DECEMBER, 1939
INDUSTRIAI, AND ENGINEERING CHEMISTRY
the temperature of vulcanization by proper mathematical relationship, it is possible and extremely useful to compute equivalent times of vulcanization when the temperature of vulcanization is varied duving the vulcanization (9, . , 11). I
I
1481
(5) Gibbons, --- Gerke, and Tingey, IND.EXG.CHEM.,Anal. Ed., 5 ,
zit, (lvaa). (6) Kelley, J. IND. ENQ.CHEM.,12, 196, 875 (1920). (7) ~ ~Ibid., 25, ~ 1400~(1933).i ~ , (81 Park. Ibid.. 22. 1004 (1930). i9) Park.and Maxwell. Ibid.. 24. 148 (1932), ( I O \ Sandstrom, Ibid., 25, 684 (1933). (11) Sheppard and Wiegand, Ibid., 20, 953 (1928). (12) Spence and Young, Kolloid-Z., 13, 265 (1913). (13) Weber, Ibid., 1, 33, 65 (1906). (14) Webster, J. Research Assoc. Brit. Rubber Mfrs., 3, 27 (1934). .
Literature Cited (1) Arrhenius, 2. physik. Chem., 4, 226 (1889). (2) Brittain, IND. ENG.CHEM.,21, 362 (1929). (3) Coe, W. S., private communication. (4)Eliel, Rubber Chem. Tech., 11, 101 (1938).
I
Effect of Reclaimed Rubber on Temperature Coefficient of Vulcanization W. S. COE Naugatuck Chemical Division of United States Rubber Company, Naugatuck, Conn.
Temperature coefficients of vulcanization were determined by free-sulfur, T-50, and modulus data for five compounds: (A) with no reclaim, (B) with alkali whole-tire reclaim, (C) with acid-type whole-tire reclaim, (D) with tread reclaim, and (E) with red tube reclaim. All compounds containing reclaimed rubber gave considerably higher values for temperature coefficient of vulcanization than the compound containing no reclaim. Of the compounds containing reclaim, B and D gave somewhat higher values than C and E.
ARIOUS types of reclaimed rubber have been used in the rubber trade for many years, but judging from the lack of data in the literature, very little work has been done on determining the effect of reclaimed rubber upon temperature coefficient of vulcanization. Probably i t has been generally assumed that reclaimed rubber would not differ greatly from crude rubber in this respect. On the other hand, data reported in the literature have shown a considerable variation when different accelerators were used ( 3 ) . I n a sense, reclaimed rubber itself may be considered as an accelerator because most types of reclaim behave as activators and reduce the amount of acceleration required to give a satisfactory rate of cure; this is clearly demonstrated in the compounds used in this investigation. Consequently, it is logical to expect that compounds containing reclaim might give different values for temperature coefficient of vulcanization from those for stocks containing no reclaim. Different types of reclaims might also be expected to yield characteristic values depending upon the reclaiming process or the kind of scrap rubber used.
Time will not be taken for a lengthy discussion of the theoretical or practical significance of temperature coefficient of vulcanization or for a literature review of this subject because these topics are well covered in the paper by Gerke ( 3 ) . Suffice it to say that values for temperature coefficient of vulcanization as they are usually recorded represent the increase in rate of vulcanization per 10" C . (18" F.) increase in temperature.
Data and Experimental Details Formulas for the compounds used in this investigation are shown in Table I. Compound A contains no reclaimed rubber and was included as a control stock for purpose of comparison. Compounds B, C, D, and E contain four of the most common types of reclaimed rubber in equal proportions of crude rubber and reclaim. Each of these formulas contains approximately 100 parts of rubber hydrocarbon assuming the rubber content of the reclaims to be 60 per cent; analyses given for these reclaims bear out this assumption substantially. The ratios of softeners and activators (pine tar, Laurex, and zinc oxide) were maintained proportional to the crude rubber content. I n general, this is justified because reclaims are softer than crude and break down more readily. Also, most types of reclaimed rubber retain sufficient quantities of zinc activation to satisfy their proportion of the compound. The amounts of antioxidant and sulfur were maintained proportional to the total rubber hydrocarbon content. The accelerator ratio was adjusted to give approximately equivalent rates of cure. The decreased proportion of accelerator in the compounds containing reclaim is clearly indicative of the strong activating or accelerating action of reclaimed rubber. These compounds were vulcanized a t four different temperatures-l35", 140°, 145", and 150' C. (275O, 284", 293O, and 302' F.)-covering the range most commonly used in the rubber trade. Duplicate samples of each compound (approximately 0.10 inch thick) were cured in opposite cavities of a 12-cavity mold in an attempt to average out slight variations in mold temperature. Several checks with thermocouples Iocated a t different positions of the mold surface showed uni-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1482
-4NALYSES O F RECLAIMS~ TABLEI. FORMULAS,
r
Compound Reclaim used Feature
A None Control
Smoked sheet Reclaim (above) Pine tar Zinc oxideb LaurexC BLEepowderd BJF Sulfur
100
Sp. gr. Acetone ext., % Ash Alkalinity (as NaOH) Carbon black Cellulose Total sulfur Rubber hsdrocarbon by difference
....
