V O L U M E 2 1 , NO. 1 1 , N O V E M B E R 1 9 4 9 The stock solution of the praseodymium sample was made by dissolving a sufficient quantity of impure praseodymium metal in 0.5 N hydrochloric acid to yield a solution containing 0.0147 gram of the sample per ml. The solution used for analysis was prepared by adding 0.40 ml. of the stock solution to 1 ml. of the internal standard solution, diluting to 15 ml., and mixing with an equal volume of 0.5 AT hydrochloric acid. The electrodes 4ere cut from 0.25-inch copper rods, as described by Fred, Xachtrieb, and Tomkins ( 4 ) . To decrease oxidation before use, the electrodes were stored in a jar Kith their tips immersed in benzene and %ere always used uithin 12 hours after they were cut. -2 hot plate was used to evaporate the solutions on the electrodes. I t was found that ahout 0 0286 nil. ma5 requiied to cover the t i p of an electiode. EXPERI\IEYThL RESULTS
K i t h each of the four standard lanthanum-manganese solutions, 21 spectra (three films containing seven each) ere made, and the ratio of intensities of the 4086.714 b. La(I1) line to the 3438.974 Iln(I1) line was determined in each case. The average value of this ratio as found for each standard solution and a log-log plot of the results made. The working curve so obtained was linear. From a determination of the intensity ratio for a solution of the pi aseodymium metal containing a known amount of added manganese chloride, the lanthanum content of the praseodymium can be calculated with the help of the working curve. Treating an average of five repeat determinations as a single result, the lanthanum contents found Rere: 38.5, 37 4, 39.7, 37.5, 33.7, and 35.3%, or a mean value of 37.0’%. The average deviation from the mean corresponds to a variation of 1.7% in the lanthanum content of the praseodymium metal, or 4 6% in the analysis of the sample.
a.
As a check of the accuracy of the analysis, a synthetic known to contain 38% lanthanum-i.e., very nearly the same amount as that found in the sample-was made up from pure lanthanum and praseodymium chlorides. This solution differed from that containing the praseodymium metal sample only in being free of minor impurities such as iron, neodymium, etc. Portions of the solutions of the synthetic sample and the praseodymium metal sample, each containing the same percentage of manganese as that used i n the analysis of the praseodymium metal, were
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compared by photographing spectra of both on the same film. Seven exposures were made tor each sample. The ratio of the intensities of the 4086.714 A. La(I1) line to the 3438.974 b. Mn(I1) line was 0.56 =t0.04 for the synthetic sample and 0.55 =t 0.05 for the metal sample. This agreement was taken as proof of the essential correctness of the analygo%) of the unaccounted for balance Tvas found to precipitate as an oxalate in acid solution. Because spectrophotometric analysis failed to show absorption bands for any other rare earth in the range 380 to 1000 mp, and qualitative spectrographic studies had shown gadolinium to be absent, it was presumed t h a t this unidentified balance was lanthanum. This is in general agreement with the spectrographic resultACKNOWLEDG\IEhT
The authors wish to express appreciation to J. B. Downs, Jr., for carrying out the chemical and spectrophotometric analyses. LITERATURE CITED
dverbach, B. L., IXD. ESG.CHEM..-4s.~~. ED.,17, 341 (1945). Churchill, J. R., I b i d . , 16, 653 ( 1 9 4 4 , . Fassel, V. A., and Wilhelm, H. A , , J . Optical SOC.A m . , 38, 518 (1948).
Fred, &I Nachtrieb, ., N. H., and Tomkins, F . S., I b i d . , 37, 279 (1947).
Harrison, G. R., “Massachusetts Institute of Technology Wave Length Tables,” New York, John Wiley & Sons, Inc., 1939. Pierce, W. C., and Kachtrieb, X. H., ISD. ENG.CHEM.,AXAL. ED.,13, 774 (1941). Rodden, C . J., Bur. S t a n d a r d s J . Research, 26, 557 (1941). RECEIVED October 8, 1948. Presented a t the Meeting-in-Miniature, Georgia Section, AYERICAKCHEMICILSOCIETY,Kovember 19, 1948. Joint contribution from t h e School of Chemistry a n d t h e State Engineering Experiment Station. Work carried o u t with t h e assistance of t h e Office of Xaval Research under Contract S6-ori-192.
Determination of Carbon by Wet Combustion PAUL S. FARRINGTON, C i R L NIE-MANY, A h D ERNEST H. SVIFT California ZnstitzLte of Technology, Pasadena, Culif.
OR situations where a Van Slyke manometric apparatus Fcannot be provided, a scheme has been devised to use the Van Slyke-Folch combustion mixture (3) in the analysis of organic solids and relatively nonvolatile liquids. -4sample of 10 to 12 mg. is heated n i t h combustion solution in a stream of carbon dioxide-free air, and the carbon dioxide evolved is absorbed in sodium hydroxide. The carbonate thus formed is precipitated as barium carbonate and determined acidimetrically. A determination requires about 45 minutes. The efficiency of the appaiatus has been tested by analyzing pure samples of several compounds. The results were accurate to +0.05 mg. of carbon. Halogens, nitrogen, and sulfur do not interieie; however, compounds that decompose to release hydrocyanic acid will give low carbon values. In comparison with other methods for the determination of caibon, this procedure has the advantage of an inexpensive apparatus which can be assembled quickly and does not require much space. I n addition, only one weighing is required for each determination. The Van Slyke-Folch combustion solution has been used in other procedures (1, 2 ) , but in these the carbon dioxide or barium carbonate has been determined gravimetrically.
