Molecular Weights of Viscous Petroleum Fractions Cryoscopic molecular weights have been determined on Midcontinent and Texas Coastal crude distillates having viscosities between 36 and 150 Saybolt Universal seconds at 210" F. A characteristic curve is obtained for each crude by plotting molecular weight against viscosity at 100" F.,and the difference between the molecular weight-viscosity relations of samples from these two
sources is used as the basis for establishing the effect of the slope of the viscositytemperature curve on molecular weight and subsequently formulating a general correlation of molecular weights with viscosities at 100" and 210" F. This correlation is thought to be superior in scope and accuracy to the one developed by Fenske, McCluer, and Cannon (3), and agrees satisfactorily with published data.
R
ECENTLY Fenske, McCluer, and Cannon (3) published a correlation expressing the molecular weights of petroleum fractions boiling within the light lubricating oil range in terms of viscosity and viscosity index. The present investigation was undertaken to obtain a similar correlation based on fractions having a somewhat wider boiling range and widely different viscosity-temperature characteristics. The molecular weights of distillate fractions from two crudes with a relatively large difference between their viscosity-temperature relations were determined by a cryoscopic method. The data were analyzed to show the direct relation between viscosity at 100" F. and molecular weight for fractions from each source, and from the information obtained from these correlations an attempt was made to establish the effect of the viscosity-temperature function on the molecular weight.
J. R. KEITH The Texas Company, Port Arthur, Texas L. C. ROESS The Texas Company, Beacon, N. Y.
For cyclohexane the correction proportional t o CY may be neglected and the equations
The molecular weights were determined by the cryoscopic method described in detail below. The freezing point constants of the benzene and cyclohexane which were used as solvents were determined from the most accurate data on heat of fusion available (6, 7, 8). These data were substituted in the following equation (easily derived from reference 9):
mol. weight of solute mol. weight of solvent mass of solute, grams mass of solvent, grams freezing point depression, c = -MiRTo2
where R
To A0
= = = = =
=
freezin point of solvent,
O
=:
r/ll 19,960 (heat of fusion data from reference 8) ml AT
(3)
Apparatus The bath container for the cryoscopic apparatus consisted of a battery jar 6 inches (15.2 cm.) in diameter and 9 inches (22.9
om.) high. The air jacket tube was 2 inches (5.1 cm.) in diameter and 8 inches (20.3 cm.) long; the freezing point tube which contained the solution was a standard 1-inch (2.5-cm.) test tube. An ice-water mixture was used in the bath, ice being added from time to time to maintain the desired temperature differential. Stirring was obtained by bubbling air through the bath at a constant rate. The solution in the freezing point tube was stirred by a nichrome wire ring actuated from a vacuum-type windshield wiper, the speed being adjusted to give about seventy-five down strokes per minute. The apparatus in this form provides a freezing point tube fitted with a device t o provide constant stirring, a 0.5-inch (1.3-om.) air jacket for insulation between the freezing point tube and bath, and an ice-water bath provided with a stirring device to assist in maintaining a constant temperature.
K.
point, cal. per mol.
C (9 = molar sp. heat of liquid solvent at TO ((4 = molar sp. heat of solid solvent at TO
The final equation for benzene is:
- 56AT) (for benzene)
Ma
This equation was checked by determining the molecular weight of a sample of resublimed naphthalene, obtaining the experimental value 128.7 against the true value 128.1. The solvents used for this work were carefully purified in order to avoid errors in the freezing point constant due to the presence of impurities. The benzene froze a t 5.5" C. and the cyclohexane at 6.2' C.
= latent t e a t of fusion of solvent at its freezing
MZ = -?%(5120 mi AT
m2 20,940 (heat of fusion data from reference 7 ) m1AT
M Z = ml 5 AT 20,500 (for cyclohexane)
c.
= gas constant per mol.
