I S D C S T R T A L AA'D ENGINEERIiVG CHEMISTRY
July, 1929
The locations of the lines in Figures 2 and 3 were calculated from Equation 3, and fcalcd in the tnbks was computed from Equation 4. Five constants ioccuring in Equation 3) were sufficient to represent the data on potassium nitrate pellets and on crystalline ammonium phosphate. These materials have such widely different properties with respect to shape of particles, angle of repose. and density, that it was thought possible that the formula might hold for other conditions. Experirnents were therefore conducted in which the conditions were Taried as widely as practicable t o test .____
'01
I
Siebed Amnoilium PPOsphate
Crystals
,
50
40
665
the general applicability of the equations. The size of the particles, 5, was varied from 0.131 to 13.5 mm., the diameter B of the orifice from 1 to 73 mm., the apparent density d from 0.4 to 6.5 grams per cubic centimeter, the coefficient of friction p from 0.380 to 1.070, and the funnel - angle q5 from 30 to 90 degrees. Thus the range of D : B varied from a value approaching zero to one of about 0.25, above which the material would not flow freely through the opening. t in the several tests varied from 0.0007 to 48.0 minutes. In every case, as may be seen in Table 111, the calculated and observed time agreed satisfactorily. The only cases in which the calculated time varied more than a few per cent from the observed were those in which the value of n : B neared its upper limit of 0.15 t o 0.26 (the limit varies with the shape of the particles) above which, the flow,if any, is not perfectly free. Equations 4 and 5 apparently represent the law governing the flow of solid particles of any density, shape, and size, provided the size is not small enough t o introduce cohesion as a factor. I n this case the particles will usually be finer than 200 mesh. It will also probably hold for any funnel angle between 20 and 110 degrees, which should cover most cases met with in engineering practice. Acknowledgment
D,,D,= sieve operiinqs b h for 0- IO m m ,approx.
.
30
*,,+
I
?,+
*I
E3= 5
"
*
B=3
''
8=2
"
.
-=,4
, , ,
"
"
1
Credit is due Mr. RIerrill E. Jefferson for the careful nianner in which he made many of the measurements used in this work. Literature Cited (1) Bridgman, "Dimensional Analysis," Yale University Press, 1922
Figure 3
(2) (3)
Mehring and Cummings, U.S. Dept. Agr , Tech. B u l l , in publication. Shaxby and Evans, Trans. Faraday Soc., 65, 60 (1923).
Dispersion of Pigments in Rubber-11' Ernst A. Grenquist THEFISKRUBBERCOMPANY, CHICOPEE F A L L S ,
MASS.
tension is the specific attracPREVIOUS paper A theoretical conception of the reenforcement of (IO)* described t h e rubber by pigments has been developed. tion existing at a surface. On account of the unsymmetridistribution of partiNew experimental evidence has been presented which leads to a better understanding of the final dispersion cal field of force surrounding cles in compounded rubber and reenforcement of a rubber compound. I t is shown molecules a t a surface, the with special reference to agmolecules adjust themselves that pigment reenforcement is influenced by (a)rubber glomeration and flocculation. in such manner as to give a It was emphasized that a corstructure, (b; the state of aggregation of proteins and natural resins, ( c ) the isotropic properties of carbonsurface of minimum potential rect understanding of t h e black particles, and ( d ) the presence of recrystallized energy. It is e v i d e n t t h a t final dispersion a n d reenenergy must be added to a forcement of a rubber comrhombic sulfur at the beginning of vulcanization. system of rubber and undispound could only be obtained with a more thorough knowledge of the structure and physical- persed pigment if additional rubber and pigment surface or chemical properties of rubber and pigments themselves and interface between rubber and pigment is to be formed. The of the nature of the vulcanization process. Kew experimental greatest part of this energy is added in form of work. Since results in regard to these particular points are presented in the work may be given back in contraction of the surface, the following investigation. this amount of energy is said to be preserved in the surface as free energy. Interfacial tension is a measure of the amount Theoretical of free energy present in the interface. Vetting, cdhesion tension, attraction (between rubber and Owing t o lack of agreement in regard to terminology, a number of conceptions considered in this paper \\Till first be Pigment) is the decrease in free surface energy taking place defined and discussed from a rubber-compounding point of when a rubber surface is brought in contact with a pigment view. surface forming an interface. Change in the distribution of pigmenis in a system rubberSurface energy or tension, free surface energy, interfacial pigment before reaching a state of equilibrium and a final Presented before the Division of Rubber Chemistry a t the 76th degree of dispersion can be classified as follows: (1) aggregaMeeting of the American Chemical Society, Swampscott, Mass., September tion-by (a) agglomeration or (b) flocculation; (2) disag10 to 14, 1928. * Italic numbers in parenthesis refer to literature cited at end of article. gregation (dispersion)-by (a) disagglomeration or (b) de-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
