September, 1934
IN D U ST R I A L A N D EN GIN E E R I N G CH E
Applebaum, S. B., J . Am. Water Works Assoc., 26, 607 (1934). Applebaum, S. B., J. 1x0.ENG.CHEM., 8, 160 (1916). Applebaum, S. B., Power, 77, 375 (July,1933). Donaldson, W., Eng. News-Record, 90,874 (1923). Ellis, D., “Iron Bacteria,” p. 136, Frederick A Stokes Co., New York, 1920. (8) Hazen, A , , “Filtration of Public Water Supplies,” 3rd ed., p. 189, John \Tiley & Sons, New York, 1908. (9) Hoover, C. P., J . A m . Water Works A s s o c . , 23, 833 (1931). (10) Ibid., 25, 181-91 (1933). (3) (4) (5) (6) (7)
ISTRY
931
(11) Johnston, J., J . Am. Chem. SOC., 38, 947-78 (1916). (12) McCrea, T. R., Water Works & Sewerage, 80, 225 (June, 1933). (13) Monfort, W. F., Water Works, 65, 169 (1926). (14) Pick, E., Instruments, 6,215 (Dee., 1933). (15) Weston, R. S., J . Am. Water Works Assoc., 23, 1272-82 (1931). (16) Weston, R. S., J. LVewEnol. Water Works dssoc., 28, 27 (1914). RECEIVED May 17, 1934. Presented before the Division of Water. Sewage, a n d Sanitation Chemistry a t the 87th Meeting of the .imerican Chemical Society, St. Petersburg, Fla., March 25 to 30, 1934.
Selection and Use of Age Resistors in Rubber Compounds RICHARD -4.CRAWFOHD, The B. F. Goodrich Company, aikron, Ohio Later a large number of coinHE early developnient of Although the discocery and use of certain orpounds were patented as accelthe rubber industry v a s ganic accelerators resulted in the manufacture of e r a t o r s which gave to rubber h a n d i c a p pe d b y two rubber articles with good aging properties, conage-resisting properties. Among serious defects in rubber articles. trol of aging by choice of accelerator was not a these appeared patents for niThey were not stable to temsaf isfactory solution to the aging problem, betro c o m p o u n d s and aromatic perature changes, and they deamines in 1917-19 ( 2 , 13, 18); teriorated r a p i d l y w i t h age. cause independent control of curing and aging f o r r e d u c i n g a g e n t s such as Although t h e p r o c e s s of vulproperties was not possible. Such a control, f o r diminishing hydroquinone canization c o r r e c t e d the first however, wus proaided by the incention of nontackiness of light colored, drydifficulty, r a p i d deterioration accelerating age resistors. Although tensile heat-cured articles in 1921 (10); with age was common until the strength is the property most used to measure for aldehyde-amines in 1922 d i s c o v e r y of certain organic accelerators, such as p-aminoaging effects, in recent years other factors have (5); and a s e r i e s of p a t e n t s covering mercaptobenzothiazole dimethylaniline, the aldehydebecome recognized as important in influencing and its derivatives. a m i n e s, and mercaptobenzothe choice of a n age resistor. Among these are Until t e n years ago the thiazole. Prior to these disthe effects of age resistors on processing, bloom, recognized method of producing coveries a number of materials and various physical properties of unaged and good-aging rubber lay in the had been p a t e n t e d for the choice of the proper accelerator. purpose of improving the ageaged vulcanized rubber. These effects are preSince not all accelerators proresisting properties of rubber, sented in detail. Superaging compounds are duce this effect, the choice was but many of them were of little discussed, and adcantages resulting f r o m the use decidedly limited. Some accelmerit and most of t h e o t h e r s of age resistors in such compounds are shown. erators w h i c h imparted good possessed some a c c e l e r a t i n g A guide is given f o r the choice of age resistors for aging conferred on rubber value, a fact which was not apspecific purposes, and reasons are shown for other properties, such as undepreciated at the time. Typical of the more useful early patsirable rate of cure, t o x i c i t y , their use in a large number of commercial rubber ents for a g e - r e s i s t i n g mateetc., which had to be accepted articles. rials are American patents by along with superior aging Murphy in 1870 (15), Moore properties. This method was not in 1901 (14), and Martin in 1922 (12), and the German an ideal solution of the agingproblem, and it was left to later and English patents of the Ostwalds in 1908 and 1910 (19, investigators to find means of controlling aging and curing 20). Murphy patented phenol, cresol, and cresylic acid, properties independently, either added to the uncured stock or as dipping solutions In 1924 Winkelmann and Gray (23) secured a patent on for vulcanized articles for the purpose of improving their nonaccelerating aldehyde-amine condensation products as resistance to aging. Moore used reducing agents, includ- age resistors. This was followed in 1927 by a patent to Cading hydroquinone, pyrogallol, and p-aminophenol hydro- well (6) covering the aldehyde-amine condensation products chloride, to preserve the adhesive properties of rubber made in the presence of acids. With the introduction of cements. Martin suggested aniline and other organic bases these materials, independent control of age-resisting and curas a surface treatment for vulcanized articles. The Ost- ing properties became possible. For the first time accelerawalds also recognized the beneficial effects of aniline on tors could be chosen to produce the desired rate of cure and rubber and stated that it could be added a t any convenient physical properties without regard to their possible effect on stage of manufacture. ( I t is interesting to note that these the aging of rubber articles, This resulted almost immediinventors considered that addition of aniline to uncured stock ately in great improvement in the quality of rubber goods or dipping the cured article in aniline were equivalent, and because the deficiencies of accelerator-sulfur combinations they, therefore, evidently did not recognize the accelerating which produced high quality but were known to produce poor effect of aniline.) aging could now be corrected by the addition of age resistors. The beneficial effect of certain organic accelerators on ag- During the past ten years a great many materials which will ing has also been recognized and has been the basis of a num- retard the deterioration of vulcanized rubber on aging have ber of patents. For example, p-aminodimethylaniline was been placed on the market; the principal ones are included used commercially as early as 1912, although never patented. in the classes of: (a) phenols, ( b ) aminophenols, ( c ) mono-
