in this study show that only about 95% of the sulfonate sulfur is attributable to the sulfonic acid group. The identity of the other sulfur components included in the sulfonate analysis has not been determined, although mercaptans, disulfides, sulfides, sulfoxides, and sulfones, if present, would not be determined as nonsulfonate sulfur in the direct method of analysis and would influence the value for sulfonate sulfur. KOsignificant amount of mercaptan or of disulfide was found in the liquors used for these analyses, but a suitable test for the other suggested types of sulfur in the presence of sulfonic acid was not available. Total Sulfur. T h e total sulfur content of spent liquor is given by the sum of sulfonate plus nonsulfonate sulfur as determined by t h e method described. This value is in good agreement, as shown in Table 11, with the result for total sulfur obtained by either the Parr bomb method ( 7 ) or
the nitric-perchloric acid procedure described by Salvesen and Hogan (9). Comparison of Direct Method with TAPPI Procedure. T h e results by the two methods for t h e determination of sulfur in spent liquor are compared in Table 111. T h e values for total sulfur are in agreement, but some variation is evident in the sulfonate and nonsulfonate classifications. T h e lower value for sulfonate and correspondingly higher value for nonsulfonate sulfur by t h e direct method reflect t h e inclusion of thiosulfate and polythicnate sulfur in the proper nonsulfonate group. The results obtained by the direct method, when viewed in terms of the accepted definition of sulfonate and nonsulfonate sulfur, provide a more realistic analysis of spent sulfite liquor than the older TAPPI method, LITERATURE CITED
(1) Feigl, Fritz, “Spot Tests,” Vol. 1, 279, Elsevier, Amsterdam, 1954. (2f)“ oge, W. H., Ph.D. thesis, pp. 18-24,
Institute of Paper Chemistry, Appleton, Wis., 1954. (3) Zbid., pp. 129-31. (4) Kolthoff, I. M., Sandell, E. B., “Textbook of Quantitative Inorganic Analysi.,” 3rd ed., pp. 590, 604, Macmillan, Yew York, 1952. (5) Kurtenacker, Albin, “Analytische Chemie der Sauerstoffsauren des Schwefels,” p. 136, Ferdinand Enke, Stuttgart, 1938. (6) Mitchell, J., Jr., Kolthoff, I. M., Proskauer, E. S., Weissberger, A., eds., “Organic Analysis,” Vol. 1, p. 359, Interscience, New York, 1953. (7) Parr Instrument Co., Moline, Ill., Parr Manual 121, 27 (1950). (8) Peniston, Q. P., Felicetta, V. F., McCarthy, J. L., IND.ENG. CHEM., ANAL.ED.19,332 (1947). (9) Salvesen, J. R., Hogan, D., ANAL. CHEM.20,909 (1948). (10) Samuelson, O., Westlin, A., Suensk Papperstidn. 51, No. 4 179 (1948). (11) Technical Association of the Pulp & Paper Industry, New York, TAPPI Standard Methods, T 629 m-53. RECEIVED for review November 27, 1959. Accepted March 21, 1960. Northwest Regional Meeting, ACS, Seattle, Wash., June 1959.
Fractio nuI The rmog ravimet ric Ana lysis P. 1. WATERS Coal Research Secfion, Commonwealfh Scientific and Industrial Research Organization, Sydney, New Sooth Wales, Australia In thermogravimetric analysis measurements are made of weight loss due to the escape of all volatile matter from a sample during heating. The new technique, “fractional thermogravimetric analysis,” extends the scope of thermogravimetric analysis by providing information on the composition or properties of the volatile matter. In one application a specific fraction of the volatile matter is trapped in the upper section of a vessel which contains the sample; the weight loss is then due to the remaining fraction. Thus b y elimination it i s possible to follow the variations in the rates of evolution of the tar, liquid, and gases from coal and similar compounds during pyrolysis. In another application, the method is used to determine carbon and hydrogen evolving in volatile form, by oxidizing carbon to carbon dioxide and hydrogen to water. A slightly modifled version is used for volumetric measurements of gas evolution; the data, combined with corresponding gravimetric measurements, make it possible to calculate the average density of the gases evolved during decomposition. This paper describes the technique and presents evidence of the repeatability and accuracy of the results.
