bluuebunny/crossref_metadata_2025 huggingface dataset:
Cloud invigoration and suppression by aerosols over the tropical region based on satellite observations
Authors: Niu F. , Li Z.
Published: February 2011

Abstract. Aerosols may modify cloud properties and precipitation via a variety of mechanisms with varying and contradicting consequences. Using a large ensemble of satellite data acquired by the Moderate Resolution Imaging Spectroradiometer onboard the Earth Observing System's Aqua platform, the CloudSat cloud profiling radar and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite over the tropical oceans, we identified two distinct responses of clouds and precipitation to increases in aerosol loading. Cloud-top temperatures decrease significantly with increasing aerosol index (AI) over oceans and aerosol optical depth (AOT) over land for mixed-phase clouds with warm cloud bases; no significant changes were found for liquid clouds. The distinct responses are explained by two mechanisms, namely, the aerosol invigoration effect and the microphysical effect. Aerosols can significantly invigorate convection mainly through ice processes, while precipitation from liquid clouds is suppressed through aerosol microphysical processes. Precipitation rates are found to increase with AI for mixed-phase clouds, but decrease for liquid clouds, suggesting that the dominant effect differs for the two types of clouds. These effects change the overall distribution of precipitation rates, leading to more or heavier rains in dirty environments than in cleaner ones.
Characterization and intercomparison of aerosol absorption photometers: result of two intercomparison workshops
Authors: Müller T. , Henzing J. S. , de Leeuw G. , Wiedensohler A. , Alastuey A. , Angelov H. , Bizjak M. , Collaud Coen M. , Engström J. E. , Gruening C. , Hillamo R. , Hoffer A. , Imre K. , Ivanow P. , Jennings G. , Sun J. Y. , Kalivitis N. , Karlsson H. , Komppula M. , Laj P. , Li S.-M. , Lunder C. , Marinoni A. , Martins dos Santos S. , Moerman M. , Nowak A. , Ogren J. A. , Petzold A. , Pichon J. M. , Rodriquez S. , Sharma S. , Sheridan P. J. , Teinilä K. , Tuch T. , Viana M. , Virkkula A. , Weingartner E. , Wilhelm R. , Wang Y. Q.
Published: February 2011

Abstract. Absorption photometers for real time application have been available since the 1980s, but the use of filter-based instruments to derive information on aerosol properties (absorption coefficient and black carbon, BC) is still a matter of debate. Several workshops have been conducted to investigate the performance of individual instruments over the intervening years. Two workshops with large sets of aerosol absorption photometers were conducted in 2005 and 2007. The data from these instruments were corrected using existing methods before further analysis. The inter-comparison shows a large variation between the responses to absorbing aerosol particles for different types of instruments. The unit to unit variability between instruments can be up to 30% for Particle Soot Absorption Photometers (PSAPs) and Aethalometers. Multi Angle Absorption Photometers (MAAPs) showed a variability of less than 5%. Reasons for the high variability were identified to be variations in sample flow and spot size. It was observed that different flow rates influence system performance with respect to response to absorption and instrumental noise. Measurements with non absorbing particles showed that the current corrections of a cross sensitivity to particle scattering are not sufficient. Remaining cross sensitivities were found to be a function of the total particle load on the filter. The large variation between the response to absorbing aerosol particles for different types of instruments indicates that current correction functions for absorption photometers are not adequate.
EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere
Authors: Pitkänen T. , Aikio A. T. , Amm O. , Kauristie K. , Nilsson H. , Kaila K. U.
Published: February 2011

