V O L U M E 2 7 , NO. 5, M A Y 1 9 5 5
805
taneous air and reagent blank. The sample in this case is simply added dropwise into the open combustion tube from a modified buret with an offset capillary tip. Of course, this method is practicable only in locations having atmospheres with little or no sulfur contamination. The open t,ube combustion system has been found feasible when air contamination does not exceed 50 to 75 y of sulfur per hour of operating time. TTit,hthe type of samples to which the method has been applied, the oxidation catalyst has been found to be satisfactory for over 1000 hours of operation. Some leaching of the cat,alyst has been noted when burning benzene or other materials which have high conihustion temperatures, but in most cases, volatilization of the catalyst is no problem if proper sample feed rates are maintained. Various types of alumina were tried as the catalyst support. rl porous form of activated alumina (Alcoa Grade F-10) proved satisfactory after calcination a t 1400’ C. for 12 hours, t,o convert it t o the lionadsorptive a-aluniiiia arid to remove sodium oxide. I t has turned out to be simpler, however, to use Alcoa-Grade T-71, which is already calcined and very pure. This contains less than 0.029;b sodium oxide. Several forms of tabular alumina have proved unsatisfactory because they lack the porosity which is ewential to good catalyst support. .U)sorption stfludiesindicated that 90 to 95% of the sulfur oxides are :ilisorbed in the first ahsorher aiid 5 to 10% in the second absorber. Cooling of the absorber system was found necessary t.o prevent, excessive evaporation of alisorbent ; cooling also gave more efficient absorption of comtiustion gases. I t is necessary to decompose the hydrogen peroxide in the absorber solutions prior to the conductivity measurements. Otherwise, the peroxide interferes hy decomposing a t the elec-
trodes of the conductivity cell. Platinum gauze has proved to be a most effective catalyst for this step, as it acts rapidly and introduces no contamination. A thin coating of platinum black on the gauze increases the speed of decomposition nearly fourfold. This coating is applied by electrolyzing the gauze in 3% chloroplatinic acid in the usual manner and polarizing it cathodically in dilute sulfuric acid. The method is intended for sulfur determinations in the range of 1 to 100 p,p.m, However, it has been applied satisfactorily to samples containing as much as 0.1% sulfur by diluting the sample with isopropyl alcohol or some other suitable solvent. I t has been used in these laboratories during the past 2 years for the analysis of several hundred samples of terpenes, aromatic hydrocarbons, and alcohols, and is finding wide use as a general method of sulfur determination. LITERATURE CITED Soc. Testing Materials, Philadelphia. Pa., “Book of .GTM Standards,” Part 5 , Method D 129-52, 1952. I h i d . , Method D 90-50T, 1952. Grote. W., and Krekeler. H., Bngew’.Clieni., 46, 106 (1938). Hagerman. D. B., ANAL.CHEM.,19, 381 (1947). Holeton, R. E., and Linch, A. L.. I h i d . , 22. 819 (1950). Polsky. J. A . Ibid., 19, 657 (1947). Strafford. S . ,andcrossley, H.. A n a l y s t . 60, 163 (1935). Walter. I < , X . , . ~ X A L .CHEM.,22, 1332 (1950). Wilson. H. S . , and Straw, H. T.. J . SOC.Cheru. Irid., 69, 79 .hi.
(1950).
Zahn. T., ISD.ENG.CHEM., .IS.
