Colloidal Bentonite-Sulfur A .New Fuiigicide A.
S. k l d ) a w ~ r ~ r , ,P\'iag:ira Sprayer :ind C1ieiiiic:d
(hiiipa~iy,h e . , Middlcport,
N. Y
essr,!tiri/ ,.cqt~,j,yit.l.,y cd ( A I L '( i&l" s16/J1,,r as sirlirrm siliaat.e, are caustic irr Ifl: p i w a r y requisites of air entirely sntisfnctory jtlngicri~c l,,Lt/,ilie,~, !llili t/l,e properties J,, cl~aracteram1 tlierefore tend to injure the plant. or "ideel" sulfur fungi/ha ? r , m pvod!i!;t, knorcri (IS (:olEoidul ben.tonitestandarclsulfur fulrgicides cidc for agricnlliirnl u w s can be to ~:oiril~rise f~,~lowilig: ~ ~ ! ~ J~ ~ fc (r: h, l b 7~dh'd e r e l c e to these rerviiicli weremost ertensivelyuse. llentonite eel 16 PRIC-S
wslei)
for liquid spray iise under tlic t,rade riame of Kolufog, arid in various cornbi~~ations with irtlicr fungicides a n d iiisccticides for botli spraying and dusting under the trade names of Kolo olodiisl., Kolritex, etc. 13r ,e($,the new product is rriaile by absorbirig molten sulfur into dry, grouird hen1,onite clay and perniitting t,he
340
March, 1934
I N D u s ’r 1%I A I, A x D IS u t; I N c: 13 t i IN G
c i i I?: M
I S T 1%Y
341
niollen siiifur to solidify in situ iii t.lx dry licntonite. A mere nieclianicul mixture of PIIIfur and bentonite does not, give a pi-odiict pes-
sessing the desired popert,ies. The details of tile corniriercial itietliorl of riiairufacturiug t h e new prorluct are ctewil~edk c r . Tlie new pro+ uct, and various rrret.liods of Irrorluotion are patented (g), and coiriinercial priiiliictim :*nil distribution are i:onductcd uniler :in eraliisivc license under t.lie patents iiieiit,ioiitxl. Colloidal heiitoiiite-sulfur was first p r d i ~ c e i l and marketed on a conirnercial scale in 1025 and immediately met with famirahle reception by fruit growers gctrcrally. An interesting incident of tlie coninier&l developnient of this new fuiigicide is the Pact that tlie ut.ilization of cdluidal bentonite iti COIIII~!. tion with tlie nranufactore of the finislied product ILOW represents one of the most import,ant, commercial uses of bentonite clay it,self.
FKIJM3. Smnm PARTICLE OF Komaoc ( X 60) BEFORE AF~(I,:R (AT RIGHT)Fon~ta~rov OF GEL BY Ansowrrox ~~~
(AT LEFP) A N D OF WATER
e mtcrial or by-products. loidal properties of the new product first attracted attention. Early in t.lie inuostigutioii it was recogiiized that bentonite-sulfur, wlien dispersed in water, resembles closely the gelatinous colloidal properties of Jhirdeaux “mernbraoes,” known to possess in a high drgree the requisite ailliesiveness and aettabilit,y. Thus, fur t.lii? first time a sulfur fungicide lriirl been produced possessing t,licw liiglrly desirable gehtt,inous or “mcrnbraiious” Iirqwt,ies of tlie hest known capper fiingicirle. At the saiiic tiiiic it was realized t.liwt, Iwssibly t,lie new pniditct rr~uldalw IN: prepared in t i substantitilly dry dispcrsilile form ftir mivenicnt use as R spray without any Iiorne-niixing oixmtions in the orchard or field hy t.lie user, as must lie done in tlie vast of certain ot,iier st,nndard fungicirles, such as Honlraux mixture. This same Pact also appeared irnportaiit it1 ooiineetion with the st,orage anil sliipnient of the material mil also gave it an important advantage in tliese respix lime sulfur solution which must be sliipped mid ii liquid form, representing considorable inconveriieure I tlie shipper and irser. Incidentally, attempts to proiiiiix! n SI). called dry lime sulfur lied not proved sat,isfactory. An additional advantage ~ i a sthe fact that tlic raw niaterials required for the production of the new i u i i g i c i i l e namely, elementary sulfur atid bentonite-were coiii~rierrially avnilalAe in sufficient quantities to supply quireinents for a product designed for t,he u which antiually require ninny tliousantls of tons of itiiridaril sulfrir rnaterial in this country alone. The raw iriaterinls were also considered t,o be reasonably inexpensive.