Abstract. We report observations of a sequence of quiet-time Earthward bursty bulk flows (BBFs) measured by the Cluster spacecraft in the near-tail plasma sheet (XGSM ~ −12 to −14 RE) in the evening sector, and by simultaneous high-resolution measurements in the northern conjugate ionosphere by the EISCAT radars, a MIRACLE all-sky camera and magnetometers, as well as a meridian-scanning photometer (MSP) in the Scandinavian sector on 17 October 2005. The BBFs at Cluster show signatures that are consistent with the plasma "bubble" model (Chen and Wolf, 1993, 1999), e.g. deflection and compression of the ambient plasma in front of the Earthward moving bubble, magnetic signatures of a flow shear region, and the proper flows inside the bubble. In addition, clear signatures of tailward return flows around the edges of the bubble can be identified. The duskside return flows are associated with significant decrease in plasma density, giving support to the recent suggestion by Walsh et al. (2009) of formation of a depleted wake. However, the same feature is not seen for the dawnside return flows, but rather an increase in density. In the ionosphere, EISCAT and optical measurements show that each of the studied BBFs is associated with an auroral streamer that starts from the vicinity of the polar cap boundary, intrudes equatorward, brakes at 68–70° aacgm MLAT and drifts westward along the proton oval. Within the streamer itself and poleward of it, the ionospheric plasma flow has an equatorward component, which is the ionospheric manifestation of the Earthward BBF channel. A sharp velocity shear appears at the equatorward edge of a streamer. We suggest that each BBF creates a local velocity shear in the ionosphere, in which the plasma flow poleward of and inside the streamer is in the direction of the streamer and southeastward. A northwestward return flow is located on the equatorward side. The return flow is associated with decreased plasma densities both in the ionosphere and in the magnetosphere as measured by EISCAT and Cluster, respectively. In summary, we present the first simultaneous high-resolution observations of BBF return flows both in the plasma sheet and in the ionosphere, and those are in accordance with the bubble model. The results apply for the duskside return flows, but the manifestation of dawnside return flows in the ionosphere requires further studies. Finally, EISCAT measurements indicate increased nightside reconnection rate during the ~35-min period of BBFs. We suggest that the observed temporal event of IMF rotation to a more southward direction produces enhanced open flux transport to the nightside magnetotail, and consequently, the nightside reconnection rate is increased.
Planktonic dinitrogen fixation in the Mediterranean Sea: a major biogeochemical process during the stratified period?
Authors: Bonnet S. , Grosso O. , Moutin T.
Published: February 2011

Abstract. This study provides extensive data on planktonic N2 fixation fluxes across the whole Mediterranean Sea, representing a variety of trophic conditions. They show that N2 fixation occurs in Mediterranean waters during the stratification period, with a clear decreasing trend from the western basin (10–76 μmol m−2 d−1) to the eastern basin (0–0.4 μmol m−2 d−1. Highest rates are measured in the less oligotrophic areas, between the surface and 75 m-depth, and 45 to 75% of N2 fixation are performed within the picoplanktonic fraction (< 3 μm). While the biogeochemical impact of N2 fixation in the eastern basin seems negligible, N2 fixation is able to sustain up to 35% of new primary production during the stratified period and accounts for up to 25% of the external "new" N supply to the western basin during that period. These data disagree with indirect estimates of N2 fixation based on geochemical tracers and nutrient budgets, who suspected N2 fixation to increase with increasing N/P ratios and decreasing stable N isotopic signature of particulate organic nitrogen and NO3− from west to east. These results finally point out the need to assess N2 fixation at other seasons characterized by less oligotrophic conditions.
Ensemble analysis of frost damage on vegetation caused by spring backlashes in a warmer Europe
Authors: Jönsson A. M. , Bärring L.
Published: February 2011

Abstract. Tree dehardening and budburst will occur earlier in a warmer climate, and this could lead to an increased risk of frost damage caused by temperature backlashes. By using a spring backlash index and a cold hardiness model, we assessed different aspects of risk for frost damage in Norway spruce forests during the present climate and for one future emission scenario. Uncertainties associated with climate modelling were quantified by using temperature data from three climate data sets: (1) E-Obs gridded observed climate data, (2) an ensemble of data from eight regional climate models (RCM) forced by ERA-40 reanalysis data, (3) an ensemble of regional climate scenarios produced by the regional climate model RCA3 driven at the boundary conditions by seven global climate models (GCM), all representing the SRES A1B emission scenario. The frost risk was analysed for three periods, 1961–1990, 2011–2040 and 2070–2097. The RCA3_GCM ensemble indicated that the risk for spring frost damage may increase in the boreo-nemoral forest zone of southern Scandinavia and the Baltic states/Belarus. This is due to an increased frequency of backlashes, lower freezing temperatures after the onset of the vegetation period and the last spring frost occurring when the trees are closer to budburst. The changes could be transient due to the fine balance between an increased risk of frost damage caused by dehardening during a period when freezing temperatures are common and a decreased risk caused by warmer temperatures. In the nemoral zone, the zone with highest risk for spring backlashes during the reference period (1961–1990), the spring frost severity may increase due to frost events occurring when the trees are closer to budburst. However, the risk in terms of frequency of backlashes and freezing temperature were projected to become lower already in the beginning of this century.
Vulcanizing from a Thermodynamic Viewpoint
Authors: Williams Ira
Published: February 2011

