Generator for 'roductioa of Pure Carbon Dioxide W. H. RAUSCHER, Rensselaer Polytechnic Institute, Troy, N. Y .
A
from the bicarbonate solution. The pressure under which the system is at all times is shown by the height of the mercury in 1. At the end of the evacuation period stopcocks G and H are closed and the generator is allowed to stand for some time. The carbon dioxide evolved by the bicarbonate solution soon begins t o blow back through the acid inlet tube into B and the mercury level in I falls. When the mercury level has dropped 20 t o 25 mm. the generator is tilted at a considerable angle to the right or left, and on cautiously opening G, A is evacuated by the oil pump to a pressure lower than that in B. Several drops of acid are drawn from the tip, so as to fall on the side wall of the joint, G is closed, and the generator is righted. When the drops of acid drain down to the bicarbonate solution, enough gas is enerated to blow back into B and cause a conthe mercury level in I . This procedure is residerable fall peated until the seal at J is finally broken. Stopcock E is opened, mercury is run into the seal to a height of about 35 mm., and E is closed. Enough acid is drawn down as before to break the seal in D. The evacuating arrangement is now disconnected and the generator put into service. If the microbubbles are not immediately satisfactory, the evacuation may be rapidly repeated, since the mercury can be withdrawn from the seal into the leveling bottle, which is reattached to E, immediately before the evacuation is started, so that air has no chance to diffuse into B. When the generator charge is exhausted, the mercury is removed from seal D through E, and the upper joint is carefully warmed to soften the glass cement so that seal D may be removed. B is then separated from A by warming the joint. I t is un-
?;UMBER of years ago Poth ( 2 ) described a n excellent
all-glass generator for the production of very pure carbon dioxide for use in the Dumas method for determining nitrogen. Several suggestions for improvement and simplification of the original design have been made by him and by others (1, 3,4). A generator based essentially on Poth's design was constructed b y the author several years ago, and the design has been gradually improved to the present form, Tvhich has given very good service in this laboratory. The construction of the apparatus is shown in Figure 1. The generator makes use of two ground-glass connections, which greatly simplify the construction and the charging operation.
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A is a 2- or 3-liter round-bottomed flask with a short neck and a 24/40 T joint. Chamber B is constructed from a 1-liter roundbottomed flask. It bears a 24/40 T joint to fit the joint of flask A , and a 14/35 -$ joint for the attachment of the mercury seal, D. The acid delivery tube is 2 mm. in inside diameter, and the tip, C, is drawn down as shown, to be about 1 mm. in outside diameter and 0.5 mm. in inside diameter. The gas outlet tube, F , which is 8 mm. in outside diameter, is made as shown to give it considerable flexibility, so that there will be little danger of snapping it off through careless handling while attaching it to the combustion tube. The bubble counter of the Poth designs has been omitted, but may be used if desired. The design of the mercury seal is indicated by the sketch. The bulbs of the seal are approximately 32 mm. in diameter, and the outermost tube is 25 mm. in outside diameter. The sleeve tube is 18 mm. in outside diameter, and the inner tube, which opens into chamber B through the 14/35 T joint, is 8 mm. in outside diameter. The distance between the upper and lower bulb centers is approximately 160 mm. The charging and starting of the generator are carried out as follows, starting with the generator completely empty: Into A is run a solution of 500 grams of potassium acid carbonate in 1200 ml. of water (assuming A is a 2-liter flask). The female joint of A and the male joint of B are carefully warmed with a flame and a small amount of low-melting Kronig's glass cement is applied to the male joint, which should be warm enough to melt it. The two joints are placed together and rotated to spread the cement evenly over the glass surfaces. When the cement is cooled, A and B are held together so firmly that no pressure the generator can develop will loosen the joint. Into B are run about 350 ml. of 50 per cent sulfuric acid. The mercury seal, D, is then attached to B exact.ly as B was attached to 9. A mercury leveling bottle is attached to stopcock E by means of a long piece of rubber tubing and mercury is run into the seal to a point well below the inner tube of the seal. E is then closed, leaving the rubber tube leading to the leveling bulb full of mercury. 4 very convenient and satisfactory arrangement for evacuating the generator consists of pressure tubing, a T-shaped and a Y-shaped glass connector, a stopcock, H , a pressureindicating tube, I,and mercury seal, J. A and B are simultaneously evacuated by an oil pump. J Since stopcock G has a capillary tip, stopcock H may be only partly opened during the first part of the exhaustion, so that air is not drawn from A up into B too rapidly because of the more rapid evacuation of B. The system should I be evacuated for about 20 minutes, during which time considerable carbon dioxide will be evolved
i" F
G
FIGURE 1. DIAGR.AM OF APPARITCS 694
695
ANALYTICAL EDITION
NOVEMBER 1.5, 1940
necessary to remove any acid whlch remains in B. The contents of A are removed and the bicarbonate solution is replenished. The generator is then ready for reassembling and restarting. The generator possesses the adrantages of the Poth generator, and in addition may be charged very quickly and easily. No hazard exists from a posqible failure of a ring seal which in other designs would permit the acid to pour into the bicarbonate solution with the probable explosion of the generator. One part of the generator is a standard flask, so that only parts B and D need to be specially constructed. The generator has proved very sturdy, and may be shaken vigorously to prevent stratification in the bicarbonate solution. Generators of this type have been used by undergraduates in this laboratory without mishap of any kind. The chief difficult? in constructing the generator is to make the tip of the acid delivery tnbe so small that too much carbon dioxide is not generated by the acid drops, bloTvn back through the seal, and wasted. Carbon dioxide must blow back occasionally to maintain the automatic operation of the
generator; therefore the tip must not hc made too small. I n such a case the generator may be easily brought to full operating pressure before being connected t o the combustion tube by tilting the generator and cautiously opening stopcock G so that several drops of acid fall on the side wall of tube C. After G is closed and the generator righted, the acid drains down to the bicarbonate and evolves enough gas to unseat the seal in D. Such a generator is very economical of reagents. Obviously, it is possible to use a Poth tip if desired. Generators of this design have been made by Ace Glass, Incorporated, Vineland, N. J. The total cost of the complete generator has been less than half of quoted prices for the Poth generator of most recent design.