sulfur which it produces. This test reproduces the actual manufacturing conditions closely and thus a uniform product in assured. Similar control tests are rnaile regularly samples from t,he rcgiilar faat,ory runs. Canadian bentonite, while apparcntly of good quality, occurs in deposits of tliiri strata and has, so far, not lieerr conveniently obtainable in the market, Bentonite frorli California, Texas, anil blre castern staies has not p r o i d entirely suitable. T h e manufacture of Ktilobase is conducted a8 follwv-: ‘l’lie bentonite is received loose in box cars, irr pieces about the size of peas, and contains approxiinately 10 per c m t moisture. It is ground in a Raymond four-roller mill irrrtil a~~pri~xi~riately 60 per ccnt will pass a 200kncsh screen ~ 1 x 1 less than 1 per cent will reinnin on a 60-mesh screen. The sulfur is groiirid until 80 per cent will pass a 200-mesh scrceii a i d less than 0.5 per cent will remain on a (iO-mesh screeti. The cquigment used in manufact,nrc is shown diagrammatically in Figure 1. Four liundred pounds of tlie ground bentonite atid two liundred pounds of tlie ground sulfur are tliorouglilp mixed in a flour blender, A, and elevated by mean* of the bucket elevator, B, to tlie hopper, C, which delivers the rnixture to a feeding device, I). The latter passes the mixture to tlie first of four steam-jackct,cd insulated screw coirveyors, arranged one above the other, E. The conveyors are Iieated by steam under ‘30pounds pressure, and tlie steam line is equipped with a pressure gage and flowmeter (not shown). I h c h alternate conveyor is equipped with a recording thermometer, and all are provided with gas vent,s (not shown). The screws in t,lie four conveyors are alternat.cly right- and left-hand so that the material is passed %fETHOD OF JiAXUFAC.UUI2E 1,ack and forth through tlie set of fonr, while the screws niay The raw materials employed are Wyoming hentotrite or all be rotat.ed in the same rlircctioii by chain drives from the Wilkinite and ground iniiieral sulfur. A good grade of 99.9 speed reducer, A’. As the iriisture of bentonite and sulfur progresses through per cent Texas sulfitr is used. Wyoming bentonite is prcferred because of its pronounced gelatinous colloidal proper- the conveyors, rrioisture iuid sulfur dioxide are evolved, so ties and the very high percentage of suspensoiils wliicli arc, t.liat, d i e n it emerges from tlie 1 conveyor, it contains only practically permanently swpensible in water. Tlie bent,oirite nliout 0.5 per wilt nioistiirc and is slightly acidic t,o methyl is tested before use by a standard quantitative laboratory red indicator, wliercas the Ixntonile is slightly alkaline to method of determining the suspensihility of tlie bent,onite- plienoli~litlialt~inbeforr 1,eing processetl. Also, the sulfur
is now thorouzlilv absorbed into the bentonite so that the niixture is granular in character The hot reaction product is delivered from t h e l o w e s t screw conveyor upon a slow-speed bclt. c o n v e y o r , F, which delivers it to a second b u c k e t e l e v a t o r , B', and also allows time for the temperature to drop well below the melting point of sulfur. The materials next pass through a hopper, G, t o a slow-speed rigidhammer pulverizer, W , the grids i n which a r e s p a c e d 'h inch apart. A f t e r leaving the pulverizer, t h e product passes to a vibrating screen, J, equipped with a 2 4 mesh s t e e l c l o t h . Fioune 4. SixrimN-IIoun SUSPEN- The fines collected SIONS OF B E V ~ ~ N I T (LEFT) E AND in the homer. K . KoLwoi; (Rrowr) are t h e i i o i u c t Kolofog. The oversize passes hy means of the couduit, M , back to the bucket elevator, B', and again to tlic pulverizer. The granular product. Kolofog is for use in liquid sprays. If a product suitable for use as a dust is desired, the material is removed from the hopper, G, by means of a conduit, not shown, and is ground in a Raymond mill to a fineness of not less than 95 per cent through a 300-mesh screen. I
"
