ANALYTICAL CHEMISTRY
1172 because these molecules are known to concentrate a t the bottom of a thermal diffusion column (3). Oil B was a refined and dewaxed residual oil and was studied without additional fractionation. The original oil had a band a t 10.35 microns and no indication of a band at 10.27 microns as shown in Figure 1,c. Hydrogenation removed this band almost completely. Spectra of two of the thermal diffusion cuts are shown in Figure 1,d. There is some broadening of the 10.35-miwon band on the short wave length side in the 80 to 90% cut from near the bottom of the column, but it appears that the band in this oil is due primarily to trans-olefin structural groups.
ACKNOWLEDGMENT
The author wishes to express his thanks to E. R. Kerr who carried out the hydrogenations, and t o J. E . Scardefield who helped with the experimental work, LITERATURE CITED
(1) Fred, M., Putscher, R., ANAL.CHEW21, 900 (1949). (2) Haak, F.A., Nes, K. van, J. Inst. Petroleum 37, 245 (1951). (3) Jones, A. L.,Milberger, E. C., Ind. Eng. Chem. 45, 268 (1953). (4) Lillard, J. G., Jones, W. C., Anderson, J. A., I bi d., 44, 2623 (1952). (5) Putscher, R.,ANAL. CHEM.24, 1551 (1952).
RECEIVED for review December 19, 1955. Accepted February
24, 1956.
Modified Com bustion Procedure for Determining Carbon and Hydrogen in Certain Organometallic Gompounds EARL L. H E A D and CHARLES E. HOLLEY, JR. University of California, Los Alamos Scientific Laboratory, Los Alamos,
N. M.
A combustion analysis apparatus and procedure are described which permit the determination of carbon and hydrogen in volatile pyrophoric compounds which may undergo pyrolysis to give nonvolatile residues.
proximately 2.5 liters per hour. This flow rate was maintained between runs to assure steady-state conditions. All stopcocks and the first ball joint on the exit side of the combustion furnace were greased with Apiezon N. This ball joint was greased to prevent any loss of the water condensing a t this point. Grease was not necessary on the other ball joints.
N T H E course of an investigation of hydrides and organo-
PROCEDURE
I
metallic compounds of magnesium and beryllium it became necessary to use combustion analysis to determine the ether content and composition of certain preparations. The properties of these compounds made i t impossible to use the conventional combustion procedure without modification. Several of the compounds were pyrophoric, others were very volatile, and some released hydrogen suddenly and in such copious quantities that, in an oxygen atmosphere, explosive mixtures resulted. An additional difficulty arose from the pyrolysis of some of the preparations and the formation of a nonvolatile residue which required exposure to oxygen a t an elevated temperature for complete combustion. A modification of the conventional combustion procedure was developed and used successfully on these preparations. APPARATUS
The apparatus as finally developed consisted of a modified Liebig combustion train containing elements in sequence as follows: Two parallel butyl sebacate bubblers for the admission of oxygen and helium. A quartz tube (15 mm. in outside diameter X 20 cm. long) containing copper oxide maintained a t 700" C. for purification of inlet gases. A U-tube containing successive sections of Anhydrone (G. Frederick Smith Chemical Co., Columbus, Ohio), Ascarite (Arthur H. Thomas Co., Philadelphia, Pa.), and Anhydrone for removal of water and carbon dioxide from inlet gases. A quartz sample tube (15 mm. in outside diameter X 18 cm. long) and accompanying furnace. A quartz combustion tube (23 mm. in outside diameter X 34 cm. long) filled with copper oxide and maintained a t 900' C. to assure combustion of carbon monoxide (3). Two U-tubes fitted with stopcocks and containing Anhydrone for absorption of water, folloved by two additional tubes each containing Ascarite followed by Bnhydrone in approximately equal amounts for absorption of carbon dioxide. A final bubbler for observation in adjusting gaseous flow rates. All connections a t critical locations were made with semiball joints, and flexible tubing was excluded from these locations. The flow rate of gas through the system was maintained a t ap-
