ANALYTICAL EDITIOX
294
oil appearing in fractions 1,2,3, and 4, plus the unsulfonatable portion of toluene content of fraction Fraction aromatic content of fraction
Vol. 3, No. 3
method in strict conformity with the Handbook method and produce parallel results. If desired, the classification could be altered somewhat to include in the headings, “Paraffins, Benzene, Toluene, and Other Aromatics,” in which case the benzene and toluene would be determined as above, the paraffins by sulfonating a sample of the dry refined oil, and other aromatics by difference between 100 and the sum of the other three. Acknowledgment
The writers are indebted to J. D. Davis of the Bureau of Mines Coal Research Laboratory for providing the series of light oils for analysis. Literature Cited
PURE TOLUENE, PER CENT BY VOLUME
Figure 2-Toluene-Xylene
Intermediates
Solvent naphtha is reported as the difference between 100 and the sum total of the benzene, toluene, and paraffin percentages. t It is clear that paraffins include only those members of the series that are in the distillate containing benzene and toluene, and small additional amounts may appear in the solvent naphtha. This arbitrary distinction was made to render the
(I) Am. Gas Assocn., Gas Chemist’s Handbook, p. 408,420 Lexington Ave., New York, 1929. (2) Colman, H. G., J . Gas Lighting, 129, 196-8 (1915). (3) Colman, H.G.,and Yoeman, E. W., J . SOC.Chem. Ind., 38, 82-3T (1919). (4) Fieldner, A. C , Davis, I. D . , Thiessen, R., Kester, E. B., and Selvig, W. A,, U. S Bur. Mines, Tech. Pafier, in preparation. ( 5 ) Harker, G , J . Proc. Roy. SOC.N . S. Wales, 60, I, 99-105 (1916). (6) James, H.W., J . SOC.Chem. I n d . , 36, 236-40 (1916). (7) Manning, A. B , and Shepherd, F. M. E., Fuel Research Board (England), Tech. Pa9er 28, 1930. (8) Sperr, F.W., and Kohr, A. A,, Gas W o r l d , 67, 146-7 (1917). (9) Thole, F.B . , J . SOC.Chem. Ind., 38, 39-43T (1919). (10) Tizard, H.T . , and Marshall, A. G., Ibid., 40, 20-5T (1921). (11) Weiss, J. M . , J. IND. END. CHEM.,10, 1006-12 (1918). (12) Wheeler, E G , and Spielman, P. E., J . Soc. Chem. I d . , 36, 396-9 (1916) (13) Wilson, D.,and Roberts, I., J . Gas Lighting, 134,225-7 (1916).
Determination of Olefin, Aromatic, and Paraffin Hydrocarbons in Neutral Oil from Coal Tar’” E. B. Kester and W. D. Pohle PITTSBURGH EXPERIMENT STATION,
u.s. BUREAUOR MINES, PITTSBURGH, PA.
A simple and rapid method for the estimation of olefins and aromatics in tar distillates has been described and shown to give reproducible results on samples of both known and unknown composition.
I
N A comparative study (7) of the behavior of coals
when carbonized under different conditions of temperature, it became necessary to scrutinize the composition of the tars formed more closely than was possible under standard routine procedures. It was particularly desired to estimate the relative amounts of olefin, aromatic, and paraffin compounds produced a t each temperature to interpret properly the secondary effects that are known to take place when carbonization is carried out at elevated temperatures. Methods Available
The method to be used must meet two requirements: First, it must be a reliable method of approximation; second, it must not be too involved or too lengthy an operation. Close limits of accuracy are not to be expected from any method because of the wide diversity of compounds in tar distillates. I n the petroleum industry such determinations have been of great interest and importance. Many methods and varia1 Received December 23, 1930. Presented before the Division of Gas and Fuel Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931. 9 Published by permission of the Director, U. S. Bureau of Mines. (Not subject to copyright.)