T
4:12
l 3 l ) l ~ S ' ~ l i I A l A, \ c D
c 11 13 M I s 'I- I< Y
G I R. E i.: I< I li ;(
Vol. ZG, No. 9
:irimwt,ic airiiner, ( i i ) wono- a i d ilisecoridary piiiiils wliicti woold be iiiisaeil eritircly if wiisiilerntioii verc re;tctim prodtiots d aromatic giiiw (iiily to a few quantitativc cqil,erinicnts in a iinrrom field. armmtic iiiiiiiics, (e) alrlcl~y~lc f aroiiiativ :%iiiiiies. In order that riibbcr compounders may liave for their sclecall chcrnicnl c o i i ~ - tion nnil use of age resistors the benefit of tiiis Imader c x p ~ rience, conclusions based on numerous rpalit,iitive comparii be ileiiioiistrtited sons are inclmlcxl with otliers for which detailed data are prcI,? axing iiiiiler ia,ri,ial st.orago or servicte conditions. Him- scnt,ed. Iopticnt of tlie riililm industry in gerroml i u x i iliixiiriwy
Tiie aililitiun of any iiiaterial tu a r u l ~ l m coirrlx)iind iiiay affect i t s properties i n hotli tlii, cured and uncured states. One of tile most
age rerktors in particular lias iiiacie iiriperative iiiore rapid testing than is Imssihle by natural aging alone. For this reasoil accelerated aging teats have heen erngloyed tu an increasing extent for the corngarison of resistance to aging of rubher cornpounds. Of these tests the Geer and Evans oven (8, 9) arid tlie Rierer and llavis oxygen bomb ( I ) are the most widely used. In the attempt to obtain quantitative information, measurcments have been made of specific physical properties of rubber stocks before and after aging. Change of tensile st.rength was the first crit.erion to be utilized aiid is still used more extensively than any other in measuring the effects of aging. That an age resistor actually docs iriiprovc resistance to aging, as judged by tensilc tests, under both natural and artificial aging conditions is well known (4). In recent years it has become recognized that t,hc effect in irirproving the tensile strength of aged cured ruhber is only one of the factors to bc considercd in selecting an age cesistor. Sonic other factors governing tlie choice are: (a) its effcct oii processing properties, (b) its tenrlenry to bloom, (e) its effect on properties otlicr than tensile strength of uriaged cured rulher, arid (d) its effect on properties other than tensilt, strength of aged cured rubber. It is the purpose of this paper to present inforination conceriiiiig the proper choice and use of age resistors by the Nbbcr cornpounder. Data are presented to illust,ratc effects to he gained by the use of age resistors rather than to serve as a critical comparison of specific materials. The age resistors meiit.ionet1in the tables sliould he coiisidered as represcntative of tlie chemical types to which they belong. Wowever, nieiribers of any given clnss vary aniong themselves in activity, aiid it sliould not be assumed that they are all of iqual v ~ l u for c any given purpose. In studying the behavior of age rcsistors, reliable and vaha b l ~gi:neraliaations can frequently he drawn from a large i i i i i i i l m of qualitative observations of a wide variety nf comxu11 of
inipOI'tRnt factors in influencing the reail? aceeptance of a riilher compounding iiigredieiit is the maimer ill wlricli it affects prmcssiirg properties. Tack, plasticity, saircliing tcndcncy, mil l h o m are factors wtiioli must be given consideration if useful articlcs are to be iriaile from a rulilxx cornpimid. Of tliese, plasticity aiid scorching tendency are perhaps the inost important from the processing standpoint. It is proposed, therefore, to discuss in mine detail tlie effect on time propertics of sereral representative agc resistors. I'I..~~TICITY. The desired plasticity ctiaracteristies of rubber compoiiiiiis are usually secured by additioii of the proper kind and amount of one or more softening agents. A number of claims have been made for the valuable softening action of various age resistors. While it is triie that they are in arrnie cases softeners for rubber, it is equally true that some are rubber stiffeners. Age r e s i s t o r s , in general, are not uutstanding in softening value, and in tlie concentrations generally recommended for rubber compounds (about one per cent) t.he resultant change in plasticity is frequently negligible. Certainly, eqoal softness can tie obtained a t lower cost by using any one of a nrirnber of coininon rubber softeners. Table I shows the net change in plasticity of smoked sheet rubber produced by the addition of various percentages of several cornmercial softencra and age resistors. T:tsi.r: 1.
ISCIWA~E IN PLASTICLTY~~ OF Bxoam Simm Rusnsrr
Pm,nircao
BY
ADDITIONOF Vawious M.wcarar.s l'L4m,cITT C,Z*Nr;E* D U C B D ST:
1%
2%
PX". 3%
The net plasticizing effect of a softener in a rubber e m paimd depends not only upon its softening action on tire mb-
ber bot also upoii its effect upon the subsequent rate of breakdown during further processing. Table I1 sliows that if one ix:r cent of age resistor is added to smoked sheet on a roll mill, the incream in plasticity of the rubber at the exid of the mixing is less than when rubber is masticated an equal length of time witliout the addition of agc resistor. Such a result might he expected, since recent data published by Cotton ( 7 ) arid liy Busse (5) indicate that hrcakdowii of rubber on a milE
I N D U S T R I A L AN D E N G I N E E R IN G CH E M I ST R Y
934
Vol. 26, No. 9
TABLE 111. EFFECTOF VARIOUSAGE RESISTORS ON CURING PROPERTIES OF REPRESENTATIVE ACCELERATORS TEMP. OF
ACCELERATOR
CURE
c.