852
0
ANALYTICAL CHEMISTRY
T
considerably improved by recent advances in design, is today a recognized laboratory tool. Ordinarily i t measures the decrease in weight of a substance due to the loss of volatile products of thermal decomposition. In the new technique described the thermobalance is used to determine continuously not only the quantity but also the quality and composition of the volatile matter being evolved; in this way the application of the apparatus has been usefully extended. The only change in the apparatus is a fine glass vessel drawn from tubing for each test as required, replacing the crucible usually employed. This vessel has two sections interconnected by a fine capillary; volatile matter from the heated sample in the lower section has to pass through reagents in the upper section before escaping to the atmosphere. The charged glass vessel is suspended from the beam of a thermobalance, and the continuously recorded decrease in weight is due to the loss of volatile matter from the sample only after the volatile matter has been treated with reagents. It can be treated in several ways-by fractional condensation or by thermal or chemical treatment-depending on the information desired. I n some instances it is possible to measure the HE THERMOBALANCE,
effect of such treatment volumetrically as well as gravimetrically. The thermobalance used in all the present experiments was the differential torsion-type thermobalance (2-4). The apparatus required, apart from the thermobalance and associated control unit, is simple and after a little practice a tube with a sample and the necessary reagents can be prepared in a matter of minutes. FRACTIONAL THERMOGRAVIMETRIC ANALYSIS
Outline of Method. The principle of fractional thermogravimetric analysis is t h a t one (or more) of t h e volatile components given off by t h e sample is selectively condensed or absorbed and conjointly weighed Kith the sample by the thermobalance; t h e loss in xeight recorded is consequently due t o uncondensed or unabsorbed volatiles, which may consist of moisture, gas, or both. The yields of the individual components are determined from a set of curves recorded under different conditions of fractionation but exactly the same conditions of pyrolysis of the sample. Figure 1 shows the basic features of the apparatus for separating volatile components. The borosilicate glass bulb, a,
e-
I
1,I 6
[: 1
iii
SCALE lNCHE5
br
a-
LtitFigure 1. Apparatus for fractional thermogravimetric analysis
containing the sample is heated by the furnace, b, and is connected by a finely drawn capillary to the small absorption tube, c. The whole is suspended by a fine wire, e , from the beam of a thermobalance. The absorption tube contains appropriate solid absorbents or reagents in finely divided state, and its temperature may be controlled by a cooling block or a small subsidiary furnace, d. The method of preparing the tubes, which are made from thin-walled borosilicate glass tubing about 6.0 mm. in internal diameter, is illustrated in Figure 2. The sample is charged through funnel i into the bulb of tube ii and weighed. Tube iii-the type most frequently used-is formed from tube ii by dram-ing the glass a t point X t o a fine capillary about 0.4 mm. in internal diameter and a few inches long to suit furnace dimensions. The upper section of tube iii is suitably packed with about 1 gram of finely divided (30 to 100 B.S. mesh) absorbents or reagents, and a glass hook is then drawn a t the top for the purpose of suspending the tube. The tube thus prepared for test weighs between 5 and 7 grams. I n some of the experiments, volatile matter is oxidized to carbon dioxide and moisture and the moisture formed is absorbed in tube iv. Tube v, the sample container used for ordinary thermogravimetric experiments, allows the complete escape
ii X
0
1
2
SCALE INCHES
Figure 2.