D 672 Tread
E 330 Red tube
62.5 62.5 1.25 3.12 1.23 1.0 0.31 3.0
62.5 62.5 1.25 3.12 1.23 1.0 0.31 3.0
62.5 62.5 1.25 3.12 1.23 1.0 0.31 3.0
Analyses of Reclaims 1.15 1.21 8.5 11.0 15.5 19.0
1.16 7.0 12.0
1.18 10.0 26.0
2.0 5.0 2.0 1.0 0.60 3.0
.. .. .. .. .. .. .. ..
B C 610 632 Alkali Acid type whole tire whole tire Formulas 62.5 62.5 1.25 3.12 1.23 1.0
0.31 3.0
0.15 12.0 1.0 1.9
Neutral 10.0 2.0 1.9
0.05 20.0 0.5 2.1
0.06 None None 1.3
60.43
55.60
57.85
62.14
VOL. 31, NO. 12
T-50 and free-sulfur data on these compounds are shown in Table 11. Modulus, tensile, and elongation values are given in Table 111. All data are averages of determinations on duplicate cures as described above. Values for temperature coefficient were determined independently by disappearance of free-sulfur, T-50, and modulus data.
Free Sulfur The free-sulfur data were determined by the sodium sulfite method reported by Oldham, Baker, and'craytor (6). This
p
100 90
p135t.
0 All reclaims, Laurex, BLE powder, and BJF are standard products of the Naugatuck Chemical Division of the United States Rubber Company. b Kadox Black Label 15 was used. 0 A zinc soap of fatty acids in which lauric apid predominates. d An antioxidant prepared from a ketone-amlne reaction product. 8 A thiazole derivative of an aldehyde-amine.
formity within * 1O F. The mold was surrounded a t the edges with asbestos and heated in an open platen hydraulic press. The temperature of each cure was carefully followed by means of a thermocouple located in the overflow between two cavities in the center of the mold. Figure 1 shows a typical temperat u r e rise curve for the first 15 minutes of one of the cures a t 145' C. The temperatures (by thermocouple in overflow between two cavities) are plotted on the ordinate a t distances from the abscissa proportional to their curing effect (assumFIGURE1. DETERMINATION OF TIME OF EFFECTIVE CURE ing a temperature coefficient of 2.0) according to a method by Brittain ( I ) . By this method the total effective cure is indicated by the area under the curve, area A plus area C in this case. Upon determining this total area and dividing by the distance along the ordinate to 145O C., we find that the effective cure over the 15-minute temperature rise was equivalent only to 12 minutes a t 145' C., represented by area B plus area C. Thus the curing effect during the first 3 minutes in the mold (area A ) was equivalent to the deficiency after that time (area B ) ; this indicates that 3 minutes should be added to the time of each cure to obtain the proper effective cure a t the desired temperature. Similar calculations a t the other temperatures gave substantially the same results. I n this work 30 seconds were allowed for time of opening the mold and quenching the cures in water a t the end of the cure. Consequently, all samples were allowed t o remain in the mold 2.5 minutes longer than the times recorded in the data tables to compensate for temperature rise and for cooling.
FREE SULFUR (%)
FIGURE2. FREE-SULFUR DATA
TABLE 11. FREE-SULFUR AND T-50 DATA Temp. of Cure, C. 135
140
145
150
135
140
145
Time of Cure, Min.