COLLOIDAL Pitormum AND PAETICLE SIZE The highly colloidal properties of bentonite-sulfur are at once apparent from t.he close reseniblance of the finished product to the bentonite itself, both with respect to its highly gelatinous character as well as to the particle size of its permanent suspensions in water, under high magnification. Tile gelatinous or hydrophylic properties are illustrated by tlie photographs shown in Figure 2, which show powdered bentonite and powdered bentonite-sulfur, respectively, in each of t.he upright beakers. The corresponding gels obtained by tlie slow absorption of approximately six parts by weight of water are showii in the inverted beakers. Except for the ycllowish color of the bentonite-sulfur jelly, its general physical properties are hardly distinguishable from tliose of the bentonite jelly. The gel structure is further exhibited when the beakers are t.apped with the fingers or
rapidly shake11 by auy nrechanicill iiieaiis which causcs the gel to vibrate rapidly. Afurther illustration of the highly hydrophylic or gelatinous character of the new product is given in Figure 3 which illustrates the appearance of a small single particle of bentonite-sulfur (Iiolofog) on a microscope slide, under a magaification of about 102 diameters, before and after absorbing a limited amount of water "floated" over the particle. The tendency of the gel to break up into more minute gelatinow particles arouud the edges of the mass is also clearly shown. With still more water (as in the case of the S6-hour suspensions, slrown in Figure 4) most of the smaller masses of the jelly become completely dispersed, forming a practically continuous plrase between t.lie rclat,ively few particles OS suspensoids arid also between tlie masses of the thicker port.ions of the jelly. The prescrice of this substantially contirruous phase of tliin jelly is disclosed under "dark-field" illumination, which slion-s an enormous Iiurriber of points of light exhibiting rapid Brownian movement (difficult to show photograpliii:irlly) corresponding to the ultramicroscopic particles of the bentonite-sulfur jrliy between t.he larger masscs and particlcs. Occasionally, with somewhat thicker suspensions or emulsoid solutions, the edges of this continuous phase or relatively t,him jelly are discernible under the microscope a t lower magnifications with ordinary illumination. Exadly similar results to tliose described in connection with Figure 3 are obtainable with small particles of pure hentonite. This is true with respect to the appearance of the more dilute suspcnsions under tlie microscope, both with ordinary illumination and with so-called "dark-field" illumination. I n fact, every microscopic procedure so far tried discloses no really definite cliaracteristic differences as between tho particles or masses of bentoniteaulfur Gelly) and those of bentonite itself. On the other hand, characteristic differences are clearly disceruibie in mere mechanical mixtures of bentonite and finely ground sulfur, although permauent (16-hour) suspensions cannot be prepared with such mixtures. Figure 4 illustrates the rather close similarity in the appearance of suspensions of these two materials (bentonite and Kolofog) obtained after 16 hours of standing, using S gram of powdered material to 500 cc. of distilled water. Furthermore, the proportion of total solids remaining in suspension under these conditions is only slightly greater for bentonite than for Kolofog when pure materials are used. It will be observed, however, that the Kolofog suspension is somewhat more milky in appearance, probably owing to the thicker or slightly more gelatinous character of the semifluid eniulsoid masms rather than to any appreciable difference in the size of the ultimate particles, as d l be explained more fully later. I'erliaps the most significant fact, as already indicated, in connection with the colloidal properties of bentonite-sulfur, is the lack of any certain ditlerciice in the particle size or appearance of its permanent (16-hour) suspensions (prepared as above) and those of the bentonite itself, which is recognized as a liiglily colloidal material, as observed under the
EIPT. 1 (2-10-321 Germ tube Germ ieneth % Dlioronr
in
3.7 4.1 5.4
10 10
in
10.9
58.1
97.1
No. of B
Y
O
oounted ~ for each tea$
iinn
EX=. 2 Germ
9%
(2-19-32) Germ tube Ieiiztlh Microns
...
n.2 0.1
lo
2.3
15
10.2
9n
77.8
400
97.1
15
160 400 8 s
EXPT.3 (2-25-3'2) Germ tulre length
Germ
0.2 0.1 0.5 4.0 23.9 98.0
I4xn'. 4 (3-11-32) Germ tabs Gcriri
length
0
...
