NATIONAL BUREAU OF STANDARDS REPORT

4861

THE CHEMICAL CHANGES OCCURRING DURING THE

DEGRADATION OF TWO COATING ASPHALTS

by

Sidney H. Greenfeld

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its headquarters in Vi ashington,

D. C., and its major field laboratories in Boulder, Colorado, is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section carries out specialized

research, development, and engineering in the field indicated by its title. A brief description of

the activities, and of the resultant reports and publications, appears on the inside back cover of

this report.

WASHINGTON, D. C.

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REP0BT

1004-11-1017 October 1, 1956 4861

THE CHEMICAL CHANGES OCCURRING DURING TJffi DEGRADATION OF TWO COATING ASPHALTS

by

Sidney H. Greenfeld

Research Associate

Asphalt Roofing Industry Bureau

Floor, Roof and Wall Coverings Section

Building Technology Division

Staff

John P. Falzone

Sidney H. Greenfeld

Shigeru Ishihara

Lawrence R. Kle'inschmid

t

Jointly Sponsored by

Asphalt Roofing Industry Bureau

and

National Bureau of Standards

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publicat

unless permi; 25.D.C. Su

cal ly prepan

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

ole or in part, is prohibited

j of Standards, Washington

:h a report has been specifiular report for its own use.

THE CHEMICAL CHANGES OCCURRING DURING THE

DEGRADATION OF TWO COATING ASPHALTS

by

Sidney H, Greenfeld

Staff

John P. Falzone

Sidney H. Greenfeld

Shigeru Ishihara

Lawrence R. Kleinschmid

t

ABSTRACT

Some of the changes that occurred in the components

of two asphalts and their water-soluble degradation products

were followed through exposures of 3500 hours in an accelerated durability machine (22-1 cycle) and 18 months outof-doors. Although the general overall trends in the two

asphalts were similar, there were differences in their

rates of degradation, the migration of the sulfur and

nitrogen compounds among their components and into their

degradation products, the changes of the molecular weights

of their components and the relative amounts of volatile and

non-volatile degradation products formed. Because of the

complexity of the system, these data are insufficient to

establish the actual mechanism of degradation of asphalt.

1. INTRODUCTION

On April 16, 1956, N.B.S. Report No. 4621, "The Degradation

of Two Coating Asphalts", was issued. It covered the percentage

changes that took place in the components of two asphalts exposed to several combinations of heat, light and water. The
5
2

components of Asphalts I and II recovered from specimens removed

after various periods of exposure to the 22-1 cycle were subjected to further analysis, as follows: Molecular weight, unsaturation and carbon, hydrogen, oxygen, sulfur and nitrogen

content were determined. The water-soluble and ethanol-soluble

degradation products were also analyzed chemically. The results of these analyses are covered in this report.

2. EXPERIMENTAL

2.1 Materials

The characteristics of the asphalts investigated are reported in Table 1.

2.2 Methods

The exposure specimens were prepared by the hydraulic1 / 2/

press method (1) and exposed to the 22-1 cycle in an accelerated durability machine within 24 hours (2). At exposure

periods of 200, 400, 600, 900, 1200, 1700, 2500 and 3500 hours,

all of the specimens were weighed and three were removed for

component and chemical analysis. Each specimen was separated

into asphaltenes, resins, dark oils and white oils by the method

of Kleinschmidt (3). The components of the three specimens

“^The numbers in parentheses indicate references listed at the

end of this report.

2 /

22 hours of dry light at 140 £5°F followed by one hour of

soaking

.

TABLE 1.

CHARACTERISTICS OF ASPHaLTS

CHARACTERISTIC ASPHALT I ASPHALT II

Softening Point,—^ °F 223 224

Penetration—^at 32°F 10 11

Penetration at 77°F 17 17

Penetration at 115°F 30 26

Susceptibility^/ 1.16 0.8 7

Loss on Heating,—^ %

CM CM O O 0.03

Pen. after Heating at 77°

F

17 17

Specific Gravity at 77°F 1.015 0.999

0 /

Durability,— days 43 75

Component Analysis (4)

Asphaltenes, % 39.0 38.4

Resins, % 10.3 9.9

Dark Oils, % 18.2- 23.3

White Oils, % 2 7.4 24.4

Ethanol Extract, % 2.8 0.7

Recovery, % 97.7 96.7

ASTM D36-26.

