Determination of Oil in Metal Turnings Improved Method and Apparatus DAVID MARGOLIS', .Alloys Recovery Company, Inc., Harrison, N. J.
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Y THE old method for determining oil in metal turnings, a known weight of sample is subjected t o repeated washing b y decantation at room temperature in a beaker of appropriate size with a chlorinated solvent such as carbon tetrachloride or a low-boiling nonchlorinated solvent such as petroleum naphtha or petroleum ether. This method has certain disadvantages. 1. The operator's complete time is required and he may be subjected to poisonous fumes from the solvent used. Solvents such as petroleum naphtha with a low boiling range constitute a fire hazard. 2. There is considerable loss of solvent by evaporation. 3. Efficiency of extraction is so poor that even after three to four washings with carbon tetrachloride the author has found evidence of residual oil upon drying the turnings after the last washing. Since the higher boiling nonchlorinated solvents 1 Present
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FIGURE2.
LOWERING OF HOT PLATE AND BEAKER
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have a much lower extraction efficiency than carbon tetrachloride the number of extractions and time required are correspondingly increased. 4. Carbon tetrachloride and other suitable chlorinated solvents are very difficult to obtain because of war conditions, and are relatively expensive.
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The following method was developed to overcome these difficulties. There is nothing particularly new about it, but it is simple and requires no expensive apparatus. I n principle it is a combination of immersion and vapor degreasing.
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APPARATUS.A 2000-ml. Pyrex beaker, a wire basket made from ordinary copper house screening, an electric hot plate, a filter or round-bottomed flask for use as condenser, diameter 1.25 to 2.5 cm. (0.5 to 1 inch) less than the beaker used, an iron ring stand with clamps and fasteners, and some copper wire. The size of the apparatus can be increased to take care of larger samples, ivhich are often necessary when a lot of material is particularly nonuniform or heterogeneous.
FIGURE1. APPARATUSDURING FIRSTOPERAA.
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TION Rubber stopper, fastened to fiask with copper wire to hold water pressure Copper wire, to fix relative positions of basket and Rask Round-bottomed flask as condenser Screen basket Turnings Solvent level Eleotrio hot plate Screen Ring stand
Figure 1shows the first operation. PROCEDURE 1. A sample which will occupy not more than about 5 to 7.5 cm. (2 to 2.5 inches) in height in the wire basket is covered with the chosen solvent, The turnings are dried pre478
June 15, 1942
ANALYTICAL EDITION
viously at 110" C. to determine moisture and volatiles at that temperature. The weight need only be sufficient to give adequate accuracy with the balance used for the amount of oil present. The solvent used is petroleum naphtha (boiling point range approximately 110 to 167" C.), which costs about 25 cents per gallon and may be secured without difficulty. The wire basket is cylindrical with a flat bottom and is made to fit snugly to the sides of the beaker, so that the vapors in the second operation must pass through the turnings. If the holes in ordinary screening are too large for the material being extracted, a finer screen or perhaps a specially designed cloth bag is recommended. 2. With the cooling water flowing, the temperature is raised to the boiling point of the solvent and held there for about 1.5 minutes. This causes intimate contact of each piece of turnings with the solvent, which results in rapid heating of the turnings and maximum solution of the oil in the solvent. The bulk of oil in very oily turnings is thus removed. 3. As shown in Figure 2, the hot plate and beaker are then lowered, so that the level of the boiling solvent is 1.25 to 2.5 cm. (0.5 to 1 inch) below the bottom of the basket. The vapors from the solvent proceed to condense on the turnings and all the oil-bearing solvent finally finds its way into the beaker. The rate of boiling and distance from the bottom of the screen to the top of the solvent should be adjusted with the following points in mind: The boiling rate should be such that the vapors condense at a slow but noticeable rate on the bottom of the condenser and drip back through the turnings, so that all the turnings are brought in contact with solvent vapors. The solvent level should be far enough from the turnings so that violently boiling liquid does not come in contact with them.
