VOL. 9, NO. 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
250
Apparatus for the Extraction of Liquids with Immiscible Solvents of Greater Density
siphoning. Secondly, the solvent must not be boiled so vigorously as to cause a turbulence in the condenser, thus setting u p pressure, a sudden release of which may also cause siphoning. With these precautions the above apparatus has been run continuously for several days without attention. The apparatus is made from ordinary laboratory material and there is no reasonable limit to its size.
LINDSAY H. BRIGGS Auckland University College, Auclcland, New Zealand
RECEIVED January 5 , 1937
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A
N ORDINARY "siphon"
apparatus similar t o the Soxhlet extractor may be used for extraction of liquids with immiscible sohents of greater density, provided the return tube is sufficiently wide t o prevent siphoning, the solvent flowing over continuously as fast as it condenses. The main disadvantage of such apparatus is in arranging the height of the siphon tube, which must vary from experiment t o experiment according t o t h e density of the solvent and the amount of liquid t o be extracted. The following apparatus has been found useful in extracting comparatively large amounts of aqueous solutions containing plant material with heavy solvents such as chloroform or trichloroethylene.
CORRESPONDENCE Calcium Chlorite as a Volumetric Oxidizing Agent SIR: I n a recent work by Donald T. Jackson and John L. ENQ.CHEM., Anal. Ed., 15, 14 (1937)] they proParsons [IND. pose the use of sodiym chlorite as a reagent for volumetric analysis and particularly for the determination of sulfur dioxide, sulfites, and bisulfites. The method is excellent. The authors quote some of my researches on chlorites, adding that the Mathieson Alkali Works, Inc., now manufactures a product containing 97 to 98 per cent of sodium chlorite which may be used for this purpose. I would like to make two observations: (1) Jackson and Parsons do not mention my article on "Reactions of Oxidation and Reduction with Chlorites" [Guzz. chim. it& 52, 58 (1922)l which NaCIOz = 2H2S04 gives precisely the reaction, 2HzSOs NaC1, that the authors assume as the basis of the titration. (2) The ability to obtain 100 per cent calcium chlorite because of the solubility of calcium chlorate and chloride in alcohol, permits, from my point of view, its more convenient use as the direct standard. The calcium chlorite solution must be made with freshly boiled water free of carbon dioxide. GIORQIORENATOLEVI
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INBTITUTO DI C H I M I C A GENERALE R. U N I V B R S I T ~ PAVIA,ITALY March 10, 1937
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The apparatus consists of a boiling flask, A , connected to a reflux condenser, B, which fits into the main vessel, C, containing the liquid to be extracted. The condensed vapor from the boiling solvent flows down through the liquid in C, forms a separate layer at the bottom, and passes over through the siphon tube, D, into A as fast as condensation occurs. In practice the solvent drops from the condenser onto the surface of the liquid in C, breaking up into smaller drops which do not fall straight through but fan out through the liquid. The essential feature is that the siphon tube can swing about the axis E-F, enabling the height of liquid in the tube to be adjusted according to the amount of aqueous extract in C and the density of the solvent. Major adjustments may be made by sliding the inverted U-tube up or down and minor adjustments by tilting the U-tube, which js then clamped to hold it steady. There are two essentials in the construction. Firstly, the siphon tube must be of sufficient width to allow t h e condensate to run over freely. Blocking with solvent owing t o the use of smaller bored tubing will immediately cause complete
SIR: The pioneering work in the preparation, properties, and uses of the chlorites by G. R. Levi and his associates is fuIly appreciated by Dr. Jackson and myself with reference to our article on sodium chlorite as a volumetric oxidizing agent in the ANALYTICAL EDITION for January 15. Unfortunately the Italian journals are not readily accessible to us. For many of Mr. Levi's references, therefore, vve have had to depend on the abstract journals and the equation to which he refers in his comments was not covered by the abstract. It has been our experience, however, that the reaction 2HzSOs NaCIOz = 2HzS04 NaCl is rather slow and not particularly suited to volumetric analysis. By the addition of a small amount of potassium iodide the reaction is markedly accelerated and i s very satisfactory for the purpose we had in mind. I n the presence of the iodide ion the reactions appear to be:
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ClOz-" 41- f 4H+ +C1' 2H20 f 212 2S03-- +2SO,--
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+ 212 + 2Ha0 f 41' + 4Hc
JOHNL. PARSONS HAMMEENILL PAPERCo. ERIE,PA. April 3, 1937
