362
INDUSTRIAL A N D ENGINEERING CHEMISTRY
lime sulfur and the partially soluble products (CaSO3,CaS203, CaSOd) when it is decomposed on foliage, it is entirely within reason to expect weathering to allow the production of polythionic acids on the precipitated sulfur. It was observed that sunlight and other natural conditions accelerate the formation of the acids of sulfur. This was quite strikingly shown when two sulfur-lime dust suspensions in water were exposed for 2 days, one closed in a flask in the laboratory and the other to open natural conditions. The suspension exposed to natural conditions lost its alkalinity so that phenolphthalein was colorless when added to the suspension, while the other remained sufficiently alkaline to give a basic reaction. It is well to consider a possible reason why the pentathionate ion from calcium pentathionate is not toxic in neutral or alkaline solution. It is not unreasonable to suppose that spore tissues are amphoteric in nature. A behavior analogous to that of amphoteric protein does not necessarily depend , ~ example, found that he on a protein-like tissue. K r ~ y tfor could duplicate Loeb’s6 work on protein by using agar, a carbohydrate. I n any case, it is conceivable that there is a
Vol. 21, No. 4
sharp line of demarcation at a certain pH, when the effect of anions becomes very marked, as in the case of Loeb’s well-known work, and this line is apparently on the acid side of neutrality. Bibliography 1-Bassett and Durrant, J . Chem. Soc., 1927, 1401. 2-Freundlich, “Colloid and Capillary Chemistry,” p. 616, E. P. Dutton & co. 3-Kruyt, “Colloids,” p. 201, John Wiley and Sons, 1927. 4-Kurtenacker and Goldbach, 2. anorg. allgem. Chem., 166, 177 (1917). 5-Lee and Martin, Science, 66, 178 (1927). 6-Loeb, “Proteins and the Theory of Colloidal Behavior,” McGrawHill Book Co., 1922. 7-Marcille, Compt. rend., 152, 780 (1911). 8-Pollacci, A f t i congrcsso intern. ckim. appl. Roma, 1, 482 (1907). 9-Raschig, “Schwefel und Stickstoff Studien,” p. 273, Leipzig University, Berlin, 1924. 10-Roach and Glynne, Ann. A p p l . Biol., 15, 168 (1928). 11-Smith, Calif. Agr. Expt. Sta., Bul2. 172, 1 (1906). 12-Sostegni and Mori, Staz. spcr. agrar. iial., 19, 257 (1890). 13-Spring, Ann., 213, 329 (1882). 14--Tisdale, Ann. Missouri Bolan. Gardens, 12, 381 (1925). 15-Young, Ibid., 9, 403 (1922). 16-Young and Williams, Sciencc, 67, 19 (1928).
Chart for the Estimation of Equivalent Cures’ C. L. Brittain GUTTAPERCHA & RUBBER, LIMITED,TORONTO, CANADA
I
N ALL heavy rubber articles the temperature conditions which obtain during curing are very different from those existing in light articles. Heat penetrates thin rubber sheets so quickly that they may be said to cure at constant temperature. Heavy articles, however, are heated very slowly, so that their cure may generally be divided into periods of rising temperature, approximately constant temperature, and falling temperature. During August, 1926, the writer developed a method of evaluating and comparing cures made under such variable temperature conditions. The principle is applicable to all cases of variable temperature cures-as, for instance, shoe-curing schedules, etc. Two papers presenting methods of estimating the curing effect of variable temperature schedules have recently appeared. Sheppard and Wiegand2 have developed equations and charts whereby curing effect may be calculated and expressed mathematically. Their method is based on the empirical relation that the intensity of curing action doubles with every rise in temperature of A” F., where A is a selected constant (in the example given, 15” F.). The method is therefore limited, in exact application, to compounds for which the temperature interval ( A ) during which the rate of cure (corresponding to intensity of curing action of the schedule) doubles is actually constant. Tests show that for many stocks the interval is not constant over the range of curing temperatures. The procedure is also limited to schedules where the rate of rise of temperature is constant. Sherwood3has developed a means of predicting the temperature rise during the cure of heavy articles, and both his and Sheppard and Wiegand’s papers present graphical methods of calculating curing effect which are not subject to the limitations mentioned in the preceding paragraph. The graphical methods have the advantage of presenting curing effect pictorially as well as mathematically. They are open to the objection that, instead of plotting the known quantity, temReceived December 5, 1928. Sheppard and Wiegand, IND.END.CHEM..20, 953 (1928). a Sherwood, Ibid., PO, 1181 (1928). 1 2
perature, one must calculate the intensity of curing action corresponding to the temperature, and plot that value. Principle of Area Diagram
The writer’s method of evaluating the curing effect of variable temperature schedules makes use of a chart of special form, termed the “area diagram.” A horizontal time scale having uniform graduations is first laid out. Any desired law connecting temperature of curing with time for optimum cure may be selected as the basis of a temperature scale. T h e vertical temperature scale is then constructed so that the distances of the temperature lines above the base line (time axis) are inversely proportional to the corresponding curing times. Then if any lines of time and temperature representing optimum cure are drawn on the chart, the rectangular area enclosed between them and the axes of the diagram will be a constant. Since the vertical distances to the temperature lines are inversely proportional to the corresponding optimum curing times, they are directly proportional to “rate of cure,” and the area then represents the product of rate of cure by time, which in any particular case indicates the state of cure of the stock. If referred to the schedule as distinct from the stock to which it is applied, the area may be regarded as the product of intensity of curing action by time, which equals curing effect. The above statement makes no reference to variable temperature cures, but the principle is easily seen to apply tothem, since if any variable temperature schedule is plotted on the chart, the area under the curve may be divided into any desired number of thin vertical strips, which may be regarded as rectangles. The sum of these small areas represents the curing effect of the schedule. In use, then, the temperature schedule under consideration is plotted on the area diagram. The resulting curve presents, graphically, the curing effect of the schedule, or the state of cure of the stock subjected to that schedule, and the area under the curve, which may best be determined by the planimeter, gives a mathematical expression of these properties. Since the known area representing.
