INDUSTRIAL AND ENGINEERING CHEMISTRY
January 15, 1929
Table 111. The first column gives the number of t,he experiment corresponding with the number given in Table 11, and the last column gives the proportion of barium sulfate (recovered from the residue after fusion) as percentage of the total, original barium sulfate obtained from the sodium sulfate. Table 111 RESIDUE FROM
Bas04 FROM
EXPT.
BaCOi Gram
RESIDUE Gram
1 2 3 4 5
0.0051 0.0047 0.0048 0.0050 0.0053
0.0047 0.0040 0.0042 0.0045 0.0046
PROPORTION ORIQINAL BaSO' Per cent 0.71
OF
31
carbonate and boiled for 2 hours, after which the resulting solutions were filtered, acidified, and precipitated with barium chloride. The results are given in Table IV. When the barite was boiled with the sodium carbonate solution for only 1hour, the proportion of precipitated barium sulfate averaged only about 98.5 per cent of the original barite. The same barite when decomposed with fused sodium carbonate gave an average of 99.93 per cent of barium sulfate precipitate. Conclusions
0.61 0.03 0.09 0.70
It is obvious that the removal of sulfur from barium sulfate by digestion with hot solutions of sodium carbonate does not The results given in the last two tables, as compared with yield such good results for analytical purposes as does the the preceding, show that nothing is to be gained by in- fusion method. Nevertheless, because of its simplicity and creasing the proportion of the sodium carbonate beyond speed, especially when combined with a method like the fifteen times the theoretical, or by heating beyond 1 hour. nitric-perchloric acid method of determining sulfur in rubber, While i t is probable that equilibrium has not yet been reached, this procedure may find some usefulness where extreme acthe reaction a t this point is so slow that it is not practicable curacy is not so important as speed; and if only a small proto attempt to force i t further. It would also appear that the portion of barium sulfate is present-15 per cent or less-it importance of first washing the barium carbonate (after may yield results well within the limits of experimental error. To adapt this method of decomposing barium sulfate t o filtering) with sodium carbonate, in order to remove all soluble sulfates, has been overestimated, and that no appreciable the determination of total sulfur in rubber by the nitric-pererror will be introduced by washing immediately with water. chlorio acid method,2 the procedure would be as follows: This will be especially true if the original solution is allowed After dissolving the rubber sample in the mixture of nitric to run completely through the filter before wa,shingis started. and perchloric acids and boiling until fumes of perchloric acid appear, allow the solution to cool somewhat, add about Table IV 25 cc. of water, then 5 grams of sodium Carbonate, and boi1 BARITETAKEN Bas01 PRECIPITATED" gently for 1 hour (or for 2 hours if native barite is present or Gram Gram Per cent 99.5 0.4980 0.5005 suspected), adding more water from time to time if necessary 99.7 0.4971 0.4986 to prevent bumping. The solution is then filtered, acidified, 99.6 0.4985 0,6005 99.5 0.5002 0.4977 and treated with barium chloride in the same manner as in a Not corrected for occlusions. the fusion method. EXPERIMENT8 WITH BARITE-Barite, the natural barium The amount of sodium carbonate recommended above sulfate, will give very much the same kind of results as the (5 grams) is sufficient to neutralize 3 cc. of 60 per cent perabove, although it requires longer heating with the sodium chloric acid and still leave fifteen times the amount of sodium carbonate solution because it is usually less finely divided and carbonate theoretically required to decompose 0.5 gram of hence presents a relatively smaller surface than the arti- barium sulfate-that is, enough for a 1-gram sample of a ficially precipitated material. Half-gram samples of native rubber compound containing 50 per cent of barium sulfate. barite, ground to 200 mesh, were boiled with about 25 cc. of While this reaction was studied especially with a view of its water and 3 cc of perchloric acid as in previous experiments, utilization in the analysis of rubber, it may, of course, find then again treated with 25 cc. of water and 6 grams of sodium applications elsewhere.
Determination of Moisture in Sugar Sirups' E. W. Rice NATIONAL SUGARREETNERY, YONKERS, N. Y.
T HAS long been apparent to the author that a definition of "moisture" as applied to low-grade sugar sirups can be merely an arbitrary one based upon certain definite conditions. This cannot indicate true moisture, since desiccation a t room temperature will remove water of crystallization from some but not from all substances that are likely to be present in final sirups. Aside from water of crystallization there are substances present which undergo continual decomposition a t a temperature as low as 70" C. Samples run by the vacuum oven sand method a t 70" C. of the Association of Official Agricultural Chemists2 have shown a continuous loss in weight of an average of 0.5 mg. per hour for various lengths of time from 20 to 50 hours. That this is
I
1 Presented before the Division of Sugar Chemistry at the 76th Mecting of the American Chemical Society, Swampscott, Mass., September 10 t o 14, 1928. 2 Assocn. Official Agr. Chem., Methods, 1925, p. 178.
decomposition seems to be assured by the fact that samples of the same sirups prepared in the same manner reached a constant weight in 48 hours in a Hempel desiccator with sulfuric acid, a t a pressure reduced to about 1 inch (2.5 cm.) and no further loss in weight was found after 10 days. This indicates that decomposition commences very soon in any method where heat is applied a t 70" C. or higher. Since the important thing is to adopt some standard method and call the result "moisture," it is undoubtedly wise to accept the method mentioned above. This does not preclude an attempt to arrive a t the same results by some quicker and easier method, and where many tests are made it is almost imperative that some simplification be introduced. It was found that with the type of sirups made at one plant by heating in a water oven near 100" C. the working time could be cut in half and the same results obtained as by t h e official method.