=i
are obtained. Since there was no logical basis for differentiation between the heat of fusion data given in references 7 and 8, the mean of the two equations was arbitrarily chosen:
Determination of Molecular Weight
where MZ MI mg ml AT
Ma
(2) 460
APRIL, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
The bath temperature was read on a thermometer graduated in 0.1" C. and was maintained constant to within 10.1" C. for each determination. The bath temperature was maintained at 2.5" C.below the freezing point of the solution. Although this temperature control was not critical for benzene, it was found that the freezing point of cyclohexane solutions was influenced by relatively slight changes in bath temperature, particularly if these occurred during or just before the freezing period. The Beckman thermometer in the freezing point tube was read by means of a low- ower magnifier. Twenty-five milhters of solvent were used in all determihations; this amount was sufficient to submerge the stem of the Beckman thermometer by a t least 1cm. The travel of the stirrer was limited to prevent it from breaking the liquid surface. Otherwise, in the case of cyclohexane the liquid splashed on the tube walls was likely to freeze and initiate freezing of the solution without supercooling. All waxy oils tested were heated to dissolve the wax before any sample was taken. Hot samples were weighed into thin-walled glass cups; the cup was added to the solution and broken with the stirrer. This method ensured against any change in composition or loss of sample. All molecular weight determinations were made with about 2 grams of magnesium perchlorate added to the solvent to serve as a drying agent. Addition of this material raised the freezing oint of the solvent slightly, but reduced the supercooling with genaene from 2-3" C. to about 0.4" C.
Freezing Point Determination Figure 1 shows the method by which the freezing point of the solution was obtained from the time-temperature curve. Point B, the maximum temperature reached after freezing begins, is determined by the rate of cooling of the solvent, the rate a t which heat is added by the stirring, and the rate a t which the freezing solute gives u p heat to the solvent after
1 J/Np
-c
FIGURE 1. REPRESENTATIVE TIMETEMPERATURE CURVESFOR A SOLUTION OF PETROLEUM DISTILL AT^ IN PURESOLVENT
461
point A has been reached. I n order to minimize the difference between equilibrium temperature B and the true freezing point, (1) the supercooling should be small, (2) the heat insulation of the solvent from the bath should be large, and (3) the temperature difference between the bath and solvent should be small. The first requirement is essential for reproducible results, since with large supercooling the concentration a t B becomes appreciably different from the initial concentration. The second and third requirements are of most importance, since preliminary work showed that, by reducing the insulation between the solution and bath and increasing the temperature difference, the line BC became quite curved for cyclohexane solutions so that the freezing points were inconsistent. Benzene solutions, however) were not greatly affected by the freezing conditions. This method differs essentially from the procedure which apparently was originally applied by Steed (IO) and further developed by Gullick (6). Their method reduced considerably the insulation between the bath and solution, used a larger temperature difference between the bath and solution, and in general also used greater supercooling. Instead of reading only points A and B on the Beckman thermometer, a cooling curve was plotted as a function of time, and the freezing point was taken as point D on Figure 1. Actually, if extrapolation were justified, it would appear to be more reasonable to take point 0 rather than D as the true freezing point. I n this investigation) however, line BC was so nearly horizontal that the temperature difference between points B and 0 was less than the experimental error of 0.001" to 0.002' C., and point B is taken as the true freezing point. It is true that the measurement of molecular weight involves differences in freezing points rather than determination of true freezing points; if the same errors were inherent in each determination they would cancel and the result would be accurate. It appears probable that these differences in procedure are minor except where the slope of line BC differs appreciably from the horizontal. In the present investigation, as in all previously published ones, the calculated molecular weight varied with the concentration of the solute in the solvent. Most of the samples seemed to associate in benzene but to dissociate in cyclohexane. It was necessary, therefore, to plot the apparent molecular weight against the mole per cent of solute and extrapolate this line to zero per cent solute in order to obtain the molecular weight at infinite dilution.
TABLE I. PROPERTIES OF DISTILLATES Sample No.
