Modifications in the Dumas Micromethod for Nitrogen Automatic Apparatus Applicable for Combustion Micromethods G . L. ROYER, A. R. NORTON, AND F. J. FOSTER Calw Chemical Division, Ameriean Cyanamid Company, Bound Bmok, N. J.
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The adjustable sleeves on the carriages are the bearing surfaces for this lateral motion. The furnaces proper are fastened to aprons which in turn slide on two bars, making possible a hackand-forth motion over the carriages. The power for moving the small furnace is obtained from B two-speed governor-controlled phonograph motor. The drive from this motor is transferred hv suitable eears to the horizontal screw which is located under the movablbfurnace. This scmw is square cut; contact and release with the movable furnace carriage are obtained by use of a split nut arrangement, the openina and closing of which are controlled bv a knob. When men. th7: furnace c& be moved by hand in any direction desirihlii when closed, it is moved by the screw. The furnaces proper are encased in a housing made from standard 5.08cm. (%inch) square stock brass tubing. The Alirax square tubing refractory lining is 2.54 cm. (1 inch) in mnside diameter with 6.3-mm. (0.25-inch) walls (Carhomndnm Company, Niagara Falls, N. Y.). The f k n t ofthe h r m tubing is cut out, leaving a small edge to hold the refractory in place. The refractory tube is cut t o give a beveled piece which can he fastened to the door of the furnace, so as to complete the lining when it is closed. The end dates of the furnace are made from Alirsx piec~sand arc held ix; position hy 1 ~ r . mplates lFigure 3, u p p r right). The b n w end phtes of rhe furnaces w h i w rome tugcthcr (Fixcue :3, luwer h41, arc i t i w into the refractory ,,hies, so that rlie two rfructory p1.ttej Come together when the movable iurnsce reaeliea tlie fixed iurnnce. All brirs parts are nickel-
HE application of automatic combustion technique to the Pregl micromethods has proved very satisfactory. Previous publications from this laboratory have described a p paratus for the determination of ash in organic compounds (6) and of carbon and hydrogen (8). The apparatus described here was designed after experience with several other automatic types. It is an adaptation of the Heraeus-type furnace (4) to an automatic combustion arrangement, which although similar in principle to that described by Hallett (A?), is different in construction and operation. The Dumas micromethod described by Pregl (7) is essentially followed, hut combustion rates, time of combustion, source of pure carbon dioxide, and method of calculation differ. While many of the points in the procedure and the apparatus are not original, the assembly and method of operation have proved to have many advantages. The apparatus was originally designed for the Dumas method, where the combustion tube must be removed from the stand to be filled for each determination, but, i t can also be used for carbon-hvdrozen. . - halogen. _ .sulfur. etc.
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Combustion Furnaces and Auxiliary Control EQuipment
-. .. rigure I snows the automatic combustion
,>l*tOd
As previously described (8, 6, 81, the platinum resistance wire is wound onto four refractory rods n,hich are held in position in the refractory end plates. In the large furnace 457.2 om. (180 inches) of 0.406-mm. (0.016-inch) pure platinum wire are used, while the small furnace is wound with 457.2 cm. (180 inches) of 0.31&mm. (0.0125-inch) platinum wire. The wire is then coated with Alundum cement (Norton Co., Worcester Mass. RA-562 fine) ttop protect arotect the platinum drttinum from voIatiIiza&on volxt,iIirs&on and ~ v itea longer hfe. Chromel-Alumel (Hoskins Mfg. Co., Detroit, Mich.) couples
furnace set up for the determination of nitrogen by the Dumas method. Figures 2 and 3 show close-up views of the stationary and movable furnaces. Both furnaces can be moved in a lateral direction on sliding carriages fastened t o the supporting ham However, the stationary furnace is locked in position at the place where it meets the mail furnace when the latter is at the end of ita motion.
