INDUSTRIAL AND ENGINEERING CHEMISTRY
582
diphenylamine indicator and titrate with dichromate solution until a darkening occurs. At this point add 5 ml. of phosphoric acid and 8 to 10 drops more of indicator. Add water to make the total volume about 250 ml. and complete the titration to the first permanent violet coloration. REAGENTS.Reagents (Fehling’s and Ost’s) for reducing sugars are prepared according to A. 0. A. C. ( 4 ) directions. Ferric sulfate solution is made by dissolving 60 grams of the hydrated salt [Fe2(S0&.9H20]in 1 liter of solution and filtering. The solution must be free from ferrous ions. Potassium dichromate is weighed to give exactly 7.7135 grams per liter of solution. One milliliter is equivalent to 10 mg. of copper. Diphenylamine is used as 0.2 per cent solution in concentrated sulfuric acid, Sulfuric acid is a 1to 7 aqueous solution. Orthophosphoric acid is the usual 85 per cent U. S. P. sirup. Lead acetate solution is a saturated solution of the neutral salt. Disodium phosphate is used either dry or as a saturated solution.
I n most instances it appears safe to omit clarification of the alcoholic extracts of apple tissue, with a corresponding saving in time. Where clarification is necessary this can be accomplished satisfactorily by addition of neutral lead acetate and centrifugation as described.
Literature Cited
Summary I n the analysis of apple tissue for sugars it is advantageous to heat the tissues in closed aluminum containers before grinding, to disintegrate, mix, and extract the heated tissue in a ]Taring Blendor, and to determine cuprous oxide by dissolving i t in ferric sulfate solution and titrating with potassium dichromate in the presence of diphenylamine indicator. The procedure is rapid and easily manipulated and the results are sufficiently accurate for the determination of sugars in many plant materials.
Vol. 15, No. 9
I
Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 5th ed., p. 138, 1940. Ibid., p. 358. Ibid., p. 497. Ibid., pp. 498, 504. Browne, C. A., and Zerban, F. W., “Physical and Chemical Methods of Sugar Analysis”, 3rd ed., New York, John Wiley & Sons, 1941. Davis, W. B., IXD.ENQ.CHEM.,NEWSED., 17, 752 (1939); IND. ENG.CHEM.,34, 217-18 (1942). Erb, C., and Zerban, F. W., IWD.EXG.CHEM.,AXAL.ED., 10, 246-50 (1935). Jackson, R. F., and McDonald, E. J., J . Assoc. Uficial Agr. Chem., 18, 172-8 (1935). Ibid., 24, 767-88 (1941). Jackson, R. F., and Mathews, J. A . , Bur. Standards J . Research, 8, 403-44 (1932). Kneen, E., and Blish, M . J., J . Agr. Research, 62, 1-26 (1941). Stegeman, R. A., and Englis, D. T., J. Assoc. Oficial Agr. Chem., 19, 480-9 (1936). Taran, E. Tu’., J . Applied Chem. (17. S. S . R.), 7,213-21 (1934). PUBLISHED with t h e approval of the director of t h e West Virginia Agrioultural Experiment Station as Scientific Paper 284.
Simple Device for Preparing Vapor-Air Mixtures J. BRENNAN GISCLARD, Bureau of Industrial Hygiene, iMichigan Department of Health, Lansing, Mich.
I
N TESTING the efficiency of a combustion apparatus
for chlorinated hydrocarbons in the atmosphere, the writer desired to introduce into the unit known amounts of solvent vapor a t rates of 1 to 2 liters per minute. A simple method of doing so, and one most nearly meeting this need, was found in the experimental work of Olsen, Smyth, and
co-workers (1). However, a modification which would ascertain by successive weighings the amount of solvent used in each run seemed desirable. A very satisfactory method was finally devised which gave precise weighings and a wide range of concentrations and required very little manipulation. Both ends of a two-way stopcock of about 8 m m . bore were cut off about 35 m a . from the base and one end was sealed. A short piece of glass tubing, 7 mm. in inside diameter, was drawn out, bent, and inserted in the two-hole rubber stopper as shown. The mixing chamber was a filter tube, the neck of which was bent a t a right angle and connected to the combustion unit. The apparatus was mounted by means of a clamp on a ringstand. In operation, the solvent to be tested, trichloroethylene, was pipetted into the bulb and the stopcock closed and weighed by suspending it in the analytical balance (by means of a wire hook not shown in the diagram). The stopcock was then inserted in the rubber stopper, suction applied, and the stopcock opened to some fixed position, depending on whether a small or large concentration was desired. A drop of phosphoric acid served as an efficient lubricant. The vapor-air mixture was drawn through the apparatus for the desired length of time, after which the stopcock was closed, removed, and reweighed while pure air continued to flush residual vapor from the chamber. The difference in weight represented the amount of sDlvent which \Tas carried over at a practically constant rate. Since the experiments were conducted a t room temperature, the evaporative loss was uniform throughout, amounting to about 1 mg. for each run. Experiments showed that. a t various openings of the stopcock and at raised or lowered positions of the inlet tube orifice a range of concentrations of from 10 to 500 p. p. m. vas easily obtained.
No 0 rubber
r
-Air
Literature Cited inlet
(1) Olsen, J. C., Smyth, H. F., Jr., Ferguson, G. E., andsheflan, L., IXD.ENO.CHEW,ANAL.ED.,8, 260 (1936).