Preparation of tubes
of volatile matter. Tube vi (sample container with vial to displace vapor) is described below. Decomposition of Sodium Bicarbonate. The efficiency of the absorption system was checked by a preliminary and relatively simple application of the method to the decomposition of a sample of sodium bicarbonate, which occurs between 100' and 225' C. with the loss of water and carbon dioxide. The results are given in Figure 3. The first experiment (curve A ) measured the combined loss of moisture and carbon dioxide, which was 36.601, by weight (theoretical value 36.9%). I n the second experiment (curve B ) the moisture was absorbed by silica gel and Anhydrone, so that the loss in weight due to carbon dioxide only was measured and found to be 25.4% (theoretical value 26.201,). I n the third experiment (curve C) both water and carbon dioxide ryere absorbed (the latter by soda-asbestos); the loss in weight of the sample was only O.lyo, confirming the high efficiency of the absorption process. Pyrolysis of a Coking Coal. The method in its application t o coal may be regarded as a very small scale carbonization assay. -4s such i t gives the weight yield of each carbonization product, but, in addition, provides information on the separate rates of evolution of tar, liquor, and gas. The curves in Figures 4 and 5 show the composition of the volatile matter as tar, "moisture," and gases when 1-gram samples of a coking coal (Kemira Bulli) were heated a t the rate of 6" C. per minute to about 735" C. (The moisture fraction may be more strictly defined as
Figure 3. Fractional thermogravimetric analysis of sodium bicarbonate Heating rate, 3" C. per minute
that part of the volatile matter which is condensable a t room temperature under the conditions prevailing in experiment C but not condensable on sand a t 120" C. as in experiment B.) I n these experiments (except experiment A) the absorption sections of the tubes were packed with absorbents or reagents (the approximate length of tube occupied by the material is indicated in parentheses). EXPERIMENT A. Determining the loss in weight due to the escape of all volatiles. Tube as in Figure 2, v. EXPERIMEKTB. Condensation of tar only, allowing the loss of moisture and gases. Tube as in Figure 2, iii, packed with sand (3 to 4 cm.) a t 125' C. EXPERIMENT C. Condensation of tar and moisture, allowing the loss of gases. Tube iii packed \T-ith sand (1 cm.); dehydrated silica gel or alumina (1.5 cm., chromatographic quality); Anhvdrone (1.5 to 2 cm.) : and sand again (0.3 em.).. EXPERIMENT D . Allowing the loss of all gases except COz and H2S. Tube iii packed as for experment C but with finelv divided soda-asbestos (1 cm.) preceding the ilnhydrone. EXPERIMENT E. Allowing the loss of "permanent" gases and methane. Tube iii packed as for experiment D but containing in addition activated gascarbon (2 to 3 cm.) after the Anhydrone. VOL 32, NO. 7, JUNE 1960
0
853
1
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CUMULATIVE WEIGHT LOSS
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TOTAL VOLATILE YATiER
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0.4
E DRY GASES (4.1°/0)
0.
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RATE OF WEIGHT LOSS 479OC.
0 300
3 TEMPERATURE
Figure 5. coal
PC)
Fractional thermogravimetric analysis of a coking
Showing separote rotes of evolution of each of the main components of volatile matter Heating rote, 6' C. per minute
. -I TEMPERATURE
PC)
120
Figure 4. Fractional thermogravimetric analysis of a coking coal A. Loss of oll volatile matter B. Loss of volatile matter noncondensable on sand at 125"C.-i.e., liquor and gases C. Loss of gases and vapors noncondensoble at 35" C., moisture removed b y Anhydrone D. Loss of dry, uncondensable gases. CO. and HzS removed by soda-asbestos E. Loss of dry, uncondensoble, and C o y f r e e gases treoted with activated carbon to absorb heavier gaseous hydrocarbons preferentially Heating rote, 6" C. per minute
IF w
ii
COMPONENl
1
f l
-
1
J
0
10 2
20p
300
4jC
51'0
500
TEMPERATbRE ("Cd
Table 1.
Temp.,
" c. 100 150 200 250 300 350 400 420 440 460 485 500
Stages of Thermal Decomposition of a Sample of Coking Coal (Kemira Bulli)
Appearanoe of Products First droplets of water and small amounts of gas Copious evolution of water Droplets of water still forming, but little gas Traces of water and very small amounts of gas Traces of water First droplets of almost colorless oil; traces of H2S (as detected by lead acetate on silica gel ) Much pale yellow oil Continued evolution of pale yellow oil and water Evolution of yellow oil Orange-yellow tar fog; evolution of H,S more pronounced and much gas given off Orange-red tar Reddish droplets of tar
Color of Fluorescence under UV Light"
... ...
...
..
