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Detection and estimation on microgram quantities of carbon
MICROCHEMICAL
13, 646-655
JOURNAL
Detection
( 1968)
and Estimation on Microgram Quantities of Carbon T. F. EGAN Bell Telephone Laboratories, Inc., Holmdel, Neu: Jersey 07733 INTRODUCTION
The positive identification of microgram quantities of organic deposits and films on electrical contacts and other small objects has long
FIG. 1.
Carbon
detection
equipment
in operation. 646
@
FIG. 2.
Addition
of filtered
QUANTITIES
barium
hydroxide
647
OF c
through
self-sealing
rubber
cap.
been a tedious, difficult problem. Organic deposits may occur on electrical contacts as frictional polymer (3) from various organic vapors or the arc pyrolysis products of adsorbed organic vapors (2). Both of these can cause an increase in contact resistance, increased erosion, and circuit failure. These deposits arc usually dark colored, amorphous, insoluble in organic solvents, and therefore difficult to characterize. They can be ignited in oxygen, however, and the resulting carbon dioxide can be detected. The major difficulty in the ignition procedure, when looking for minute quantities of carbon, is to insure the complete exclusion of air, which contains about 0.0% carbon dioxide by volume.
64348
EGAN
A simple, rapid (20 minute) technique has been developed for the detection and estimation of organic deposits in the range of 0.8 pg (lower limit) to 50 pg of carbon. The sample is ignited in oxygen and the resulting carbon dioxide is bubbled through barium hydroxide to form insoluble barium carbonate (Fig. 1). Several variations of this procedure have been reported in the literature (1,5,6). In the present method, the use of self-sealing rubber caps, hypodermic needles, and syringes simplifies the necessary operations and assures the exclusion of air. For instance, freshly filtered barium hydroxide can easily be added to the oxygen-filled centrifuge tube (Fig. 2) without admitting air. After thorough ignition of the equipment during the “blank” run, the centrifuge tube containing the barium hydroxide can be removed from the equipment and inspected with a stereo microscope to be certain of the complete absence of any barium carbonate precipitate. The centrifuge tube can then be replaced on the exit needle of the combustion tube for the ignition of the sample. These operations are simple and foolproof, since air is automatically excluded by the self-sealing rubber. EXPERIMENTAL
METHOD
Reagents 1. Approximately 2.5% barium hydroxide is used to detect the carbon dioxide. This is filtered and transferred to a lo-ml syringe, fitted with a Swinny adapter and refiltered through a 0.45-,U membrane filter into a Pyrex bottle with a self-sealing rubber stopper, (No. 2330, A. H. Thomas). The air is flushed out of the bottle with oxygen via hypodermic needles prior to addition of the reagent. 2. Lecture bottle or larger tank of pure oxygen. Apparatus 1. Figure 1 shows the arrangement of the combustion system. It is mounted on a/a inch phenol fiber panel (Fig. 6) with a cutout at the bottom to accept two plastic boxes where the necessary tools, accessories, and spare parts are stored. 2. The combustion tube is clear fused silica with a graded Pyrex glass seal at one end (Engelhard Industries, Amersil Quartz Division). 3. The glass end is joined to a Pyrex tube with a male Luer taper joint (Ace Glass Company). The dimensions are shown in Fig. 3A.
,uLg QUANTITIES
OF
649
c
(A) 10Nlf1ON
TUBE
(8) CARBON DIOXLDE TRAP
FIG. 3.
Accessories
for carbon
;Irtection
method.
stereoscopic microscope
FIG. 4. detectable
Axial illumination against a black quantities of barium carbonate.
background
for observing
smallest
650
EGAN
FIG. 5. Comparison of centrifuged barium from ignition of weighed samples of dextrose.
LLA FIG. 6.