666
flocculation. ( a ) is the tendency of unwetted particles to group or spread, whereas (b) is the same tendency of vetted particles. These changes can take place during the milling operations as well as during vulcanization. Diffeerent t?,pes of particles are encountered before final dispersion is obtained in a ruhber compound-primary particles, the size and shape of which are regulated by the molecular forces of cohesion; sccandary particlcs, thosr formed as a result of aggrtqqtion from primary particles.
Microscopical nrawlng Approximately 5aoo x
Flgure 1-No Breakdown.
Relution between uelting, iiilrrfncial leruion, and dispersion Dispersirtg agents known in rubber compounding are substances that reduce the interfacia1 tension hetween the pip. ment particle and the rubber. The smaller the interfacial tension the weater will be the attraction between the filler and the rubber. The intensity of the wetting or adhesion tension regulates the tendency to aggregation and consequent.ly the dispersion. Both physical and chemical changes at the surface of the pigment particles may take place during milling and vuleanizat.irm which would iniiuence the interfacial t.eiision and cause changes in the permanent dispersion of the particles. That chemical elianges actually occur at tlie surface of certain pigment. parbicles during vulcanization has been shown by Pohle (92). On the other hand, Wicgand (20) point,s out that dispersing agents may profoundly affect the consistency of the rubber phase and that proper dispersiori cannot take place when t,he viscosity of the ruhber falls helow a certitin point. According to I h s e r (12),certain pigmcrits reach a, maximum dispersion during milling follou;ed by aggregation when tlre mastication is continued. The consistency of rubber is influenced not only by inastication ~ t i dsofteners, but also by various compouiiding ingrcrlients, such as accelerators, antioxidants, and certain dry powders. The powders ktve h e t i studied in detail by IIurlstori (17). Finally, the application of heat and the action of sulfur during vulcauizntion produce the most pronounced cbangcs in the consistency and strength oi the rubber phase. According to theoretical considerations developed by Eartell and Osterhof ( I ) and experimental work by Hock (14) and others, different pigmcnt.s would he wetted to different degree by the rubber, the wetting power being specific in its relation to a certain pigment. The wetting power would be
1‘01. 21, No. 7
a function not only of the surface energy of the rubber, but also of the specific attractions operating between the filler and the rubber a t the interface. I n rubber compounding the pigments to a great extent are forcibly inserted in the rubber by mechanical means and the pigment becomes wetted by tlie rubber to a certain definite degree, this being dependent upon the magnitude of the decrease in free surface energy. During the milling large amounts of free surface energy are developed and the surface of the rubber is brought in contact with that of the filler. The free surface energy of the interface is then more or less rapidly decreased by the specific forces in the filler and t.he rubber acting upon each other and wetting is procured. This may take place instantaneously or i t may vary with the accumulation of surface-active substance in the interface. The point in the processing a t which maximum wetting occurs is not known. The degree of wetting seems to be low during milling and during the first part of vulcaniantion when the plastic Bow of rubber reaches a maximum. The greatest possible surface developed during milling is the prerequisite for maximum decrease in surface energy or maximum transformation of work into a bond of filler-rubber, which is stronger than the cohesion of the rubber molecules tliemselws. From above considerations it would seem evident that the final reenforcement of a rubber compound is governed and defined by the following three fundamental factors: (1) The free surface energy of the system, a measure of which is the interface between rubber and pigment in square meters per kilogram of compound. This will be influenced to a considereble extent by the particle size, shape, uniformity, and dispersion of the pigments. (2) Intensity of wetting of the pigments by the rubber, or of rubber by the pigments. It can be expressed in the numerical difference in dynes per centimeter or ergs per square centimeter between the surface tension of the pigment against air and its interiaclal tension against rubber, according to theories developed by Bartell and Osterhof ( I ) . This will be regulated by the dispersion, the nature of the rubber and pigment surfaces. and by surface-activesubstances adsorbed in the interface. (3) The strength of the rubber mstrix in kilograms per square centimeter. This will be inRuenced by degree of polymerization, state of globular structure. action of dissolved substances and cornpounding ingredients.