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FIGURE 1. AUTOMATIC COMBUSTION FURNACE 79
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
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FIGURE 2. CLOSE-UP VIEWOF FURNACES
in each furnace lead to iudividual millivolt meters, calibrated by correlation with a standardized meter. The thermocouple from the standard meter is put into the comhustion tube in the p s i tion at which the temperature is t o be correlated. The combustion furnaces with their assembly are mounted by means of two brackets ou a supporting bar, which is in turn supported from a base in which auxiliary control equipment is located. Two Vmitrans of 7.Sampere capacity (United Transof former Corp. New York, N. Y.) serve as variable the voltages for roducing heat in the two furnaces. Two knobs which operate t f e governor and speed controls of the motor can be adjusted from the top Of the base. An (Walser Automatic Timer Co., New York, N. Y.) on the front panel controls theJength of time the motor and the he@ in the small furnace are m operation. A signal-type snap switch controls the power for the whole apparatus, while individual switches control the separate units which may have to be turned off independently.
Glass Apparatus ~h~ dimensions of the glass follow those specified in the "Recommended Specifications for Microapparatus, Part 11, Dumas Nitr? en" ( 1 ) . Quartz combustion tubes have been found more satisfxtory than glass and often last more than 6 months. Attempts to connect the apparatus by ground-glass joints have not been too successfulbecause of the inflexibilityof the setuD.
Source of Pure Carbon D i o x i d e The Kipp generator with various modifications to ensure delivery of pure carbon dioxide, generatms producing pure carbon dioxide from carbonates by both acid treatment and heat. and amaratus for controlline the delivew of Dure carbon bioxideirom dry ice are used'ior the D&as micro procedure. I n this laboratory most of these have been tried and the latter has proved satisfactory for several years. Since the same carbon dioxide used to make dry ice is used to fill the tanks, it was decided to try to use tank carbon dioxide (conversation with J. A. Baty of the u. S. Rubher Company prompted this investigation). The Pure Carbonic Corporation (telephone conversation with Mr. Dean of the Newark office) suggested that 5 pounds of gas be bled off from a new tank while it was in a vertical position with valve up. This rapid exhaust should eliminate most of the air, which should he on top, and give as pure carbon dioxide as is obtained from dry ice. Experimentation in the use of tank
carbon dioxide led to a procedure in which a constant blank of 0,010 cc, for a determination was obtained. It was found that the Pressure Of the Carbon dioxide entering the combustion tube affected the h l a d value obtained. If the pressure was low, high blank values were obtained. I n using a gasometer (6) the pressure is rather high, about 38 em. (15 inches) of mercury at the start of the determination. With the dry ice generators the pressure varies, depending upon the type of valve used. Using tank carbon dioxide, about 20 cm, (8 inches) of mercury eontsjned in a 100-d. cylinder with a T-tube served satisfactorily as the pressure regulator. The excess exhaust gas is washed with acid to eliminate mercury vapor and expelled through a hood to remove any health hazard. A container inserted in the exhaust carbon dioxide line stores ignited fine copper oxide, used in thetemporaryflling. can he given for the high pressure necesNo sary to obtain low blank values, but experimentation shows that a rather tight packing of the combustion tube and high Dressure of carbon dioxide entering.the tube givc the best rebulrs. Using the I.i$ lircwirr, enre must he t:ikrn to have all rulhcr connwtiun.+in con 1 condition n n t l tlmefore the ruhher stopper and the tubing connection to the azotometer must be changed frequently.