carbonate
precipitates
++==!y ~ I 370
Phenol
fiber panel for equipment,
obtained
J, n-2
IJ.~ QUANTITIES
OF c
651
4. The clamps which support the combustion tube 2.5 inches away from the panel are modified microclamps (No. 323s A and B, A. H. Thomas Company). 5. The flowmetcr is a Matheson Company panel mount No. 621PBl with a microvalve and a No. 610 metering tube, l-100 ml/minute. 6. The oxygen lecture bottle is secured to the back of the panel by a wall mount. 7. A reducing valve is used to control the lecture bottle oxygen pressure. 8. Two Luer-Lok hypodermic syringes of 2-ml and lo-ml capacity are needed. The lo-ml syringe is for filtering the barium hydroxide into the storage bottle, and the 2-ml syringe is used for transferring barium hydroxide to the centrifuge tube. 9. A stainless steel Swinny adapter is used to hold the membrane filters (No. XX30 012 00, Millipore Corporation). 10. Cellulose ester membrane filters, 13-mm diameter and 0.45-p pore size for the Swinny adapter are needed. 11. The oxygen tubing connector through the panel is a No. 6394, Cole-Parmer Company. 12. Platinum wire gauze, 52 mesh, 0.004-inch wire, 2-cm long, tightly rolled to completely fill diameter of combustion tube. 13. Mica “N” Midget welding torch No. 0405 with a 3-inch head and “N” recess tip size No. 7. This is modified as shown in Fig, 1. 14. Tescom gas-oxygen “Little Torch” with modified straight brass nozzle, 0.5inch long, and O.075-inch diameter hole (Fig, 1). 15. Hypodermic needles No. 20, %-inch long, and 2-inches long, and No. 22, 1.9inches long. 16. Pyrex centrifuge tubes (see Fig. 3E), 1.5-2 inches long. 17. Self-sealing rubber stoppers modified as shown in Fig. 3D. 18. The carbon dioxide trap (Fig. 3B) is required for admitting air through the self-sealing rubber stopper to the barium hydroxide bottle after withdrawing solution with the hypodermic syringe. 19. Porcelain boats Coors 110, 6 X 4 X 30 mm long. 20. Platinum micro ignition boat, Pregl, 5 X 4 X 16 mm long. 21. Platinum dish formed from 0.002-inch foil (Fig. 3C).
652
EGAN
Procedure Insert platinum gauze and porcelain or platinum boat into the combustion tube (see Fig. 1). Adjust oxygen flow to 50 ml/minute at 2 lb pressure. Connect the oxygen delivery needle (No. 20, 2-inches long) to the male Luer joint of the combustion tube. Put a self-sealing rubber cap on a clean centrifuge tube and insert the oxygen delivery needle through the cap to the bottom of the tube. Then insert the oxygen outlet needle (No. 20, y&inch long) close to the delivery needle (Fig. 3). Allow the oxygen to flow through the combustion and centrifuge tubes for at least 2 minutes. Ignite the platinum gauze with the Tescom torch and the empty boat with the Mica torch to bright red heat (700SOO’C) for at least 2 minutes. Shut off both flames after this ignition. Reduce the oxygen flow to l-2 ml/minute. Next fill the 2-ml hypodermic syringe with barium hydroxide solution using a No. 22, l.Binch needle. Remove the needle from the syringe and place it in 1% acetic acid preparatory to further cleaning. Put the Swinny attachment with a 0.45-p membrane filter on the syringe. Attach a clean No. 22, l-S-inch needle to the Swinny adapter, expel a few drops of barium hydroxide, wipe the needle with a clean paper towel, and carefully insert the needle through the rubber cap to the bottom of the centrifuge tube. Inject the barium hydroxide solution to a height of 15-20 mm (about 0.2 ml). Withdraw the barium hydroxide needle, wipe the tip, and insert it in a cork. Store the syringe in the panel clamp (Fig. 1). Adjust the oxygen flow (5 ml/minute) so that bubbles are slowly entering the reagent. Ignite the platinum gauze and empty boat for at least 2 minutes. Turn off the burner for the boat, but continue the oxygen flow and keep the platinum gauze at red heat for 2 minutes. Then cool the platinum. Remove the oxygen outlet needle from the rubber cap and carefully withdraw the centrifuge tube from the oxygen delivery needle, making certain that it is not loosened at the Luer joint and no air is admitted. Remove the oxygen delivery needle and replace it with a clean one. Examine the barium hydroxide in the centrifuge tube with a stereo microscope at 10-15 magnification with a black background and axial illumination (Fig. 4) to be certain that a ‘blank” has been obtained. When very small quantities of barium carbonate are present, the
,tf;
QUAKTITIES
OF
c
653