Literature Cited (1) Lowe, E, Ti’., and Guthmann, W. S.,IND. ESG. CHEM.,Anal. Ed.,
4.440 119321. (2) Poth, E. J,, Ibid., 3, 202 (1931). (3) Ibid., 11, 518 (1939). (4) Shelberg, E. F., Ibid., 10, 704 (1938).
Determination of Copper in Mineral Oils Titrimetric Extraction, Using Dithizone A. G. ASSAF AND W. C. HOLLIBAUGH Massachusetts Institute of Technology, Cambridge, Mass.
T
HE work on oxidation of mineral oils in the presence of
copper catalyst which is being carried on in these laboratories has necessitated a test for the measurement of traces of copper in oxidized oils. The procedure developed is one which employs dithizone (diphenylthiocarbazone) for titrimetric extraction of the copper. The various complex organic substances and methods for analysis for copper (and other metals) have been discussed by Conn, Johnson, Trebler, and Karpenko (2), Fischer ( d ) , Wichmann (8), etc. Many procedures for the analysis of copper have been described. The spectrophotometric method of Liebhafsky and Winslow (7) was tried but discarded because of the extreme precautions involved. Fischer’s titrimetric “two-color” method employing excess dithizone was also tried; however, inconsistent results were obtained because of the difficulty of matching the various shades of purple obtained a t the end point. The procedure described herein is one of extractive titration which is somewhat similar to that employed b y Wilkins, Willoughby, Kraemer, and Smith (9) in the determination of traces of lead in biological materials. The method consists of oxidizing a sample of the deteriorated oil with a mixture of nitric, sulfuric, and perchloric acids, and evaporating the colorless solution almost to dryness. The residue is dissolved in redistilled water, the p H adjusted, and the solution finally titrated with a standardized solution of dithizone in carbon tetrachloride.
Preparation of Reagents Concentrated sulfuric acid, concentrated nitric acid, and distilled water are all distilled from Pyrex glassware. Baker’s 72 per cent redistilled perchloric acid need not be distilled again, but is transferred to a Pyrex bottle. The dithieone reagent is prepared (7) by shaking 0.1 gram of Eastman dithizone with about 25 ml. of c. P. carbon tetrachloride; the solutionis filtered,
transferred to a separatory funnel, and shaken with an equal volume of 0.2 N ammonium hydroxide, the resulting brownishyellow carbon tetrachloride layer being discarded. Four additional extracts of the aqueous layer are made, 10 ml. of carbon tetrachloride being used each time and then discarded; the last portion of carbon tetrachloride should show a greenish tint. A 25-ml. portion of carbon tetrachloride is then added, and the aqueous layer is acidified with 3 N perchloric acid added d r o p wise. After the funnel has been shaken to transfer the dithieone to the carbon tetrachloride layer, the aqueous layer is discarded and the dithizone solution washed twice with redistilled water. The solution is filtered into a glass-stoppered Pyrex glass bottle by means of a filter paper moistened with carbon tetrachloride to remove the water. The filtered dithizone solution is finally diluted to 400 ml. with c. P. carbon tetrachloride, and should be stored in the dark. The standard copper solution is made by dissolving Mallinckrodt’s c. P. copper in nitric acid and evaporating to dryness. The final residue is treated with 2 to 3 drops of glacial acetic acid to make it more soluble, and is then transferred quantitatively with redistilled water to a volumetric flask. The final concentration should be about 2 micrograms (2 X 10-6 gram) of copper per milliliter of solution. The pH of the copper solution is adjusted to 3.5 by adding a few drops of 0.04 per cent bromocresol green and the proper amount of dilute ammonium hydroxide. All equipment is of Pyrex glass and must be washed with dithizone and flushed with c. P. carbon tetrachloride before use.
Standardization The apparatus used for the titrimetric extraction consists of a Pyrex buret graduated in 0.05 ml. and a Pyrex separatory funnel made with about 20 cm. of 25-mm. tubing, a pair of No. 11 glass joints (the male being sealed at both ends, acting as a stopper), and a stopcock of 2-mm. bore. The walls of the funnel are indented by heating the glass in spots and pushing inward with a blunt-pointed rod. Between the 25-mm. tubing and the stopcock is about a 1.25-cm. (0.5-inch) length of 7-mm. tubing wherein the carbon tetrachloride layer settles after se aration. The stopcock is lubricated with grease at the ends a d e t h y l e n e glycol in the center. After lubrication,