Up to the present time thermochemical data in regard to vulcanization have been concerned largely with the heat of reaction of sulfur. This was a logical first step. The heat liberated is proportional to the sulfur which is combined, and the heat associated with the change in physical properties of the rubber is indicated to be quite small. A study of the free energy change for the reaction isoprene → natural rubber indicates that such a process is possible if the proper conditions can be found. A study of the thremodynamics of the most important side reactions might help establish conditions for the formation of the rubberlike polymer. A study of the free energy of the rubberlike isoprene polymer should assist in the comparison of this product with natural rubber. The vulcanized properties caused by incorporating a finely divided powder into rubber are associated with a relatively small energy change. A study of the reactions: chloroprene → vulcanized polymer and chloroprene → plastic polymer → vulcanized polymer, appears to be a probable source of information regarding the nature of change from plastic to nonplastic condition.
Control by Individual Incorporation of Vulcanizing Agents
Authors: Twiss D. F.
Published: February 2011

The individual incorporation of vulcanizing agents without a concurrent milling operation, i.e., by some form of diffusion process, originated with Thomas Hancock. Sulfur had been previously used as a dusting powder, e.g., by Lüdersdorff in 1832, and the storage of the dusted rubber must have led to gradual penetration of the sulfur into the rubber and possibly to effects of accidental vulcanization, especially if such rubber became exposed to sunlight, as was definitely the case in 1837 in Hayward's solarization process. But Hancock's well-known patent specification gives the first description of the deliberate incorporation of sulfur by a diffusion process for the purpose of subsequent heat vulcanization. This patent also describes and claims the compounding of rubber with mineral fillers and with asphaltum; it explains how “by immersing the caoutchouc in melted sulphur (at a temperature ranging from about 240° to 250° Fahrenheit)” or by “heating sheets of caoutchouc to about 200° and sifting and rubbing flour of sulphur on it” one can blend sulfur with the rubber, so that by subsequently raising the temperature “to 300°, or from 300° to 370° .… the change is produced”. The “change” was the term used by Hancock “for brevity's sake” to describe the desired effect.
A Theory of Elasticity, Viscosity and Swelling in Polymeric Rubber-Like Substances
Authors: Frenkel J.
Published: February 2011

The nature of the characteristic elasticity of rubber and other rubber-like substances has been elucidated by Kuhn and Mark, who showed that it is due to the ability of the thread-like molecules of these substances to fold or curl by free rotation of the separate monomeric elements about the single bonds linking them together into a long hydrocarbon chain. A curled form of these thread-like molecules being more probable than an extended one, they must display a tendency to curl simply because of their heat motion, without any actual forces tending to produce such an effect. As a result, an extension of a rubber-like body (without change of volume), entailing a similar average extension of all the molecular chains constituting it in a definite direction, is resisted by an elastic force proportional to the energy of heat agitation, that is, to the absolute temperature. This situation is quite similar to that which is found in the case of an ideal gas. The pressure exerted by the latter on the walls of the vessel containing it is due, not to a mutual repulsion of the molecules, as was believed long ago, but simply to their heat agitation. The main difference consists in the fact that, instead of a pressure, the heat agitation (free rotation) of the thread-like molecules produces a tension, increasing with the average degree of extension in the given direction. This difference is associated with a difference in the sign of the heating effect produced by a mechanical deformation: whereas a gas is heated on compression and cooled on expansion. In the case of rubber we find an exactly opposite behavior.
Sterols. L. The Isolation of Caoutchicol
Authors: Marker Russell E. , Wittle Eugene L.
Published: February 2011