meniscus is clouded and small white crystals may be seen moving in the liquid. This condition represents about 1 rg of carbon. In hundreds of tests, when the recommended procedure was followed a complete “blank” was always obtained. The equipment should be reignited as described if a “blank” is not obtained. After confirming the “blank,” disconnect the oxygen-carrying rubber tube from the combustion tube, place the sample in the boat and reposition it in the combustion tube. Reconnect the rubber tube to reinstate the flow of oxygen. Adjust the oxygen flow rate to 50 ml/ minute and sweep the air out of the system for 2 minutes. Reduce Reinsert the oxygen delivery needle the oxygen flow to 5 ml/minute. to the bottom of the centrifuge tube and insert the oxygen outlet needle. Ignite the platinum gauze to red heat. Heat the sample gradually to 700/8OO”C (bright red). Maintain this temperature for a minimum of 2 minutes.l Slowly remove the Mica torch from the sample but continue heating the platinum gauze for at least 2 minutes, after which the Tescom torch is also turned off. The oxygen flow should be continued for l-2 minutes during the cooling period to completely sweep out the last traces of carbon dioxide. Remove the oxygen outlet needle, then withdraw the centrifuge tube from the oxygen delivery needle. To detect traces of barium carbonate precipitate, inspect the tube as shown in Fig. 4. To estimate visually the weight of precipitate obtained, it is necessary to centrifuge the tube for about 5 minutes to compact the barium carbonate. Figure 5 illustrates the amounts of barium carbonate produced from the ignition of measured quantities of carbon, using dextrose as the source. RESULTS AND DISCUSSION
When the lower limit of 0.8 rg of carbon is to be observed, it is convenient to use the illumination shown in Fig. 4. The small white crystals of barium carbonate ( + 13 pg) glisten as they move about in the barium hydroxide. There are a few radicals, such as carbonate, cyanide, and cyanate, which contain carbon but are commonly considered inorganic, that 1 If the sample consists of a base metal, the oxygen bubbling into the barium hydroxide may stop because the base metal is consuming the oxygen. In that case increase the oxygen rate so that bubbling is resumed.
654
EGAN
would decompose at high temperatures to produce carbon dioxide. Sulfur in organic or inorganic compounds would also decompose under the conditions of this method to form SOS, which would react with the barium hydroxide to form barium sulfate. Ingram (4) suggested a packing of manganese dioxide (at room temperature) to remove the sulfur trioxide or sulfuric acid. It is a simple matter to differentiate between barium carbonate and barium sulfate, since the carbonate is readily soluble in dilute hydrochloric acid, while the sulfate is not. Certain precautions are necessary during the search for organic contaminants on ferrous metals, since some of these contain carbides that would produce carbon dioxide on ignition. This procedure is useful as a qualitative test and for the visual estimation of small quantities of organic contaminants. For example, the appearance of barium carbonate equivalent to 5, 10, and 20 pg of carbon (from dextrose) is shown in Fig. 5. Visual estimation of quantities larger than 20 pg of carbon is not recommended. A few preliminary gravimetric determinations gave results of 91-97% of the theoretical carbon content from weighed samples of dextrose. Here again the membrane filters, self-sealing rubber caps, and hypodermic needles facilitated the exclusion of air during the centrifuging and washing operations. The equipment is portable and can be used with two small butane or acetylene torches if natural gas is not available. It has been used in a manufacturing plant to detect organic contaminants on thin film circuitry. SUMMARY A simple, rapid technique is described for detecting 0.8 pg or more of carbon. The sample is ignited in oxygen and the resulting carbon dioxide reacts with barium hydroxide to form barium carbonate. The carbon dioxide normally present in air has been an impediment in ignition methods for detecting microgram quantities of carbon. In the described technique the use of self-sealing rubber stoppers and hypodermic syringes and needles permit the necessary manipulations with the complete exclusion of air.
ACKNOWLEDGMENTS The author gratefully acknowledges tions of Mrs. G. R. Munier.
the experimental
work
and helpful
sugges-
@
QUANTITIES
655
REFERENCES F., Microchemical detection of carbon and sulfur. 2. Anal. Chem. 56, l-13 (1917). 9. GERMER, L. H., AND SMIT.H, J. L., Activation of electrical contacts by organic vapors. Bell System Tech. J. 36, 769-812 (1957). 3. HERMANCE, H. W., AND EGAN, T. F., Organic deposits on precious metal contacts. Bell System Tech. J. 37, 739-814 (1958). 4. INGRAM, G., Some further absorption properties of manganese dioxide. Microchim. Acta 1953 (l-2), 71-78. .i. JOHANNSON, A., Volumetric determination of carbon and hydrogen in organic microcombustion. Anal. Chem. 26, 1183-1185 (1954). 6. LUIS, P., CARDUCCI, C. N., AND S6, A., Ultramicro detection of carbon, carbonates, and bicarbonates. Microchinl. Acta 1967 ( l), 156-165. 1.
