ANALYTICAL EDITION
200 N =I’-I+K P’ = P- - N_.
R
ACKNOWLEDGMENTS
0.514 P’ - I 0.514 P’ - I = ,= 0.514 (0.321 0.00009S) 0.835 0.000098 0.514 P’ - I - 0.514 P’ - I or 0.514 (0.321 0.00009P) - 0.835 0.00009 P = 0.54 (P’- S)
+ +
Vol. 6 , No. 3
+ +
+ +
where N = polarizing effect of the optically aotive nonsugar6 P’ = true direct polariaation of the raffinose and sucrose S per cent sucroee R = per cent raffinose K = neutraliaation correction to be obtained from Table VI an proportional to either b or P and milliliters of lead used per 100 ml. of leaded solution
-
The following notes on the technic of the method may be of value : 1. If amyl alcohol is used to break the foam while deairing, do not use more than 3 or 4 drops, because this alcohol is optically active and is not volatile at room temperatures. 2. Make all filtrations under wetted bell jars resting on wetted rubber mats, or with the filters covered with large cover glasses. Discard the first 10 t o 15 ml. of each filtrate. 3. The amount of ammonium phosphate necessary t o delead may be determined by adding small incremental amounts and testin for complete precipitation by testing a drop with a solution of potassium iodide or with a further crystal of ammonium . An undue excess of phosphate must be avoided, or each 1 ram excess per 100 ml. depresses the direct polarization 0.35’ 4. As much as 0.1 gram of sodium hydrosulfite may be added with the inverting acid if the solution is dark. 5. The calculated percentages of sucrose and raffinose should be corrected for the volume of the lead preci itate. In molasses this may be done by deducting 1 per cent opthe calculated percentage from itself. This correction will be proportionately less on higher purity products, varying with the decrease in impurities and amount of lead acetate used.
phosphate E.
The writers wish to acknowledge their appreciation to the many chemists who have assisted in this work, especially to B. F. Jones and D. H. Xingsley for their care and patience in the great amount of analytical work involved; to R. J. Brown and E. H. Hungerford for their valued suggestions; to Geo. Goldfain and G. E. Stevens for the single-acid method analyses; to A. H. Edwards for the determinations of the invert sugar in the sugar used in this work; and to the various sugar companies which kindly furnished the molasses samples used. LITERATURE CITED (1) Assoc. Official Agr. Chem., Official and Tentative Methods, p. 373 (1930). (2) Brown, IND.ENQ.CHEM.,17,39 (1925). (3) Browne, “Handbook of Sugar Analysis,” p. 221,Wiley, 1912. (4) Browne and Gamble, J. ISD.ENG.CHEM.,13,793 (1921). (5) Jackson and Gillis, Bur. Standards, Sci. Paper 375, 169-71 (1920). (6) Kindt, Ind. saccar. {tal., 26, 50 (1933). Anal. Ed., 5, 221 (1933). (7) LundeU, IND.ENQ.CHIOM., (8) Osborn and Brown, Facts About Sugar, 27,434 (1932). (9) Paine and Balch, ISD.ESG.CHEM.,17, 240 (1925). (10) Paine and Balch, J. Am. Chem. SOC.,49, 1019 (1927). (11) Sohoorl, Arch. Suikerind., 33, 273 (1925). (12) Schoorl, 2. Untersuch. Lebensm., 57,566 (1929). (13) Vosburgh, J . Am. Chem. SOC.,43, 219 (1921). (14)Walker, J. IND. ENQ.CHEM.,9, 490 (1917). (15) Zerban, J. Assoc. OficiaZ Agr. Chem., 12, 158 (1929). (16) Zisch, Facts About Sugar, 27,211 (1932). R ~ C ~ I VOctober ED 5, 1933. Presented before the Division of Sugar Chemistry a t the 86th Meeting of the American Chemical Sooiety, Chicago, Ill., September 10 to 16, 1933.
Determination of Minute Quantities of Sulfide Sulfur C. E. LACHELE, National Canners Association, San Francisco, Calif.
T
HE method developed in the western branch laboratory
of the National Canners Association for the determination of small quantities of volatile sulfide sulfur is a modification of that described by Drushel and Elston (3). The principal differences are in the method of evolution and the type of apparatus used in collecting the stain on the lead acetate paper. The sulfide gas upon evolution from an acid solution is continuously carried along and through a lead acetate-impregnated paper diaphragm by a stream of an inert gas such as nitrogen, The nitrogen, by intimately diluting the sulfide gas, permits a uniform coating of lead sulfide and sweeps the reaction flask free from residual sulfide gas. A uniform deposition of the stain is further aided by means of a 1-to 2-inch (2.5- to 5-cm.) bed of small glass beads or standard Ottawa sand. The impregnated paper disk is closely fitted between two ground-glass joints of thick-walled glass tubing which are held together by a band of Gooch rubber tubing so that all gas leaving the reaction flask must pass through the paper. Under the conditions of the experiment sulfur dioxide does not interfere and only the sulfide which is evolved by acid is determined, The diameter of the chamber tube employed is governed by the amount of sulfide present. For amounts of volatile sulfide sulfur between 0.008 and 0.080 mg. a 32-mm. tube was found to be satisfactory, and under these conditions an accuracy of 10.002 mg. of sulfur is possible. The delicacy of the test is increased by using chamber tubes of smaller diameter.
STANDARDS The paper found to give good results was Schleicher and Schull No. 589 black ribbon filter paper. It is sensitized by soaking for one hour in a saturated neutral lead acetate solution and air-dried by vigorous waving, followed by an air blast. The paper may then be cut in disks to fit the appropriate chamber tube. Indications are that impregnated paper will retain its sensitivity for several months if kept protected in a closed container. Standard stains are prepared by evolving the sulfur from weighed samples of Bureau of Standards steels such as No. 14b basic open hearth steel containing 0.031 per cent of volatile sulfur, This method of standardization was found preferable to the usual practice of diluting strong standard sodium sulfide solutions, as the dilution necessary to obtain small amounts of the standard resulted in immediate oxidation of some of the sulfur. After deposition of the lead sulfide stain the disks are thoroughly washed in distilled water and dried between sheets of white blotting paper. They are preserved by keeping them in the dark while not in use, as oxidation to colorless lead sulfate occurs when exposed to sunlight, particularly in the case of very faint stains. ’ METHOD The sample is placed in a 1000-cc. Erlenmeyer flask with about 100 cc. of distilled water and the system swept with nitrogen to remove excess air, after which 50 cc. of 1 to 1 hydrochloric acid
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
May 15,1934
(special arsenic-free hydrochloric acid gives a perfect blank for this work) are added by means of a dropping funnel. Some operators may prefer to use 100 cc. of 1 to 1 phosphoric or sulfuric acid to eliminate the necessity for a moist cotton plug for absorbing any escaping hydrochloric acid fumes. The contents of the flask are heated to boiling and a stream of nitrogen (about 5 mm. of pressure) is continually passed through the system until all sulfide has been evolved. The residual gas is washed out of the flask by increasing the nitrogen stream (to about 30 mm. pres-
n
for absorbinn HC1 tumes
Rubber tubing