0
10
1.4
2n
28.0
52.3 97.4 750
$0 400 850
.
MHPCII,1934
i N D l J S T I< I A 1.
A N D
E N G I N E E I< I N G C €€ E M I S T R Y
343
iiiicroscope even w d e r very high magnification. I n fact, it is extremely difficult to distinguish between the suspensions of the two materials in this way even when the suspensions are prepared in such manner as to contain the same proportion of bentonite to water. This is illust,rat,ed in Figure 5, which shows photomicrographs of permanent (Ishour) suspensions of bentonite ( A ) arid Kolofog ( B ) prepared as described above and carefully concentrated to a slight extent so as to contain the same proportion of bentonite to water, the sulfur in the Kolofog suspensions representing an excess of suspended solid amounting to approximately 30 per cent of the weight of the bentoil The appearance, under the same conditions, of ely the same percentage (30) of a well-known brand of commercial wettable sulfur temporarily suspended in tlie same amount of permanently suspended bentonite is shown in Figure 5C. It seems reasonable to conclude from this quantitative comparison that a considerable proportion, a t least, of the suspended sulfur particles in Kolofog arc really submicroscopic in d mensions under this magnification of 102. The main significance of the preceding cornprisons is that this new material possesses colloidal properties similar to those of the highest grade of bentonite, which, as previously stated, is generally recognized as a highly colloidal substance. RELATION OF COI~LOIDAL PnoPmTiEs TO ADIIESIVENEGS, ETC.
slides by means of test tube dusters. Drops of a spore suspension were then placed upon the slides wliieli were put in inverted moist chambers and sealed with water. AfIer a period of hours, generally around 24, the germination counts were made under the low power of a microscope. The method has been described in detail by McCallan (5). With low concent.ration of sulfur, particularly around 1 to 5 per cent, the toxicity, as determined by this mettiod, of the sulfur in the form of bentonite-sulfur is of an entirely different order of magnitude from that of 300-mesh ground "wettai,le" suliur when calculated upon the basis of the proportion of sulfur present. Also, substantially greater toxicity is obtained by this method with bentonitcsulfur containing '/$ per cent of sulfur than is ohtained with 100 per cent of standard 300-mesh ground sulfur, both being used as dusts and then moistened with water (Table I). In conneotion with toxicity tests of bentonite-sulfur dusts (Kolodust, etc.), Wilcoxon and McCallan (7) state: " A p parently, Kolodust retains its effectiveness after the rain test better than the other modified dusts. A possible explanation for this lies in tlie fact that the modification litis actually produced a change in the physical state of the sulfur, a i d therefore it has qualities superior to that of sulfur dusts modified merely by mechanical additions." This statement is unusually significaiit in view of the exteiisive investigations TOXICITY, SAFETY, carried on by these workers over a period of years on t,he toxicity of sulfur fungicides generally.
The extreniely high toxicity of fused bentonite-sulfur in comparison with that of a inechariical mixture of piire 300mesh ground sulfur and ground bentonite, or with merely wettable sulfur generally is hest explained on the basis, of the submicroscopic character of a considerahle proportion at least, of the sulfur present. in the bentonite-sulfur and to its highly colloidal character generally, altliough ot,lier explanations have been suggested. Numerous direct dehrminations, by the spore count method, of the relative toxicity of bentonitc-sulfur (Ilolofog) in comparison with ground 300-mesh sulfur and typical ground wettable sulfurs Iiave been made. These t,ests were conducted in accordance witli the technic worked out by McCallan (5) atid Wilcoson and McCallair ( 7 ) . Such tests have uniformiy sliown that, spore germination is prevented or reduced to a substant,ial minimum, with radically lower concentrations of sulfur in the form of hentonitoeulfur than in any other form. Control tesbs on the toxicity of bentonite itself were always carried out in connection with these tests. Tables I and I1 give typical results ohtained by this metlrod. The dusts --ere placed on 1 X 3 inch (2.5 X 7.6 cc.) glass
TABLEXI. TOXICITY OF PDSED BENTONITGSULWUR MECHANICALLY MIXED I N BENTONITE *ED OF G K W N D SULFUR MECUANICALLVMIXEDIN BENTONITE DUST
5 % bentooite-adfur (cootaining :?ab/,% sulfur) BQeiuaieet to I*/.% aulfurin tile form of bentonite-su1iur */a% bentonite-sulfur (contniiiina 33'/,Yo sulfur) equivalent to 0.11 1% sulfui in tlie lorm of bentanite-sulfur Grouiid 50U-mesb d i u r 9% am-ineah around sulfui (over 98% sulfur) enuivalent t o over (.%I% nulfur the form of wettable sulfur % 300-meah ground pulfei (over DS% sulfur) eauivalent "\o over 0.32% sulfur I" the f o r m of ret.table sulfur
Control No. of sports counted ior e*sli teat
.. 14.9 50.9 53.6
...