0
8:
724 725 726 727 4697 4698 4699 4700 4701
0.8509 0.8805 0.9013 0.9212 0.8708 0.8811 0.8978 0.9153 0.9273
2655 2654 2657 3002 2656 3001 2659 2658 2660 2661
0.9047 0.9111 0.9200 0.9273 0.9340 0.9365 0.9371 0.9478 0.9632 0.9752
Saybolt Universal Viscosity H H Vis-Detd. Viscosity Slope at at oosity Benlooo F. 210' F. Factor 100' F. 210' F. Index zene Midcontinent 42.0 225 3i:il 95.0 256 -1 325 255 389 245 330 54.0 424 144 97 1540 101 505 242 263 554 77.8 35.6 59.0 167 255 -88 276 --8 256 38.6 90.0 247 325 244 57.5 390 404 166 ii:5 446 1200 248 86.0 513 488 71 240 243 2950 138 604 545 69.7 302 Av. 249 Texas Coastal 44.0 33.5 221 54.0 34.6 ii4 242 72.0 35.5 ioi 209 -92 257 86.0 36.5 299 240 -59 260 3 9 . 2 300.4 303 4-2.6 275 139 146 39.5 301 309 277 169 40.5 300 325 287 386 47.4 303 403 100 -40 317 1.600 71.0 300 507 207 -62.3 350 12,460 15.7 314 621 317 -149 413 Av. 302
...
...
...
... ... ...
...
Outside of recommended range of Equation 7A.
... ...
+2f
... ... ...
... ... ... ...
Mol. WeightCyclohexane Av. 231 323 430 549 284 324 44 1 512 604
228
222 242 259 268 287 287 292 316 348 405
221 242 258 264 281 282 289 316 349 409
324
427 552 280 324 443 513 604
Predicted Mol. Wt. FigEquaure tion 3 7A
iii
426 562
...
330 436 503 6@4
... ... ... 265
281 282 288 314 350 409
... *..
404 483 a
...
iiii
462" 511a
... ... ... ... ... ... ,..
345 395 4290
Deviation, % Value Value from W g - from Equsure tion 3 7A
... ... --12.5 5.4
+i:il9 -0.24 +1.81 +1:85 -1.58 -1.95 0.0
... ...
.
...
- ... 0.8 -10.0 -15.4
... ...
0.0 0.0
... ... ... ...
0.0
+9.4 +4.89
+b:iS
-0.35 -0.63 +0.28
+i:is
462
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 29, NO. 4
TABLE11. COMPARISON OF MOLECULAR WEIGHTDATAWITH PREDICTED VALUESFROM FIGURE3
-Density60° F. Humble A orude: Furfural raffinate Filtered through clay Original lubricating dist. Acetone extract Furfural extract Mirando crude, lubricating dist.: Acetone raffinate, acid treated and contacted Acid treated and contacted Acetone extract Furfural extract Columbia crude, lubricating dist.: Furfural raffinate Acetone raffinate, contacted Acetone extract Furfural extract Pa. crude, residuum: Furfural raffinate Furfural raffinate, dewaxed and contacted Acetone extract Midcontinent dist.: Furfural raffinate Furfural raffinate, dewaxed, acid treated, and contacted Original lubricating dist. Outside of recommended range of Equation 7A.
Saybolt Universal Viscosity VisViscosity Slope cosity 130° F. 100' F. 210" F. Factor Index
0.9226 0.9370 0.9410 0.9605
0.8984 0.9123 0.9163 0.936 0.9626
506 444 498 468 1445
0.9410 0.9486
0.9166 0.9241 0.9358 0.9536
0.9205 0.9260
Detd. Mol. Wt.
Predicted Mol. Wt. From From Fig- Equaure tion 3 7A
Deviation, Value VaE from from FigEquaure tion 3 7A
56.3 51.7 53.0 50.4 64.5
274.7 48 284.2 18 285.6 12 296.2 -20 314.0 -101
372 347 337 315 337
375 353 354 331 307
403 375 378 361 376
+0.80 +1.73 +5.05 +5.07 -8.90
+8.30 +8.06 +7.10 +14.6 $11.6
620 477 513 935
54.0 50.4 50.0 56.0
297.0 298.0 306.3 317.0
-25 -24 -55 -110
341 316 312 322
333 328 314 296
372 361 353 362
-2.35 +3.80 4-0.64 -8.07
+9.1 $14.2 4-13.1 +12.4
0.8973 0.9019 0.9466 0,9597
512 639 908 1645
54.5 58.3 58.0 66.5
297.7 26 278.7 24 305.8 -64 315.3 -123
365 377 329 344
366 370 316 310
386 396 372 373
0.0 -1.85 -3.95 -9.90
+5.75 -I-5.04 +13.1 +8.44
0.8830 0,8882
. ...