tions thereof have been tried and used, some of which have been shown to be subject to gross errors. In 1925, Ormandy and Craven (IS) suggested treatment of the oil with 80 per cent sulfuric acid, followed by a distillation to the end point of the original oil as a method for the determination of the olefins in the oil. Kattwinkel’s method (10) consisted in first removing both olefins and aromatics of a benzene distillate with 3 volumes of a mixture of 30 grams of phosphosus pentoxide in 100 cc. of concentrated sulfuric acid, and then estimating the olefins alone from a fresh sample of oil with concentrated sulfuric acid containing 5 grams of boric acid per 100 cc. That this method is far from accurate may be seen from Table 9 on page 357 of the reference given. By the method of Arnold (g), who investigated the olefin and aromatic contents of primary tars, the former group was estimated by removal with a saturated mercuric acetate solution, while the total olefins and aromatics were determined by treating a fresh sample of the fraction under study with two volumes of methyl sulfate. No data on synthetic mixtures are given. .Brame and Hunter (3) investigated the composition of cracked distillates. Their determination of olefins depended on the per cent loss to 85 per cent sulfuric acid in a Babcock
‘
INDUSTRIAL AA-D ENGINEERIA'G CHEMISTRY
July 15, 1931
bottle, and of aromatics on the aniline-point method of Tizard and Marshall (15). They then fractionated the original oil, brominated each fraction, distilled to remove unbrominated compounds, and recovered the unsaturates by debromination with the zinccopper or aluminum-mercury couple. The unbrominated portions were treated with 4 volumes of 98 per cent sulfuric acid and again with 2 volumes to ascertain the aromatic content. The method used by Mighill (18) for estimating olefins in a gas oil consisted in treating a volume of the oil with twice its volume of concentrated sulfuric acid. The mixture was shaken in a bath of ice water during the treatment and then centrifuged, the reduction in volume representing the olefins. The aromatic content was obtained by treating the unattacked oil with fuming nitric acid. KOdata are given on known mixtures. In this procedure the use of concentrated sulfuric acid would remove some a t least of the aromatics in addition to the olefins. The Bureau of Mines laboratory has found that a petroleum distillate containing 13.5 per cent aromatics when subjected to this treatment suffered a loss of 18.5 per cent of its aromatic content. Egloff and Morrell (4) used 80 per cent sulfuric acid in their method for determining olefins because it has little effect on the aromatics. The unattacked oil is washed and distilled to the end point of the untreated oil, the total loss in volume from the acid treatment and the distillation being taken equal to the volume of olefins present, from which the percentage is calculated. The aromatics are determined by treating the distillate with a special nitrating mixture. The volume of nitrated compounds so obtained is multiplied by a factor which gives the percentage of aromatics present. The nitrolayer method for the determination of aromatics in tar distillates, however, is not accurate in that it can be used only in the case of limited concentrations of aromatics (14). Also, the volume of the nitro layer varies with the particular aromatics present (5). The results obtained by Egloff and Morrell on synthetic mixtures containing benzene, toluene, amylene, octylene, and paraffins from gasoline treated t o remove the olefins and aromatics, are shown in Table I. of Olefins and Aromatics according to Egloff and Morrell SAMPLE 1 SAMPLE 2 SAMPLE 3
Table I-Determination
Found
Olefins Aromatics
Found
Found
%
%
%
%
%
%
12.5 12.5
16 0 12.7
16 6 16.6
21.2 10.9
20.0 20.0
18 2 22 7
Lomax and Pemberton (11), following the suggestion of Ormandy and Craven (15), treated the low-boiling fractions of cracked spirits with 80 per cent sulfuric acid, distilling the unabsorbed oil to the original end point. The distillate was treated with 98 per cent sulfuric acid and again distilled to the original end point. The residue remaining after this distillation was explained on the grounds that the initial treatment with 80 per cent sulfuric acid did not completely absorb or polymerize the olefins present. I n their work on a cracked spirit having a maximum boiling point of 95" C., Lomax and Pemberton found that the residuum after the final distillation amounted to as much as 4.9 per cent of the original oil. Similar results appeared in the 95-125' and 125-170' fractions. Howes (9) points out that in the 80 per cent sulfuric treatment, some polymers may form which will not have a boiling point high enough to cause them to remain with other polymerized products in the residuum from the distillation, and the calculations for the olefins will be correspondingly low. Griffith (8) treated tar distillates with 2 volumes of 80 per cent sulfuric acid to remove the olefins, washed with water, caustic soda, and finally with water, and distilled to the end