Pale blue
Intense pale blue Greenish blue Yellowish green Yellow Orange-yellow Sonfluorescing (but violet in cooler part of tube)
... Only traces of red tar but more water droplets ... Mainly water and gas ... Last traces of tar ... Water and gas only a Fluorescence under ultraviolet light is used to distinguish between water and hydrocarbons and to indicate qualitative changes in the hydrocarbons. Fluorescence will occur even with very dilute solutions; it is especially marked with complex organic molecules in which the nuclear framework is particularly rigid-for example, polycyclic aromatic and heterocyclic compounds ( 1 ) . 510 530 560 575
854
ANALYTICAL CHEMISTRY
Figure 6. Distillation of tar and liquor fractions collected during pyrolysis of Kemira Bulli coking coal
Differences betrreen the results of successive experiments give the follom-ing yields of volatile products from Kemira Bulli coal heated to 650" C.:
A - €3, 5.2% tar B - C, 6.3% moisture C - D, 0.7% carbon dioxide (mainly) and hydrogen sulfide D - E, 0.9% gaseous and volatile hydrocarbons (other than methane), and ammonia E - F, 4.1% "fixed" gases consisting of methane, hydrogen, carbon monoxide, and nitrogen -4 - F, 15.8% total volatile matter yield up to 650" C. Figure 4 shows that most of the tar and liquor are evolved below, and most of the noncondensable gases above, 525°C. The tar and moisture fractions condensed in the absorption tube on sand at
Figure 7. Effect on weight loss of passing volatile matter evolved from coking coal through beds of materials at 640"
C. 15-
Sand 4. Empty tube Normal test 5. Silica gel Coke 6. Alumina Heating rate, 5.9' C. per minute using tube of type iii, Figure 2
1.
CUMULATIVE WEIGHT LOSS
t
z
2. 3.
room temperature (as in experiment C for a coking coal but using only sand to trap the products) can be further analyzed in subsequent thermogravimetric experiments to gain information on the distillation range of the tar. Examples of the simple distillation of tar and liquor fractions collected during pyrolysis of the coking coal are given in Figure 6 . In each experiment the original condensation tube containing the tar and liquor was detached from the sample section, by breaking and sealing off the capillary, and then heated a t the rate of 6 ° C . per minute. Factors Affecting Evolution of Volatile Matter. I n experiments with
t 0 8 -
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RATE OF
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TEMPERATURE ('CJ
60
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.
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RATE OF WEIGHT LOSS A82
TEMPERATURE ( 'CJ
Figure 8. Thermogravimetric curves obtained by oxidation to carbon dioxide and water of total volatile matter evolved from a coking coal heated at 6.0" C. per minute A. 6. C.
Loss of COz, moisture, and N Loss of COn and N. Moisture separated b y Anhydrone Loss of N. Both COz and moisture absorbed
some highly swelling coals sand was introduced into the pyrolysis tube to prevent possible blockage of the outlet caused by excessive swelling of the sample. Fears t h a t the sand might cause some cracking of the volatile matter and affect its yield and rate of evolution proved to be without foundation, as confirmed by the results of "cracking" experiments given in Figure 7 . I n the first experiment, volatile matter from a 1-gram sample of Kemira Bulli coal was passed through a bed of sand contained in the upper section of the tube (iii, Figure 2) heated to 640" C. The experiment was repeated using, instead of sand, finely divided coke, silica gel, alumina, and an empty tube for a blank experiment. Only the two surface-active highly absorptive materials-silica gel and alumina-caused significant cracking of the volatile matter; it was, therefore, concluded that because sand a t 640" C. has no appreciable effect on the yields of the volatile matter, it is unlikely to affect the course of decomposition a t the temperatures of coal pyrolysis (300" to 550" C.) when mixed with coal. Comments on Method. One of the useful features of the technique is t h a t the various stages of decomposition can be followed visually: One can actually see the moisture or oil droplets forming in the exposed stem of the capillary. The presence of minor constituents, such as hydrogen sulfide, can be detected by introducing a thin layer of indicating reagent into the absorption section of the tube. Table I lists the changes observed in experiment D. Each experiment with the sample of Kemira Bulli coal was repeated several times, to assess its repeatability statistically. The precision of these experiments mas good, as Table I1 indicates, and was not appreciably affected by modifications in the methods of packing the absorption tubes or changes in quantities of reagents. The physical separation into components by fractional condensation is not absolute. Nevertheless, because of marked differences in physical characteristics, the main fractions-tar, moisture, and various gasescan be effectively separated. The results (Figure 6) have demonstrated that the distillation ranges of the tar and moisture fractions are so different as to be well separated under the conditions of experiment B. A number of experiments were conducted to find out whether the silica gel used for trapping tar and moisture (experiments C and D) would adsorb and retain some gas which would otherwise have escaped, for such adsorption, if appreciable, would affect the accuracy of the method. "Guard" tubes containing 2 to 3 grams of silica gel were placed in the gas stream after the absorpVOL. 32, NO, 7, JUNE 1 9 6 0
0
855
10
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08
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l O T A L VOLATLE ‘4 MA‘TER
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, ,060.6 W
a b-
w z
-
u O0.6 L -
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-
0 2 0.2
0 300
500
400
600
700
Figure 9. Rates of evolution of carbon, hydrogen, and oxygen (by difference) from a coking coal Heating rate,
6’ C.