Because of the highly reactive materials handled-for example, dimethylberyllium, magnesium hydride, aluminum hydride, and beryllium h y d r i d e s o m e satisfactory method was needed whereby the material could be easily weighed and placed into the combustion system. This was accomplished by using a small tin capsule which could be introduced with the sample and completely oxidized in the course of the combustion. These capsules were made from pieces of tin 4 cm. square, about 3 mils thick, and weighing approximately 0.6 gram. After a sheet had been folled on a mandril, the side and one end were sealed by cnmping. The open capsule was placed in a weighing bottle, taken into a drybox, filled with the inert gas of the box, taken out, and weighed using another bottle as a tare. The capsule and bottle were taken back into the drybox; the capsule was loaded, sealed by crimping, taken out of the drybox, and reweighed. Sam les of 50 mg. were found to be a convenient size. Azer weighing, the capsule containing the sample was placed quickly in a quartz boat which had been fired previously in a muffle furnace a t 1000" C. for a t least 1 hour. The boat containing the sample was introduced through a semiball joint immediately into the sample-furnace region. Just prior to this operation the absorption train had been attached to the system, the stopcocks opened, and the flow of helium begun. Because of the rapid release of hydrogen and other explosive gases from some of these materials during combustion, it was necessary to use pure helium during the initial stage of heating. After the more volatile portions of the sample had had time to pass through the combustion furnace, the flow of oxygen was begun. Cnder these conditions one sample could be run about every 2'/2 hours. After the sample had been placed in position and the system closed, the furnace surrounding the sample tube was turned on a t its maximum power of 800 watts until the maximum operating temperature of about 1050' C. was reached. This high temperature was used to destroy any stable carbonates which might have been formed during the initial heating of the sample. At a sample temperature of about 600" C. the helium was stopped; pure oxygen was then admitted and continued for the remainder of the run. It was noted that a large consumption of oxygen occurred between approximately 850" and 900" C. due to the burning of the tin. For this reason the flow of oxygen into t h e system had to be increased to maintain the rate of 2.5 liters per hour through the exit bubbler. The temperature of 1050" C. was reached in 25 minutes and mas maintained until the visible moisture on the exit side of the combustion furnace had disappeared. At this
1173
V O L U M E 28, NO. 7, J U L Y 1 9 5 6 time the run was terminated. The amounts of carbon and hydrogen were obtained in the usual manner from the weight gains of the corresponding absorption tubes.
Table 11. Combustion of Standard Succinic Acid Carbon and- Hvdroeen Determination Hz0 found, Hydrogen, % Ratio mg. Calcd. Found Found/Chd. 94.2 i 0.24 5.12 5.14 zt0.014 1.0039 &0.0027 2 8 . 4 i O . 2 4 5.12 5 . 1 O i 0.046 0 . 9 9 6 1 ~ 0 . 0 0 9 0 D
DETERMINATIOY OF BLANK CORRECTION
Nine blank runs (Table I ) were made with the collecting train in position and the combustion and purification furnaces a t their operating temperatures. The nine runs include those made with freshly charged tubes and also after carbon dioxide and water from a combustion had been absorbed. Under these conditions no distinguishable differences were noted. The weight gain or loss per hour of run was determined, from which the mean and the standard deviation of the mean were determined. The uncertainty given is 2 X the standard deviation. The blank for carbon dioxide n-as found to be 0.030 f 0.016 mg. per hour and for water -0.005 =t 0.012 mg. per hour. Because a ran usually lasted no more than 2 hours, a blank correction was thus found to be unnecessary. Combustion of the tin used showed that it gave 0.22 mg. of water per gram of tin and 0.03 mg. of carbon dioxide per gram of tin. COMBUSTION OF STANDARD SA-MPLE
Succinic acid, Eastman Kodak Co., white label purity, was burned to determine the efficiency of the combustion apparatus. The acid was dried for more than 2 hours in an oven a t 110' c. The results are shown in Table 11.
Table I.
Evaluation of Blank Correction for Carbon Dioxide and Water
Time of Run, Hours
Wt. Gain, Mg. 0.2
t
1.5 1.0 1.5 1.7 1.7 10.0 2.0 2.0 15.0 36.4
Gain, Mg./Hour Carbon Dioxide 0.13 0.00 0.00
0.0 0.0
-0.12 0.00 0.03 0.05 0.15 0.03
-0.2 0.0 0.3 0.1 0.3 0 4
0.1 1.5 -0.2 1.0 0.0 1.5 0 0 1.7 0.0 1.7 -0.1 10.0 0.0 2.0 0.0 2.0 15.0 0.0 36.4 Bv. wt. gain per hour:
Water 0.07 -0.2 0.0 0.0 0.0 -0.01 0.0 0.0 0.0
Deviation, A
0.10 0.03 0.03 0.15 0.03 0.00 0.02 0.12 0.00
For COz = 0.030 mg. For Hz0 = -0.005 mg.
-
For COz =
-
For HzO =
4-
Carbon, % Calcd. Found 205.1 k 0 . 2 304.9 f 0.30 40.68 40.57 i 0.06 62.3 1-0.2 91.2 i 0.30 40.68 39.95 f 0.19 C o t Found, Mg.