295
point of the original oil. The difference in volume before and after this treatment was considered due to the removal of unsaturated hydrocarbons. A portion of the distillate from this treatment was then shaken with 2 l / 2 volumes of 96 per cent sulfuric acid, and from the contraction the percentage volume of aromatics was calculated. No data are given on known mixtures. It is rather doubtful if 96 per cent sulfuric acid is strong enough to remove all the aromatics, because this laboratory has found that a sample of pebroleum distillate containing 13.5 per cent aromatics lost only 70 per cent of its aromatic content on 5 minutes' shaking with the required volume of 96 per cent acid. The mixture was warmed during agitation. The recommendation was made by Griffith that all light oils boiling below 180" C. should be removed and examined separately. The latest and most accurate method for the olefin and aromatic determination on petroleum distillates is that of Faragher, Morrell, and Levine (5). In this method the total olefins and aromatics are first determined by treatment with 91 per cent sulfuric acid, followed by a distillation to a point 5" above the original end point of the oil, and a further treatment with 98 per cent sulfuric acid. The total reduction in volume represents the total olefins and aromatics. The latter alone are then obtained by first removing the olefins from B fresh sample of oil with sulfur monochloride, nitrating with a special nitrating mixture, and removing the aromatic nitro compounds with 95 per cent sulfuric acid. Tables of analyses of known mixtures are gi-c.en, showing that the method will give accurate results on a petroleum oil whose total olefin and aromatic content does not exceed 50 per cent. However, if this total is above 50 per cent, the error in the olefin percentage, which a given error in the aromatic content of the olefinfree oil will cause, increases as this total rises toward 100, if the ratio of aromatics to olefins is high as in tar distillates. Few, if any, of the neutral oils of coal tar contain less than a 60 per cent total of olefins and aromatics and, therefore, such a method would be likely to lead to appreciable errors. Furthermore, sulfur monochloride produces so viscous a solution when shaken with tar distillates that the errors introduced from losses in handling become large. It also reacts with naphthalene and anthracene. The Egloff and Morrell method (4)might have proved satisfactory except that the nitro layer becomes miscible with the paraffins when the concentration of the former is too high or too low. If the nitration is then followed by a treatment with 95 per cent sulfuric acid to remove the nitro compounds, the acid layer turns so viscous and gum-like that an accurate separation is impossible. Method Adopted
One hundred cubic centimeters of neutral oil are shaken with 300 cc. of 80 per cent sulfuric acid for 5 minutes and permitted to stand 30 minutes before the acid is drained off. It is then allowed to stand another 30 minutes in case additional acid should separate, which is also drawn off. The reduction in volume, R1, is recorded and the oil distilled to a point 5' higher than the end point of the untreated oil. To the volume of distillate is added a small correction factor which may be considered a constant for oils of a given boiling range and which is computed in the earlier runs from the total volume distilled, minus the total volume of distillate and residuum. After this correction is made, the volume reduction, Re, from distillation is determined, computed to the whole oil basis, and added to R1. From the sum, the percentage of olefins is obtained. Twenty cubic centimeters of distillate are then shaken with 60 cc. of 98 per cent sulfuric acid for 5 minutes and allowed to
ANALYTICAL EDI l'IOIV
296
___-_ Calcd.
%
%
1
31.8
31.6 31.1 37.4
Found
37 2 16.3 33 8 35 0 19 95 24 0 37 2 16 3 16 3 a Faranher. Morrell, and periment w s s impossible. 2 3a 4 5 6 7 8 9
T a b l e 11-Analysis of S y n t h e t i c M i x t u r e s AROMATICS------
___-_
OLEFINS------
ANALYSIS
Vol. 3, s o . 3
Diff.
% -0.3 -0.7 $0.2
Calcd.
Found
PARAFFINS
Diff.
Calcd.
NAPKTHENES
AND
Found
E N DPOINT OF
Diff.
