Maan Lib. Aerie. Dopt. Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/determinationoftOOschrrich Issued June 15, 1910. United States Department of Agriculture, BUREAU OF CHEMISTRY— Circular No. 56. H. W. WILEY, Chief of Bureau. THE DETERMINATION OF TOTAL SULPHUR IN ORGANIC MATTER. By Herman Schreiber, Assistant Chemist, Bureau of Chemistry. INTRODUCTION. A great many methods have been proposed for the determination of total sulphur in organic matter, but probably only two of these are either easy to manipulate or accurate, namel}", the Barlow-Tollens,'^ or absolute method, and the Osborne,^ or peroxid method. When the latter is applied to solid material, however, it leaves much to be desired in the way of ease of manipulation and speed, and has absolutely no claim to exactness of detail. It is true that the water used for mois- tening the sample is measured and the sodium carbonate is weighed, but the amount of sodium peroxid added varies with the material ana- lyzed and with the rate at which the reagent is added. The amount of acid which must be added after fusion is also an unknown factor; it varies in each case which necessitates making the solution alkaline again, and then acid. These, however, are not all of the difficulties encountered. The fusions have a tendency to burn and blow out of the crucible, and this happens most frequently when the determina- tions must be rapidly made, for the peroxid method has a dignity all its own and will brook no haste or impatience. All of these objections were keenly realized when it became necessary to make about 100 sulphur determinations in a recent research. An ideal method for this determination should embody several features: First, it must not call for excessive amounts of reagents, nor such as will interfere with the precipitation of the barium sulphate or contaminate the precipitate; second, the reagents employed must serve two purposes, i. e. , they must destroy all of the organic matter a J. Amer. Chem. Soc, 1904, 26: 341. &U. S. Dept. Agr., Bureau of Chemistry Bui. 107, Revised, p. 23. 43669— Cir. 56—10 and all of the sulphur must be fixed and oxidized to sulphate; third, the method must be fairly rapid and not require a large amount oi practice, so that an analyst can make the determination from time to time without great delay and difficulty. It is difficult to outline a method which will meet all of these con- ditions, but after making quite a number of experiments the follow- ing procedure was evolved, which seems to fulfill the requirements more nearly than the peroxid method. THE PROPOSED METHOD. Weigh 1 gram of material in a nickel crucible of 100 cc capacity, add 10 cc of a solution made by dissolving 100 grams of sodium nitrate and 150 grams of sodium hydrate in 500 cc of water. Then add 5 grams of crystallized magnesium nitrate and stir with a platinum rod, making sure that the mass is thoroughly mixed and that the sample is broken up as much as possible. Wash down the material adhering to the stirring rod and sides of the crucible with the smallest possible amount of water. (This is essential since the addition of much water will prolong the subsequent heating unnecessarily.) Heat for one hour on a hot plate covered with a thin sheet of asbestos paper, keep- ing the temperature at about 130° C. Then put the cover on the cru- cible, tilting it in such a fashion as to leave an opening for the steam to escape and heat further for one hour at from 150° to 160° C, or until the material is entirely dry. If the fusions begin to bump, lower the heat so that the covers will not be jarred down tight on the crucibles, and the material lost by frothing. When the mass is entirely dry, put the covers on tight and heat gradually until the temperature reaches 180° C, then heat for thirty-five minutes, maintaining the tempera- ture at about 180° to 200° C. These temperatures were determined by laying the thermometer down on the hot plate. Now set the crucible (with the cover on tight) into a round hole in a piece of asbestos board, so that about 1.5 inches of the lower part of the crucible shall project below the asbestos board as Lunge '^ has directed, the asbestos board to be laid flat. Heat with the Bunsen burner for half an hour, allowing the flame to just touch the bottom of the crucible during the first fifteen minutes, and then with the full heat during the last fifteen minutes. (Never let the inner cone of the Bunsen burner strike the crucible.) During the first five minutes of heating with the full flame keep the crucible in an upright position, then remove the cover and tilt the crucible so as to fuse any material which may have crept up the sides. Then return the crucible to the upright position, replace the cover, and heat for ^yq minutes more. When the fusion has solidified, and before it has entirely cooled, place "Chemisch-Technische Untersuchungs Methoden, 1904, 