REAGEhTS
Combustion Solution. Pour 60 ml. of 30% fuming sulfuric acid into a flask containing 40 ml. of 8570 phosphoric acid, and add 10 grams of chromium trioxide and 1 gram of potassium iodate. Heat to 140 O to 150’ C. and swirl or stir for 1 to 2 minutes. Cool and store in small glass-stoppered bottles. If fuming sulfuric acid is not available, use 20 grams of phosphorus pentoxide, 85 ml. of 95% sulfuric acid, and 15 ml. of 85% phosphoric acid with the stated quantities of chromium trioxide and potassium iodate. Sodium Hydroxide. Dissolve 5 grams of sodium hydroxide in 20 ml. of water, add 1 ml. of 1 F barium chloride, and centrifuge. Dilute to 250 ml. Barium Chloride Reagent, 1 F in barium chloride and 0.001 F in hydrochloric acid. APPAR4TUS
The Iiraissl tube, A , shown in Figure 1 is packed with 20 to 30-mesh Ascarite or soda lime, and 95% sulfuric acid is placed in the bubble counter, B. The 15-ml. centrifuge tube, M , is connected to head D by means of a 14/20 T joint. The stopcock, E, is lubricated with phosphoric acid, but grease may be used in the other stopcocks. A plug of glass wool moistened with distilled water is placed in tube F to remove any hydrofluoric acid. The disperser, K , is made from a short length of Zircofrax tubing (12-7P.89, Carborundum Company) sealed to Pyrex tubing and
ANALYTICAL CHEMISTRY
1424
closed at one end with a glass plug. The disperser inlet tube should be moistened with a drop of glycerol, so that it will move freely in the rubber stopper. The bottle, H , contains 0.5 F sodium hydroxide which is protected by a soda-lime t,ube. A 15ml. centrifuge tube serves as the absorber, G. I n Figure 2 the soda-lime tube, S, is made from 7.5 em. of 10rnm. tubing.
Table I.
Results of Carbon Analysis by Wet Combustion Method
Sodium oxalate
PROCEDURE
Weigh a 10- to 12-mg. sample into tube N. Moisten the ground surface on head D with 85% phosphoric acid, then attach M, Before attaching tube G to the assembly, allow 2 to 3 ml. of the sodium hydroxide to flush out the section below pinchclamp J . By adjusting stopcock L maintain air flow through the apparatus at, 3 to 4 bubbles per second. After 5 minutes open J and slowly admit sodium hydroxide to within 2 to 3 cm. of the top of G . Pour 5 to 6 ml. of combustion solution into cup AVand reduce the air flow to 1 to 2 bubbles per second. Stopcock C must be closed before stopcock E is opened to admit the combustion fluid to tube ill; otherwise bubbles of the viscous liquid will be formed in D and combustion mixture will be blown up into the outlet tube. When most of the fluid has entered M, close stopcock E and open stopcock C. With the air flow a t 3 to 4 bubbles per second, warm the upper portion of the solution in MI then the lower part. Do not apply the heat strongly in one spot, as the reaction may proceed suddenly and evolve a large quantity of carbon dioxide, When gas evolution begins, observe bubble chamber B. If reverse flow starts, close C for a few seconds to prevent flow of carbon dioxide into A . Continue heating until the solution has boiled vigorously for 5 minutes. Cease heating and fill .If to within 2 to 3 mm. of the inlet tube with 95% sulfuric acid. Close C during this process. Do not admit air through E while adding the acid. After reopening C, allow the air flow to continue a t 3 to 4 bubbles per second for 3 minutes. Slide the disperser inlet tube up through the stopper until the disperser is well above the solution, then close stopcock L. Detach the rubber tubing from the disperser inlet tube, and fill this tube with carbon dioxide-free distilled water by means of a long capillary dropper. Carefully draw most of the water through the disperser but do not admit air. After removing the stopper, quickly rinse the bottom of the stopper, the outside of the disperser, and the walls of tube G with carbon dioxide-free distilled water.
Potassium hydrophthalate
p,B’-Dichloroethyl sulfide Adipic acid
Milligrams of Carbon Present Found 2.92 2.95 2.15 2.16 1.87 1.84 1.86 1.88 1.65 1.68 1.88 1.92 4.51 4.54 6.29 6.26 5.33 5.33 5.61 5.61 2.73 2.76 5.84 5.85 5.38 5.43 5.20 5.20 5.47 5.51
acid until thr solution is colorless. Centrifuge; then discard the solution with a dropper. Rinse down walls of the tube mith 1 to 2 ml. of hoiled distilled watw. Add 1 drop of phrnolphthalein and 3 to 4 drops of 1 F barium chloride. Decolorize, if necessary, n