No
CURE
AGE
RESISTOR
ALDOL-
PHENYL- DI-&
a8NAPHTHYLNAPHTHYL- N A P H T H Y L - PHENYLENEAMINE AMINE DIAMINE
127
Zimate
115
Captax
138
Heptene base
138
Tuade
127
Zimate
115
Captax
138
Heptene base
138
Tuade
127
PHENYL-
AMINES
AMINE
p,p'-DIAMINODIPHENYLMETHANE
7 281 295 288 285 183 232 211 253 292 169 232 253 225 253 125 185 243 260 255
309 329 285 288 295 232 236 303 309 336 225 281 282 272 266 155 211 268 264 278
232 346 336 295 302 189 225 246 281 267 232 274 278 260 260 172 248 253 309 281
18 301 309 285 288 162 246 275 295 313 183 232 239 253 253 105 182 226 258 253
853 767 693 697 710 955 835 815 835 780 853 800 770 733 743 945 815 795 770 730 EP. C M . )
770 683 630 647 653 830 750 775 735 720 775 710 703 683 663 870 790 790 720 715
795 740 707 678 705 770 760 785 775 740 823 753 740 723 723 885 785 765 770 730
840 787 720 703 727 930 840 840 785 785 873 800 803 787 770 975 853 783 787 747
56 97 120 116 113 29 48 56 69 84 35 63 70 84 90 21 40 49 64 77
42 77 91 93 91 35 54 46 55 63 20 56 63 63 63 21 43 49 60 70
11 53 77 77 65 18 28 33 41 49 19 39 39 43 43 14 27 35 42 49
CZ-
NAPHTHYLAMINE
Min. E F F E C l' ON T E B S I L E STRENGTH (KG. PER SQ. CM
Tuade
2,4-DI-
MIXBD AMINODIDITOLYL- PHDNYL-
10 20 30 45 60 10 20 30 45 60 10 20 30 45 60 10 20 30 45 60
7 295 3 13 295 279 160 253 278 287 315 158 229 243 241 218 98 169 239 268 267
35 320 302 281 295 200 295 292 309 309 141 218 243 241 229 98 171 239 279 267
7 295 302 285 278 188 239 281 315 327 113 230 225 232 243 120 186 229 265 264
'
7 281 309 301 294 190 288 304 309 296 153 211 218 246 253 102 204 240 268 274
J
EFFECT ON ULTIMATE BLONQATION ( P E R C E N T )
10 20 30 45 60 10 20 30 45 60 10 20 30 45 60 10 20 30 45 60
900 780 730 715 715 895 850 830 813 815 905 803 785 770 757 920 815 790 760 740
788 730 693 690 713 847 823 790 770 755 870 805 797 757 723 930 850 800 790 750
830 753 730 700 712 940 855 840 815 800 905 840 770 773 780 925 810 790 765 750
960 763 730 720 737 855 805 785 760 725 870 800 780 760 763 895 840 785 750 730
EFFECT' ON STRESS AT 5w PER CENT ELONQATION (KQ. PER
Zimate
115
Captax
138
Heptene base
138
10 20 30 45 60 10 20 30 45 60 10
20 30 45 60 10 20 30 45 60
..
55 73 77 63 21 28 35 39 42 19 35 42 49 50 15 28 38 49 56
26 71 84 77 69 21 37 43 56 56 19 29 35 42 49 15 26 38 50 57
chanicallv abraded or until the comDound has been exDosed to indirect light-as through a glass window-or stored in a warm place. Instances are known where no bloom occurred during the first six months of storage but became quite noticeable a t the end of a year. The only way to be sure that objectionable bloom is not encountered is to compound the stock intelligently, store various cures under different conditions, and make periodic examinations for bloom. If objectionable age-resistor bloom is encountered, there are several methods to combat it: 1. Use less age resistor or a different age resistor. Sometimes a mixture of age resistors can be used to advantage t o eliminate bloom, at the same time maintaining or even improving the age-resisting properties of the compound. 2. Change the acidity of the compound. Some age resistors bloom at a lower concentration in a basic stock than in an acid stock. 3. Use another accelerator. 4. Eliminate bloom due to other constituents. Other constituents, even when blooming in only slight amount themselves, will sometimes induce bloom of the age resistor. 5. Change the type or concentration of oils. The type and amount of oils used sometimes chan e the limiting concentration of an age reuictor, possibly because oftheir solvent action upon it.
..
60 72 70 63 20 29 35 46 49 18 32 41 42 42 15 28 35 46 49
.. 56 72 70 61 23 42 46 63 67 19 33 37 42 44 18 32 42 56 70
..
53 84 77 70 14 28 32 33 39 21 35 42 43 52 14 27 34 49 53
EFFECT ON PROPERTIES OF UNAGED CUREDRUBBER While the ready acceptance of rubber compounding ingredients depends in large measure upon their effects on processing and curing properties, nevertheless the outstanding reason for using age resistors is that they impart some desirable property or properties to vulcanized rubber. The primary object of using age resistors, of course, is to secure improved resistance of rubber compounds to deterioration on aging. However, research during the past few years has shown that chemicals can be made which will imDart other desirable properties. That is, if the proper age ;esistor is used, propertiesimportantin the service life of the rubber are improved even in unaged rubber. These properties are tensile strength (in some cases), quality of overcures, resistance to flex cracking, and resistance to abrasion. As might be expected, the improvement becomes more marked as the age Of the cured rubber increases* TENSILESTRENGTHAND MODULUS.Improved tensile strength and increased modulus are probably due to the accelerating Power of the age resistors, 01 to their activating effect on accelerators, as shown in Table 111. Although
September, 1934
INDUSTRIAL AND ENGINEERING TABLEIv.
.LGE RESISTOR^ Aldol-a-naphthylamine Phenyl-a-naphthylamine Phenyl-@-naplithylainine Ditolylamine Di-@-naphthyl-p-phenylenediamine Synthetic product -1 Synthetic product B b Diaminodiphenylmethane Diaminodiphenylami ne a
b
PROPERTIES O F
MELTIKQPOIST
COLIXERCI.IL
AGE
RESISTORS AFFECTING BLOOW
CRYBTALLIZIKG TENDENCY
hlAX. EFFECTOF PERCENTAGE OILS NONBLOOMING I N cO!vfPD. SOLUBILITY IN PURE O N BLOOMING IK OILS G U MSTOCK TENDENCY
SOLCBILITP I N RUBBER
c. Xot definite: S B 62: B loa; B Lou-: N B 235; NB Low; NB Low; KB 93; B 127-134; B
935
CHEMISTRY
None, resinous; K B L o a ; NB High: B S o n e , liquid: N B High. U None: sirupy; N B
High; N B Medium: B Medium; High; XBB Very low: N B Medium; B
None, sirupy; NB Low; N B High: B
High: N BB Medium: Low; B
High: N B High: N B Medium; B High: N B Very low: N B High: NB High,; NBB Medium: Low: B
Above 3 1 Above hbove 3 Above 1 1
5 5 5
5
Increase Decrease Decrease None Increase Decrease Sone Decrease Decrease
B =, favorable t o blooming; NB,= favorable t o nonblooming. .1 misture of trimethyldlhydroquinoline and its polymers.
high tensile strength is usually not the most important property of a rubber compound from a service standpoint, it is a useful one because many specifications contain tensile requirements. Increased modulus is sometimes undesirable. OVEIZCURES.The improvement effected by age resistors in overcured stocks is important from a service standpoint because increased uniformity of cure in thick masses of rubber can be obtained in commercial practice. In other lyords, bad effects due to overcure a t the surface of thick articles can be reduced. It appears obvious that this will result in improved abrasive v,-ear in such articles as tires and conveyor belts, and improved flexing life of belt and tire carcasses. FLEXURE CRACKI.SG.xellen (17) noticed that certain age resistors improved resistance to flexure cracking of tires. This property of age resistors is now regarded as of the highest commercial importance. The factors which appear to be more or less definitely involved in flex cracking are oxidation, cure, pigment dispersion, inclusion of dirt or other foreign material, and grade of rubber used. Other factors of importance are pigment loading, acceleration, type and concentration of reclaim, and softeners, That oxidation is a factor in flexure cracking has been shown by Kea1 and Sorthain ( I @ ) , and Jones and. Craig (11) have shown that certain age resistors reduce this tendency. The effect of cure is shown by the experience of several years with flex cracking tests of tread compounds which indicates that increasing cure beyond the optimum tends to decrease flex cracking resistance. The influence of pigment dispersion on flexure cracking is shown by tests of rvell-mixed us. poorly mixed batches of the same compound :
being equal, the resistance to flex cracking of tire treads depends upon the accelerator used.