ASTM D5-52. - S = P115 - P

3 2

P

77

ASTM D6-39T

0 / — 51-90 - 22 hours a day exposure

to 51 minutes of light followed

by 9 minutes of light + cold

(4o°F) water spray.

- 3

-

were combined and the ethanol extract, the molecular weight, unsaturation and carbon, hydrogen, oxygen, sulfur and nitrogen

content determined on each of the components. The water in

which the specimens were soaked daily was filtered and evaporated to dryness in a vacuum evaporator at 120-13 5°^. The

solids were analyzed chemically.

The methods of analysis have been reported previously (4)

and are outlined below for information:

Molecular Weight - This is an empirical, ebullioscopic

procedure of Matteson (5)>in which the boiling point rise

of benzene produced by the unknown is compared with that

produced by materials of known molecular weights at a definite concentration.

Unsaturation - The material is dissolved in chloroform and

treated with a Wijs solution in the dark (6). Iodine adds

to the double bonds.

Carbon and Hydrogen - The specimen is oxidized to CO2 and

H2O in a stream of oxygen in the presence of copper oxide

(7) and the CO2 and H2O are collected in absorption tubes

and weighed.

Oxygen - The specimen is pyrolysed in a stream of nitrogen

and passed over hot carbon, where all of the oxygen is

converted to CO. The CO is converted to CO2 by iodine

- k -

pentoxide and absorbed in ascarite in an absorption tube

and weighed. The procedure is that of Unterzaucher (8),

as modified by Aluise (9), Hinkel and Raymond (10), and

Dundy and Stehr (11).

Sulfur - The material is oxidized in a Parr bomb at

*+50 psi and the sulfur, as sulfate, is titrated with

a barium chloride solution to the monopotassium rhodizonate endpoint (12).

Nitrogen - The specimen is burned in oxygen and the gases

passed over hot copper to remove the excess oxygen and

over hot copper oxide to convert all of the carbon and

hydrogen to CO2 and water. The CO2 and water are absorbed

in a 50% aqueous potassium hydroxide solution and the

nitrogen measured volumetrically . This method was

developed by Alford (13).

3. RESULTS

The analyses of the components of asphalts I and II at

various periods of weathering are presented in Tables 2 and

3, respectively. At each period of exposure the proportion of

each component, expressed as a percentage of the original coating, is reported. The unsaturation is expressed as the number
.

,* '
table

2.

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(CONTINUED)

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(22-1

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TABLE

3

.

ASBHALT

II

(CONTINUED)

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- 5 -

of double bonds per gram and per molecule to facilitate the

interpretation of the data. The elemental analyses are expressed as percentages of the components.

The asphaltenes were analyzed before they were extracted

with ethanol and, therefore, include the contributions of the

relatively small proportion of the ethanol extract.

Table b contains the determinations made on the watersoluble degradation products. Because these products were not

quantitatively recovered the weight losses of the asphalts are

reported instead of the quantities of water-soluble materials

collected

.

Table 5 contains the analytical data on the ethanol- soluble

degradation products. Because of the small portions of - these materials, very little work was done on them, particularly

on those from asphalt II.

Tables 6 and 7 contain the analyses of the components of

these two asphalts made periodically during the first 18 months

of exposure out-of-doors. The results are based on separations

of individual specimans and, therefore, have more variation

than the previous analyses. Because of the limitations of

time and sample size, it was not possible to obtain complete

analyses on all of the components of the specimens exposed outof-doors.

TABLE

U.

WATER-SOLUBLE

DEGRADATION

PRODUCTS

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7.

OUT-OF-DOOR

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- 6 -

4. DISCUSSION OF RESULTS

*+.1 General

The origin of petroleum and the changes that occur during

the conversion of petroleum and petroleum products to carbon

dioxide and water are only vaguely understood . Some of the

changes that occur during the conversion of the organic source

materials to crude petroleum have been studied by numerous

investigators (14), and several hypotheses of the conversion

exist, but the evidence is insufficient to enable any of them

to be considered more than an hypothesis.

The chemical constituents of the lighter fractions of

petroleum have been studied more arduously than those in asphalt

and considerable information has been accumulated on their compositions and properties. As the size of the molecules increases, less is known of them; almost nothing is known of the

individijal molecules in asphalt and very little has been reported on the chemical nature of asphalt.