Microscopic Structure of Crude and Masticated Rubber
Experimental results presented by Freundlioh aud Hauser (6),Sebrell, Park, and Martin (28), Van Rossem (27) and others indicate that ordinary rubber is a very closely packed inass of discrete latex globules. The increase in plmticity upon milling is due to their partial destruction. The milky whiteness characteristic of wet rubber is well known. The lyophilic protein layer between the latex globules absorbs coiisiderable amounts of water, changing the index of refraction of the structural phases. Samples of rubber were put through the mill to assure uniform thickness of approximately 2.50 mm. Two grams of each sample were then boiled nit11 100 cc. of water for different lengths of time. Slides m r e prepared as quickly as possible after extraction, by squeezing tlre sample between glass slides and scaling the edges with Canada halsam, Microscopical exaniinatiori of thin sections of ruhber that has been thus treated with water gives indiostioiis in regard to itsstructure. Smoked sheets (Figure I) that had been treated with water for only 4 hours showed a typical granular strueture uixicr the microscope, interspersed, however, with clear homogeneous areas optically empty, indicating that the original structure had been destroyed to a certain degree during coagulation and sheeting a t the plantation and probably during the treatment with water and preparation of the slides. Unmilled rubber that had been treated with water
July, 1929
INDUSTRIAL A N D ENGINEERING CHEMISTRY
for 72 hours absorbed about 3 per cent of water (increase in weight). The water extract of the rubber became more and more acid with prolonged extraction, showing a pH of 5.2 (colorimetrically) after 48 hours and 4.5 after 144 hours, indicating a decomposition of the natural resin glycerides and liberation of organic acid. Blended sheets that had been broken down for from 2 to 90 minutes showed a gradual destruct.ion of the granular structure. The small rubber globules seemed capable of more resistance toward disintegration than the larger ones (Figure 2 ) . Dead milled rubber did not give the opaque color, the granules had disappeared to a great extent,, and the proteins now appeared in the rubber mass in form of large aggregates. The natural rubber resins also aggregated morc and more duriiig the milling operations. Rubber that had been extracted with acetone when treated with water showed the granular structure to have disappeared completely. These microscopical results verify certain observations previously made by Klein and Stamberger (18). These authors, however, worked with benzene solutions of rubber and not with the crude rubber itself, as in this invcstigation. Crude rubber when mixed with sulfur and treated with water showed that introduction of sulfur into rubber also had brought about a destruction of the granular structure. Similar experiments made with compounds containing zinc oxide and carbon black proved negative, as the minute particle size of these pigments, which is considerably less than the dismeter of the latex globules (0.1 to 0.5 micron as compared to an average of 2 microns for latex according to Hauser) hides the appearance of the globules and makes it impossible to conclude whether they still persist or are destroyed. Considering the decrease in plasticity encountered in case of zinc oxide (173, it may be possible that the granules are destroyed to a greater or less degree.
