Vacuum Distillation Equipment for Volatile Solids LUTHER BOLSTAD AND RALPH E. DUNBAR N. Dak.
Sorth Dakota Agricultural College, Fargo,
DURISG
the preparation of a quantity of aluniinurii ethoxide (1) considerable difficulty was encountered in the final purification when the usual vacuum distillation equipment was used. Troublesome condensation, even leading to complete clogging in the delivery tubes! often prevents distillation. Special equipment failed to give satisfactory results ( 3 ) . Furthermore, where the product must be repeatedly distilled there is considerable loss and possible contamination during transfer of the distillate from receiver to original flask. Similar conditions are likewise encountered when distilling benzophenone, phenyl cinnamate, and similar compounds. The apparatus, as illustrated, was designed and constructed t o eliminate many of these difficulties.
P
Two round-bottomed flasks, A and B , of suitable capacity (50 to 500 ml.) are attached to a glass Y-tube, C, of large diameter (15 to 25 mm.). The upper end of this Y-tube is sealed to a short length of 8-mm. glass tubing, so that it may be attached to a thermometer by a small section of rubber tubing a t D. A convenient side arm, E, is provided for evacuating the entire equipment. The solid to be distilled is placed in flask A , the vacuum is applied, and flask B is cooled with running water. The application of heat to A causes the solid to distill, the temperature being recorded as usual on the thermometer. If the distillation is to be repeated, A is now thoroughly cleaned, the vacuum is again a p plied, B is heated, and A is now cooled as the receiver. This process may be repeated indefinitely. I n case it becomes necessary further to subdivide the distillate at some definite temperature, the flask being used as the receiver may be replaced by one of the type shown a t F. A simple turn of 180” will throw either flask into position as the receiver. Rubber stoppers, or preferably ground-glass connections (@, may he used throughout in constructing the equipment.
Literature Cited (1) Adkins, H., J. Am. Chem. SOC.,44, 2175 (1922). (2) Carlson, W. A., IND. ENG.CHEM.,ANAL.ED.,10, 644 (1938). (3) Morton, A. A,, “Laboratory Technique in Organic Chemistry”. p. 101, New York, McGraw-Hill Book Co., 1938.
Identification of Rust on Iron and Steel
I
RALPH 0. CLARK Gulf Research & Development Company Pittsburgh, Penna.
N SOME investigations in this laboratory it was necessary
to identify rust on lubricated ferrous alloys. Visual inspection could not be relied upon because of the similarity in appearance betiveen rust and petroleum gum. Ordinary chemical tests were not applicable, since most of them brought about the removal of some of the base metal along with the rust. Removal of the rust b y pressing solvent-impregnated filter or gelatin paper onto the specimen proved unsatisfactory; with all the solvents tried, the base metal was preferentially dissolved. While these tests were unsatisfactory on the whole, those obtained with gelatin paper were much better than those in which ordinary filter paper mas used. This suggested the use of gelatin paper moistened with water rather than a rust solvent. Subsequently i t was found that gelatin paper moistened only with water mas capable of removing an amount of iron rust sufficient for testing, without affecting the metal itself.
and drying. The hypo-eliminator (Kodak Formula HE-1) is prepared as follows: Water Hydrogen peroxide, 3% dmmonium hydroxide, 3% Water t o make
600 ml. 125 ml.
100 ml. 1 liter
After iixing, the paper is washed 30 minutes in running water, immersed for 6 minutes in the above solution, washed for 10 minutes in water, and dried. About 6450 sq. cm. (1000 sq. inches) of paper may be processed in 1 liter of solution. Paper processed in this fashion may be stored in stoppered bottles indefinitely. To carry out a test the gelatin surface of the dry paper is moistened slightly with distilled water and pressed firmly against the specimen: Continuous pressure on the paper is unnecessary, owing to the inherent adhesive property of the moist gelatin. After 15 to 30 seconds the paper is removed, care being taken to avoid stripping the gelatin coating from the paper base, Should it be impossible to remove the paper without this happening, the back should be moistened with distilled water and allowed to
Procedure The gelatin paper was prepared by fixing unexposed glossy photographic paper in sodium thiosulfate solution (200 grams in 1 liter of solution), treating in a hypo-eliminating solution (1) 464
ANALYTICAL EDITION
July 15, 1943
stand for a minute or so, before another attempt a t removal is made. After removal from the specimen, the test paper is immersed in 10 per cent hydrochloric acid containing 0.05 er cent potassium ferrocyanide. Upon development a Prussian glue pattern of the rusted surface is obtained. The development time should be relatively short (10 to 15 seconds) in the case of freshly rusted surfaces if an accurate rust pattern is desired. With aged or worn rust it may be necessary to extend the time of development to one minute or more. The pattern is usually more distinct if the paper is dried with heat. The Prussian blue developed in the gelatin has little tendency to diffuse and, contrary to filter paper prints, clear, sharp patterns result. Potassium ferrocyanide is preferred agent since the to potassium as a latter tends to give a blurred and indistinct image.