EMICH,
13, 646-655
JOURNAL
Detection
( 1968)
and Estimation on Microgram Quantities of Carbon T. F. EGAN Bell Telephone Laboratories, Inc., Holmdel, Neu: Jersey 07733 INTRODUCTION
The positive identification of microgram quantities of organic deposits and films on electrical contacts and other small objects has long
FIG. 1.
Carbon
detection
equipment
in operation. 646
@
FIG. 2.
Addition
of filtered
QUANTITIES
barium
hydroxide
647
OF c
through
self-sealing
rubber
cap.
been a tedious, difficult problem. Organic deposits may occur on electrical contacts as frictional polymer (3) from various organic vapors or the arc pyrolysis products of adsorbed organic vapors (2). Both of these can cause an increase in contact resistance, increased erosion, and circuit failure. These deposits arc usually dark colored, amorphous, insoluble in organic solvents, and therefore difficult to characterize. They can be ignited in oxygen, however, and the resulting carbon dioxide can be detected. The major difficulty in the ignition procedure, when looking for minute quantities of carbon, is to insure the complete exclusion of air, which contains about 0.0% carbon dioxide by volume.
64348
EGAN
A simple, rapid (20 minute) technique has been developed for the detection and estimation of organic deposits in the range of 0.8 pg (lower limit) to 50 pg of carbon. The sample is ignited in oxygen and the resulting carbon dioxide is bubbled through barium hydroxide to form insoluble barium carbonate (Fig. 1). Several variations of this procedure have been reported in the literature (1,5,6). In the present method, the use of self-sealing rubber caps, hypodermic needles, and syringes simplifies the necessary operations and assures the exclusion of air. For instance, freshly filtered barium hydroxide can easily be added to the oxygen-filled centrifuge tube (Fig. 2) without admitting air. After thorough ignition of the equipment during the “blank” run, the centrifuge tube containing the barium hydroxide can be removed from the equipment and inspected with a stereo microscope to be certain of the complete absence of any barium carbonate precipitate. The centrifuge tube can then be replaced on the exit needle of the combustion tube for the ignition of the sample. These operations are simple and foolproof, since air is automatically excluded by the self-sealing rubber. EXPERIMENTAL
METHOD
Reagents 1. Approximately 2.5% barium hydroxide is used to detect the carbon dioxide. This is filtered and transferred to a lo-ml syringe, fitted with a Swinny adapter and refiltered through a 0.45-,U membrane filter into a Pyrex bottle with a self-sealing rubber stopper, (No. 2330, A. H. Thomas). The air is flushed out of the bottle with oxygen via hypodermic needles prior to addition of the reagent. 2. Lecture bottle or larger tank of pure oxygen. Apparatus 1. Figure 1 shows the arrangement of the combustion system. It is mounted on a/a inch phenol fiber panel (Fig. 6) with a cutout at the bottom to accept two plastic boxes where the necessary tools, accessories, and spare parts are stored. 2. The combustion tube is clear fused silica with a graded Pyrex glass seal at one end (Engelhard Industries, Amersil Quartz Division). 3. The glass end is joined to a Pyrex tube with a male Luer taper joint (Ace Glass Company). The dimensions are shown in Fig. 3A.
,uLg QUANTITIES
OF
649
c
(A) 10Nlf1ON
TUBE
(8) CARBON DIOXLDE TRAP
FIG. 3.
Accessories
for carbon
;Irtection
method.
stereoscopic microscope
FIG. 4. detectable
Axial illumination against a black quantities of barium carbonate.
background
for observing
smallest
650
EGAN
FIG. 5. Comparison of centrifuged barium from ignition of weighed samples of dextrose.
LLA FIG. 6.