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This minimizes the possibility of a residue of oil-bearing solvent on the turnings. A further precaution concerns the possibility of bumping if some fine turnings pass through the screen in step 2. It may be necessary to remove the beaker from direct contact with the hot plate and insert an intervening layer of asbestos if bumping occurs. In the case of the petroleum naphtha used, the lower boiling fractions do the vapor-degreasing and they are subsequently easily removed from the clean turnings by heating on a hot plate under a hood. For example, from a batch of turnings containing 10 per cent of oil a sample of about 150 grams was taken. The extraction was performed as described above and the clean and dry turnings were weighed. The extraction was repeated in the same way using carbon tetrachloride, and the turnings were again dried and weighed. A difference of only 0.2 gram Kas observed between the weights obtained in the two extractions. This error is probably due to the crude balance used. For a determination of this sort this can be considered excellent. In other words, the petroleum naphtha was satisfactory. The errors in sampling far overshadow any errors in this determination. Xodifications in t h e details of the procedure can easily be made according t o the product being extracted and the solvent being used. Many mechanical improvements in the setup could be made, b u t i t is questionable whether the expenditure of time and money is warranted. Obviously this method can be used t o clean oil-covered solids on a laboratory scale.
Determination of Traces of Copper in Wort, Beer, and Yeast IRWIN STONE Wallerstein Laboratories, 180 Madison Ave., New York, N. Y.
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NCREASED interest has been shown recently in the determination of copper in beer (2) and collaborative analytical work has been undertaken b y the Association of Official Agricultural Chemists (1). The methods studied in this collaborative work, which were considered the most practical and best of those available, were a direct xanthate method involving dry-ashing of t h e sample and a diethyldithiocarbamate method, including a wet-digestion as well as a hydrogen sulfide and dithizone separation t h a t could be omitted at the discretion of the collaborative analyst. This increased activity led the author t o prepare for publication t h e copper methods which this laboratory has been using in studies of wort, beer, and yeast. The results of these studies Till be published elsewhere. The details of the methods reported herein were worked out after considerable preliminary experimentation t o obtain optimum conditions for the various operations. Originally, a method was developed for determining the copper directly on the sample without preliminary ashing or wetdigestion. While good recovery of added copper was obtained, the results were not completely reliable for the copper originally present in many of the samples. The presence of stable copper complexes and t h e difficulty of counteracting interferences in the direct method indicated the need for destruction of organic matter present in the samples. In the present method a dry-ashing is employed rather than a wet-digestion because of its simplicity and the fact t h a t high blanks are obtained due t o traces of copper in the large volumes of concentrated acids usually employed in the
wet-digestion methods. The copper is determined photometrically as t h e diethyldithio complex after extraction with amyl acetate (3). Iron is the only common metal which is normally present in the wort, beer, or yeast in amounts sufficient t o interfere by forming a colored complex with the reagent. This interference is eliminated by the use of 2,2'-bipyridine (a,a-dipyridyl) as suggested by Parker and Griffin (4). The 2,2'-bipyridine combines with the iron and prevents i t from reacting with the copper reagent. This expedient greatly simplifies the procedure by avoiding the usual lengthy acid-hydrogen sulfide separation. The possible interfering effect of calcium ions is prevented b y avoiding alkaline reactions with consequent precipitation of calcium phosphate and by using a large excess of t h e copper reagent. A further advantage of this method is that most of the reactions are conducted in a single centrifuge tube and in the case of worts and beers no filtrations are involved. The spectrophotometric data relating t o the copperdiethyldithiocarbamate color have been worked out (3) and need not be repeated here. Calibration curves (Figure 1) have been made at two separated points on the spectrum (440 and 540 millimicrons), thus extending the range of copper concentrations covered without loss of accuracy. This permits the ready selection of the most suitable conditions (cell length, wave length of light, and optimum reading of instrument) for the amount of copper present in the particular sample used. The instrument employed throughout this work was the Aminco neutral wedge photometer, but the principles involved are readily adaptable to other visual or photoelectric photometers.