0.8599 0.8659 0.9062
905 1060 908
91.8 95.8 72.1
218.9 224.8 259.5
110 103 57
585 594 420
592 591 448
490a 492" 437"
i-1.20 -0.50 4-6.67
-16.3 -17.2 +4.05
0.8930
0.8688
580
67.2
240.4
95
485
472
442"
-2.68
-8.88
0.8995 0.9140
0.8759 0.8902
808 963
72.2 76.0
251.2 254.3
74 66
491 472
465 466
444a 448"
-6.30 -1.27
-9.50 -5.10
....
.... ....
.... 0.9842
FIQURE2. RELATION OF MOLECULAR WEIGHTS TO SAYBOLT VISCOSITYAT 100" F. ON MIDCONTINENT AND UNIVERSAL TEXASCOASTAL CRUDEDISTILLATES
Available data on the solubility of wax in the solvents indicated that, a t the maximum concentration used in any determination, the wax in the oil would be just completely dissolved in the benzene, whereas in cyclohexane the high freezing point constant allowed the concentrations to be kept small enough to be well below the solubility limit.
Description of Samples The samples used in this work were chosen with a particular view to establishing the molecular weight-viscosity relations for all distillate stocks from two representative crudes. Since
~
FIQURE3. RELATION OF MOLECULAR WEIGHTSOF PETROLEUM FRACTIONS TO SAYBOLT VISCOSITIES AT 100' AND 210' F.
the distillates from these two crudes were dissimilar in viscosity-temperature characteristics, it was anticipated that the magnitude of the effect of viscosity-temperature slope on the molecular weight also could be estimated. Nine distillates from a Midcontinent crude were obtained from plant crude pipe stilling equipment, and ten samples of Texas Coastal distillates were obtained from a vacuum distillation operation. Precautions were taken to avoid contamination, but the fractionation was that normally maintained. Table I shows physical properties of these samples as well as the molecular weight data. Viscosities were run at 68", 122", and 212' F. on a standardized Vogel-Ossag viscometer
APRIL, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
and-at loo", 130°, and 210" F. on a standardized Saybolt instrument. These data were plotted on the A. s. T. M. viscosity-temperature chart, and average lines drawn to establish the mean viscosities reported in Table I.
Correlation of Data The viscosity data shown in Table I are particularly significant in that each group of samples has, within itself, a constant viscosity-temperature relation. The viscosity-temperature function used to express this relation was the viscosity slope factor (V. S. F.) of Bell and Sharpe (1): (4)
where t and t1 are any two temperatures, and the H scale is an arithmetic scale superimposed on the viscosity scale of the A. S. T, M. viscosity-temperature chart in such a manner that where to
HID 870 log log
= V k =
Vkto
+ 0.8) + 154
any temperature kinematic viscosity, centistokes
(5)
463
by definition, V. S. F. = Hi000 - H ~ I O O by assumption, mol. wt. = A V. 5. F. B
+
(44
(6)
where A and B are constants depending only on the viscosity a t some fixed temperature, in this case 210" F. Combining Equations 4A and 6, mol. wt. = A H l o o o
- A H2100+ B
=
+
A HIOOO C
(7)
since Hzloois constant. Equation 7 shows that the molecular weight is a linear f unc~ constant viscosity a t 210" F. Corresponding tion of H l o ofor to this constant viscosity, there will be a value of H2100, say H'zloo,from which the values of H'looofor the two crudes can be obtained by adding to it their respective slope factorsi. e., 302 for the Texas Coastal and 249 for the Midcontinent distillate. Since the two curves on Figure 2 are experimental relations between H l o o o and molecular weight, it is clear that the intersection with each curve of the line (Equation 7) for the particular 210" F. viscosity associated with H'zloo will be given by the point on each curve for which Hlooo = H'IOOO for that crude. In this manner all the diagonal straight lines on Figure 3 were obtained. It is also possible by a similar procedure to locate lines of constant viscosity slope factor or viscosity index on Figure 3. The molecular weight data in Table I1 were compared with the final correlation to check the accuracy of the original conclusion that the viscosity slope factor varied linearly with the molecular weight. The determined viscosities of these samples were used to obtain the predicted molecular weights included in Table 11. I n spite of the widely different processes employed by which products of greatly different properties were obtained, and the fact that the molecular weights had been determined by a slightly different procedure, the agreement between predicted and determined molecular weights is rather satisfactory.