67.2
...
81.4
...
27.8
900
It follows from t,lie foregoing dliat field data oil the arnouiit of sulfur remaining on the foliage and fruit, after weathering, etc., must be interpreted in view of the toxicity or nature of the sulfur residue and not merely in t,ernis of the total sulfur as has freijucntly been done. It has also been observed that the toxicity of bentonite-sulfur (Kolofog) is significantly increased by the addition of hydrated lime. This is contrary
344
I N D U S T R I A L A N D E X G I N E E R I N G C H E M I ST R Y
to the generally prevalent view that hydrated lime or a base producing an equivalent increase in the hydroxyl-ion concentration of sulfur suspensions produces a substantial decrease rather than an increase in toxicity. Since Alexander (1) and Wherry (6)have shown that the ultimate particles of pure bentonite probably h a r e a laminar structure with submicroscopic dimensions and also that a limited proportion are j u s t v i s i b l e microscopically in two d i m e n s i o n s (length and breadth) b u t submicroscopic in thickness, it seems plausible that the submicroscopic proportion of the bulfur in bentonite-sulfur, previously mentioned, is absorbed or adsorbed on or betxeen the flat w r f a c e s of t h e b e minute l a m i n a r particles of b e n tonite. This seems more probable in view of the fact that Kherry (6)has suggested that the wateradsorptive or gelforming properties of bentonite are clue to a similar absorption or a d ~ o r p FIGURE6. RELATIVESPEEDOF REAC- tion of water between the layers or TION OF VARIOUS SULFURS WITH CALCIUM HYDROXIDE lkaflets of t h e q e minute bentonite particles. Since the gel-forming properties of bentonite are not appreciably affected by the adsorption of fluid sulfur, it further appears probable that in the gel formed from bentonite-sulfur the adsorbed water ih superimposed over the layer of adsorbed sulfur. Additional strikingly convincing evidence of the extremely minute dimensions of the sulfur particles in bentonite-wlfur is furnished by a determination of the rate or speed of chernical reaction between the sulfur in this form and solution9 or -115pensions of calcium hydroxide as conipared with that of ot!ier forms of conirnercially available wettable or suspen-ii,le sulfur. In Table I11 is shown the amounts of materiali which were placed in suspension and the amount of soluble reaction product calculated as sulfur. These results are shown graphically in Figure 6. I n carrying out this comparison of the relative speeds of reaction of bentonite-sulfur and wettable sulfur, the reaction mixtures were placed in 100-cc. stoppered cylinders, in 100 cc. of water and maintained a t 96" F. (35.6" C.) in a thermostat, with equal stirring, in order to speed up the reaction so as t o complete it in a reasoiialdp time. The reaction progressed with unexpected swiftness. The transformation of sulfur into polysulfide was striking, and it mas easy to tell the relative relocity of reactions by the depth of yellow color in solution. S o attempt was made to determine polysulfide as such, owing t o the fact that, in filtering the mixtures, considerable ovidation inevitably took place. Instead of de-
Vol. 26, No. 3
termining the polysulfide, the total sulfur in solution was determined, which would include not only polysulfide but thiosulfate, sulfites, and sulfates. A blank run on the Kolofog and on the sample of wettable sulfur showed no sulfur in solution in the case of Kolofog and a negligible trace in the case of the wettable sulfur. The wettable sulfur employed is stated by its manufacturer to have a sulfur particle size ranging between 1 and 5 microns with an average of 3 microns. Since the speed of a chemical reaction between a solid in suspension and a reacting substance in solution is known to be proportional in general to the surface of the solid (other factors being the same), i t follows that the relative speeds under these circumstances are a n indirect measure of the relative particle size of the different suspensions. The radical difference in the speeds shown by the