The permanent 6lling of the combustion tube is made as follows: Ahout 0.5 cm. of asbestos is Daeked down into the tlp end of the tube, followed with about-13 cm. of coarse copper oxide and another 0.5-cm. plu of asbestos. A 6-cm. copper m m m which h a s hem me&usfv reduced. is next inserted into the tube, then another' 0.5-om. "plug of asbestos followed with about 6 cm. of coarse copper oxide. A 6nal 0.5-om. asbestos plug holdq this errnnnend. The arotomct6r is aitnehcd t o the eouibusrion tube bv me:ins of h?nvy-walled tubing. so t b h t the az(,tnuicter and i.omburrion tuoe meet ~ I n s st o glass. The stqm,rki nre opeiicd in such Q mnnner that 11.8 ens Hows throueh rhe tube. rxnrlliii~tlir n u which is in the tubeto the atmosDh&e. T1.e stationnry iurnarr id broigLtt forawd over the rombmtion tube, so r l n t the pemrmnnmt tilling lrpeomcs hcited. After about 2 miiiirt~rrhr sroorock 31 ilic rinht-hand side of the nDDaratus is closedmd the'two-wav sto&ck on the azotometerk iurned. allowing the q t s to pn& inti, the azotomcter. I V h n microbubbles nre ol,tninrd, the aropvork is rlosed and t h e small m o u n t of RBJ which has collected in thP top of the azotomcter is rrmoved tw meins of the Icvelinc bulb: then t h P twn-wn\' 6 1 0 ~ cock is opened again to the azo&met&. The movahle furnaie is then pulled into position, about 5 cm. from the stationary furnace, and brought over the tube proper by pulling the furnace forward. The automatic switch is set for about 20 minutes. During this 20 minutes the movable furnace moves over the sample, carrying out the combustion, and the motor is set so that the travel is about 5 cm. (2 inches) in 20 minutes. At the end of this time, the current is automatically shut off bv the time switch. The oDerrttor I
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hydroxihe are avaibble for this cdncentration.
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volume of the hiank and 0.5 ~ e cent r of the obseGed volume are
variation ih room teiperature which o;dr the kntl're ye& may be from 25' to 36' C. If the room temperatures vary only over narrow limits, a constant percentage correction is satisfactory.
Discussion The procedure using automatic combustion for the Dumas method gives results which are more reproducible, and the
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INDUSTRIAL AND ENGINEERING CHEMISTRY
time necessary for a determination is less, than by the regular Pregl procedure. Another reason for automatic combustion is the reduction of man-hour time necessary for operation. Automatic combustion makes the burning rate uniform and therefore more reproducible conditions are obtained. The total elapsed time for a single analysis is about 40 minutes, of which about 20 minutes requires the operator’s attention, including the time for weighing the sample. The results obtained have the same accuracy as those r e ported for the Pregl microprocedure. The apparatus is checked once or twice a week on standard compounds. The average value for nitrogen obtained on 20 analyses of a standard sample of 2-amino-1-naphthalene sulfonic acid was 6.29 per cent with a limit of error (2u) of ~ 0 . 1 3per cent. The theory for this compound was 6.28 per cent.
Acknowledgment The authors wish to acknowledge the assistance of A. F. Mincz and W. L. Hatton in the construction and design of
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the automatic apparatus. Acknowledgment is also made to other members of the microchemical laboratory, especially to R. Koegel, for contributions made during the development of the procedure.
Literature Cited (1) Am. Chem. SOC.,Committee on standardization, Division of Analytical and Micro Chemistry, IND.ENG.CHEM., ANAL.ED., 13,574 (1941). (2) Hallett, L. T., Ibid., 10, 101-3 (1938). (3) Milner. R. T.,and Sherman, M. S., Ibid., 8, 331 (1936). (4) Niederl, J. B., and Niederl, V., “Organic Quantitative Microanalysis”, p. 84, New York, 1938. (5) Ibid., p. 63. (6) Norton, A. R.,Royer, G. L., and Koegel, R., IND.ENG.CH~M., ANAL.ED., 12,121 (1940). (7).Pregl, F., “Quantitative Organic Microanalysis”, 2nd English ed., tr. by Fylernan, Philadelphia, P. Blakiston’s Son & Co., 1930. (8) Royer, G. L., Norton, A. R., and Sundberg, 0. E., IND.ENG. CHI&, ANAL.ED., 12,688 (1940). PRESENTED before the Division of Analytical and Xicro Chemiatry a t the 102nd Meeting of the AMERICAN CHE.WCAL SOCIETY. Atlantic City, N. J.