%
%
%
%
%
%
45.2
46.3 46.9 36.6
+1,; $1. I 0.0
23.0
22.2 22.0 26.0
-0.8 -1.0 -0.2
PARAFFIN
OILUSED % 240
36.6 26.2 205 37.2 46.5 240 32.6 -1.2 36.4 t1.7 31.0 34.7 31.5 240 -0.5 -1.1 33.9 +1.4 21.3 43.4 44.8 21.6 -0.3 240 46.4 -0.95 +0.1 19.0 34.6 240 +0.85 45 55 34.5 -0.6 -0.3 23.7 42.1 +0.9 34.2 41.2 34.8 240 $1.1 -1.0 36.5 38.3 -0.1 25.2 36.6 26.2 240 -1.3 38.6 15.0 $1.4 46.4 46.5 -0.1 240 37.2 -1.0 15.3 $1.0 38.2 46.5 0.0 37.2 46.5 Levine method caused polymerization during the sulfur monochloride treatment t o such an extent t h a t continuation of ex
settle as in the 80 per cent treatment. From the contraction, 0.19 cc. is deducted in the case of known mixtures, because this represents the solubility of the paraffins in 98 per cent sulfuric acid. The corrected value, is then computed to the whole oil basis from the equation
producible is seen from the duplicate determinations on samples 1, 9, and the identical pair, 2 and 8. On the distillate of a 1000" tar having s maximum boiling point of 350" C., an analysis in duplicate gave the results shown in Table 111. T a b l e V-Olefins
where Tis is volume of oil used for the aromatic determination, and R:, the volume of aromatics in the original sample. Table I1 lists the results obtained in the analysis of known mixtures. Analysis of sample 2, containing benzene, toluene, xylene, paraffins, and cyclohexene, was made after the Faragher, Norrell, and Levine method, but when it was applied to sample 3 which contained styrene, indene, naphthalene, xylene, and paraffins, polymerization became so pronounced that even an approximate separation into layers could ngt be obtained. Knowns of the same composition as samples 2 and 3 appear in 8 and 9, respectively, and were analyzed according to the procedure just described, as were also samples 1, 4, 5, 6, and 7. The latter group was made up from cyclohexene, indene, styrene, benzene, toluene, xylene, naphthalene, and a paraffin oil having an end point of 240" C. T a b l e 111-Analysis of Distillate of 1000a T a r SAMPLE OLEFINS AROMATICS TOTAL c/, ?4 % ," 1 27.4 72.1 99:5 2 26.1 72.8 98.9
TEMP. AND
RUN
--_
.mno B-12 Bill 600
B-13 700' B-10 B-9 Rnna
B-2 B;3 900 B-4 B-5 B,-S 1000
and A r o m a t i c s in N e u t r a l Oil of Tar Distillate, R o d a Series (Max distillation temp., 300' C.) Av. OLEAROOLEFINS MATICS TOTAL FINS
%
%
%
9.4 10.2
53.4 54.7
62 8 64.9
14.1
67.8
81.9
16 3 15 1
74 4 78 5
90 7 93.6
17.1 16.4
77.5 76.0
94 6 92.4
16.2 11.5 12.9
80.3 84.8 83.7
96.5 96.3 96.6 98.7 98.8 -99.5
15.7 83.0 B-6 18.2 80.6 B-15 16.6 82.9 B-50" 1100 18.4 80.0 B-7 19.3 79.8 B-17 15.5 81.8 B-16 a Mixture of Roda, Dunhar, and
Av. AROMATICS
%
Av TOTAI
%
%
9.8
54 0
63 8
14.1
67.8
81 9
15.7
76 4
92 1
16.7
76 7
93.4
13.5
82.9
96 4
16.9 16.6
81.8 82.9
98 7 99 5
98.4 99.1 17.7 80.5 98 2 97.3 Derby not computed in average.
I "
T a b l e IV-Olefins TEMP.AND
and A r o m a t i c s in N e u t r a l Oil of Tar Distillate,
E l k h o r n Series (Max. distillation temp., 300' C.) RUN OLEFINS AROMATICS TOTAL
500" A-17 600'" A-15, 16 700": A-7 800' A-12 900'' A-2 1000°' A-21, 22 1100': A-5
%
%
%
12.5 13.1 18.2 18 9 18.6 16.0 15.6
50.3 56.0 74.5 78.3 80 6 82.8 83.7
62.8 69.1 92.7 97.2 99.2 98.8 99.3
and A r o m a t i c s , E l k h o r n Series T a b l e VI-Olefins (Percentages on dry-tar basis; max distillation temp., 300' C ) NAPHTHENES TOTAL TEMP. AND OLEFINSAND AND R U N OLEFINS AROMATICS PARAFFINS AROMATIC
% 500' A-17 600': A-15, 16 700°, A-7 800' A-12 900" A-2 1000°: A-21, 22 llOOo, A-5
4 6 4.6 7.0 6 3 5 7 3 5 2 9
% 18 19 28 26 24 17 15
4
4 5 1 7 9 5
% 13 10 2 0 0 0 0