carbonate
precipitates
++==!y ~ I 370
Phenol
fiber panel for equipment,
obtained
J, n-2
IJ.~ QUANTITIES
OF c
651
4. The clamps which support the combustion tube 2.5 inches away from the panel are modified microclamps (No. 323s A and B, A. H. Thomas Company). 5. The flowmetcr is a Matheson Company panel mount No. 621PBl with a microvalve and a No. 610 metering tube, l-100 ml/minute. 6. The oxygen lecture bottle is secured to the back of the panel by a wall mount. 7. A reducing valve is used to control the lecture bottle oxygen pressure. 8. Two Luer-Lok hypodermic syringes of 2-ml and lo-ml capacity are needed. The lo-ml syringe is for filtering the barium hydroxide into the storage bottle, and the 2-ml syringe is used for transferring barium hydroxide to the centrifuge tube. 9. A stainless steel Swinny adapter is used to hold the membrane filters (No. XX30 012 00, Millipore Corporation). 10. Cellulose ester membrane filters, 13-mm diameter and 0.45-p pore size for the Swinny adapter are needed. 11. The oxygen tubing connector through the panel is a No. 6394, Cole-Parmer Company. 12. Platinum wire gauze, 52 mesh, 0.004-inch wire, 2-cm long, tightly rolled to completely fill diameter of combustion tube. 13. Mica “N” Midget welding torch No. 0405 with a 3-inch head and “N” recess tip size No. 7. This is modified as shown in Fig, 1. 14. Tescom gas-oxygen “Little Torch” with modified straight brass nozzle, 0.5inch long, and O.075-inch diameter hole (Fig, 1). 15. Hypodermic needles No. 20, %-inch long, and 2-inches long, and No. 22, 1.9inches long. 16. Pyrex centrifuge tubes (see Fig. 3E), 1.5-2 inches long. 17. Self-sealing rubber stoppers modified as shown in Fig. 3D. 18. The carbon dioxide trap (Fig. 3B) is required for admitting air through the self-sealing rubber stopper to the barium hydroxide bottle after withdrawing solution with the hypodermic syringe. 19. Porcelain boats Coors 110, 6 X 4 X 30 mm long. 20. Platinum micro ignition boat, Pregl, 5 X 4 X 16 mm long. 21. Platinum dish formed from 0.002-inch foil (Fig. 3C).
652
EGAN
Procedure Insert platinum gauze and porcelain or platinum boat into the combustion tube (see Fig. 1). Adjust oxygen flow to 50 ml/minute at 2 lb pressure. Connect the oxygen delivery needle (No. 20, 2-inches long) to the male Luer joint of the combustion tube. Put a self-sealing rubber cap on a clean centrifuge tube and insert the oxygen delivery needle through the cap to the bottom of the tube. Then insert the oxygen outlet needle (No. 20, y&inch long) close to the delivery needle (Fig. 3). Allow the oxygen to flow through the combustion and centrifuge tubes for at least 2 minutes. Ignite the platinum gauze with the Tescom torch and the empty boat with the Mica torch to bright red heat (700SOO’C) for at least 2 minutes. Shut off both flames after this ignition. Reduce the oxygen flow to l-2 ml/minute. Next fill the 2-ml hypodermic syringe with barium hydroxide solution using a No. 22, l.Binch needle. Remove the needle from the syringe and place it in 1% acetic acid preparatory to further cleaning. Put the Swinny attachment with a 0.45-p membrane filter on the syringe. Attach a clean No. 22, l-S-inch needle to the Swinny adapter, expel a few drops of barium hydroxide, wipe the needle with a clean paper towel, and carefully insert the needle through the rubber cap to the bottom of the centrifuge tube. Inject the barium hydroxide solution to a height of 15-20 mm (about 0.2 ml). Withdraw the barium hydroxide needle, wipe the tip, and insert it in a cork. Store the syringe in the panel clamp (Fig. 1). Adjust the oxygen flow (5 ml/minute) so that bubbles are slowly entering the reagent. Ignite the platinum gauze and empty boat for at least 2 minutes. Turn off the burner for the boat, but continue the oxygen flow and keep the platinum gauze at red heat for 2 minutes. Then cool the platinum. Remove the oxygen outlet needle from the rubber cap and carefully withdraw the centrifuge tube from the oxygen delivery needle, making certain that it is not loosened at the Luer joint and no air is admitted. Remove the oxygen delivery needle and replace it with a clean one. Examine the barium hydroxide in the centrifuge tube with a stereo microscope at 10-15 magnification with a black background and axial illumination (Fig. 4) to be certain that a ‘blank” has been obtained. When very small quantities of barium carbonate are present, the
,tf;
QUAKTITIES
OF
c
653