The sample, cured in a special mold, is 15.2 X 20.3 X 1.3 cm. It is backed by a piece of heavy frictioned fabric. There are three crosswise grooves about 0.4 cm. deep and 0.65 em. apart. Strips 2.54 em. wide are cut lengthwise which, when bent, resemble a section that might be cut from a tire. These 2.54-om. strips are flexed on the Henry L. Scott belt flexing machine over a 3.18-em. pulley. The rate of flexing is 12,600 or 10,000 flexures per hour, depending upon which of two machines is used. It has been found that this test will give consistent results which generally check road. tests on tires within reasonable limits, and will allo\!T fairly accurate estimation of the influence of various factors in flex cracking. Table V shows the results of this investigation.
Microscopic examination of reclaim-rubber mixtures has shown that most reclaims do not dissolve in or flux with rubber but disperse in small particles as a pigment does. .I lumpy reclaim or one which disperses poorly would, therefore, be expected to act like dirt or poorly dispersed pigment. In testing for the effect of age resistors on flex cracking it is important to use clean, high-grade rubbers, and to secure good pigment dispersion. ABRASION. S o t much information is available p n the effect of age resistors on resistance to abrasion of rubber compounds. Claims have been made that certain age resistors have a large effect in improving tread wear. Preliminary tests have failed to show great improvement due to age resistors but have indicated that some improvement can be expected when age resistors are used. Laboratory data have been obtained for phenyl-P-naphthylamine on several machines, some of which (notably the Bureau of Standards type) seem to give results agreeing with road test data. Comparison on this machine of a typical high-grade tread accelerated with the aldehyde-amine accelerator Pullman, with and without phenyl-P-naphthylamine, a t optimum cure are shown below, The time of cure was 60 minutes a t 146" C., and 0.75 per cent of age rePistor on the rubber n-as used :
3
nd is tapered at the ends.
The presence of dirt and other foreign material affects flex cracking resistance, as indicated b y the fact that cracking usually starts, both in road-tested tires and in laboratory samples, at the interface between such materials and rubber (cf. Street, 21). That the grade of rubber influences flex cracking is shown by Table VI, which gives results of tests on t,he same compound with different rubbers. The statement that pigment loading probably affects flex cracking of treads is based on factory experience which has shown flex cracking resistance to vary as carbon black loading is changed. Experience has shown too that, other things
TABLE \-. EFFECTO F P I G M E N T D I s P E R S I O X O S FLEXCR.ICKISG OF LSAGED TREAD STOCK (Compound is intermediate-grade tread and contains 0.75 per cent phenyl@-naphthylamine on the rubber: Scott machine test) iYo, OF
FLEXURES
TEMP.TO C.4CsE OF FIRST COMPOUND MILL CRACKING
c.
(1) Poor inixa (2) ?or mix (3) Good mixb
60 Cold 60
28,560 33,750 47,444
(4) Good mis
Cold
63,745
(1) Poor mix
60
28,560
( 2 ) Poor mix
Cold
39.757 49,343 76,552
(3) Good mix (4) Good mix
60
Cold
OPIKIONO F TESTOPERATOR
Small cracks in grooves; worst of group Small cracks in grooves; better than (1) Very small cracks and pinholes in grooves: better than (2) Few pinholes in grooves: best compound of group Crack across groove; worst compound of group Cracks in grooves: better than (1) Cracks in grooves: better than (2) Small cracks in grooves; best compound of erouD
OF TABLE VI. EFFECTOF KIXDOF RUBBERON FLEXCRACKISG UNAGEDTREAD STOCK
(Diphenylguanidine-hevarnethylenetetramine used as accelerator; machine test) h-0, O F
Scott
FLEXURE3 TO CAUSE
FIRST KIND O F RUBBER CRACKING .4PPEhR.ANCE A F T E R FLEXIKG (1) Blend of amber and smoked sheets 417,698 Good (2) Smoked sheets 319,762 Not a s good as (1) (3) Rolled brolin 278,978 Much worse than (1) or ( 2 ;
Some clieinicals of doribtfid d u e hefore aging will irkcrease flex resistance after aging. p,p'-Diaininodi~iiiei~yImctlianc has sonre value after aaine but none before: " -iurrage Of t w o or m"re testa. ~,and d P-nnplitliyl-p-l,treiiylerieililliese data indicate that a arnine has valiie in aged slight improvement in abras b c k but none in unaged sive resistance niay be exstock. pectcd in the presence of The comparison of flexing a11 age resistor even nlien properties of various coixitlie tread has not been aged. p o u n d s b y nieans of the Scott belt flexingmachineas EFFECTOF AGE RESISTOI~S d e s c r i b e d above is timeiix ~'II~IFEIWIES OF AGEI) c o n s u m i n g b e c a u s e it is CUXD RUBBER necessary to test a relatively large number of s a m p l e s , The beneficial effects of and the number of samples age resistors become more which can be tested at one marked as the samples are t i m e is n o t g r e a t . For aged. Properties of aged these r e a s o n s some canrubber compounds afrected prisons have been mrtde b y t h e p r e s e n c e of a g e 011 tlie R u b b e r S e r v i c e resistors are tensile strength Laboratories (R. 5. L.) flexa n d elongation, modulus, ingtnachine. This machine flex cracking r e s i s t a n c e , has four wheels on a single, abrasion r e s i s t a n c e , and motor-driven shaft. These flexing life of tire and belt wh eel s are approximabely carcasses. 