6
7
8 9 3 2 1
% 23 24 35 32 30 21 18
0 0 6 4 4 4 4
Analysis of Neutral Oil from Tar Distillates
The mixed-type compounds, such as styrene and indene, were calculated as olefins, as they are removed with the purely olefinic substances by the initial treatment with 80 per cent sulfuric acid. That they are regarded as aromatics by some is recognized by the writers, who admit the deficiencies of the method in failing to classify them as a separate group. It will be observed that the olefins as a rule are consistently low. This is possibly owing to incomplete polymerization of the olefins by 80 per cent sulfuric acid. The high aromatic contents are a result of this and the solution of certain paraffins in the concentrated acid or in the acid solution of aromatic sulfonic acids. This method of analysis, although not so accurate as might be desired, yields a fair estimate of the olefins, aromatics, and paraffins in a tar oil, which was the end sought. As a routine analysis in the survey of the gas-, coke-, and by-product-making properties of American coals, it consumes a minimum of time and gives consistent results. That these results are re-
Analyses were carried out on the neutral oils in the tar distillates from the carbonization tests on Roda (1) and Elkhorn (6) coals, the series ranging from a 500" C. carbonization temperature to 1100" C. In some cases less than 100 cc. of neutral oil were available. No correction for the solubility of the paraffin fraction in the 98 per cent sulfuric acid was made because the composition of the tars vary widely from one carbonization temperature to the next, and an extremely small quantity of paraffins is available for running these solubility determinations from the neutral oils of high-temperature carbonization tests. The correction factor for the neutral oil of a low-temperature tar obtained from a carbonization of Roda coal in a rotating Fischer retort a t 500" C. amounts to 0.5 cc. If this is applied to all the neutral oils in the.series, the aromatic content as found would be lowered by about 2 per cent of the values given and the paraffin content correspondingly raised.
July 15, 1931
INDUSTRIAL AND ENGINEERING CHEMISTRY
Tables IV and V give the percentage of olefins and aromatics in the neutral oil of the two series of tars, the difference between the and '0' being the percentage Of paraffins and naphthenes. Tables VI and VI1 show these percentages computed to a dry-tar basis.
297
Acknowledgment
The codperation of J. D. Davis of the Bureau of Mines Coal Research Department in providing the series of tars for analysis is hereby gratefully acknowledged. Literature Cited
Table VII-Olefins and Aromatics, Roda Series (Percentages on dry-tar basis; max. distillation temp., 300' C.) TOTAL Av. Av. NAPH- OLENAPH- OLETEMP, AND RUN 600' B-12 B-11 600" B-13
. B-10
mynv o
B-9 800 B-2 B-3
-..B-4
anno
OLE- ARO-
THENES AND
FINS
THENES
FINS
AND AV. AV. AND AND PAR- ARO- OLE- ARO- PARAF- ARO-
FINS
MATICS
%
%
%
%
%
FINS
MATICS
%
%
3.2 3.9
18.2 21.1
12.6 13.6
21.4 25.0
%
5.0
23.9
6.3
28.9
3.6
19.6
13.1
23.2
5.0
23.9
6.3
28.9
5.3 5.1
24.1 26.4
3.0 2.1
29.4 31.5
5.5 5.6
24.7 25.9
5.2
25.3
2.5
30.5
1.7 2.6
30.3 31.5
4.8 3.4 3.6
23.8 25.3 23.4
5.6
25.3
2.1
30.9
1.0 1.1 0.9
28.6 28.7 27.0
3.9
24.2
1.0
28.1
5.0 4.2
24.1 21.0
0.4 0.1
29.1 26.2
4.8
21.5
0.5
26.3
AFFINS MATICS
B-5 B-8 10000 4.8 25.3 0 . 4 30.1 B-6 5 . 2 23.0 0 . 4 28.2 B-15 B-20" 0.1 25.2 4 . 2 21.0 11000 B-7 4 . 7 20.2 0 . 4 24.9 0 . 3 28.7 5.6 23.1 B-17 4.1 21.3 25.4 0.7 B-16 a Mixture of Roda, Dunbar, and Derby
FINS MATICS
not computed in average.