meniscus is clouded and small white crystals may be seen moving in the liquid. This condition represents about 1 rg of carbon. In hundreds of tests, when the recommended procedure was followed a complete “blank” was always obtained. The equipment should be reignited as described if a “blank” is not obtained. After confirming the “blank,” disconnect the oxygen-carrying rubber tube from the combustion tube, place the sample in the boat and reposition it in the combustion tube. Reconnect the rubber tube to reinstate the flow of oxygen. Adjust the oxygen flow rate to 50 ml/ minute and sweep the air out of the system for 2 minutes. Reduce Reinsert the oxygen delivery needle the oxygen flow to 5 ml/minute. to the bottom of the centrifuge tube and insert the oxygen outlet needle. Ignite the platinum gauze to red heat. Heat the sample gradually to 700/8OO”C (bright red). Maintain this temperature for a minimum of 2 minutes.l Slowly remove the Mica torch from the sample but continue heating the platinum gauze for at least 2 minutes, after which the Tescom torch is also turned off. The oxygen flow should be continued for l-2 minutes during the cooling period to completely sweep out the last traces of carbon dioxide. Remove the oxygen outlet needle, then withdraw the centrifuge tube from the oxygen delivery needle. To detect traces of barium carbonate precipitate, inspect the tube as shown in Fig. 4. To estimate visually the weight of precipitate obtained, it is necessary to centrifuge the tube for about 5 minutes to compact the barium carbonate. Figure 5 illustrates the amounts of barium carbonate produced from the ignition of measured quantities of carbon, using dextrose as the source. RESULTS AND DISCUSSION
When the lower limit of 0.8 rg of carbon is to be observed, it is convenient to use the illumination shown in Fig. 4. The small white crystals of barium carbonate ( + 13 pg) glisten as they move about in the barium hydroxide. There are a few radicals, such as carbonate, cyanide, and cyanate, which contain carbon but are commonly considered inorganic, that 1 If the sample consists of a base metal, the oxygen bubbling into the barium hydroxide may stop because the base metal is consuming the oxygen. In that case increase the oxygen rate so that bubbling is resumed.
654
EGAN
would decompose at high temperatures to produce carbon dioxide. Sulfur in organic or inorganic compounds would also decompose under the conditions of this method to form SOS, which would react with the barium hydroxide to form barium sulfate. Ingram (4) suggested a packing of manganese dioxide (at room temperature) to remove the sulfur trioxide or sulfuric acid. It is a simple matter to differentiate between barium carbonate and barium sulfate, since the carbonate is readily soluble in dilute hydrochloric acid, while the sulfate is not. Certain precautions are necessary during the search for organic contaminants on ferrous metals, since some of these contain carbides that would produce carbon dioxide on ignition. This procedure is useful as a qualitative test and for the visual estimation of small quantities of organic contaminants. For example, the appearance of barium carbonate equivalent to 5, 10, and 20 pg of carbon (from dextrose) is shown in Fig. 5. Visual estimation of quantities larger than 20 pg of carbon is not recommended. A few preliminary gravimetric determinations gave results of 91-97% of the theoretical carbon content from weighed samples of dextrose. Here again the membrane filters, self-sealing rubber caps, and hypodermic needles facilitated the exclusion of air during the centrifuging and washing operations. The equipment is portable and can be used with two small butane or acetylene torches if natural gas is not available. It has been used in a manufacturing plant to detect organic contaminants on thin film circuitry. SUMMARY A simple, rapid technique is described for detecting 0.8 pg or more of carbon. The sample is ignited in oxygen and the resulting carbon dioxide reacts with barium hydroxide to form barium carbonate. The carbon dioxide normally present in air has been an impediment in ignition methods for detecting microgram quantities of carbon. In the described technique the use of self-sealing rubber stoppers and hypodermic syringes and needles permit the necessary manipulations with the complete exclusion of air.
ACKNOWLEDGMENTS The author gratefully acknowledges tions of Mrs. G. R. Munier.
the experimental
work
and helpful
sugges-
@
QUANTITIES
655
REFERENCES F., Microchemical detection of carbon and sulfur. 2. Anal. Chem. 56, l-13 (1917). 9. GERMER, L. H., AND SMIT.H, J. L., Activation of electrical contacts by organic vapors. Bell System Tech. J. 36, 769-812 (1957). 3. HERMANCE, H. W., AND EGAN, T. F., Organic deposits on precious metal contacts. Bell System Tech. J. 37, 739-814 (1958). 4. INGRAM, G., Some further absorption properties of manganese dioxide. Microchim. Acta 1953 (l-2), 71-78. .i. JOHANNSON, A., Volumetric determination of carbon and hydrogen in organic microcombustion. Anal. Chem. 26, 1183-1185 (1954). 6. LUIS, P., CARDUCCI, C. N., AND S6, A., Ultramicro detection of carbon, carbonates, and bicarbonates. Microchinl. Acta 1967 ( l), 156-165. 1.
EMICH,