25.4 cm. in diameter m d TENSILE STRENGTH. Tlie a b o u t 2.54 cm. wide, In m a i n t e n a n c e of t e n s i l e each wheel are twelve slots properties of aged rubher in esclr of which is fitted a was the first observed effect molded sample of special and is now so well k n o m design. The srtmplas prothat it is not necessary to ject from the wheels 1.9 em. discutis it in d e t a i l . In and, w h e n rotated, strike general' aFe resistors are eftwo s m o o t h idler pulleys fective with either acid or and a r e t h e r e h y f l e x e d basic accelerators, and tlie 1050 times oer minute. deeree of orotection denends Experience has r;iiown that stocks containing a higlr perupon the chemical nature of the agemsistor. l'riniarg diamines (m-toluyleiiediamine, p,p'diaminodiplrenylniethane, 2,4-rli- centage of carbon black are perhaps the most suitable for amino diplien~hninc)are gPoerally ineffe[~t,ivefrornthe stand- flex testing with this machine. The failure of the samples point of preserving tensile strength. Aldehyde-amines are extends through a range from tiny pinlioles tlirough checks somewhat more effective and in high conccntration (3 to 5 per and cracks to conrplete breaks. It is not unusual for a good cent) coinpare favorably with the best,age resistors. Secondary tread stock to require xs many as 4,000,000. flexures before amines (i~i-P-napiithyl-pyhenylenediamine, mixed ditalyl- cracking though. Four samples of each stock are tested are very effective preserra- a t one time. comparisons of various stocks are based on amines, plienyl-~-naplithylan~ine) visual inspection, and good agreement on repeated t.ests is tives of tensile stren@h in both tlie bonih and oven tests. obtained. This method is made clear by the following exTABLEVII. EFIECTow P ~ ~ E N ~ L - ~ - N A ~ Ho rT I%EX ~ ~ Y ~ amples: , A ~ ~ wStock ~ : A cont,:tining no age resistor was flexed with CRACKIKQ RESISTANCE OF A Tamn C O M I ~ J N UNAGED U AND stocks B and C (wliich contained age resistor) for a total of AoEn IN TliE GEEROvEW 1,000,000 flexures. At the end of t,!iis time all four samples (DipBenylgunnidine-hexametliyienetetrsi,i"~ trend: S c o t t msr,hioe test: euie, 55 zninutes st 146- C.) of .4 were completely broken or cracked across the face. N" n i Sucli samples are rated 10. Samples with no cracks or pinholes are rated 0, nnd all others proportionally on a scale between 10 and 0. None In Table VI11 are r!iuwn t,lie effecis of several age resistors on the flex cracking resistance of three tread stocks as measured by the R. S. L. machine. The comparison is on the basis noted ahove, and the data are therefore roughly qoant~itative comparisons. Aging was carried out in the Bierer hornb for 48 hours a t 70" C. and 21.1 kg. per sq. em. FLEXCBACKIKG.The effect of age resistors on the flex oxygen pressure. Aged samples did not receive as many cracking resistance of tread stocks is also more striking after flexures as unaged stock. It vas found that, if both unaged aging. Sovenday Geernven aging rougliiy quatln~plesthe and aged stocks were flexed the same number of times, no tendency of a diphenylguanid~e-hcxaniethylenetetramine comparisons could be made, because either the aged stocks tread stock to crack in tile absence of age resistor. If 0.5 per would all be rated 10 or the unaged stocks would all be rated cent phenyl-~-naphtliylamineis added to the compound, the 0. Table VI11 does not show, therefore, an accurate quanrracking tendency after 7day Geer-oven aging is less than titative coinparison of the flex reGtance of any single cornf'?.
Zllnr Pl,enii-B-'ihpl'l,l'ylniiiiiie
4.16 4 a2
100 106
~
~~~~
I pi D U S T R I A L A N D E N G I IC' E E R I S G C H E M I S T R Y
September, 1934 TABLE
\m.
EFFECT O F AGE RESISTORS OK
F L E X CRACKING RESISTAWE OF (R. S L. machine test)
.
TEMP. O
c.
146
Polybutyraldehyde-aniline (Pullman) tread, 43 % black on rubber
146
IIercaptobeneothiazole tread, 40% black on 1wbber
138
None Phenyl-&naphthylamine Synthetic product A Phenyl-@-naphthylamine Synthetic product A None Phenyl-&naphthylamine Aldol-a-na hthylamine Mixed ditofylamines Di-p-tolylamine Synthetic product A Synthetic roduct B 1&Napht$lenediamine Di-8-naphthyl-p-phenylenediamine 2-Mercautobenaimidazole None Phenyl-&naphthylamine Synthetic product A Phenylcumylamine Di-p-tolylamine Synthetic product B
45
60
45
pound before and after aging. It does show, however, the relative value of various age resistors before aging and a similar comparison after aging. ABRASIOXRESIST~KCE.As mentioned above, the resistance to abrasion of even unaged treads may be better in the presence of an age resistor than in its absence. Table IX shows that, when the tread is aged, this improvement becomes greater. TABLE
Ix. EFFECT O F AGE RESISTOR O S THE RESISTAKCE -4BR.4SIOS O F AN AGEDT R E S D STOCKa
__
TO
(Bureau of Standards tvDe machineb) VOL.
0 . i 5 y OA G E REEISTOR ON
RUBBER
.4QINQ PERIOD
Loss
PER 1000 REvoLurIoNs OF .4BRAsIVE
Days
cc .
0
0 i
I
14 14 21 21
4.56 4.32 4.53 4.00 5.08 4.08 6.43 5.12
R A'ING ~
Unaged
Aged
MILEAGE INDICATED 100 106 101 114 90 112 71 89
AGED I N B l E R E R B O M B
40 24 11.55 None 71 Phenyl-&naphthylamine 24 6.46 22 48 20.36 None 53 48 8.57 Phenyl-@-naphthylamine a Pullman tread stock, optimum cure. b This machine uses a medium-coarse aloxite wheel for the abrasive. T h e sample is clamped t o a lever arm and is abraded against the periphery of the wheel. The load is applied b y means of weights on the end of the lever arm. T h e abrasion loss is measured by volume loss in cc. per 1000 revolutions of the abrasive. T h e conditions of operation for these tests are: aiae of wheel, 30 X 7.5 cm.; size of sample, 2.5 X 15.25 X 0.95 c m . ; speed of abrasive, 60.55 meters per minute; and total load, 5.54 kg. c Each figure is the average of two or more tests.
FLEXING LIFE OF TIRE CARCASSES.Since some air is present in tire cords at the time they are coated with carcass stock, it might be expected that an age resistor mould improve the aging properties of tire carcasses and hence the flexing properties of aged tires. An experiment designed to test this effect showed that, although there was no improvement in the unaged stock, 0.25 per cent of phenyl-b-naphthylamine on the rubber doubled the flexing life of a tire carcass after 14 days in the Geer oven. In this test, improvement in flexing life due to age resistor became apparent after 5 days of Geer-oven aging.