.A 1.44 1.04 0.69 0.23 0.08 1.37 0.95 0.63 0.31 0.09 1.28 0.58 0.23 0.06 1.28 0.57 0.23 0.07
25 38 50 75 100 18 27 36 54 72 13 25 38 50 9 18 27 36 25 38 50 75 100 18 27 36 54 72 13 19 25 38 50
- 1.6 - 8.4
-14.6 -22.9 -26.4 1.0 8.4 -15.0 -22.8 -26.4 2.6 -10.0 -16.2 -24.0 -27.6 2.6 - 9.7 -14.5 -23.2 -27.5
-
-
Compound
B % Free S 1.20 0.96 0.78 0.44 0.29 1.12 0.85 0.65 0.43 0.20 1.07 0.59 0.30 0.17 0.97 0.52 0.27 0.11 T-50, OC. 6.5 -10.2 -14.5 -21.5 -24.3 - 7.4 -12.2 -15.0 -23.5 -25.3 9.1 -14.0 -19.0 -24.9 -27.8 - 9.6 -16.5 -20.0 -25.2 -27.6
C
D
E
1.18 0.83 0.56 0.22 0.09 1.11 0.73 0.48 0.22 0.07 1.05 0.51 0.15 0.05 0.97 0.40 0.15 0.03
1.19 0.88 0.72 0.42 0.26 1.07 0.79 0.65 0.39 0.20 1.05 0.54 0.28 0.16 0.96 0.48 0.25 0.09
1.16 0.84 0.63 0.30 0.16 1.08 0.75 0.57 0.29 0.13 1.06 0.66 0.22 0.11 1.02 0.47 0.23 0.09
-
6.1 -11.3
--10.2 6.0
-
-
-
-
-
3.1 8.4 -13.3 -19.6 -23.3 4.0 -10.0 -14.3 -20.8 -24.0 4.7 -11.0 -15.3 -22.2 -24.7 - 5.6 -12.3 -16.0 -22.9 -25.0
-15.3 -20.9 -25.7 7.2 -12.9 -16.9 -21.9 -26.5 9.1 -14.4 -18.7 -26.2 -28.4 9.6 -16.0 -18.6 -26.4 -28.7
-
-14.3 -19.9 -23.2 4.7 -10.6 -14.8 -20.0 -23.6 6.2 -11.4 -15.7 -21.7 -24.7 - 7.7 -12.9 -16.5 -21.5 -24.4
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
DECEMBER, 1939
l6?5 2435 790
(Figure 2) are typical. A logarithmic scale was used for the temperature axis because the resulting curves were straighter and more suitable for interpolation; this also added to the convenience of replotting the times of identical cure on a logarithmic scale for determination of temperature coefficient of vulcanization. Curves for the other compounds containing reclaim were similar to those for B and were omitted in this graph to avoid confusion of lines in close proximity. This practice was also followed in the succeeding graphs for T-50 and modulus. A value of 0.5 per cent free sulfur was selected as appropriate for determination of times required to reach an equal degree of vulcanization. This value is not only in the most accurate portion of the curve of free sulfur against time, but also corresponds closely with optimum tensile properties of these compounds. The use of these time values to determine temperature coefficient of vulcanization will be discussed after consideration of the other data.
1955 2670 785
T-50 Test
2i90 2530 745
(4, 6) for following degree of vulcanization of rubber com-
method is precise and fairly rapid. It seems to offer the most accurately reproducible method for determining temperature coefficient of vulcanization. The free-sulfur data were plotted against time of cure to determine the time necessary to obtain identical values or similar degree of vulcanization a t the four different temperatures. Curves for compounds A and B
TABLE m. DATAON MODULUS(AT 500 AND 700 PER CENT ELONGATION), TENSILE STRENGTH AND ELONQATION Temp. of Cure, C 135
Time of Cure, Min. Property" 25
;Tens E%i1e
38
Elong. 500% FZ!1e Elong.
50
;E% Tensile Elong.
75
100
;00002
Tensile Elong. 500% &%%e Elong.
140
18
5009'
E&e Elong. 27
36
54
72
145
13
;00002
Tensile Elong. 500% 700% Tensile Elong.
75:02
25
38
9
14
27
36
1620 3400 845
19iO 3415 820 2i60 3370 800 2000 2960 780
ii9o
2710 865 1540 2715 895 1850 3075 800
Tensile Elong.
1770 3065 815
75o":z 750000%
750000% Tensile
Elong. 500%
E"%e Elong. 500% 700% Tensile Elong. Tensile Elong. 5007 700% Tensile Elong.