EXAMPLES AND DISCUSSIOh
The materials burned in the apparatus were mainly hydrides and organometallic compounds of beryllium and magnesium containing ether and other contaminants. The materials included : Beryllium hydride Beryllium borohydride Dimethylberyllium Methylberyllium hydride Aluminum hydride
~
0.0495
Typical results from three different runs are given in Table material are given, followed by the data obtained from a combustion of the same material. The blank spaces indicate either the absence of a substance in the sample or else the impossibility of obtaining those data. In the hydrolysis of dimethylberyllium the amount of methane found by mass spectrographic analysis of the gas was broken down into hydrogen and carbon in the ratio of 3 to 1 for inclusion in the table. In the combustion of dimethylberyllium the amounts of hydrogen and carbon collected as water and carbon dioxide, respectively, were in the ratio of 3.00 to 1, indicating good precision for the run. Other than for compounds containing organic groups, the direct comparison between hydrolysis carbon and combustion carbon means little. However, these values were necessary in order to obtain the data for a direct comparison between the hydrogen resuks of the two methods. For example, the beryllium hydride compounds frequently had appreciable amounts of dimethylberyllium present in addition to diethyl ether. For this reason the per cent of methane evolved from the sample during hydrolysis had to be measured so that a correctiori could be applied to the combustion carbon results to give a measure of the ethyl ether content of the sample. This, in turn, permitted an evaluation of the hydrogen balance and the calculation of the amount of hydride hydrogen present in the sample.
Table 111. Comparison of Combustion and Hydrolysis Analyses
~
\Et
2 X 0.0369 4-
Blank correction:
Material MezBe (hyd.) MezBe (comb.) AlHa (hyd.) AlHa (comb.)
2U
0'0495 d K 4
10,0164
BeHz (hyd.) BeHz (comb.)
=
For CO? For HzO
*0.0122 = =
Aluminum borohydride Lithium aluminum hydride Magnesium hydride Diethylmagnesium
111. The data obtained from an independent hydrolysis of the
0'0482 = 0.0369
=
0.9973 =k 0.0015 0.9821 i 0.0047
X ( t X A*) Zt - 1
dG
=
2 X std. dev. of mean For CO,
0,0096 0.0361 0.0002 0.0002 0.0002 0.0000 0.0002 0.0002 0.0015 0.0482
0.08 0.19 0.01 0.01 0.01 0.00 0.01 0.01 0.01
Std. dev. from mean of single observation = c =
For HtO
t X A2 0.0150 0.0009 0.0014 0.0382 0.0015 0.0000 0.0008 0.0288 0.0000 0.0866
Sample, Mg. 2 0 5 . l i 0.2 62.3i0.2
0.030i 0.016mg./hour -0.005 i 0.012 mg./hour
Sample Carbon Hydrogen Wt., Mg. Source Mg. % S o u r c e Mg. 77.8 46.83 60.19 11.71 46.3 28.26 61.04 7.07 .41Ha 2.97 50.7 AlHs 47.4 2.74 Ether 10.37 21.85 Ether 2.16 44.8 5.92 BeHz MezBe 0.18 0.40 IMezBe 0.045 BeHa 33.4 4.48 MezBe 0.13 0.39 MezBe 0.03 Ether 0.79 2.38 Ether 0.17
% 15.05 15.27O 5 86 5.78 4.56 13.21 0.10 13.41 0.09 0.51
0 Hydrogen-carbon atom ratio for this sample was 3.00 t o 1 and in agreement with expected ratio.
ANALYTICAL CHEMISTRY
1174 The completeness of combustion and the over-all behavior of the apparatus were tested and proved satisfactory by burning succinic acid as a standard. There remained, however, the question of whether a relatively large quantity of ether, as was liberated from such materials as beryllium hydride etherate, would be burned completely or whether only partial combustion B-ould occur upon its passage through the combustion furnace. This was tested by burning a sample of purified ether in the apparatus. The ether was introduced from a sealed tube equipped with a breakoff seal, which was broken after the tube had been sealed into the system. The ether \\*asthen vaporized and carried into the combustion region by means of helium passing over the opening of the tube. By this method, a sample of ether weighing 63.3 mg. gave 99.17~of the expected amount of carbon dioxide and 99.3% of the expected amount of mater. Also, completeness of combustion was indicated when the amount of active hydrogen determined by hydrolysis checked with that found by combustion on compounds where this comparison was possible. Some workers ( 4 ) have found that successive cycles of heating a quartz tube above l l O O o C. with subsequent cooling cause porosity in the quartz, which might eventually develop into leaks in the tube. Also, the use of copper oxide in quartz a t high temperatures tends to weaken the quartz eventually to the point where a slight strain will cause it to crack.