SUPERAGIXG COMPOUNDS During the past three years a new compounding technic has been developed relating to "superaging" compounds. The essential features of this technic are the use of relatively large amounts of powerful accelerators (usually thiurams), with or without auxiliary acceleration, and relatively small amounts or no added sulfur. They may also contain selenium
1,250,000 1,250,000 1,250,000 1,250,000 1,250,000 2,800,000 3,000,000 3,000,000 3,000,000 3,000,000 3,000,000 3,000,000 1,700,000 2,200,000 3.000.000 4,000,000 4,000,000 4,000,000 4,000,000 4,000,000 4,000,000
350,000 350,000 350,000 350,000 350,000 120,000 750,000 750,000 750,000 750,000 750,000 750,000 240,000 750,000 350.000 1,000,000 1,000,000 1,000,000 1,000,000 1,000,000 1,000,000
8.50 0.33 1.30 2.00 1.25 10.00 0.75 9.50 2.75 1.00 3.00 3.00 10.00 10.00 8.50 5.50 0.50
10.00 1.25 1.25 3.00 3 75 10.00 1 50 6 25 3 25 1 50 2 25 3 50 10 00 6.50 10 00 10.00 2.00 2.00 2.00 3.00 4.50
1.00
0.50 4.25 2.00
or tellurium. The outstanding property of compounds produced by this method is their extraordinary resistance to aging by accelerated tests such as the Bierer bomb, the Geer oven, and the high-temperature autoclave, even in the absence of age resistors. At first glance this property would seem to render superfluous the addition of age resistors to such compounds. That this is not necessarily so is shown by Table X (from data published by the R. T. Vanderbilt Company, 22) which shows the effect of one per cent phenyl/3-naphthylamine on the rubber in a superaging tire friction. OF TABLEx. EFFECT
RELATIVE
AGED I N QEER O V E N
None Phenyl-&naphthylamine None Phenyl-@-naphthylamine None Phenyl-&naphthylamine None Phenyl-@-naphthylamine
RUBBER
Min.
75
Polybutyraldehyde-aniline (Pullman) tread, 45% black on rubber
ON
CURE
U N A G E D T R E A D COMPOUNDS
NO.OF FLEXES .4ged Unaged
1% AGE R E s I 6 T O R
OF
CURn
COMPOCND
AGEDAND
937
PHENYL-b-XAPHTHYLAUIXE
AGING
ON A SUPICR-
COMPOUND (26)
(Tensile strength, kg. per s q . cm ; elongation, per cent) 14-Dau BIERER ~ - H RAIR-BOIB . ORIGINAL BOXBTEST TnsTb TenTenTenA Q RE~ sile Elongasile Elongasile ElongaSISTOR CCRE" strength tion strength tion strength tron Man. Sone 15 269 800 219 750 173 690 30 279 750 191 710 171 720 45 274 730 169 690 144 740 60 270 730 164 680 118 660 Phenyl-& 15 261 800 234 740 199 680 215 700 193 700 naphthyl- 30 288 750 amine 45 271 720 204 700 176 700 (1% on rub- 60 255 720 183 670 160 715 ber) A t 138.3' C. b A t 1 2 i 0 C. and 5.6 kg. per sq. om. pressure.
If the other properties of superaging compounds were as superior as their aging properties, standard compounding practice would be obsolete and superaging compounds would find universal acceptance for the production of all kinds of rubber goods. That this has not occurred may be due to too short acquaintance with superaging compounding or to lack of knowledge of the results attainable. It appears more probable, however, that the change in structure which produces the aging properties also produces other fundamental properties differing from those of standard compounds, some of which may not be desirable. Superaging compounds are not superior in all respects to properly compounded stocks based on standard compounding. They have been found inferior to properly compounded standard type compounds for water resistance, abrasion or flexing under heavy loads, flex cracking, freezing, and resistance to overcure due to sulfur migration in service. They are little or no better than the best standitrd type compounds for sun checking and oil resistance. Their comparative value for the latter service depends a good deal on the temperature of test. At elevated temperatures they are usually better, at room temperature they may not be. They are superior to standard type compounds in all kinds of accelerated aging tests and in high-temperature service in
tained. @or esaiiiple, if age resistors A arid 13 are under cmsiileration, and both are of equal value in bonrb and oven aging, A nray be of great value in increasing resistance to Hex cracking, wliile B isof littleoruo value; A m a y have bail staining properties, while I3 is r e l a t i v e l y nonstaining; A may have little value in protection agailist deterioration a t high teniperatures, while I3 is outstanding in this respect. It is necessary, therefore, to determine which properties are desired for a particiilar art.icle and choose the age resistor which will best maintain them. The ctioice of the best age resistor for any specific use must dcpeiwl upon wide experience and critical krrowlcdge of corupoition and sen-icc factors involred. In Tablc SI11 arc list,ed some of tlie reasons ior using age rc&ors in tyiical rubber fitocks. Tlrc fact that sge resistors improve natural, bomb, and oven :iging aiid also niinimiao the effect of variation in cure is cominun to all stocks and is not nrcntioncd iii the table.
-rawI.sXIIT.
RELSUM FOB IJSIXG AOE REM
I?.uBnER STOCKS :\SI)OTIiEI MAT
KO. l.Ul 1.8, (.*I 4,:ii 5.56 5 50 f i !92 6 . !a
fi. 0.60 0 . 5'3 2.21
2.u; f . 'I8 .i81 :i .ti4
a . 50
Cr. 0.87 U.82 2 . !l:i :3.4lI 4.25 4.6s 5.41 e.54
c,. 1.25 I . 17
R .3:1
100 10 2 100 74
.. ..
loo 7x
7.56
100 66
4 27
liX
74 75
R? 70 64
4x 51 52 41
.. .. 48
.kltlimigh tlex cra.cking propertics of sitperaging stocks liare proved inferior, both by laboratory fiex crncking texts and by r o d t.ests on tires, they can be ilnproved by the ailditiori of a properly cliosen age resistor. This is illiistrated for a superaging belt covcr conipo!iiul (Laboratory test) by Table XII. T a ~ mXII.