Eo"$ Tensile Elong.
18
l0iO 2675 875
lSi0 3020 775
50
150
A
Tensile Elong.
Tensile Elong. 19
-
:o"o"g
Tensile Elong. 500 % 700% Tensile Elong. 500% K Z i e
Elong.
1i i o 2640 835
1580 2765 835 lie0 2930 790 lis0 2820 790 1580 2970 815
iiio
2880 885 1480 2740 795 1640 3180 820 li00 3245 830 1450 2920 825
Compound C 560 860
B
D 830
1450 690 680
1920 700 1140
1935 695 1000
iiio
810 830
2350 740 1250
24io 765 1165
2030 740 1010
2490 690 1370
2440 690 1344
1960 660 1020
2340 655 1350
2590 680 1410
2070 685 660
2230 655 910
2575 670 865
1540 700 700
2040 705 1165
2i20 710 1060
lf85 700 885
2340 690 1220
2400 700 1195
20io 700 965
2385 675 1320
2465 690 1355
2i70 700 1030
2375 650 1210
2500 670 1340
2070 685 600
2075 640 1020
2445 665 925
1490 675 800
2090 700 1185
2i85 705 1155
1930 710 880
2385 695 1195
2500 700 1235
2i80 715 1020
2280 670 1300
2530 695 1340
2280 700 1005
2270 655 1180
2605 670 1355
1965 675 645
1965 645 980
2270 635 880
1870 740 865
2085 690 1175
2i80 700 1165
2040 710 970
2370 695 1210
2460 695 1250
2080 695 1040
2330 690 1235
2485 695 1320
2iio 690 1050
2200 650 1140
2485 670 1265
1940 660
1870 635
2230 650
1483
E 1225 1970 775
2i65 2520 750 1340 2100 805
iiio
2360 780
1930 2650 780 2090 2610 760 2045 2630 775
i4io
2215 795 li20 2500 795
Because of the rapid rise in popularity of the T-50 method
pounds, it is natural to use this test for determination of temperature coefficient of vulcanization. This is by far the easiest and most rapid type of determination for this purpose, and it seems to be entirely satisfactory for most practical uses. However, several slight complications may enter into T-50 determinations with stocks containing reclaim unless special precautions are taken. In the first place, reclaimed rubber already contains a certain percentage of combined sulfur, and although the rubber is thoroughly replasticized in the reclaiming process, this combined sulfur is revealed by the T-50 test. All four of the reclaims used for this investigation showed T-50 values between -20 and -21" C. in the uncured state. These values were obtained by cutting test pieces from laminated sections of these reclaims in the condition they are supplied to the rubber trade. This laminated condition gives good resistance to breakage due to tear when pieces are elongated for the test. Samples of 610,672, and 330 were elongated 500 per cent, and 632 was elongated 350 per cent; all were frozen to -35" C. and released, and the T-50 point was taken during temperature rise. This property of reclaimed rubber manifests itself in compounds containing reclaim by lowering the T-50 value of the
1990 2580 770 2080 2475 745 2020 2385 745
too
90 80
70 Go 50
1330 2300 810 1840 2455 780 1920 2475 760
20
2045 2455 730
IO 1850 2280 755
Modulus and tensile are expressed i n pounds per square inch: elongrttion in per cent.
9 I
I
0
-10
I
-20
T-50("G)
FIGURB 3. T-50 DATA
I
-30
-1
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
1484
short cures as shown by the curves in Figure 3. Unfortunately the ultimate values attained by the cured stocks are not correspondingly reduced by the presence of reclaim. Consequently, the range of T-50 values for stocks containing reclaim is slightly shorter, and some of the accuracy of the test is lost. Furthermore, compounds containing reclaim tend to have lower breaking elongations, and more trouble may be experienced with sample breakage in attempting to run such stocks a t a high elongation favorable to the test. The usual care should be taken to have the freezing temperature of the samples a t the first of each run well below any possible T-50 values.
t-
i
z2001 2000
21800
-
A-140°C.