ANALYTICAL EDITION
32
The use of nearly 60 grams of combined dish, sand, and rod and the many weighings necessary to determine moisture in 1 gram of sirup make a cumbersome task and it was with great pleasure that the author welcomed the method of Bidwell and Sterling.* As soon as apparatus could be made the method was tried out, but with only partial mccess because the same continuous decomposition was encountered and no definite end point was found. Several tests showed that by using identical conditions and a definite time interval concordant results were possible on sirups of moderate or low invert sugar content, but with invert sugar of 25 per cent or over the results were unreliable and the residue in the flask after distillation was seriously blackened. At about this stage an oil bath was substituted for a sand bath with improved results, but the method was considered as limited to blackstraps and sirups of low invert sugar content. With the thought in mind to precipitate any calcium present as chloride and that some molecular rearrangement might cause a more ready release of water present, a distillation determination was tried with 2 grams of powdered sodium oxalate added to 15 grams of sirup. The result was a quicker distillation and less blackening of the residue. Another test with 10 grams of sodium oxalate gave results that were even better. Inasmuch as blackstrap has a considerable quantity of suspended particles and sodium oxalate is only sparingly soluble, the question arose as to whether the improved results were due to the chemical or physical effect of the sodium oxalate. To determine if finely divided material would assist in the distillation, 10 grams of Filter-Cel were added. The result was rapid evolution of the water, 8
Vol. 1, No. 1
and after 4 hours’ heating the residue showed no indication whatever of blackening or decomposition. While a small amount of water continued to distil over, the major part was over in 1 hour and the slight additional amount a t the end of 3 hours made the total in close agreement with the percentage as indicated by the official method. As an indication of the effect of the Filter-Cel it was noted that the same rate of distillation of the toluene could be maintained with the oil bath at 127” C. as a t 143” C. without Filter-Cel. The advantages of the distillation method as set forth by Bidwell and Sterling were found to be true, especially the advantage of a 15-gram sample and a single weighing. The total time consumed is a t most 4 hours, during which the operator is occupied but a few minutes at the start. The most satisfactory manipulation is to put half of a roughly weighed 10-gram portion of dried Filter-Cel into a flask and then weigh off 15 grams of sirup into a capsule formed from a piece of thin waxed paper resting in a 15-cc. Gooch crucible. After weighing, the paper may be lifted out of the crucible and sirup and all dropped into the flask, after which the second half of the Filter-Cel is added and the distillation carried out as described by Bidwell and Sterling. Comparison of Distillation Method w i t h Official Method for Determination of Moisture in Sugar Sirups 3 HOURS’ VACUUM SAMPLE BATR FILTER-C&tDISTILLATIONOVEN INVERT Grams Per cent Per cent Per cent A Sand 1 Oil
B
Sand Oil Oil
1 IU
Sterling, IND.END.CHEM.,17, 147 (1925).
Evaluation of Stibnite‘ I-De termination of Sulfur Wallace M. McNabb and E. C. Wagner UNIVERSITY ox PENNSYLVANIA, PHILADELPHIA, PA.
tendency for the evolution method to yield results for sulfur use in primers were described in 1918 by Cushman,2 slightly lower than those obtained by bromine oxidation. and were incorporated into the specifications of the Table I-Comparison of Sulfur Determinations by Evolution a n d Bromine Oxidation Methods United States Ordnance D e ~ a r t m e n t . ~I n the recommended EVOLUTION METHOD BROMINE OXIDATION method for sulfur this element is oxidized by action of bro% % 21.38 21.14 mine and glacial acetic acid, and after suitable further treat21.28 21.15 ment, including removal of antimony by use of aluminum 21.40 21.14 21.10 powder, it is precipitated and weighed as barium sulfate. Av. 2 1 . 3 4 Av. 2 1 . 1 3 This procedure, Cushman states, was adopted a t the Frank21.77 21.72 21.78 21.72 ford Arsenal “as giving fairly quick and accurate results.” 21.70 Elsewhere in the same article occurs the declaration: “All 21.76 21.73 other methods for the determination of sulfur have been reAv. 2 1 . 7 8 Av. 2 1 . 7 3 jected as leading to inconsistent results.” This condemnaThe differences of 0.21 and 0.05 per cent appeared to be tion specifically includes fusion methods, evolution methods, and electrolytic methods, and is offered without supporting significant, and not accidental. As the bromine oxidation is clearly a method for total sulfur, and as the evolution method \data. Wofk on the analysis of stibnite in 1917 showed the ap- can determine only sulfide (and oxysulfide) sulfur, it was Tplicability of the evolution method, the sulfur being disen- suspected that the variations might be due to the presence gaged as hydrogen sulfide, absorbed in ammoniacal cadmium of free sulfur in the stibnite. To test the two methods with solution, and determined iodometrically by an adaptation respect to their ability to indicate a distinction between total of the familiar procedure. There was noticed a constant sulfur and sulfide sulfur, a specimen of artificial black antimony sulfide was analyzed for sulfur by both methods, and a 1 Received July 11, 1928. 10-gram sample was extracted with carbon tetrachloride and Cushman, J. IND.ENG.CHEM.,10,376 (1918). the free sulfur weighed. a U. S. Army Ordnance Dept., Sfiec. 60-11-14(July 24,1923).
M
ETHODS for the analysis of stibnite intended for