II (II' AOE ~ ~ E S i i i T o t t u ON FLEX
CRAcKrNG
KI:si~r.\vucsox'h S;ui~I.:,*A< HELT Covatl CoME.nura
2.50
"
fiidices on i a i i ~ ebaais a i 'Td~loY I I f
CIIOICE O n AX ZIGE HESISTTOII
Age resistors are as specific in their effects on tlie service qualities oi rubber articles as accelerators, and they must he chosen as carefully if the most desirable results are to I,e ob..
perrtuies
To prevent
the srtiori of Iimm on the rubber, mniiltxiri 'esilier,ey, Slid inaintniri vdiierion
To retard H c i rmokieir. improve resistanre to
abrasion, and improve tho lhent and corrmion reaiatanae "f the
To ~ieverit IAY separation fruiii building oporatieg
or
OlUQPB
To preuont eoftening and crackin. Tu retsid dintking and reduce innikiiig To 1)reYent hsideiring and cracking To maintain Boribility of tightly ouied or over. cured atoek 'To ~ i c v e n develonment t of *'id i n the tube T o prevent melting or hsrdeninq To orevent meltirii. or hardeiiiriv
I N D U S T R I A I,
September, 1934
AT iD E N G I N E E R I N G C H E M I ST R Y
439
TABLEXIII. (Continued) OUTSTANDING SPECIFICREASONSF O R USING AGE RESISTORS Very essential t o insure good aging T o prevent stiffening and shortness of cover T o minimize discoloration on aging T o improve flex resistance and heat resistance T o improve flex resistance and heat resistance T o prevent resinification and maintain flexibility T o maintain adhesive properties
11.4TERIAL
Sponge rubber R'ire H a r d rubber Sulfur-free stocks Low-sulfur stocks Latex-fiber combinations Rubber base adhesives
OCTSTAlDING SPECIFIC RE.4SONS F O R U S I N G AGE RESISTORB T o maintain adhesive properties T o prevent drying out oi the film To prevent checking, chalking, and cracking T o improve weather exposure test T o prevent deterioration of surface t o which applied T o prevent deterioration of surface t o which .ipTop dressing plied Linseed oil T o retard drying T o maintain adhesive properties Oil-base adhesives Sitrocellulose and lacquers T o stabilize and prevent embrittiement To prevent embrittlement Paper
-MATERIAL Rosin-base adhesives Fly stickies -4sphalt Asphalt paint Tire paint
OTHER M.4TERIALS
Balata Chicle, Pontianak, etc. Rosin
TABLE
T o prevent resinification T o prevent resinification T o prevent oxidation which catalyzes deterioratl'on of rubber goods
XIV.
CAUSES AXD
REMEDIES FOR
TYPEOF DETERIORATION 1. Loss of tensile strength a t ordinary temperatures 2. Decrease in elongation 3. General hardening
VARIOCS
TYPES^
Oxidation
Oxidation oi rubber, oxidation of free or combined sulfur, or continued cure Surface oxidation destroying the Tendency of highly compounded bonding action of the rubber for aged stocks t o smudge Chalking j the pigments Development of odor Oxidation, giving rise t o volatile, terpene-like materials Oxidation catalyzed by resinous in- The oxidation of rubber is autocatagredients, drying oils, deteriorated lytic rubber in compound, deteriorated rubber in contact, metal salts or soaps in compound, or contact with certain metals Effect of under- and overcures ............
]
4. 5.
6.
7.
8.
9. Effect of curing above optimum temp. 10. Brittle skin formation 11.
Softening by water or steam
.................... High-temp. service, surface oxidation, or surface overcure due t o suliur migration Water penetration a n d reversion
Oxidation a n d reversion 12. H e a t deterioration 13. Oxidation of solvent-swollen rubber Swelling often affords easier access t o oxygeq 14. Oxidation of free or combined sulfur High free or combined sulfur; overcures 15. Acid formation on oxidized surface Moist, oxidized. sulfur products retained on surface Acid hardening of surface 16. Effect of inorganic acid materials 17. Melting or sticky uerishina Oxidation a n d reversion . . 18. Loss of adhesive bond t o metal (brass-copper plate) 19. Copper poisoning of rubber stocks 20. Flexure cracking
OF
DETERIORATIOS OF RUBBER COMPOUNDS
CACSE
F~EMEDY
Diaryl amines, aldehyde-amines, or ketone-amines Same as 1
Low-melting diaryl amines are especially good
Same as 1
Kaxes, petrolatum, or paraffin also help
Same as 1
Leave out rosin oil or other readily oxidizable materials I n contact with easily oxidizable materials, use of age resistor is essential
Same as 1
Same as 1 Same as 1
Age resistors flatten curing curves and impart better aging t o poorly cured articles Same as 1
.4ldeh,yde-amines and certain diarylamines
A41dol-a-naphthylamine is mended
.4ldehyde-amines, polyprimary amines
Improvement notable in water bags and steam hose. aldol-a-naphthvlamine is recohmended
recom-
....................
Same as 11 Same as 11
Effect is seen in gaskets and gasoline hose
....................
Polyprimary amines Polyprimary amines, diaryl amines
Acid deterioration of fire hose cover
Same a8 15 Same as 15
Noted in t a n k linings Often Been in water bottles and pure gum articles
Softening a t interface
Diaryl amines
Accelerated oxidation
Same as 18 Diaryl amines
....................
COMMENT Use any highly active age resistor
....................
Lon-melting diaryl amines are especially good
Same as 20 21. Growth of cracks on flexing .................... .................... Diaryl amines Eliminate dirt from stock 22. Cracking originating from dirt nu.................... clei in .. stock . ~ .~ ~ Same as 22 ................... 23. Ply separation in service .................... Diaryl amines a polyprimsry amine . . . . . . . . . . . . . . . . . . . . 24. Internal heating by flexure .................... Aldehyde-amines, polyprimary amines . . . . . . . . . . . . . . . . . 25. Development of tack in d r y heat Oxidation ' cures a Commercial age resistors which belong t o t h e classifications given in this table are: Aldehyde-amine condensation products: Diaryl amines: Aldol-a-naphthylamine Phenyl-a-naphthylamine Acetaldehyde-aniline Phenyl-6-naphth ylamine Butyraldehyde-anili ne Di-8-naphthyl-p-phenylenediamine Polyprimary amines: Mixed ditolylamines Benzidine Synthetic product . 4 2,4-Diaminodiphenylamine 4,4-Diaminodiphenylmethane 2.4-Diaminotoluene ~~~
+
The ways in which rubber may deteriorate are manifold. It is often not possible to correct completely a given difficulty merely by adding an age resistor. It may be necessary to change the accelerator, the accelerator-sulfur ratio, the pigmentation, or the cure. However, the use of an age resistor is always an additional improvement or factor of safety. Types of deterioration which may be remedied by the use of certain classes of age resistors are shown, together with their causes, in Table XW. It should be understood that not all members of any given group will remedy the type of deterioration given. Age resistors are often specific in their effects, and Table XIV is intended merely as a guide in the selection of classes of age resistors suitable for the purpose in question. ACKNOWLEDGMENT The author's thanks are due R. P. Allen and W. L. Semon for aid in the preparation of this paper, especially the secticns
on bloom and on the causes of and remedies for rubber deterioration.