IiI'D USTRIAL A N D ENGINEERING CHE;WISTRY
April, 1929
Ccmprisn ef Temperature -Time Relaiions for Equivalent Cure3 of Rubber Stochs
AREA DIAGRAM #d-INTERVAL l3i4
1
1554,in ReDresents Ootimum CUR of #Ill Stack
1 1 1 -
E94 292
I
Pre5s Cures Ion Slobs of L 2 o z Frictiojed Belt DuckI
15~10' 100 6 ;;jrnurn 1606 1027
A -5vrfoce 8 - C e n t e r Am;i
34
14p,y.~~;+hlsk-
C -5urfaca
24.1 154
D -Centor
&&
1
I
363
On the chart are shown temperatures taken by means of thermocouples built into the material, during the cure of two slabs of frictioned belt duck. The areas developed by the different curves indicate the over- and under-cures of the stocks a t different points in the slabs. The amounts of the over- and under-cures are indicated by expressing the different areas as percentages of the area which represents optimum cure. (2) Temperature-time curves showing optimum cure on thin molded sheets of high-grade tire tread and friction stocks are shown on Figure 1 by curves B and C, respectively. In these cases the temperature interval during which rate of cure doubles is not constant over the curing range. IL'o simple equation was found for these curves. To obtain the area diagram of Figure 4, curve C was drawn to an open scale and corresponding values of temperature and time were read off. After selecting the time scale and a suitable area (15 square inches) to represent optimum cure, the temperature scale was arranged by proportion as before. On Figure 4 are plotted the results of a thermocouple test on a tire cured in a watchcase heater. Since the chart is applied to the stock from which it was developed, an accurate indication of the state of cure of the friction stock in different parts of the tire is obtained. Comparison of Figures 4 and 5 illustrates the value of the area diagram in presenting the curing effect under conditions of variable temperature. The temperature scale of Figure 5 has uniform graduations. The form of the curves in Figure 5 and the areas under them are entirely misleading as far as the state of cure of the stock in different parts of the tire is concerned. (3) Figure 3 shows an area diagram with the temperature scale designed to fit the case where rate of cure is assumed to double for every rise in temperature of 15" F. I n this case the distance of any temperature line above the datum is a constant factor (1/X) of the distance, for the next, 1-degree, higher line, and X ' j = 2 or X = 1.0473. The 270" F. line is 6.0 inches above AREA D I A G R A M #7 i N T E R V A L 151
I
0
20
IO
33
4c
I
I \
--ye:-
._. . , . .....
50
I
CJ
optimum cure is a constant, if the curve encloses this area the stock is in the state of optimum cure. If the area is less than that for optimum cure, the stock is undercured, and if more, overcured. Applications
Three examples of actual construction and use of the area diagram are given below: (1) The original chart was derived from experimental press cures on a high-grade belt friction, resilient energy and tensile product being used as cure criteria. It was found that the time for optimum cure was halved, or the rate of cure doubled, for every increase in temperature of 13.5' F. The curve showing optimum cure of thin molded sheets, A , Figure 1, is a straight line on semi-logarithmic paper, having the approximate equation T = 350.15 - 44.15 log t , where T is temperature in degrees Fahrenheit, and t is time in minutes. The area diagram of Figure 2 is drawn from this formula. The time scale is 1.5 inches = 10 minutes. From the equation the time for optimum cure a t 300" F. is found to be 13.674 minutes. This is represented on the time scale by a length of
w 4X 1.5 = 2.0511 inches. 10
An area of 15 square inches was
selected to represent optimum cure. Then, by definition, the 15 = 7.313 inches above 300" F. temperature line must be 2.0511 the base line. The distance up for any other temperature line is found by simple proportion. For example, when T = 290, t = 23.04, and the 290' F. line is -X 7.313 = 4.34 inches above the base line. Now a time of 23.04 minutes is represented on the time scale by-23.04 X 1.5 = 3.46 inches and 3.46 x 4.34 = 10
15.02 (approx. 15) square inches.