Colorimetric Microdetermination of Arsenic after Evolution as Arsine E. B. SANDELL, University of Minnesota, Minneapolis, Minn.
S
EVERAL methods for the colorimetric determination of arsenic after evolution as arsine have been described. Morris and Calvery (3) decompose the arsine by passing it through a heated fused silica tube, dissolve the deposited arsenic in nitric acid, and after the evaporation of the latter determine arsenic by the molybdenum blue method. Taubmann (4) absorbs the arsine in silver sulfate solution, precipitates the excess of silver with chloride, oxidizes the arsenic in the filtrate t o the quinquevalent condition by boiling with bromine water, and finally applies the molybdenum blue method. The time required for a determination is about 3 hours. The following method is based on the absorption of arsine in an acid solution of mercuric chloride containing permanganate. Arsine is thus oxidized in one step t o arsenate, and arsenic can then be determined in the solution b y adding a n excess of ammonium molybdate-hydrazine sulfate and heating t o obtain the molybdenum blue. Cassil and Wichmann (9)have used mercuric chloride solution for the absorption of arsine in a microvolumetric method for arsenic based on iodometric titration. The following procedure is designed for amounts of arsenic ranging from 1t o 15 micrograms. Approximately one hour is required for a determination. The directions for the evolution of arsine are similar t o those of the A. 0. A. C. (1).
of about 0.5 mm. The absorption vessel, C, is drawn from a test tube, and should have a capacity of 8 to 10 ml., with the tapered rtion of such dimensions that 1.35 ml. of absorbing solution will c v e a depth of 6 to 7 cm. A short piece of glass tubing, D,having an internal diameter approximately I 111111. rester than the external diameter of tube B, is placed in the a%aorption vessel to break up the bubbles of gas and provide more absorption surface; it should be completely covered by solution. The apparatus used should be tested for its ability to absorb arsine completely by running a known amount of arsenic.
Reagents
A
B
Apparatus Cassil and Wichmann ( 2 ) have described an apparatus for the evolution and absorption of arsine in mercuric chloride solution, which doubtless can be adapted to the procedure below. In the present work the apparatus consists of a 50-ml. Erlenmeyer flask closed by a one-hole rubber stopper from which leads a tube, A (Figure l), containing at its lower end one or two plugs of glass wool impregnated with lead acetate. This tube is connected by means of a short section of rubber tubing to the delivery tube, B, which is drawn down to a capillary tip having an opening
FIGURE^. APPARATUS
FOR
ABSORPTION OF ARSINE
Stannous chloride, 40 grams of stannous chloride dihydrate in 100 rul. of concentrated hydrochloric acid. Potassium iodide,. 15 grams in 100 ml. of water. Zinc, 20- to 30-mesh, “arsenic-free”. Mercuric chloride., 1.5 n-a m s in 100 ml. of water. Potassium permanganate, 0.03 N , 0.10 gram in 100 ml. of water. Discard the solution when a precipitate of manganese dioxide forms. Ammonium molybdate-hydrazine sulfate. Prepare fresh daily by mixing 10.0 ml. each of solutions A and B and diluting to 100 ml. with water. Solution A: Dissolve 1.0 gram of ammonium molybdate in 10 rnl. of water and add 90 ml. of 6 N sulfuric acid. Solution B: Dissulve 0.16 gram of hydrazine sulfate in 100 ml. of water. Standard arsenic solution. To prepare a 0.100 per cent arsenic solution, dissolve 0.1320 gram of arsenic trioxide in 2 or 3 ml. of 1 N sodium hydroxide, dilute with water make acidic with hydrochloric acid, and dilute to 100 ml. From this stock solution, prepare by dilution a standard solution containing 0.010 mg. of arsenic per milliliter.