4.2 Asphalt Flux

During the normal refining process of petroleum the more

volatile constituents of the petroleum are removed by distillation. Because the process is conducted in the absence of oxygen

and at temperatures at which cracking does not occur, few

changes to individual molecules take place. When the lubricating

- 7

-

oils have been removed, a heavy, viscous residuum remains in

the still pot. The residuum is the raw material, or flux, from

which the coating-grade asphalt is made by means of a hightemperature oxidation process called "blowing". The component

and chemical analyses of the fluxes of the two asphalts and

the two coating-grade asphalts are shown in Table 8.

While both of the fluxes were semi-solids at room temperature, the viscosity-temperature coefficients were very different

and the flux of asphalt I was much more fluid at 210°F than was

that of asphalt II. The average molecular weight of the flux

of asphalt I was 880, and that of asphalt II was 1150. The

range of molecular weights in flux I was much greater . In

separating flux I into its components, a relatively large

amount of material could not be removed from the fuller ? s earth column ( 7 . 8%) . This probably was similar to, but more

polar than the resinSc Flux II had significantly more dark

oils and less white oils than flux I. Flux I contained more

sulfur and oxygen than flux II.

During the blowing process, the fluxes were oxidized at

about 450°F for varying periods of time and products were removed from the still when the charge had the desired softening

point. At a softening point of approximately 225°I , the
.
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- 8 -

molecular weights of both asphalts had increased and had

approximately doubled (1970 and 2230, respectively ) „ The

asphaltenes had increased, primarily at the expense of the

resins and dark oils, both in quantity and molecular size 0

The white oil fraction of asphalt II was the only other portion

that had changed significantly in molecular weight, having

decreased appreciably,,

During the blowing process there was a 1% increase in the

oxygen content of the asphalts, but no other significant chemical changes occurred „ Thus, in summary, the blowing process

seems to have oxidized the asphalt and increased its molecular

weight, producing n-pentane-insoluble material of high molecular weight at the expense of some portions of the n-pentanesoluble fraction of the asphalt

„

b„3 Molecular Weight Changes During Exposure

When the two asphalts were exposed to both natural weathering and light, heat and water in the laboratory, further changes

took place „ Because many of the changes are complex and tend to

counterbalance other changes, the asphalts were separated into

simpler groups [reported in (l5)f and the chemical changes

occurring in each group were followed.

The molecular weight of each of the asphalts, which had increased during the blowing operation, began to decrease on exposure to the forces of degradation--light , heat, and water. In

- 9

-

asphalt I, the molecular weight of the asphaltenes increased during blowing from 1850 to 3700? decreased to 2250 (Table 2) during

3500 hr of exposure to the 22-1 cycle and to 1950 (Table 6) after

6 months out of doors, Similarly, in asphalt II, the molecular

weight of the asphaltenes increased from 2200 to M+00 during blowing and decreased to 2550 (Table 3) and 2850 (Table 7) for the cor

responding two exposures,, Although the molecular weight decreased

appreciably, the quantity of asphaltenes increased during exposure

The lowering of the average molecular weight was accompanied by a sharp increase in oxygen content, which served to maintain their

poor solubility in n- pentane 0 In asphalt I, the molecular weight of each of the pentanesoluble fractions did not change appreciably during the blowing

operation and, also, changed little during exposure to the 22-1

cycle. However, in asphalt II, the molecular weight of the white

oils was almost halved during blowing, but increased progressively

during exposure to the 22-1 cycle. Those of the resins and dark

oils decreased slightly during blowing and continued to decrease

during the early periods of exposure, but soon increased to their

values in the residuum. Thus, during exposure, in both asphalts

the molecules seemed to have returned to the size they were before

the high-temperature oxidation process. Quite possibly, those

molecules which were changed by blowing were most susceptible to

change during exposure.
,* .

.
10

Of course, chemically and physically the asphalt that remained

after 3500 hours of exposure was very different from that which came

from the still pot.

b 0 k Chemical Changes

The chemical changes that have taken place may be stated as

follows

;

The unsaturation decreased during exposure as the asphalts

were oxidized (Table 9)» But, under the assumption that one oxygen

molecule reacted with each double bond, it was found that the decrease in unsaturation was much greater than that required by the

increase in the oxygen content of the asphalts 0 In asphalt I this

decrease was about eight times as great and in asphalt II about

five times. The loss of the other double bonds may have been the

result of more complete oxidation of the components of the asphalt

into products that were actually removed from the asphalt. These

weight losses, which amounted to 2b a b% and ±7 0 b% for asphalts I

and II, respectively, will be discussed later.