and the K scale is a n arithmetic scale superimposed on the temperature scale of the same chart in such a manner that 210" F. has a K value of 0.0, and 100" F. a K value of 1.0. Since both H and K values can be obtained directly from tabulations (1) rather than by calculation, this method offers a convenient means for expressing directly the arithmetic slope of any straight viscosity-temperature line on the A. S. T. M. chart. Table I also shows that the viscosity slope factors are apparently dependent only on the nature of the, crude from which the samples were obtained and are independent of the actual viscosities and molecular weights of the distillates. I n Figure 2 the molecular weight data are plotted against H l O O o;~ . the corresponding Saybolt Universal viscosity a t 1C)O" A smooth curve can _ _F . . 3 also shown for convenience. be drawn through the data for each set of samples, but the location of the two lines on these coordinates indicates a considerable difference in the reO F PREDICTED MOLECUL.4R WEIGHTS TABLE 111. COMPARISON WITH DATA FROM THE LIT~RATURE lation between the molecular weight and the visPredicted Deviation, % cosity a t 100" F. for the two types of stocks invesVisMol. Wt. Value Value tigated. Near the upper end of these curves the Saybolt COSFrom From from from Universal ity Detd. FigEquaFigEquamolecularweight of a Midcontinent distillate is ap9 Viscosity In- Mol. ure tion ure tion Literature proximately 60 per cent higher than the molecular &. looo F. 210° F. dex Wt. 3 7A 3 7A Citation Extract 3: weight of a Texas Coastal distillate of equal vis403 385 f 1 . 3 0 -3.20 4 7 . 4 108 398 Original 0,8751 213 54.6 57 365 385 396 f 5 . 5 0 f8.20 0.9218 440 Cut 1 cosity a t 100" F. Obviously, therefore, a third 403 386 4-4.90 + 0 . 5 0 4 7 . 4 112 384 Cut2 0.8762 207 variable must be introduced to account for this de412 384 +4.30 -2.80 4 6 . 4 126 395 Cut3 0.8581 175 451 403 f 6 . 2 0 -5.20 5 1 . 0 126 425 Cut4 0.8514 224 viation in molecular weights; as will be shown beExtract 4: low, this variable can be the viscosity slope factor. Original 0,8772 269 5 1 . 0 101 425 421 396 -0.90 -6.80 Cut1 0,9170 558 60.0 63 395 405 414 + 2 . 1 0 + 4 . 8 0 The curves presented in Figure 2 are also lines Cut3 0.8692 267 5 1 . 7 109 413 436 399 f 6 . 3 0 -3.40 438 . . . -1.57 ... Cut 4 0,8534 215 49.6 ... 445 of constant viscosity slope factor, the actual Extract. 5: values being 249 for Midcontinent and 302 for ... 477 . . . -0.62 6 8 . 0 ... 480 Original 0,8838 586 497 . . . 4-9.73 .... .. 8 6 . 0 . .. 453 Cut 1 0.9170 1235 Texas Coastal distillates. It was assumed, there488 . , . +7.25 73.5 ... 455 Cut2 0.8956 726 . fore, that evaluation of the effect of viscosity 481 . . . -3.80 6 4 . 0 . ,. 500 0,8708 440 Cut 3 . .... 481 . . . -3.77 6 2 . 0 ... 505 0,8602 393 Cut 4 slope factor on molecular weight would permit Extract 6: formulation of a correlation that would be ap.. .... 557 . .. 4-1.09 89.0 . . . 551 Original 0.8899 984 567 ... f 5 . 7 7 85.4 . . . 