per minute. 75
-2
Figure 10.
+
W a
a _ a
21
5C
v Lo
0”
Pyrolysis of
calcium acetate u
-
Rate of weight loss Cumulative weight loss Heating rate, 1.45’ C. per minute
--
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,\ TEMFERCTURE
Figure 11.
5cc
e:)
Volumetric and gravimetric evolution and calculated density of dry noncondensable gas from a coking coal Heating rate, 6’ C. per minute
856
t’ion tube in experiments C and D. The gain in weight of these guard tubes during the carbonization experiments did not esceed 3.4 mg. and this mas attributed to adsorbed gas and, possibly, moisture. Because of the small amount of silica gel in the absorption tube and the fact that it is partly impregnated with tar and moisture, the amount of gas retained would be much less than 3 mg. This inaccuracy would be n-itliin the limit of experimental error in the cumulative weight-loss measurements and insignificant so far as the rate-ofweight-loss measurements are concerned. On t’he other hand, in esperinirnts involving the condensation of tar, the tar appears to be complctely trapped by the finely divided materials in the absorption tube and there is no evidence of losses due to the escape of tarry matter in the form of fog. Two further factors n-ere examined as possible sources of error. The first was the effect of capillary constriction on the flow of volatile matter. It \$-as found that the t’otal pressure drop across the capillary and the packed absorption tube (iii, Figure 2) 17-as only on the order of 2-inch water gage for air flowing a t 10 ml. per minute, which is the niasimum rate of flow likely to be experienced in tests of this type. This order of pressure mriation over the sample (which is within the range of day-to-day changcs in barometric pressure) ivould not materially affect the course of its decomposition. Secondly, a slight film of carbonaceous matter may be deposited on parts of t’he capillary stem; measurements shon-ed that, the weight of this deposit is on the order of 0.1 mg. or less, and is not significant as a source of error.
ANALYTICAL CHEMISTRY
ULTIMATE ANALYSIS
OF VOLATILE MATTER
Outline of Method. I n t'his application of fractional thermogravimetric analysis the amounts of carbon and hydrogen in t h e volatile matter during t h e deconiposition of a sample of organic material are calculated from recorded weight-loss curves. The carbon and hydrogen are converted into carbon dioxide and water, respectively, by passing the volatile matter through a section of tube containing a mixture or layers of finely divided copper oxide n-ire and -4rneil catalyst a t 640" C. T w o esperinientsare necessary: I n the first, a tube as in Figure 2 , iii. allows the complete escape of both carbon dioxide and water; in the second, a tube as in Figure 2, iv, traps the n-ater by silica gel and Anhydrone in the uppermost section and :illon-s the escape of carbon dioxide. From the recordings of these two experiments, curves for the evolution of volatile carbon and volatile hydrogen can be easily plotted. Furthermore, it is possible to derive a cur1.c for osygcw (inciudiiig errors) by subtracting the combined carbon and hydrogen curves from the ordinary thermogravimctric curve of the total volatile-mat ter evolution. Figure 8 shows the results of experiments on 0.3-gram samples of the Keniira Bulli coking coal. I n the third experiment (curve C) both the moisture and the carbon dioxide were absorbed, and the recorded total loss in weight u p to 700' C. proved to be only 0.6%, presumably due mainly to nitrogen. This shows that the organic constituents of the volatile matter, including not easily oxidizable methane, were efficiently oxidized by the copper oxide and Arneil catalyst. The separate rates of
I
,
Table
II.