465
Experimental Tests performed on solvent-cleaned, specially prepared, rusted iron and steel strips using the procedure described gave satisfactory analytical patterns of the rusted surface. Tests made on clean, freshly polished iron strips failed to give a Prussian blue color even upon prolonged development. The test apparently is specific for iron oxide; attempts to remove sulfide films from copper or lead specimens were unsuccessful. This was attributed to the fine structure and close adherence of the sulfide film in contrast to the rather flaky and ~ o o s e ~held layer. v ferric
Literature Cited (1) Crabtree, Eaton. and Muehler. J . Phot. SOC.Am., 6 , 6 (November, 1940).
An Improved Salt Bridge for Polarographic and Potentiometric Measurements DAVID N. HUME AND WALTER E. H4RRlS School of Chemistry, University of JIinnesota, RIinneapolis, Minn.
A
I”; E X T E R K A L reference electrode is frequently used in potentiometric and polarographic measurements. The connection to the solution is by some type of a salt bridge. The ideal salt bridge, in addition to eliminating the junction potential, should have a low resistance (especially in polarography) , should not contaminate the solution being used, and should be easy to handle. A number of bridges have been described in the literature, none of which incorporates all the desired features. The inverted-U bridge of Irving and Smith (a), with ground-glass plugs at the ends, has been widely used in potentiometric work but has a n undesirably high resistance for polarography if the reference electrode is to be used as the anode. A bridge of this type, 40 cm. long, when filled with saturated potassium chloride, was found to have a resistance of about 7000 ohms, some 6500 ohms being
attributable to the plugs. Laitinen (3) has described an inverted-U bridge with sintered-glass ends which has a lower resistance but which, in common with other all-glass designs (1, 4 ) , is rather cumbersome to use. The authora have found the very simple bridge illustrated in Figure I to be highly satisfactory. The saturated calomel electrode, A , is connected to the cell with a piece of ordinary soft rubber tubing. B , 6 mm. in inside diameter, filled with saturated potassium chloride. The rubber tube terminates in a short length of glass tubing filled with 3 per cent agar jell, also saturated with potassium chloride. When it is to be used, the free end of the bridge is simply plugged into the cell. The reference electrode may be kept permanently out of the way and the necessity of simultaneously adjusting two cells in a thermostat to connect \Tith an unbendable glass bridge is eliminated. Figure 1 shows how an intermediate agar plug, D,having the bame composition as the cell liquid, may be used if contamination with potassium chloride is undesirable. If traces of potassium chloride are not objectionable, the free end of the bridqe may be inserted directly into the solution. For this purpose it is convenient to have a thin, coarsely-sintered glass plug at the tip of C. The agar is still desirable to prevent mixing by convection. The end of the bridge is kept in potassium chloride solution R-hen not in use. The resistance of such a bridge 56 em. long was found to be only 600 ohms. For a polarogram showing a diffusion current of 10 microamperes, the error in half-wave potential due to I R drop in the bridge would be about 3 millivolts. This error is negligible for most purposes and may, of course, be decreased b y the use of a shorter bridge or larger tubing. If exact values of half-wave potentials are desired, the resistance of the cell and bridge may be measured and the correction applied whenever necessary. For potentiometric titrations, in which a low bridge resistance is not essential, plug D is conveniently replaced by one of ground glass, as in the bridge of Irving and Smith (9).
Literature Cited
FIGURE 1
(1) Bright, W. M., and Miller, E. L.,IXD.ENG.CHEM.,ANAL.ED.,9, 346 (1937). (2) Irving, G. W., and Smith, N. R., Ibid., 6 , 4 8 0 (1934). (3) Laitinen, H. A., Ibid., 13, 393 (1941). (4) Stern, H. T., J . Phyr C h e m , 29, 1583 (1925).