tions were negligible, they were not made on the runs; however, they were included in calculating the per cent error. The weighings were carried out on an Ainsworth Chainomatic balance (Wm. Ainsworth and Sons, Denver, Colo.). An attempt v a s made to estimate the weights to a few hundredths of a milligram so that their reproducibility was within the limits of 5 0 . 1 mg. Hence, for each weight recorded a possible error of f 0 . 2 mg. mas allowed (because weighings were made by difference). I n addition to the weighing uncertainty, an allowance was made for the carbon dioxide and water blanks, 0.05 and 0.02 mg. per hour, respectively, including the uncertainty in the blanks. The per cent errors in the carbon dioxide and water yields were figured separately. The total uncertainty (in per cent) for a given determination was taken as the square root of the sum of the squares of the uncertainties in the weight of the product-Le., carbon dioxide or water-and in the original sample weight. From these considerations it is possible to predict the expected precision for a combustion of any sample of given size. Because different substances yield varying amounts of carbon dioxide and water, a specific sample size n-hich would ensure a certain per cent accuracy cannot be given. The sample size should be so chosen that the per cent uncertainty for the product of lowest yield is within the desired limits. ACKNOWLEDGMENT
PRECISION AND ERROR
The absorbents used were Ascarite and Anhydrone. It has been reported ( 1 ) that Ascarite will absorb carbon dioxide completely a t a flow rate as high as 0.5 liter per minute until its weight has increased about 20%. Anhydrone has been reported ( 2 ) to be as good a desiccant as phosphorus pentoxide a t a maximum flow rate of about 5 liters of gas per hour and absorbs up to 60% of its weight of water. Even though an initial copper oxide furnace and an absorption tube containing Anhydrone and Ascarite were used, a small blank wa9 found, as has been shown. Because the blank correc-
Acknowledgment is made to T. W. Newton and J. F. Lemons for their helpful suggestions concerning this work. LITERATURE CITED
Altieri, V. J., “Gas Analysis and Testing of Gaseous Rfaterials,” p. 98,American Gas Association, New York, 1945. (2) Hillebrand, W. F., Lundell, G. E. F., “Applied Inorganic dnalyses,” pp. 44-5,Wiley, New York, 1944. (1)
(3) Ibid., pp. 627, 630. (4) Lundell, G. E. F., Hoffman, J. I., Bright, H. A., “Chemical Analysis of Iron and Steel,” p. 161, Wiley, New York, 1931. RECEIVED for review January 27, 1956. Accepted April 4,1956. Work done under t h e auspices of the U. S. Atomic Energy Commission.
Assay for Platinum Metals in Ores and Concentrates 1. HOFFMAN, A. D. WESTLAND, C. L. LEWIS,
and
F. E. BEAMISH
University o f Toronto, Toronto, Ontario, Canada
T h e r e are n o data recorded t o indicate the precision achieved by t h e various methods used for the fire assay of p l a t i n u m ores. In the following report platinum m e t a l s ores and concentrates have been examined by direct assaying and by m e t h o d s involving leaching prior to fire assay. The silver-platinum metals beads were examined spectrographically. The data obtained suggest that for ores and concentrates no advantage is to b e gained b y t h e elaborate, time-consuming leaching methods.
I
still used by some analysts as a preliminary treatment before fire assay. This process converts the bulk of the minerals to simple dissolved constituents and with subsequent treatment there is some isolation of base metals. There is no published evidence that better results are obtained by these time-consuming procedures. A unique opportunity was presented to evaluate the efficiencies of fire assay and leaching practices by an invitation to take part in a reconnaissance survey. The fire assay for platinum ( 2 ) was being investigated in the authors’ laboratory and it was considered desirable to obtain some information regarding losses with assays of ores.
T IS generally recognized that there is an appreciable lack of
precision in platinum metal values obtained from various laboratories which use different methods of fire assay. Experience has shown that the numbers vary by as much as a factor of 10. These discrepancies may be due in part to variations in procedure and technique. Leaching processes were developed many years ago and are 1
Falconbridge Metallurgical Laboratories, Richvale, Ontario, Canada.
APPARATUS, REAGENTS, AND ORES
A pyrometrically controlled Williams and Wilson 15-kva. Globar-type assay furnace was used for all the fire treatments. Spectrographic examinations of the silver beads were made on an Applied Research Laboratory 2-meter grating spectrograph (36,600 lines per inch). Zinc metal dust, Purple Seal grade, obtained from City Chemical Co., New York, N. Y., was used. Litharge, soda ash, borax glass, and calcium oxide, used in the