In asphalt I, the carbon-hydrogen ratios of the components

remained relatively unchanged during exposure, which in combination

with the constancy of molecular weights and relatively small melting range tend to indicate a uniformity of molecular species.

The decrease in refractive indices of the oil fractions during exposure (Table 2) may then be attributed to a decrease in branching

and a loss of double bonds. In asphalt II, however, the carbonhydrogen ratio tended to decrease (Table 3) for all but the white

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11

oils (which are already very close to paraffinic in nature), indicating that the material remaining behind is more paraffinic than

that being removed,, The refractive index decrease was somewhat more

restricted because the materials remaining in each component of the

asphalt as degradation progressed were of increasingly higher molecular weight.

The sulfur and nitrogen contents of both asphalts decreased

progressively during exposure; both of these materials were present

in some of the molecules that became water soluble. Apparently,

however, the reaction that made the molecules water soluble did not

take place at the sulfur or nitrogen bonds ( 1 6 ) , for no oxidized

forms of sulfur or nitrogen were found in the degradation products.

Some of the sulfur compounds migrated into the aslphltenes during the early stages of exposure. In asphalt I this migration

(probably a polymerization of some of the maltenes) actually increased

the concentration of sulfur in the asphaltenes, while in asphalt II

the concentration remained the same. In both cases, an appreciable

amount of the sulfur in the asphalt moved into the asphaltenes.

In asphalt I the nitrogen compounds seemed to weather from the

resins and dark oils, while in asphalt II, only the resins lost an

appreciable amount of nitrogen compounds. The early increases in

asphaltenes in both asphalts carried sufficient nitrogen into that

fraction to maintain its nitrogen content almost constant for about

*+00 hours of exposure.

12

The material that was weathered from the asphalts went into

water-soluble and volatile degradation products„ Only the former

were collected for analysis „ The magnitude and probable composition

of the latter will be discussed later,, The water solubles (Table 4)

were highly oxidized, acid materials having appreciable nitrogen and

sulfur. Although in a general way these products were similar during the entire exposure period, specifically there were many differences present in the products collected during the various exposure

intervals. These differences will be discussed in a later report.

Chemically, the nitrogen content of the degradation products of

asphalt I increased and the sulfur content decreased progressively

ft as degradation proceeded. In those of asphalt II, both nitrogen

and sulfur increased.

The ash is composed primarily of contaminating materials introduced by the reaction of the degradation products with the aluminum alloy specimen backings and supports and with dust that has

fallen into the collecting jars while they were uncovered.

4.5 Ethanol Extract

Very little has been said concerning the ethanol extract of

the asphaltenes. This material was not discovered until most of

the chemical analyses had been completed and it is included in the

data reported on the asphaltenes. However, it was extracted from

the asphaltenes and analysed where sufficient material could be

recovered. Physically, this extract is the portion of the film

- 13 -

that forms on the surface of asphalt as it weathers and is not soluble in water or n-pentane; hence, it remains with the asphaltenes

after the asphalt has been extracted with n-pentane.

Before exposure, about one to three percent of a material soluble in hot ethanol was present in the asphaltenes „ This material

had about four percent oxygen. After 400 hours of exposure, the

material extracted from the asphaltenes with hot ethanol contained

over 10% oxygen. At other exposure periods its oxygen content was

in the range of 11 to 14% for both asphalts. Only asphalt I yielded

sufficient ethanol extract for further analysis. The nitrogen content dropped from about 1,5% before exposure to about 0,8% after

1700 hours of exposure. The carbon-hydrogen ratio dropped slightly

along with the small decreases in both carbon and hydrogen. Insufficient material was available for sulfur analysis. This material

seems to be an intermediate degradation product,

4,6 Quantitative Considerations

The above qualitative discussion of the changes that occurred

in the two asphalts has shed some light on what transpires during

exposure, but for a better understanding, the data must be examined

quantitatively.

All of the complete chemical analyses accounted for between

98 and 100% of the material being analysed, introducing a maximum

of two percent uncertainty in any particular analysis. In the

component analyses there was usually about two to three percent of

-Immaterial that remained on the fullers earth and was not included in

the material that was collected for analysis,, This loss was composed of a material of the same molecular weight as the resins and,

when removed, was found to be similar to the resins in many other

respects. As an approximation, it has been included in all calculations as so much additional resin.