above data seems conclusive evidence that the sulfur particles in bentonite-sulfur are radically smaller than those of any known commercially obtainable wettable sulfur; this applies to the temporarily suspensible portion of the bentonitesulfur as well as to the permanently (16-hour) suspensible portions of the new product. These data also demonstrate that electrolytes, which are known to decrease the suspensibility of bentonite-sulfur, do not have any pronounced effect upon the particle size of the sulfur itself; otherwise the speed of the reaction would rapidly fall off, as it progresses, which is not the case. O F BENTONITETABLE 111. COMPARATIVE SPEEDS O F REACTION SULFUR AND WETTABLE SULFUR r
REACTIOX ~IIXTWRE
24 hours
ToraL SULFUR REACTED-48 72 96 hours hours hours
% Kolofog, 3.07 g. ( = 1 6. sulfur); hydrated lime, 1 g. Wettable sulfur, 1.29 g. ( = 1 g. sulfur) ; hydrated lime 1 g. 300-mesh sulfur, 1 g.; hydrated lime, 1 g. Blank on 3.07 g . Kolofog Blank on 1.29 g . wettable suliur
%
% 94.42
4.47
7.79
15.7
2.29 0.00 0.005
3.98 0.00 0.005
28.98
2.42 1.158 0.00
0.005
% 51.83
20.12
6.63 0.00
0.005
With respect to the safety of bentonite-sulfur, the fact that the bulfur is present in elementary form rather than in that of soluble sulfur compounds, as is the case with lime sulfur solution, for example, insures a wide margin of safety of the material to the foliage or growing plant. Thus, this new product represents really important progress toward the *ohtion of the fundamental problem outlined a t the beginning of this paper-namely, the provision of a sulfur fungicide of evtremely high toxicity, which, a t the same time, possesses a wide margin of safety. On the other hand, the highly gelatinous and sticky character of bentonite-sulfur accounts for its adhesiveness, wettability, and spreadability ; the jelly becomes more fluid an more water is absorbed and finally, with the addition of still more water, as in the case of the spray tank suspension, forms a liquid dispersion of the extremely minute masses of the jelly with a substantially continuous phase of very thin jelly between these particles, a s explained above. Upon drying down, the colloidal bentonite-sulfur tends to become irreversible or, perhaps more accurately speaking, partially coagulates, especially on the surface, forming a relatively insoluble coating over the foliage or the surface of the plant t o which i t has been applied. In this respect the nelT product differs radially in an important respect from the ordinary "stickers" and wetting agents which have previously been proposed for this purpose. Thus, the new product combines to a high degree the essentially inconsistent or opposed properties of adhesiveness or weather-resisting properties and wettability as already emphasized above. Electrolytes, except weak electrolytes or very dilute solutions, tend to break up the gelatinous structure of bentonitesulfur jellies. I n this manner the adhesiveness of the ma-
I N D U S T R I A L A N D E N G I N E E R I N G C H E 31 I S T R Y
March, 1934
terial may be controlled, an important point in connection with the removal of arsenical residues where this is desired or necessary. Hydrated lime (added to the spray mixture) permits renioval of the residue without decreasing the adhesiveness in any objectionable degree.
FIELDDATAOK FUNGOUS DISEASECONTROL While it is believed that the final test of the control value of a fungicide is to be found in the actual commercial results obtained and the satisfaction which the material gives in the hands of the grower himself, nevertheless actual data on the percentage of total scab on the fruit, with and without the use of the fungicide, the percentage of scab infection on the foliage during the growing season, etc., is of' considerable significance in this connection. Illustrative field data given by Boyd (3) are as follows: FENQICIDE Liquid lime aulfur Kolofog spray Check
APPLE^ SPOTTED B Y SCAB Baldwin
M o I n t 08 h
%
%
17.3
3.7
11.2 83.3
50.4
.3.1
TREATMENT
345 SCAB
% Check Kolofog, 3 lb. in 50 gal. Kolofog, 4 lb. i n 50 gal.