667
lished work of H. Mueller, who by theoretical reasoning assumes a difference in the rate of roagulation between spherical and non-spherical particles. This perhaps explains variations in dispersability of different batches of the same black frequently encountered in rubber compounding. X-Ray Ezamination-Debye and Schemer (5) have derived an equation connecting breadth of diffraction lines of crystalline particles with particle diameter. X-ray experiments were performed to establish if this also holds true for carbon black. Previous work reported by I'ickles (21) and Goodwin and Park (Ku) mentions the same type of patterns with a breadth of line which follows the microscopically estimated order of particle size. X-ray photographs were taken of various types of black, the particle size of which was determined microscopically, the blacks being dispersed in rubber in a cpcentration of 30 per c,ent. Practically identical patterns were obtained in all cases, probably due to a superimposing of rubber and pigment patterns, and it was not possible t o discriminate between the different samples, althongh the particle size of thc various blacks probably ran from an average of 0.1 to 0.4 micron. It also seems that the x-ray method gives indications only in regard to the ultimate unit particle or crystal, but not in regard to its distribution or dispersion. The same patterns were obtained both when the pigments were well and poorly dispersed.
Carbon Black
PARTICLE SIZE AND SHAPE-The question of particle size and shape of carbon black is of considerable importance and very little experimental work on this subject has so Ear appeared in tho literature. Investigations by Spear and Moore (24), Peterfi (EO), and more recently Goodwin and Park(8,aand b), andHock (15) showthedi6cultyiuobtaining a complete dispersion of the Mack. The particle size of the pigment as dispersed in rubber is not necessarily the same as individual or primary particle size. I n a previous paper (10) it has been shown that it is possible to distinguish between different types of black from the degree of pigmentation of a mixture of rubber and carbon black, containing 0.5 per cent of pigment. This method, however, gives an indication of the dispersability of the black hut not of the uitimate pnrt,icle size. The particle-size determination is extremely difficult, especially in case of different t.ypes of gas black. I n order to study the individual particle size, several 0.1gram samples of gas black have been dispersed in a inixt,iire of ether-alcohol (50:50) with 0.01 pcr cent of saponin as protective colloid and allowed to sland for 12 hours to obtain scdimentation of uudisnersed and appreirated m:iteriaI. The individual, practically spheric& particles- whicli- were est.imated to range in an order of magrritrrde from about 15 to 200 m,u.
The actual shape of the particles was studied, using a11 Aximuth stob (26). It was Sound that. the snspeiisionn eontained both isotropic and anisot.ropic particles, the anisotropic having a much greater tendency to aggregation than the isotropic. The observation evidently conforms u.ith unpuh-
Figure 2-20-Minute Breakdown. Microacepicnl Drawing Approximately 5000 x
Wlien t h e l>lackswere compresscd in the form of powder in golatin capsules for 2 minutes under 50 pounds (3.5 kg. per sq. ern.) pressurr and photograjrhs taken the broadening of the diiTraction lines mentioned by previous antliors was observed with incmasing particle size. In cases whero the difrerenccs in particle size were very small the patterns became more and morc alike, and in such cases it is necessary to
samples. Tlic hexagonal symmetry of graphite (4, 6 , 16) and the anisotropic particles observed ultra-microscopically in carbonbliiclt suspensions sceni to support claims that the blacks are composed of a mixture of crystalline and amorphous carbon. WETTIKGCAPACITY-T~~wetting capacity of gas black was studied both in wbtcr suspcnsiori and in rubber. A
IAVDUSTRIAL AND ENQIh'EERING CHEMISTRY
F68
series of hnffer solutions was made up ranging from a pH of 2.2 to 8, using MeIIvaine's citric acid-phosphate standards. 0.2 cc. of a 0.001 M solution of fuchsin and 50mg. of gas black were added, and the suspension was incubated at 100" C . Triple-distilled conductivity water of a pH of 7.1 (coiorimetrically) wasusedin thiswork. It wasfoundthatthedyewasah sorbed readily by the carbon black in buffer solutions on t.he acid and alkaline sides, hut more slowly around the neutral point. The control solutions (buffer and fuchsin) did iiot show any alteration of the color. The same result was ohtitined when the pH of the aqueous medium was adjusted hy addition of acid or alkali. It was concluded that t.lie adsorp. tion power of carbon black reached a minimum around the neutral point and increased on the acid and alkaline sides, although there was no noticeahle difference in the rapidity of absorption at a pH of 6 or that of 2.
