinitesimal thickness and of infinite diameter, rotating with constant angular velocity in a fluid of infinite volume (IO). This .~oiiiinuiiic:tt.ioiiis concerned with the practical realization of the first two requirement’s: tlic second two are easily satisfied (6). Si1-c.r :tiid I