2-
AP
1I600
3 v)
JA-145'C.
error of measurement is a t a mininium; on the other hand, values too close to the breaking point are undesirable because of the steep rise in modulus with elongation. I n determining times of equivalent cure, care must be taken in selecting the standard modulus for reference in order to obtain uniformity of results. The modulus values here reported were obtained on a standard Scott tensile machine with compensating head (correction for gage) and a spark recorder. It was operated a t the standard speed of 20 inches per minute. Values for compounds A and E were obtained a t 700 per cent elongation and those for B, C, and D a t 500 per cent. All values for modulus, tensile, and elongation represent an average for three strips on each of duplicate cures (six separate determinations). The moduli were plotted against time on a linear scale (Figure 4). I n selecting modulus values for determination of times to equivalent cure, an attempt was made to choose a position in the most significant portion of the modulus curves, about 200 or 300 pounds per square inch below peak values. The following values were used: A a t 1500 pounds per square inch, B a t 800, C and D a t 1100, and E a t 1800.
1400
Calculations and Discussion of Results
0
g1200 1000
800 600 40 0
VOL. 31, NO. 12
I
IO
I
1
I
I
I
I
I
20 30 40 50 60 70 80
I
I
90 IO0
TIME (MIN.) FIGURE4. MODULUS DATA
The T-50 values for compounds A and E were determined from an elongation of 500 per cent, compounds B, C, and D, from 350 per cent. After stretch, the samples were conditioned by being placed in water a t 20" C. for 5 minutes; this step is important in determining uniform, reliable, and reproducible values. The samples were then frozen in an acetone bath a t approximately - 70" C.; this freezing temperature is not too important so long as it is approximately 10" C. below any observed T-50 values. Tension on the samples was then released, and the temperature was raised fairly rapidly (6" or 8" C. per minute) until some of the samples showed signs of contraction, the rate of temperature rise was then reduced to 2" or 3" C. per minute and the T-50 values determined in the usual manner. A T-50 value of -20" C. was selected for determination of times to obtain equivalent cure. Here, as for free sulfurs, the selected value corresponds closely with optimum curing conditions, Curves for compounds A and B are shown in Figure 3.
The values usually given for temperature coefficient of vulcanization represent the increase in rate of cure for each 10" C. increase in temperature. I n order to obtain such values, the times to reach equivalent cure, as determined above, were plotted on a logarithmic scale against the temperature of cure (linear scale), and a straight line was drawn in best position with respect to the four points thus established (Figure 5). The ratios of the interpolated times a t two temperatures 10" C. apart represent the values for temperature coefficient of vulcanization as recorded for all compounds in Table IV. Proper curing times a t any temperature can be interpolated from a straight line on semilogarithmic paper as shown in Figure 5 or calculated from the equation for such a line, which would be as follows:
T
=
where T = temperature, M , K = constants t = time, minutes
O
M - Klog t C.
K is a function of the temperature coefficient of vulcanization, k , and is here designated: K = 1O/log k
thus T
=
M -(lo log l / b g IC)
5 A-T-50 IlI II: 8-FREE A-FREE S
I Y
8-T-50
Modulus Some observers ( 2 ) feel that modulus values are preferable to other data for computation of temperature coefficients of vulcanization, primarily because modulus is of more direct significance in commercial stocks than the other properties used for this purpose. However, the modulus method offers the disadvantage that determinations of times to reach equivalent cure must be computed on under-optimum tensile cures-that is, on the rising portion of the modulus curve (Figure 4). On near-optimum tensile cures the modulus values are so nearly equal that accurate time interpolations are impossible. Also, special precautions must be taken in obtaining modulus data for this purpose. It is desirable to obtain values a t fairly high elongations so that the percentage
H
#m r-
101
'
135
1
1
I
140
145
I50
TEMPERATURE ('(21
DETERMINATION OF TEMPERAFIQURE 5. GRAPHIC TURE COEFFICIENT OF VULCANIZATION
1
INDUSTRIAL AND ENGINEERING CHEMISTRY
DECEMBER, 1939
This is actually a slight corruption of the integrated form of Arrhenius’ equation for dependence of reaction rate upon temperature, which would have us plot log t against the reciprocal of the absolute temperature to obtain a straight line. However, the above form serves for practical purposes in the comparatively narrow temperature range used for most rubber vulcanization. Given either the proper times of cure a t two different temperatures or the proper time of cure a t one temperature and a value for temperature coefficient of vulcanization, we can obtain values for constants M and K and then calculate proper conditions a t any time or temperature. COEFFICIENTS OF TABLEIv. TEMPERATURE Compound By free sulfur By T-50 By modulus
Av.
