246
VOL. 7, NO. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
for 0.040 to 0.070 per cent; and 1gram for over 0.070 per cent. Sodium hydroxide can be used for an absorbent, and when transferred to a beaker should be oxidized with either sodium peroxide or bromine water, and boiled. This method can be put on a production basis by installing a 4- or 5-tube heavy-duty combustion furnace and working 4 or 5 samples a t one time. Keeping the bent end of the tube a t nearly the same temperature as the center is important. Therefore, the ordinary furnace should be remodeled so as to keep the hump of the tube heated to the same temperature as the center (Figure 1). When determining sulfur on ferro alloys, and especially
in the case of high-carbon alloys, use 2 or 3 grams of tin and run the gas for 2 hours.
Literature Cited (1) Guerdras, A., Aciers spbciaux, 6, 75 (1931). (2) Holthaus, C., 2. angew. Chem., 38, 330 (1925). (3) Jannasch, P., "Praktischer Leitfaden der Gewichtsanalyze," p. 188 (1904). (4) Kassler, Chern.-Ztg., 57, 573-4 (1933). (5) Schmita, F., Stahl u. Eisen, 39, 412 (1919). (6) Seuthe, A., Ibid., 52, 445-6 (1932). (7) Vita, A., Ibid., 40, 933 (1920). RECEIVED February 1, 1936.
Determination of Water in
By-product Sulfur LOUIS SHNIDMAN. Rochester Gas and Electric Corp., Rochester, N. Y.
T
HE appearance of by-product sulfur on the market (3, 4,6, l l ) , through the adoption of liquid purification methods and sulfur-recovery processes (7, 8, 1416) in the purification of manufactured, natural, and refinery gases, has necessitated proper methods of analysis. The byproduct sulfur cake, if made by the ferrox process, consists essentially of water, free sulfur and iron oxide, with small quantities of sodium salts; if made by the thylox process, it consists of water, free sulfur, and a small amount of inorganic residue (sodium carbonate, sodium thiosulfates, sodium thiocyanate). The sulfur cake, as it comes from the filters, consists of a yellow-gray sticky mud containing about 60 per cent water. To handle it readily, the water content must be kept under 60 per cent. I n preparing the cake a t the plant, the water content has been employed as a guide as to the quality of the product made, and this requires a rapid and reliable method for the determination of water in the sulfur cake. It had been the author's practice to dry a quantity of sulfur cake in an oven a t about 60" C., through which air was passed for 48 hours. This procedure was too slow for plant control purposes, and a search of the literature was made in an attempt to discover a more rapid method. In the methods of sulfur analysis reported in the literature (1, 8, l a ) , the water or moisture content is determined by drying a known weight of material for one hour a t 100' to 105" C. in an oven and calling the loss in weight water. This method could not be used for by-product sulfur cake, because of the presence of oils and organic matter that might be lost by drying a t 100" to 105', as well as the danger of loss of sulfur due to volatilization and oxidation to sulfur dioxide. With such a procedure the loss at 100" to 105" would be greater than the water content. Fresenius (6) and Lunge (10) determined the moisture content of sulfur by drying a t 70" for a period no longer than necessary, but do not state how long this period may be. With these points in mind, a study was made to develop a rapid and accurate method for determining water in sulfur cake.
Experimental Work Thirty-gram samples of by-product sulfur were dried a t 100" C. in an oven through which preheated air was passed for different intervals of time. The samples were cooled in a desiccator and the percentage loss was determined. Table I presents these results, which show that there was a progres-
sive loss of material with increase in time. What the true moisture content is cannot be ascertained from these data. (The true moisture content of the sulfur cake was 42.4 per cent, as determined by the method developed below.) TABLEI. Time Interval
LOSS
WHEN HE.4TED AT 100" c. Loss by Weight
MWL
70
15
12 4 26 6 43 9 46 7
30 60 120
Loss of sulfur was found to have taken place, as indicated by the presence of sulfur crystals in the cooler portions of the exit air tube. The odor of sulfur dioxide was present in the oven, indicating that some oxidation had taken place. Any volatile oil and other products would likewise be lost. The foregoing data point out that any method for determining water in by-product sulfur cake by heating a t 100' C. in an oven tvould be inaccurate. I n order to develop a method, some standard for reference is required. Such a standard method for water in by-product sulfur cake was developed by progressively lowering the temperature until no free sulfur was volatilized or oxidized. Samples of sulfur cake were placed in a quart jar which was closed by a tight-fitting rubber stopper. Through glass tubes inserted in the stopper a current of dry purified air was passed over the samples. The apparatus was placed in anooven and the temperature in the jar maintained to within *l C. The outlet tube from the oven passed into an Erlenmeyer flask in such a manner that the air bubbled through dilute sodium hydroxide solution to remove any sulfur dioxide and volatile products that might have been driven off. All samples were dried to constant weight. Examination of the outlet tube and the sodium droxide solution was made for the presence of sulfur, sulfur ioxide, and oils that might be lost by volatilization or oxidation.
t;y
Starting a t 100" C., the temperature was progressively lowered by 10" intervals. It was found that somewhere between 45" and 50" C. represented the highest temperature to which sulfur cake could be heated without loss of sulfur or other volatile matter. Further study within this range showed that 47' * 2" C. was the highest temperature to which by-product sulfur cake could be heated in an oven through which dry-purified air was passed with no loss of sulfur or other volatile components. The results obtained
JULY 15, 1935
ANALYTICAL EDITION
247
by drying sulfur cake a t 47" ;f; 2", employing the procedure outlined above, were used as a standard for reference. The above method, while accurate, was too slow for plant control purposes; hence, the following rapid method was developed and studied. By the use of the new method, the water content of by-product sulfur cake could be determined within 3 hours, with a high degree of accuracy. The method, which was a modification and adaptation of the A. S. T. M. standard method for determining water in petroleum products (d), was flexible, simple, and lent itself for plant control operation.
Procedure Figure 1 presents a diagram of the apparatus used. The procedure adopted was as follows: Samples of by-product sulfur cake (25 grams) were weighed into the copper still, 150 ml. of gas oil and 150 ml. of rectified light