536 Cut2 0.8894 855 plicable to other stocks. Some data obtained 545 . , . -10.9 7 6 . 8 ... 612 Cut 3 0.8708 634 .. .. .. 576 ... -3.85 8 0 . 5 . .. 597 0,8639 650 Cut 4 several years ago, by using a somewhat differ312 310 f 0 . 6 0.0 95 310 77.6 37.3 1 0.867 ent cryoscopic method (Table 11),were compared 337 333 - 0 . 3 -1.48 95 338 113.4 4 0 . 1 0.867 2 -0.57 96 350 352 348 f 0 . 6 139.7 4 2 . 0 0.869 3 with Figure 2; it was concluded that the visfO.28 371 363 f 2 . 5 166.6 4 4 . 0 102 362 0.870 4 cosity slope factor varied linearly with molecular +0.27 383 375 + 2 . 4 196.7 45.9 102 374 0.871 5 4-4.92 317 320 f 3 . 9 102.3 3 7 . 9 15 305 0.932 6 weight, provided that the viscosity a t any one f1.22 304 332 - 7 . 3 10 328 188.5 4 1 . 8 0.933 7 -0.56 322 354 -9.5 8 356 0.934 312 46.1 8 temperature were constant. On the basis of this f0.27 335 370 -9.2 369 573 5 3 . 0 -22 0.938 9 conclusion, a general correlation can be formu371 404 -8.2 0.00 404 6 5 . 7 -4 0.934 1021 10 298 306 -2.0 +0.66 8 7 . 0 37.5 57 304 0.888 11 lated from the data in Figure 2 by calculating -1.43 337 344 -3.4 151 41.8 73 349 0.888 12 -0,27 369 373 -1.3 258' 47.2 73 374 0.896 13 the position of diagonal lines of constant Saybolt -1.80 0.900 350 51.0 58 390 380 383 -2.6 _14 _ Universal viscosity a t 210" F. This correlation 251 1.013 464 54.0 4 1 330.9 376 389 f 1 3 . 6 +17.6 ( 4 ) 308 0.8868 113 4 0 . 3 93 336 8 343 332 4-1 8 -1.48 is given by Figure 3, where the lines of constant viscosity a t 210" F. are established as follows: ~
INDUSTRIAL AND ENGINEERING CHEMISTRY
464
A comparison of Figure 3 with data from recent literature is presented in Table 111. I n addition, molecular weights were calculated from the following equation developed by Fenske, McCluer, and Cannon ( 3 ) : mol. wt. = 240
+
Saybolt viscosity at 100” E’. 28.0 305 - viscosity index
32,310 Iogio
(7.4)
for all samples shown in Tables I, 11,and I11 which fall within the recommended range for this equation (molecular weights of 300 to 425). Although it is not possible to calculate the respective probable accuracies of the two methods for predicting molecular weights, an inspection of the comparisons as presented indicates that Figure 3 covers a wider spread of both viscosities and viscosity slope factors with less probability for large errors. A very rough estimate of the probable error of values obtained from Figure 3 is about * 3 per cent. An attempt was made to correlate all of these molecular weight data with the viscosity a t one temperature and the specific gravity, substituting a viscosity-gravity function for the viscosity slope factor. Although a general trend could be shown, the viscosity-gravity function (as measured by Watson’s characterization factor, 11) was not sufficiently interchangeable with the viscosity slope factor to permit formulation of any definite relation. It was concluded that the slope of the viscosity-temperature curve was a more desirable variable for use in correlation of the molecular weights of petroleum fractions.