(1) Am. Gas Assocn., Rept. of Sub-committee on Survey of Gas- and Coke-Making Properties of American Coals, Proc. A m , Gas Assocn., 1930. (2) Arnold, H., 2.ongew. Chem., 36, 266 (1926). (3) Brame, J. S. S., and Hunter, T. G., J . Inst. Petroleum Tech., 13, 794 (1927). (4) Egloff, G . , and Morrell, J. C., IND.ENG.CHEM.,18, 354 (1926). (6) Faragher, W. F., Morrell, J. C., and Levine, I. M., IND. ENQ.CHEM., Anal. Ed., 2, 18 (1930). (6) Fieldner, A. C., Davis, J. D., and Reynolds, D. A., IND. END. CHEM., 22, 1113-23 (1930). (7) Fieldner, A. C.,Davis, J. D., Thiessen, R., Kester, E. B., and Selvig, W. A., "Survey of Gas-, Coke- and By-product Making Properties of American Coals." Bur. Mines, Tech. Paper. In preparation. (8) Griffith, R. H., "The Analysis of Gas Oils and Hydrocarbon Oils from Tars," Am. Gas Assocn., Rept. of Sub-committee on Evaluation of Gas Oils, p. 9, 1930 Convention; J. SOC.Ckem. l n d . , 48,2521' (1929). (9) Howes, D. A., J . Insl. Petroleum Tech., 16, 54 (1930). (10) Kattwinkel, R., Brennstof-Chem., 8, 353-358 (1927). (11) Lomax, E. L., and Pemberton, E. S., J. Inst. Petroleum Tech., 12, 57 (1926). (12) Mighill, T. A,, A m . Gas Assocn. Proc. 146s (1927). (13) Ormandy, W. R., and Craven, E. C., J . Insk. Petroleum Tech., 11, 533-6 (1925). (14) Riesenfeld, E. H,, and Bandte, G., Erdd! und Teer, '2, 491 (1926). (15) Tizard, H. T., and Marshall, A. G., J. Soc. Chem. I n d . , 40, 20T (1921).
Scorching, and Other Plasticity Changes in Rubber Compounds on Heating' E. 0. Dieterich and J. M. Davies PHYSICAL RESEARCH LABORATORIES, THE13. F. GOODRICH COMPANY, AKRON,OIiro
A method is described which employs the Goodrich It does not appear that this p e r a t u r e coefficient of plastometer for detecting the initial stages of Vulmethod has any advantages in plasticity of compounded canization of u m ~ r e drubber compounds. Reduction economy of time and material in Plasticity, at stmdard room temperature, of test over plastometric measurerubber stocks with the Goodrich plastometer ( I ) , it was pieces previously heated for various intervals at selected ments such as used by B a l l observed that frequently an temperatures is used to determine the degree of cure (a) and adopted by several abrupt drop in plasticity Valand thus to estimate safe operating temperatures and laboratories, nor does it afford d exactness possible with ues occurred at temperatures periods. Examples of the application of the ~ ~ ~ t h o the surprisingly low as compared to a variety of ComPotlnds are Presented- Other ternt h e l a t t e r m e t h o d . As with those of factory cures. Perature effects, such as heat stiffening and softening, pointed out by other observers This suggested that the inwhich have not Previously been reported, are illustrated. (4, the Williams plastometer is less sensitive than the Goods t r um e n t m i g h t easily be adapted t o the estimation of the scorching tendencies of differ- rich instrument, so we might expect the latter to bring out ent compounds. This note will describe the methods adopted small differences which would be obscured in tests on the for demonstrating the changes in plasticity which take place former. Moreover, since the Goodrich plastometer measures a t temperatures corresponding to those of mixing mills and two factors, softness and retentivity, the exact nature of the calenders. Since it is intended only as a description of ex- changes produced by heating are easily visualized. It is perimental methods the general nature only of the stocks used generally, but not invariably, true that both the softness in illustration will be given; detailed reports of the behavior factor and the retentivity vary in the same way with difof accelerators, retarders, etc., are planned for future publica- ferent treatments of the same compound. Three methods have been used in this study. tion. METHOD1-The temperature coefficient of plasticity is The literature on rubber contains frequent references to methods of measuring relative scorching of accelerated mixes. measured. The differences in the curves for compounds This has been reviewed by Thies (3) who proposed that the which set up at relatively low temperatures and those which relative solubilities of compounds a t the end of various do not are shown in Figure 1. The sharp break in curve 3 periods be used as an index of the degree of cure and thus at a temperature near 90" C., and the marked decrease in afford a means of comparing the activities of accelerators. plasticity above this temperature are evidence that the stock has been cured fairly tight in the preheating time of 30 Presented before the Division of Rubber 1 Received April 7, 1931. the time required to that the test pieces Chemistry at the 81st Meeting of the American Chemical Society, Indianapouniformly warmed throughout. The other two curves, one lis, Ind.. March 30 to April 3, 1931.
I
N THE study of the tem-
"*