Precision of Fractional Weight-Loss Experiments
Results pertaining to pyrolysis of Kemira Bulli coal given in Figures 4 and 5. R = mean value of n tests. s = standard deviation h-0. Cumulative Max. Rate Temp. of of Loss of Wt. to of Wt. Loss, Max. Rat: of Tests 650' C., % '%/Min. Wt. Loss, C. n Experiment z = t s X * S z * s A. Loss of all volatile matter 7 17.2 0.88 0.028 479 2 0.19 B. Loss of liquor and gases 4 12.0 0.36 0.41 0.008 495 5 C. Loss of dry gases 5 5.7 0.15 0.28 0.010 504 6 D. Loss of dry gases less CO, 5.0 0.22 0.23 and H2S 3 0.002 504 2 E. Loss of "fixed" gases 2 4.1 0.04 0.16 0.00 510 7
evolution of carbon, hydrogen, and oxygen (by difference)-the ultimate composition of the volatile matter-are plotted in Figure 9. Assessment of Accuracy. The accuracy of t h e method of oxidation as tested by using pure compounds whichvolatilizeor decompose in known ways.
oxygen (by difference), compared with theoretical values of 62.0, 10.4, and 27.6%. I n investigations of the deconiposition of organic compounds by this method one source of error is the weight of residual vapor in the bulb, which may
EXAMPLES. The determined values of carbon and hydrogen for naphthalene, evaporated a t a controlled rate by slow heating, were 93 + 0.057, and 6.21%, respectively, compared viith theoretical values of 93.7 and 6.29%; the weight of the sample of naphthalene (about 45 nip.) was corrected for the residual vapor in the bulb (about 0.9 mg.), which was measured gravimetrically. Another known compound-calcium acetate-which decomposes between 300" and 600" C. with the formation of acetone and calcium carbonate (Figure 10). gave the following results: The total loss in weight of the sample between 300" and 600" C. was 35.65 0.25%',, the theoretical value being 36.6%. The composition of the volatile matter was 60.7 =t0.03% carbon, 10.6 + 0.15% hydrogen, and 28,7%
I
Anhydrone Silica gel
eI o ,
(to flow mete(
(Moisture condensed>
*
Anhydrone I
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l
o
497
Silica gel
(Moisture' and tar condensed)
Sand
r--TXT--i .,latile 1
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TE'4aEQATJRE
'A1
Sample/ heated at-+&& k°C/min.
1
I
I
Coal
I
matter 1
I
I I
("C)
Figure 12. Rate of evolution of carbon in form of total volatile matter or noncondensable gas from a coking coal b y the volumetric method Heating rate, 6 ' C. per minute.