Temderdur* OF.
ra5
cu !E
OF
soxJ>; CORD rlw IN d T c ,
cA5E MOLD 5te(m Tempe'oture 271'E-Time 52 Min5,
A'ea Under Curve Ovtside Ply, Undeb J i d w a l 21.00" Between'rrod and rdUr 18.1 3 Imide PI,, Under 3 dwoli 13.3
Cu ve RepreZents Temp of Pa0
1 2
Oplimurr Cure IAO 107
Ob
89
INDUSTRIAL A N D ENGINEERING CHEMISTRY
364 the base. Then the 269' F. line is
of 1.0473
6.0 or 5.730 inches,
and the 268' F. line is -of 5.730, or 5.471 inches, above the 1.0473 datum, and so on. Such a continuous calculation is extremely accurate when done by logarithms. A check on the results is provided by such obvious values as the distance for the 255" F. line which is one-half of 6.0 or 3.0 inches, and for the 240' F. line which is one-half of 3.0 or 1.5 inches, etc.
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schedule and not to the state of cure which would be produced in any particular stock (see paragraphs 3 and 4 in the summary). The greatest value of the area diagram in this connection is the accurate means it provides of making relatively small changes in the characteristics of any one schedule, while still retaining the original curing effect, or for the purpose of changing the curing effect by a desired amount. Summary of Characteristics of Area Diagram
''0
IO
20
30
40
50
80
79
60
Tim- Minutr5.
KO definite area for optimum cure is assigned to this diagram, since it is intended as a general chart to be used in comparing similar cures on an approximate basis only. I n Figure 3 are shown some shoe-curing schedules whose characteristics are summarized in Table I. Table I
CURVE A B
c
D'
TOTAL MAX. SCHEDULE TIME TEMP. Minutes P. Pressure cure: Forboots 170 Fortennis 150 Forcrepe 190 Box-heater forboots 8% hours
DRAWN AREAS
TO
SCALEA scale
270 260 240
A A A
260
B
Bscale
36.8 18.0 8.9 12.9 = 38.7 on A scale
Since the stocks which would be cured in the different heats are generally of different types and would follow very different laws of equivalent cures, the areas shown in the table must be regarded as referring only to curing effect as a property of the
1-The diagram provides an accurate means of evaluating the curing effect of any given variable temperature schedule no matter how irregular. The process is reversible; i. e., when a schedule having a certain curing effect is desired, it is merely necessary to construct one with the proper area, having regard, of course, to proper heating and cooling periods. 2-The results are presented both graphically and mathematically. 3-Where absolute accuracy is desired, the chart may be drawn in accordance with the equivalent cure relation of the stock for which it is to be used, whether that relation is of simple exponential form or not. (The danger of applying any one equivalent cure relation to a great variety of stocks is shown by the three curves of Figure 1. Widely different results will be obtained if the equivalent of any one given cure is calculated by the three relations.) 4-If only approximate results are desired, a series of diagrams can be drawn, based on different equivalent-cure relations, and cures for any stock can be calculated by means of the diagram most suited to it. 5-The same chart may be accurately applied to any number of stocks having the same form of equivalent cure relation, whether the individual stocks are quick or slow curing, it being merely necessary to find the area representing optimum cure of each stock. 6-The charts can be cheaply reproduced from tracing paper drawings by any dry printing process which does not distort the printing paper. Acknowledgment
Acknowledgment is due Gutta Percha &- Rubber, Limited, for permission t o publish this article.
Effect of Neutralization of Chrome Leather upon Fat Absorption' Henry B. Merrill and Joseph G. Niedercorn A. F. GALLUN& SONSCORPORATION, MILWAUKEE,
HE extent to which chrome leather is neutralized before fat-liquoring is known to have a powerful influence upon the successful outcome of the fat-liquoring operations. I n a previous paper Merrill* showed that the total amount of sulfonated neat's-foot oil taken up by chrome leather is independent of the pH value to which the leather has previously been brought. More recent experiments have shown that this is true only under the peculiar conditions obtaining in the experiment. I n the previous work the leathers were brought to different pH values by means of phosphate buffers, which replaced all the acid sulfate of the leather in every case.
T
1 Presented under the title "Acidity of Chrome Leather and the Absorption and Distribution of Oil during Fat-Liquoring" before the Division of Leather and Gelatin Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928. Merrill, IND. ENQ.CABX.,30, 181 (1928).
*
WIS.
I n neutralization as ordinarily carried out with a limited amount of mild alkali, such as borax or sodium bicarbonate, this is not the case, as only a part of the acid is neutralized. The writers have found that when chrome leather is neutralized to different extents by borax or sodium bicarbonate, the rate of taking up of sulfonated oil by the leather is greater the more sulfuric acid is not replaced. The amount of fat absorbed, from a liquor containing an excess of oil, in 1 hour, increases with the percentage of sulfuric acid left in the leather before fat-liquoring. The quantity of oil absorbed is independent of the specific neutralizing agent employed (at least for the systems studied), and is not directly connected with the pH value of the neutralizing solution, except in so far as that controls the sulfate content of the leather. With increasing time of fat-liquoring the effect of acidity on total oil