Further examination of the mechanics of collecting the degradation products reveals that these materials were not recovered

quantitatively. As a first approximation, based on previous

quantitative recovery, it can be assumed that the formation of

degradation products is equal to the weight losses of the asphalts.

Because the water-soluble degradation products are about 35% oxygen,

it would be required that about two-thirds of the loss go into the

water-soluble products and one-third would go elsewhere; namely,

into volatile losses. However, from the dry-light and oven exposures ( 15 ) it was known that no appreciable volatilization occurred,

even at 200°F. Therefore, these volatile losses resulted directly

from the reactions that took place in the presence of water, as

well as light and heat. Because the products varied as degradation

progressed, it is logical to believe that the proportions of volatile and non-volatile products varied as well.

Thurston and Knowles (17) reported that for each mol of oxygen

absorbed by the asphalt, a mol of oxygen went into CO2 and H2 O

formation. No other volatile products were reported there or in
.
- 15 -

any other reference. Therefore, all volatile loss in the following discussion will be considered to be CO2 and H20 o Logically,

then, all of the sulfur losses must have gone into the non-volatile

water-soluble degradation products, offering a convenient tracer

for determining the exact amount of these products that have been

formed. Then the carbon and hydrogen losses can be properly distributed between the volatile and non-volatile degradation products

Because nitrogen can be introduced into the system by direct reaction with some of its oxides always present in the atmosphere

(18), it will be considered separately.

The sulfur distributions in the asphalts and water-soluble

degradation products are shown in Figures 1 and 2 . These curves

closely parallel those of the change in the components themselves

(15). The migration of the sulfur into the asphaltenes during the

period in which the asphaltenes were increasing is readily apparent

as is the gradual progressive transfer of sulfur-containing materials from the maltene fractions to the water-soluble degradation

products

.

Figures 3 and 4 contain the oxygen distributions for the two

asphalts, considering the asphalts as entities, and the degradation products. All of the data are expressed as percentages of

the original asphalt in order to have a common basis for comparison. A number of very interesting observations may be made from

these curves. Both asphalts continuously increased in oxygen
•

*


I 0h

16

content despite the fact that they were losing considerable weight.

At 3500 hours each had picked up just under two percent of oxygen.

This oxygen pickup niust be added to the actual weight losses to

determine the net losses of the asphalts. The curves representing

these figures are shown in Figures 3 and 4, also.

The curves labeled "water-solubles formation" were calculated

from the quantity of sulfur lost from the asphalt and the percentage of sulfur found in the water-soluble degradation products.

These curves are always lower than the weight-loss curves.

The carbon and hydrogen lost from the asphalt and not present

in the non-volatile degradation products was assumed to have gone

into the volatile products as CO2 and H2 O. Each hydrogen molecule

picked up roughly eight times its weight of oxygen and each carbon

atom two and two-thirds times its weight. Thus very large quantities of CO2 and H2 O were formed, as indicated in Figures 3 and b.

While the data during the early part of the exposure are in agreement with thfe previously mentioned results reported by Thurston

and Knowles, as degradation progressed the proportions of CO2 and

water formed became significantly larger.

! r U < \ ii QJ i O | y i X l ’<1



- 17 -

In the cases of both asphalts the nitrogen contents increased slightly and then leveled off as degradation progressed.

The nitrogen increase may have come from the oxides of nitrogen in the atmosphere reacting with the unsaturated portions

of the asphalt (18). However, the effect is small and of

about the same order of magnitude as the errors involved in

the nitrogen determination.

4.7 Outdoor Exposures

The results of the first 18 months of out-of-door exposures

are reported in tables 6 and 7° The data* are incomplete, primarily in molecular weight and nitrogen measurements, and show

less tendency toward specific trends than the more closely

controlled laboratory exposures. However, there seemed to be

a tendency of the molecular weights of the components of

asphalt I to decrease while in asphalt II, those of only the

asphaltenes decreased; those of the white oils increased (as

in the laboratory exposures). Except for the resins in asphalt

I, the carbon-hydrogen ratios of all of the components have

remained fairly constant. All of the components have increased

in oxygen content. The migrations of the sulfur and nitrogen

These results are based on the analyses of individual specimens.



Nitrogen

Content

A

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- 18 -

compounds were erratic and little can be said about them. In

general, possibly because individual specimens were involved,

the results of the out-of-door exposures have not yielded

significant trends.