95.7
1.6 1.5
A4CKNOTVLEDGJlEST
Acknowledgment is made to hIax L. Tower, H. W. Dye, and J. F. Les Veaux, of the Siagara Sprayer and Chemical Company, Inc., and to H. H. Wheteel, L. RI. Massey, and R. A. Hyre, of Cornel1 University, for valuable data and suggestions in connection with the preparation of this paper. LITERa4TUKE CITED (1) .%lexancler, Jerome. CoZZoid L S ~ / m j ~ o . s i.Tfonograph, ~~n~ 11, 99 105 (1924). (2) Hanks, H. TV., U. S. Patent,. 1,850,850 (.kug. 18, 1 9 2 5 ) : McS., Ibr'd., 1,934,989 (SOY. 14, 1933). Daniel, (3) Boyd, 0. C., Mass. Fruit Growers Assoc., Rspt. 38th Ann. Meeti n g , 1932. (4) D y e , H. I T , , u n p u b l i s h e d dicta. (5) hlcC'allan, Y. E. A , , ('ornell Univ. Agr. Expt. Sta., J I e m . 128, 10-12 (1930). (ti! \Vherrg', E. T., private coniiiiunication (quoted by Alexander, f), J . W a s h . .4cuCi. Sei., 7, 578-S3 (19171.
Rubber Plasticity Control Significance and Value of Recovery Measurement of Williams Plastometer J. H. DILLOS,Firestone Tire and Rubber Company, Akron, Ohio
T
HE original compression plasticity test for rubber, as covery after removal of the load. This definition, when given developed by Killiams ( I d ) , consisted in measuring the quantitative form, applied only to one type of measuring incompressed height (y value) of a 2-cc. rubber sample strument, the Goodrich plastometer. Hence, the definition after a standard time of compression under a 5 k g . load a t a was purely arbitrary and was juqtified only in that it took standard temperature. No account was taken of the increase account of one more variable than does the Williams u value. Karrer designed a plastometer in height-i. e., recovery, of the ( 7 ) which was also adapted to pellet after removal of the load. Experiments to determine the practical value the measurement of recovery, The distinction between plastic and in which the compressive flow and pseudoplastic flow in of the recovery measurement of the Williums force acted for a definite shortthe compression test, as applied plastometer in rubber plasticity control testing time interval. The plastometo rubber, was first made by van are described. An empirical relation between y ter platens were of the same type Rosseni and van der Meijden value and time of milling was found for gum (IO). They measured deformaas those used by van Rossem and rubber o n a cold laboratory mill. This relation tion of masticated rubber under van der hfeijden; that is, the load as a function of time of platen faces were of the same furnishes a concenient method of analysis of the compression, and then removed area (one sq. em.) as the ends of Williams plastometer indices. The relation the load and measured the rethe cylindrical pellet. Asimpler between these indices was investigated with recovery as a function of time. plastometer (8) which differed spect to amount and method of breakdown of the They showed that the ratio of only in that it operated under a rubber and to the degree of set-up of typical facthe plasticity to tlie elasticity dead load was designed for conin the masticated r u b b e r is a trol work. tory stocks. No marked advantage of the rerapid function of temperature, The arguments of the various covery measurement over the usual y calue measincreasing from zero a t 16" C. to investigators (6,10,12)in regard urement, from a practical standpoint, was disto the significance of recovery in a v e r y l a r g e v a l u e a t 70". coz)ered for the samples of crude rubber and rubber plasticity measurements have Karrer (6) adopted the viewstocks tested. Some results obtained with a n been of definite value in clarifypoint of van Rossem and van der Xeijden and suggested a definiing what had been a somewhat extrusion plustometer operating at high rates of tion of plasticity which included vague conception of plasticity shear are given which indicate that the extrusion the total deformation of a pellet a m o n g r u b b e r technologists. type of plastometer offers a better criterion of plasof standard dimensions under a Certainly the basic idea, as mainticity of rubber than does the compression instrus t a n d a r d c o m p r e s s i v e force tained by Karrer, van Rossem, ment. acting for one second and its reand van der Meijden, that the