Conclusions 1. Molecular weights of petroleum fractions from two crude sources were related directly to the viscosities of the
VOL. 29, NO.4
fractions a t 100’ F., a separate curve being obtained for each crude. 2. The differences shown by these two curves were used as a basis for estimation of the effect of the viscosity-temperature function on molecular weight. The final correlation was presented in a form to permit prediction of the molecular weight from viscosities a t 100’ and 210” F. 3. Molecular weight data from the literature were compared with this correlation, and it is concluded that the molecular weight of any petroleum fraction can be predicted with a probable error of *3 per cent. The actual error depends largely on the accuracy with which viscosities can be determined, but it appears that, if reasonable care is exercised, the predicted molecular weights will be well within the usual accuracy of engineering calculations.
Literature Cited (1) Bell, T. G., and Sharpe, L. H., Oil Gas J . , 32, No. 13,13 (1933). (2) Davis, G . H. B., and McAllister, E. N., IND.ENQ.C R ~ M 22, ., 1326 (1930). (3) Fenske, M. R., McCluer, W. B., and Cannon, M. R., Ibid., 26,
976 (1934). (4) FitzSimons and Thiele, Ibid., Anal. Ed., 7,11 (1935). ( 5 ) Gullick, N. J., J . Inst. Petroleum Tech., 17,541 (1931). (6) Huffman, H.M., Parks, G. S., and Daniels, A. C., J . Am. Chem. SOC.,52, 1547 (1930). (7) Huffman, H. M., Parks,G. S., andThomas, S. B., Ibid., 52, 1032 (1930). (8) Rotinjam, L., and Nagornow, N., 2.physik. Chem., A169, 2031 (1934). (9) Schottky, “Thermodynamik,” pp. 339-42 (1929). (10) Steed, A. H., J.Inst. Pekoleum Tech., 16,799 (1930). (11) Watson, K.M., Nelson, E. F., and Murphy, G. B., IND.ENO. CHEM.,27, 1460 (1935).
RECEIVED October 8, 1936. Presented before the Division of PetroIeum Chemistry at the 92nd Meeting of the American Chemical Society, Pittaburgh, Pa., September 7 to 11, 1936.
CONTROL OF ROPE IN BREAD CHARLES HOFFMAN, T. ROBERT SCHWEITZER, AND GASTON DALBY Ward Baking Company, New York, N. Y.
HE development of rope in bread has been for many years one of the most troublesome problems of the baker. The disease develops in various types of homemade as well as commercial bread. Lloyd and McCrea (la), Cohn e t al. (5), and Bunzell and Forbes (3), among others, studied rope in the h i s h e d loaf. The work of Laurent (IO), Vogel ( I S ) , Fuhrmann (S), and Lloyd et al. (11) showed that several strains of spore-forming bacilli were responsible for the disease. These organisms have come to be regarded generally as members of the B. mesentericus group. The spores of these bacilli are very resistant to heat and thus are able to survive baking temperatures and subsequently grow in the bread during hot and humid weather. Although rope has been definitely proved to be the result of the growth of bacterial spores, the sources of infection have never been clearly shown. Watkins (20) contributed a method of inoculating sterile bread slabs with a boiled flour mixture containing the suspected rope organisms. Lloyd e t al. ( 1 1 ) and Brahm (8) developed plating methods which
T
Other ingredients than flour, particularly yeast, malt, and malted products are the chief sources of rope in this country. Rope can be avoided by the selection of ingredients through careful laboratory control. Ingredients of unknown origin and characteristics should be subjected to careful laboratory examination before being used in bread making. were not suitable, however, for materials containing solid particles. Voitkevich (19)developed a method using loaves of bread for the test media. Little was accomplished through use of these methods, and no one has demonstrated scientifically all of the important sources of the rope organism. Russell (16) in 1898 suspected yeast but had no evidence showing the degree of infection of the yeast or other ingredients. Russell’s important observations appear to have been ignored by early investigators. Flour was blamed, and the literature freely referred to this ingredient as the source of the disease. European investigators were in agreement with this viewpoint. Watkins (20) regarded flour as the only material responsible for the appearance of rope in bread. So