A 2.14 2.05 1.88 2.02
B 2.51 2.50 2.42 2.48
C 2.28 2.28 2.22 2.26
VULCANIZATION
D
E
2.57 2.47 2.34 2.46
2.28 2.19 2.11 2.19
Reviewing the values found for temperature coefficients of vulcanization by the three different methods (Table IV), it is to be noted that the values obtained from free-sulfur data are higher for every compound than those determined by modulus. Several sets of data in the literature on various accelerators also bear out this behavior (3). The values determined by T-50 are, in general, between those by the other two methods and very close to the average values for all three methods. This may be considered another advantage for the T-50 method in that i t does not give extreme values either way. All methods agree very well in indicating that compounds containing reclaimed rubber give higher values for temperature coefficient of vulcanization than a compound containing no reclaim. Also, the alkali whole-tire and tread reclaims give higher values than acid-type whole-tire or red tube reclaims. No general theory seems to be available to explain this behavior of compounds containing reclaim except the assump-
1485
tion that reclaimed rubber promotes a different type of acceleration, very much as a different accelerator might. Other compounds that have given high values for temperature coefficient of vulcanization in the literature have been plain rubber-sulfur (100 to 6 . 5 ) ,crotonaldehyde-aniline, and butyraldehyde-aniline. The literature on activated us. unactivated mercaptobenzothiazole type accelerators has been somewhat contradictory.
Conclusions All compounds containing reclaimed rubber gave considerably higher values for temperature coefficient of vulcanization than the compounds containing no reclaim. Of the compounds containing reclaim, B and D gave somewhat higher values than C and E. Temperature coefficient values determined from modulus data were, in general, somewhat lower than those obtained by the free-sulfur method. The values determined by T-50 lay between those by the other two methods and very close to the average values for all three methods. Of the three methods, the T-50 has the advantage of simplicity and speed and is quite adequate for most practical purposes; the free-sulfur method is probably most accurately reproducible and not unduly difficult to perform; the modulus method, although preferred by some investigators because of the greater practical significance of this physical property, involves considerable discretion in selection of conditions.
Literature Cited
c.
(1) Brittain, L., IND. ENQ.C H E M . , 21, 362 (1929). (2) Eliel, K. W., Rubber Chem. Tech., 11, 101 (1938). (3) Gerke. R.H.. IR’D. ENO.CHEM..31. 1478 (1939). (45 Gibbons, W. A., Gerke, R . H., an‘d Tingey, H. C., Ibid., Anal. Ed., 5, 279 (1933). (5) Oldham, E. W., Baker, L. M., and Craytor, M. W., Ibid., 8 , 4 1 (1936). (6) Tuley, W. F., I n d i a Rubber World, 97, 39 (1937).
Vulcanization of Latex C. E. BRADLEY United States Rubber Company, Mishawaka, Ind.
During the last decade latex has established its position as an important raw material of commerce, supplementing dry rubber in many cases rather than displacing it. Principles of compounding and vulcanization adapted to its own peculiar nature have been developed. Research is steadily improving the quality and methods of transportation, and simplifying its control in manufacturing processes. Although fundamentally its vulcanization technique is similar to that of the parent industry, latex permits a wider latitude in choice of operating conditions which bids fair to increase its usefulness and extend its application. This paper covers latex vulcanization in general, including rubber deposited from compounded latex as well as vulcanization of latex per ae.
HE commercial possibilities of rubber latex were first outlined by LaCondamine and Fresneau nearly 200 years ago. They made a memorable report on this product which they obtained from certain trees in South America during explorations in that country. I n connection with his description of methods for preparing various useful articles from latex, Fresneau (9) says: “But all these things can only be executed on the spots where the trees grow, as these juices soon lose their fluidity.” Although his statement was well grounded and the inherent difficulties in transportation of latex did long delay its general use, today, thanks to industrial research, fleets of steamers are conveying millions of gallons of latex annually across the seas, and the tank car is delivering this material a t the factory door wherever it may be situated. Almost 100 years later, in 1824 and 1830, Hancock (3) filed patents on “impregnating felt, wool, cotton, hair and fibrous materials”, and the making of “dress or wearing apparel, fancy ornaments, figures, etc.”, using the milk of the rubber tree, imported from South America. I n his experiments on shipping latex in “good sound barrels”, most of t h e material coagulated, however, and he considered the plan impracticable.
T