1:428. [Cir. 56] the crucible in a 600 cc beaker with 150 cc of distilled water and cover with a watch glass. Put the crucible cover in the beaker, beside the crucible, and slightly rotate and tilt the beaker so that all parts of the crucible shall be touched by the water. Run in 13 cc of hydro- chloric acid (specific gravity 1.19) from a burette and again rotate the beaker slightly. Tip the crucible so that the other side comes in contact with the acid liquor, allow it to stand a few minutes, and remove the crucible and cover, washing the liquid adhering to them back into the beaker by means of distilled water. Any fused material adhering to the sides of the crucible can easily be removed with a stirring rod. Place the beaker on the steam bath and heat for about half an hour and then let it stand in the cold over night. Filter and wash the insoluble residue. Heat the filtrate on the steam bath or otherwise, and precipitate with a 10 per cent barium chlorid solution. In all of the determinations here reported the solutions were precipitated by heating on the steam bath, adding 10 cc of barium chlorid to the solution quickl}^ and stirring as soon as the precipitate began to form. After adding the barium chlorid the solutions were allowed to remain on the steam bath about one hour, and were then removed to the table and stood in the cold over night, after replacing any water lost by evaporation. All filtrations, except the solution of the fusions of the barium sulphate with sodium carbonate, were filtered through S. and S. blue ribbon filter paper. The fusions of the barium sulphate were filtered through white ribbon filter paper and all precipi- tates were washed with cold water. In this method a crucible loses from 0.3 to 1.3 grams of its weight in each determination, an average of 0.9 gram as calculated from 20 determinations. By the peroxid method the crucible loses from 1.2 to 2 grams of its weight in a fusion, an average of 1.4 grams based on 13 determinations. Using a griddle hot-plate, 14 by 18 inches, 18 fusions can easily be made in a day. The only way in which a deter- mination can be lost is by heating too rapidly on the hot-plate, thus causing it to boil over or spatter. DESCRIPTION OF SAMPLES AND ANALYTICAL BESTJLTS. Total sulphur was determined by both the peroxid method and the proposed method on five samples of dried white of eggs, three of which were made from the same lot of eggs by boiling with various amounts of copper sulphate, washing free of copper, and drying and grinding; one was a sample of commercial dried albumin; and one was the white of eggs boiled in the shell, dried, and ground. Sulphur was also determined on four samples of mustard seed, and one sample of ground mustard. A is pure white mustard, B is black mustard containing 64 per cent of charlock, O is commercial ground mustard, D is pure LCir. 66] brown mustard, and E is commercial ground seed. These samples were furnished by the Microchemical Laboratory. Sulphur was also determined on five samples of vulcanized rubber furnished by the Contracts Laboratory. The 60 determinations were made without repeating any, except No. 8136, unless a loss occurred by the leaking of the crucible. This happened in three instances onl}^, so that the work represents fairly well the results which the two methods will give under the same con- ditions without repetition and selection of results. Twelve determina- tions were made at a time with each kind of material, two determinations on each sample, and two blanks. The results obtained are given in Table 1. The peroxid fusions were not hurried, but were allowed to fuse for three or four hours. No. 8136 is a sample of rubber tubing which was not ground very finely, and which had been found to con- tain about 50 per cent of free sulphur. These facts probably account for the discrepancies in the determination. [Cir. 56] § S • g ;^^ g + I + + + ?3 o t* t» g^ s § g3 ?5 g! ^'S uS3 S ?5S 2 : SS ^S rH^H C^) < r>< OiC 00 CO «OI> i-IO • lOTtI M(M CCM (M(M iOt}< t)<(M • eoeo 5050 «co tot^ lO-* eoeo th mim coim mm S^ ^m S m OO OO OO OO OO S OO OO OO OO OO ss i8§ g8 S? no iC iC lO © Old !m So So OO >o oS OO So 'O (3 [Cir.56] ,0 oM I a^ • o o «5 g S 5 w o •55 04 t^ 05 S K CO ?4 CO t-^ AS "SO* 00 » eowi c^c4 coco t^t-^ §3S So. I' 5§s lis d g s S^ S8 12s feS^gg "g.' T)i' c^ c>j -^ -^ t^ t^ r>^ 06 icc^ (oci t-eo u^t^ooo r-l CO 00 Oi tH i-H 0(NOS Losses of sulphur on charring. J. Amer. Chem. Soc, 1904, 26: 354. [Cir. 56] 14 DAY USE RETURN TO DESK FROM WHICH BORROWED LOAN DEPT. This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. l05ep'63Ef SEP 7 01963 RECDXty RECEIVED NOV 0 2 1995 qiRCULATION DEPT. -mm FEB - 8 1 SUBJecr TO RECALL IMMEDIATELY SEP1S'64-5PI« JUN 13 1976 K&CW. MflriPTS FEB 01 1996 LD 21A-50m-ll,'62 (D3279slO)476B General Library Uoiversicy of California Berkeley m iru 6^407 U.C.BERKELEY LIBRARIES CDSl^DE^^^ -Jt .^ "; ' '. .