5 . SUMMARY AND CONCLUSIONS

When asphalts are exposed to light, heat and water

numerous and complex chemical changes take place. Oxidation

occurs and results in the formation of volatile and nonvolatile degradation products. Over a third of the weight

losses occur from the formation of CO2 and H2O. Two-thirds of

the losses go into a water-soluble material that is highly

acidic. A third product that is insoluble in water and npentane remains on the surface of the coatings.

Sulfur and nitrogen are in the molecules that polymerize

during the early periods of exposure to form asphaltenes and

resins and are also present in the water-soluble degradation

products. Based on the constancy of sulfur, the water-soluble

degradation products that are formed are almost equal in

weight to the measured weight losses, and the volatile products

are about two and one-half times the weight losses. A small

increase in total nitrogen in the system during the early

stages of degradation may indicate reaction of the asphalt

with the oxides of nitrogen always present in the atmosphere.

- 19 -

Differences existed between the two asphalts and the

manner in which they degraded „ The principal differences were

in the rate of degradation and in the molecular weight changes.,

Secondary differences were obvious in the way the sulfur- and

nitrogen-containing molecules migrated through the asphalt

and into the degradation products.

20

REFERENCES

(1) Greenfeld, S. H. , "A Method for Preparing Uniform Films

of Bituminous Materials", A.S.T.M. Bulletin No. 193,

50-53, Oct „ 1953.

(2) Gpeenfeld, S. H. , "The Effects of Thermal Shock on the

Durability of Asphalt Coatings Under Accelerated Test",

ibid . , 46-50.

(3) Kleinschmidt , L. R. , "Chromatographic Method for the

Fractionation of Asphalt Into Distinctive Groups of

Components", J. Res„ N.B.S. 163-166, 1955 (RP2577).

(4) Greenfeld , S. H, , "Report on the Evaluation of TwentyOne Coating-Grade Roofing Asphalts", N 0 B.S 0 Report No.

4732, 1956.

(5) Matteson, R. , "Modified Molecular Weight Apparatus",

Anal. Chem. 22, 172-175, 1950.

(6) Federal Specification TT-P-l4lb, Method 506-1.

(7) Niederl, J. B. and Niederl, V., "Micromethods of

Quantitative Organic Analysis", John Wiley & Sons, Inc.,

New York, N. Y. , 1952.

(8) Unterzaucher , J. , Ber. 73B . 391-404, 1950.

(9) Aluise, V. A., et al, "Oxygen in Organic Compounds",

Anal. Chem. 1£, 347-51, 1947.

21

(10) Hinkel, R. D. and Raymond, R. , "Direct Semi-Microdetermination of Oxygen in Organic Substances" , Anal. Chem.

21, 470-9, 1953.

(11) Dundy, M. , and Stehr, E. , "Determination of Oxygen in

Organic Materials by a Modified Schutze-Unterzaucher

Method", Anal. Chem. 21, 1408-13 , 1951.

(12) Sundberg, 0. E., and Royer, G. L. , "Microdetermination

of Halogen and Sulfur", Anal. Chem. l8>, 719-24, 1946.

(13) Alford, W. C. , "Microdetermination of Nitrogen in

Organic Compounds", Anal. Chem. 24, 881-84, 1952.

(14) Van Ness, K. , and Van Westen, H. A., "Aspects of the

Constitution of Mineral Oils", Elsevier Publishing Co.,

Inc., New York, N. Y. , 1951.

(15) Greenfeld , S. H. , "The Degradation of Two Coating

Asphalts", N.B.S. Report 4621, April 1958.

(16) Schriesheim, A., and Greenfeld, S. H. , "The WaterSoluble Degradation Products of Asphalt". Presented

before the Symposium on Bituminous Materials, American

Chemical Society, Dallas, Texas, 1958.

(17) Thurston, R. R. , and Knowles, E. C. , Ind. & Eng. Chem.

11 , 320, 1941.

(18) Stephens, E. R. , et al, "Reactions of NO2 and Organic

Compounds in Air at Concentrations of PPM", Ind. & Eng.

Chem. At the publishers.

22

ACKNOWLEDGEMENT

The Project wishes to acknowledge with thanks the help

of Vito Aluise, of the Hercules Powder Company, W. C. Alford,

of the National Institutes of Health, and Rolf Paulson, of

the National Bureau of Standards for their generous assistance and suggestions in developing the analytical procedures.

The Project is also grateful to H. R. Snoke and Alan Schriesheim

for their continuous consultation and encouragement.
,* . I
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