Vol. 21, No. 7
Vulcanization
The dispersion of pigments in rubber during vulcanization as reported in a previous paper has hedii further studied, hut
in this case the whole process has been watched continuously under the microscope. Various compounds were cured in a steam-heated micropress developed by Hauser and Hunemorder ( I S ) . (See also Hauser, 11.) The investigations are not yet, concluded, hut a short summary will be 6' wen of the most important results obtained. CRUDERuBnER-when unmilled smoked sheet was heated for 16 minutes a t 140' C., distinct brownish masses began to appear in tiie focus of tiie microscope, indicating a gradual formation of resin aggregates (Figure 3). They showed no signs of melting or decomposition when the rubber was heated to 150" C. or above. The resin glycerides evidently are :Idsorbed originally in a highly dispersed state on the siirface of tlie latex glol~olesand probably to a great extent remain in such a state when the coagulrition process is concluded. The formation of resin aggregates seems to he due to a destruct.ion of the rubber structure hy heat in tlie samc manner as during mastication. (Compare with section on microscopic structure, See also Fry and Porritt, ?.) The soluhility and chemical reactivity of these aggregated resins are naturally decreased to a great extent when they change from the highly dispersed to the aggregated state. The crude rubber exhibited a pronounced plastic flow during tlie heat,ing, which ceases very slowly. .. . * . RusnEn AKD SULFUR-T~C mobility of the rubber comes ' ' r' to a very sudden stop during the first minutes of heating if . ..,e, . I' sulfur or sulfur and accelerator are added to the system, as 0 has been also hrouglit out hy Hauser ( 2 1 ) . Aggregat.ioii of resin crystals takes place when rubber is heated wit.11 sulfur, Figure 3-Crude Rubber at 140" C. 600 X and in addition there seems to he a crystallization of various The distinct white m a s e r are resin aggregates. The black areas represnf dust and impuritier present in the rubber. mineral matter. I n this case, however, the resin aggregates show dissolution and disintegration to a certain extent and It was not possible to establish t.lie presence of any water- it seems that a reaction takes place between the ruhher resins soluble chemically active ingredients. When 1 gram of and the sulfur (88). carbon black was digested with 100 cc. of boiling water of During milling some of the sulfur particles are dissolved pH 7.1 under refiux for 1 hour and then filtered, there vas no in the iiot rubber on the mills and crystallize out in form of change of the pH of the water. The alkali absorption of the small rhombic crystals when the mass cools (Figure 4). These black was 1.90 per cent (NaOH and phenolphthalein); the rhombic crystals disappear (Figure 5) during vulcanization acid absorption none (IICI and phenolphthalein). The ace- at a low temperature, around 60" C., without any noticeable tone extract was 0.18 per cent. melting, as was established by using :in electrically heated The wetting of carbon black in compounded and cured "Quetschkainmor," where the temperature could he raised rubber or the intensity of the bond pigment-rubber was gradually from room to vulcanization temperature. They studied. Microscopical sections of highly compounded tread seem to sublime directly into the rubber. This fact is of stocks containing ahout 25 per cent of carbon black were importance as solution of sulfur in rubber evidently is a preprepared and studied under stretch. Small pieces of cured reyuisite of vulcanization. The large undissolved