LITERATURE CITED (1) Bierer, J. M., and Davis, C. C., IND. END.CHEY.,16, i l l (1924).
(2) Boggs, C. R., U. S. Patent 1,296,469 (1919). (3) Busse, W. F., IND.ESG. CHEV.,24, 140 (1932). (4) Cadwell, S.M., IhLd., 21, 1017 (1929). ( 5 ) Cadwell, S. M . , U. S. Patent 1,417,970 (1922). (6) Ibad., 1,626,784 (1927). (7) Cotton, F. H., Inst. Rubber I n d . Trans., 6 , 487 (1931). (8) Geer, W. C., I n d i a Rubber W o r l d , 55, 127 (1916). (9) Geer, W. C., and Evans, W. W., Rubber Age (London), 2, 30s (1921). (10) Helbronner, ii., British Patent 142,083 (1921). (11) Jones, P. C., and Craig, David, IND. ESG.CHEX.,23, 23 (1931). (12) Martin, R . B., U. S. Patent 1,410,699 (1922). (13) hleeus, E. de, I h i d . , 1,229,724 (1917). (14) Moore, L. R., I b i d . , 680,387 (1901). (15) Murphy, ,John, I h i d . , 99,936 (1870).
I iV D U S T R I A L A N D E 2; G I K E E R I N G C H E M I S T R Y Neal, A. M.. and Northam. A. J.. IND. ENG.CHEM..23. 1449 (1931). Nellen, A. H., Rubber Age (N. Y . ) ,24, 373 (1929). Ostromislensky, Iwan, U. S. Patent 1,249,180 (1917). Ostwald, Wolfgang, and Ostwald, Walther, British Patent 10,361 (1910). Ostwald, W'olfgang, and Ostwald, Walther, German Patent 221,310 (1908).
Vol. 26, No. 9
121) Street. J. N.. IXD. EKG.CHEX..24. 559 119321. (22) Vanderbilt Co., R. T., Vanderbilt .'?ews, 2 (3),'31, 33 (1932). (23) Winkelmann, H. -1.,and Gray, H., U. S. Patent 1,515,642 (1924). R E C E I V E D December 27, 1933. Presented before the Division of Rubber Chemistry at the 86th Meeting of the American Chemical Society, Chicago, 111, September 10 t o 15, 1933.
HAULING A DEPHLEGMATOR TO THE REFINERY SITE FOR
A
DUBBSUNIT IN UPPERAssau, INDIA
Gases from Cracking Hydrocarbon Oils GUSTAVEGLOFF AND J. C. MORRELL, Universal Oil Products Company, Chicago, 111.
T
HE oil industry is developing more and more along the line of synthesis because of the enormous quantities of unsaturated hydrocarbons which it is producing from the cracking of gasolines, naphthas, kerosene, gas oils, fuel oils, and crude petroleum. These unsaturated hydrocarbons are present not only in the cracked products comprising gasoline, kerosene, and tractor, stove, furnace, Diesel, and fuel oils, and asphalt, but also in the gas produced. The volume of cracked gas now available yearly is over 300 billion cubic feet (8.4 billion cubic meters) averaging over 20 per cent of unsaturated hydrocarbons with some exceeding 50 per cent. The volume of cracked gasoline per year is 7.6 billion gallons (28.85 billion liters), which contains an average of about 20 per cent of unsaturated hydrocarbons. The potential significance of processes by which olefinic or unsaturated hydrocarbons may be converted into organic chemicals, gasoline of high knock rating, lubricating oils, solvents, and resins is apparent when one considers the enormous quantities available in cracked gases and producible from hydrocarbon oils. Among the products obtained from cracking oil under conditions of elevated temperatures and pressures is hydrocarbon gas having high heating value which is a t present largely used as a fuel. This gas can be fractionated to obtain ethylene, propylene, butylenes, butadiene, acetylene, and other unsaturated hydrocarbons which makes it a source of enormous quantities of pure hydrocarbons to be used in synthetic chemistry. The amount of gas produced in the cracking process is governed by several factors, notably the composition of the charging stock and the operating conditions of time, temperature, and pressure used during the processing of the oil. The problem of utilization of 300 billion cubic feet of cracked gas is simplified by a knowledge of the chemical composition of the gases.
The object of the present work is to study the cracking of various oils, particularly from the viewpoint of gas formation and its composition, especially when producing commercial yields of gasoline.
CRACKING EXPERIMENTS Cracking tests were made on various stocks including gasoline, naphtha, and kerosene from Midcontinent crude oils; kerosene distillate, a mixture of heavy naphtha and light gas oil, and gas oils from California crude oils; topped crude oils from Midcontinent and Somerset crudes and Mt. Pleasant and Refugio (Texas) crude oils. The operating pressures of these runs varied from 250 to 750 pounds per square inch (17.57 to 52.73 kg. per sq. cm.) and the temperature from 875' to 975" F. (468' to 524' C.). The products from the cracking tests were: gasoline, representing from 52 to 76.8 per cent of the charge; flashed liquid residue in various amounts up to 47.1 per cent; and the gas representing from 164 t o 1182 cubic feet per barrel. The calorific values of the gas, where determined, ranged from 1280 to 1590B. t. u. per cubic foot (11.37 to 14.11 Calories per liter). The Somerset topped crude was cracked to produce gasoline, gas, and coke. Gasoline, gas, and liquid residue were produced in all other runs. The apparatus employed in carrying out the tests was a continuous cracking unit varying in charging capacity or throughput from a proximately 1 to 35 gallons (3.8 t o 132.6 liters) per hour, depening upon the types of charging stock, the operating conditions, and the results desired. The apparatus comprised a continuous tubular heating coil, a reaction chamber, an evaporating or flash chamber, a fractionator, a condenser and receiver, and a stabilizer for the cracked gasoline. The full operating pressure was maintained upon the heating coil and reaction chamber, The evaporating or flash chamber and the remainder of the system were under a reduced pressure relative t o these ele-