Figure 13. Apparatus for determining amount of carbon present in noncondensable gases from heated coal sample VOL. 32, NO. 7, JUNE 1960
a
857
be on the order of milligrams. It may be minimized by inserting a vial with a capillary outlet into the sample container as in Figure 2, vi. This arrangement has a twofold effect: It reduces the free space above the sample and thus the quantity of residual vapor; the expansion of the air in the vial with rising temperature causes a n air leak through the capillary, which assists in purging volatile products from the bulb. VOLUMETRIC ANALYSIS
OF
VOLATILE MATTER
Evolution of Noncondensable Gases. T h e evolution of permanent
gases can be measured gravimetrically, as in experiment C (Figure 4), or volumetrically. The gravimetric measurements divided by t h e corresponding volumetric measurements give t h e average density of t h e gases a t a n y chosen temperature. For volumetric measurements the tube assembly in Figure 2, iii, was used, except that the top of the tube was not suspended from the thermobalance but connected to a soap filmtype of gas flowmeter of 5-mL capacity. Readings of gas flow were taken every minute. Rates of evolution of gas by weight and by volume (converted to N.T.P.) obtained in parallel experi-
ments are represented in Figure 11 by curves i and ii. The curve of the variation of gas density with temperature was drawn by dividing values on curve i by corresponding values on curve ii; the resulting curve, iii, is in satisfactory agreement with curve iv plotted from density values calculated from gas analyses of a 10-gram assay made under comparable carbonizing conditions. Evolution of Carbon in Volatile Form. The results of gravimetric experiments t o determine the rate of evolution of carbon in volatile form are shown in Figure 8, B. Besides being measured by weight, carbon dioxide can also be measured by volume using t h e floLTmeter. The values obtained by t h e two methods (converted to S.T.P.) for the same coal sample are plotted in Figure 12, i and ii. These curves show satisfactory agreement, apart from a slight temperature shift. To determine the amount of carbon present in noncondensable gases as carbon dioxide, carbon monoxide, and hydrocarbons, the gases (after the tar and liquor had been condensed from the volatile matter, as in experiment C) were passed through a section of tube containing copper oxide and Arneil catalyst a t 640" C. The gases were completely oxidized to carbon dioxide and
water. After the water had been trapped, the flow of carbon dioxide was measured. Curve iii, Figure 12, shows the variation in the rate of evolution of carbon dioxide, and hence of carbon, with carbonizing temperature. Figure 13 shows diagrammatically the tube assembly and indicates the successive stages of treatment of the volatile matter in this experiment. ACKNOWLEDGMENT
The author thanks H. R. Brown, Officer-in-Charge of the Coal Research Section, C.S.I.R.O., under whose direction the work was carried out, for help and encouragement. LITERATURE CITED
(1) Braude, E. A., "Determination of
0rg:Fic Structures by Physical hlethods, E. A. Braude and F. C. Nachod, eds., Chap. 4, p. 138, Academic Press, New York, 1955. (2) Waters, P. L., C. S.I. R . 0. Coal Research Section, Rept. Ref. T. C. 18 (1956). (3) Waters, P. L., J. Sci. Instr. 35, 41 (1958); Coke and Gas 20, 252, 289, 341 (1958). (4) Waters, P. L., Suture 178, 324 (1956). RECEIVED for review December 22, 1959. Accepted March 31, 1960. Work undertaken as part of the program of the Coal Research Section, Commonweath Scientific and Industrial Research Organination, Australia.
Visible and Infrared Spectroscopic Determination of Trace Amounts of Silicones in Foods and BioIogicaI Materials H. J. HORNER, J. E. WEILER, and N. C. ANGELOTTI Analytical and Spectroscopy laboratories,
,Since the introduction of silicones to the food and drug industry, numerous problems involving the determination of these materials in trace amounts have arisen. Because silicones give no color tests or distinctive reactions, it was necessary to develop special extraction and concentration techniques to obtain samples in a form suitable for analysis. The scope of this investigation has extended from the analysis of foods to the detection of silicones in human lung tissue, blood, and animal organs. A chemical silicon determination may b e applied, provided residual silica content does not interfere. A more definitive infrared technique has also been evolved for the detection and measurement of si I icones
.
858
ANALYTICAL CHEMISTRY
Dow
Corning Corp., Midland, Mich.
W
of silicones t o the food and drug industries, a need arose for the development of techniques for the determination and identification of these materials in trace amounts. Food and Drug Administration regulations require that when silicones are used in the processing of foods or pharmaceuticals, the residual silicone content in the finished product be known or be able t o be determined analytically. This residual content generally falls in the part per million range. Because of their chemical inertness silicones cannot be detected by simple chemical tests. Several methods of detection are applicable t o the determination of silicones in this range: radioactive tracer techniques in which the silicone in a tagged ITH THE INTRODUCTION
form is used in the processing step; a n internal standard technique where a known amount of a more easily analyzed element or compound is added to the silicone with subsequent analysis for this material in the sample; spectrophotometric silica determination; and extraction and concentration of the silicone followed by a n infrared examination of the extract. The radioactive tracer technique was not thought feasible because of the expense and the equipment needed for this type of analysis. The internal standard technique, although satisfactory, is not considered generally applicable because the additive may respond differently to treatment for analysis than the silicone. Because of the obvious shortcomings of the first