particles treads were stretched 200 to 300 per cent and placed in solid slowly assume a inore and more spherical shape and finally carbon dioxide until completely Frozen. Small pieces of this melt at about 120" C., forming lurge globules. Tliese s l o ~ l y stretched, hard, and frozen compound were now cut a t right decrease in size, the speed depending on the accelerator and angle against the stretch, and, immediately before any re- other compounding ingredients present in the system (Figures covery had taken place, immersod in a solution of sulfur 6 and 7). From a dispersion point of view the presence of chloride in carbon bisulfide. The samples were hardened and tlie small rhombic crystals is advisnble. The large sulfur sections prepared in the usual way. particles when melting usually produce an aggregation of The stretched microsect.ions of cured carbon-black treads adherent carbon-Mack particles as lins been showii in a preshowed a marked formation of vacuoles elongated in the di- vious paper (10). After the heating is discontinued, a crystalrection of stretch, indicating that the bond between pigment lization of free sulfur takes place at differenb lengths of time, and rubber had heezi broken in various places, hut chiefly depending on the compounding ingredients used. Various around aggregates of black or other pigments. (See also types of sulfur crystals are encountered wiiicli have been Green, 8.) It was not possible to establish any change in the studied and described in detail by Hauser (22) and others. distribution or orientation of the individual carbon-black ZINC O S I D E AND CARBON BLACK-The observations in particles. This seems to conform with observations by regard to the dispersion of zinc oxide and carbon black Stamherger (25), who has come to the conclusion that with during vulcanization can be summarized as iollows: When carbon black tlie adsorption probably involves the forma- zinc oxide was added to a rubber-sulfur mixtiire and the systion of a new gel structure, the structure of the original tem heated, a dissolution of pigment particles was observed. rubber which has been destroyed by milling being in effect This evidently was due to tiie formation of soluble zinc soaps restored. (29, 2). The flocculation of pibmerits in a mixture containing
.
.,
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
689
increased tremendously, because the original rubber structure had been destroyed. (Compare uith section on microscopic structure.) It wasvery difficult to disperse the pigments on the mill. The sine oxide showed a greater tendency to form secondary particles during vulcanization than carbon black. The free sulfur crystallized out almost. immediately after the system had cooled down. Acknowledgment
Figure 5-Two minutes at 140e C . The rhombic sulfur crystals have disappeared and the plastic Row of the rubber beginning to tense.
The author wishes to express his thanks to E. A. Hauser for his advice and suggestions in regard to the experiment.al work which was, in part., carried out in connectionwith his course in applied colloid chemistry at, Rlassachusetts Institute of Techiiology during the summer of 1928. He also acknowledges Iris indebtedness to E. 1'. W. Kearsley, of the Fisk Research Laboratories, for help received in the experimental work, and to Messrs. Aborn and Brow-n, of the x-ray laboratory in the Department of Applied Chemistry a t Massacliusctts Institute of Technology, for informiition and kind interest in the study of carbon black. Literature Cited
Figure 6-Ten minuter at 140- C . The last tracer of sulfur are disappearing.
minutes at 140" C. Distinct pigment aggregates are visible
P i g w e 'i-Forty-(lue
Flgures 4 f a ? - R u b b e ~ - S u l f u r - ~ ~Black-Zinc ~b~~ guanidine. 600 x
Oxide-Stearic
5 per cent of zinc oxide was most prominent during the first minutes of vulcanization (140' C.), but was followed by deflocculat,ion. When rubber was heated with carbon black a considerable flocculation of the pigment alone, there even though no sulfur was present due to an increased mobility of the rubber. The resiii crystals had a great adsorptive tendency towards t.he carbon-black particles and frequently acted as nuclei for aggregates, as was shown in a previous paper (IO). The formation of crystals from the free sulfur was considerably inhibited by the carbon-black particles, this probably being partly due to their adsorptive capacity toward sulfur and partly because they fill up the rubber matrix forming a close network, which prevents the formation of large sulfur crystals in the rubber. SrEAKIC ACID-When stearic acid was added to the above rubber compounds there seemed to be a greater formation of resin aggregates during mastication than in previous cases, perhaps because the r u b l w structure was destroyed to a greater extent. The plastic flow of the rubber increased during vulcanization. ACCzLEmToa-The effect of various accelerators as noted uiider the microscope during vulcanization was ch%racteriaed by the speed u,ith which the sulfur disappeared from the system. This varied from 3 to 15 minutes, depending on the accelerator and type of compound, when the temperaiure was raised immediately to 140" C. a t the beginning of vnleanization. 'The plastic flow of the rubber and the length of time until the free sulfur began to crystailiae out also varied wit,h different accelerators. ACETONE-EXTRACTED RuBBEE-~~hen extracted rubber was heated under the microscope the plastic flow of the rubber
Add-Di-o-tolyl-
11) Bartell and Osteihof, Colloid Symposium Monowaph, Vol. v, p. 113 (19271. ( 2 ) Brdford and Winkelmam, IND. EN^. CHFX., 15, 32 (1924) (3) Clark, "Applied X-Rays." p. 179. McGraw. Hill Book C o . , h-cw York, 1927. (41 Debyc.Scherrei, Z,, 277, 2s3 (19161.
(51 Ewnld, Siirb. moth. physik. boyer., Nos. 316-7 (1914). (6) Freuiidlich end F i a ~ s c r Kolloid-2.. , Erg. Bd., 36 (19251. ' ( i )Pry and Poiiiit. Trans. Inil. Rubber Ind., 3, 2113 (lY27). (8) Goodwiii and Prrk, IN". ENz. Cnsvr., 10, lo) 621, (61 708 (1928).
(9) Giecir. Ibid.. IS. 1029 (192Ii. (10) Grenquist. Ihid., PO, 1073 (1928). (11) Hnurer, Colloid Symposium Monograph. Vol. V1, p. 207 (lY2S). (121 Ilnuser. C o w Lectures, p. 38, hondon, 1928. (la) iiauser arid Huoemorder, I d i 6 Rubber World, 79, 59 (1923). (141 Iiock. Koulschuk, 1986, 131; 1911, 207; I n d i a Kubbar J., 74. 419, 463
(1927).
(15) Hock, Klulrchuk. 1918, 262.
.. . (191 Martin atid Davey. J. SOC.Chrm. Ind., 44, 317T'l19251 (20) l'etcrfi. Koufiihuk, 1911, 196. (211 Pickicr, l i o n s . l m i . Rrbber lnd., 1. S5 (19261. (22) . . Pohlc. z. uiii. .Mikioskob.. . . 41., 183 (1927). . . (231 Sebrell. Park,and Maxtin, in%>. RNO. CHBVI.,17,1173 (1923). (24) Spear and Moore, Ibid., 17.936 (1826); IS, 418 (1926). (25) Stlmberger, Kolldd-Z., 48. 295 (1927). (26) sZeKvary, z. Phyiik. 84, si (1933): as, 248 (1924). (271 Van Rossem, Chrm. 1VmkbIod. 10, 9 (19ZJi. ( 2 8 ) Weber, Orig. Cum. 8th Intern. Cons. Appl. Chem., 9, 95. (29) Wiegand. Indio Rubber J . , 13. 31 (1927).
Correction In my article entitled "Thc Recovery of Bromine from Sea Water," which appeared in the May, 1929, issue of INDnsTniAL AND ENCrNEEnlNG CnEmsCnu, the next to the last Sentence in the first paragraph ia the second column on page 441 should read: It is believed that a press could bc operated on an 8-hour cycle, durrinp which time approximately 70 pounds of filter cake would be produced per hour, which would contain from 65 to 70 per cent moiSture.-CHAS. M . A. STINS