Caoutchicol (C30H50O), a new alcohol, was isolated from a crude rubber extract (jelutong). It does not precipitate digitonin. It forms a monoacetate, a dibromide and can be reduced to a dihydro derivative. Dihydrocaoutchicol forms the ketone, dihydrocaoutchicone, on oxidation.
Measuring the Permeability of Rubber to Various Gases
Authors: Carpenter A. S. , Twiss D. F.
Published: February 2011

The rate at which a gas passes through a sheet of rubber-like material and the rate at which a gas is absorbed by a block of the material both depend on the same factors, solubility and diffusion constant. The magnitude of these factors can be measured by absorption experiments carried out under specified conditions and the results can be used to assess the permeability of the material in sheet form. Experimental methods and suitable apparatus are described for following absorption and the manner of interpreting the results in terms of permeability is given. Besides such advantages as accurate temperature control, convenient size and ease of handling of the apparatus, the small size of the test-piece, and the elimination of the difficulty of producing uniform thin sheets free from pinholes, the method has the advantage that both factors, solubility and diffusion constant, can be assessed independently; this is not normally possible with direct permeation measurements. Some experimental results are tabulated.
The Instability of Hevea Latex
Authors: Stamberger Paul
Published: February 2011

In a study made on plantations in Malaya, it was found that the cause of instability is not the same for both fresh and preserved latex. The autocoagulation of fresh latex, as it will be shown, is not caused by the acid formed by bacterial action on the serum components (autoacidification). Coagulation takes place, in fact, when decomposition of the serum components is prevented by the addition of strong antiseptics. These experiments, carried out in 1938 and 1939 in Malaya, support Whitby's view that autocoagulation is not due to autoacidification, but is probably caused by enzyme action on the protein or other serum components of the latex. The behavior of preserved latex is entirely different. Coagulation on storage was found to be due to acid formation and neutralization of the preserving agent applied. Decomposition of serum components was found in cases when coagulation did not take place, which would naturally influence the further behavior of latex. The action of the preserving agents is not a simple one. Inhibiting bacterial growth and preventing decomposition are not enough to keep the latex in the liquid, colloidal state. In addition to antiseptics, chemical compounds which act specifically as coagulation preventatives must be present. Rhodes recommends 0.1 per cent ammonia in addition to sodium pentachlorophenate. This small quantity of ammonia, as it was found, is the specific substance, probably an enzyme poison, which prevents coagulation. A number of additional substances in combination with sodium pentachlorophenate were tried, and it was found that adjusting the hydrogen ion concentration on the alkali side was not sufficient to prevent coagulation, although bacterial decomposition was inhibited. Observing the changes in the specific conductivity of latex during storage was the most satisfactory method found to measure the value of preserving agents or combinations of preserving agents. An increase in the specific conductivity of latex was found after a few days' storage, provided that the preserving agent did not inhibit decomposition of the serum components. From this increase in conductivity on storage, it could be predicted whether or not the preserving agent tested would give satisfactory results, or whether or not the concentration of the preserving agent was sufficiently high.
Zinc Oxide—A Product of Complex Physical and Chemical Properties
Authors: Depew Harlan A.
Published: February 2011

In the space available, it is obviously impossible to give more than an outline of the differences in pigment zinc oxide, of the significances of these differences, and of some of the methods by which these differences can be controlled. It is hoped, however, that the reader will conclude that zinc oxide is a product of complex physical and chemical properties, and that the manufacturer is able to manufacture zinc oxide of special properties to fit normal and unusual requirements.
A Torsional Hysteresis Test for Rubber
Authors: Mooney M. , Gerke R. H.
Published: February 2011

The mechanical hysteresis of rubber has been measured by almost every conceivable method, many of them simple but inexact. During recent years, however, the practical importance of hysteresis in rubber has been gaining recognition, and consequently a number of more elaborate and relatively exact methods and devices for measuring hysteresis have been developed. The present article describes a torsional hysteresis test. Although the apparatus required is quite simple, the test is accurate and may be regarded as a satisfactory test for many purposes.
Reactions between Compounding Ingredients during Vulcanization of Rubber
Authors: Bott E. C. B.
Published: February 2011

The calculations indicate that reactions (1), (3), and (5) can take place and proceed to virtual completion, whereas reactions (2) and (4) are not possible. They indicate also that the addition of extra sulfur to mixes containing litharge is necessary, and is in accordance with a custom long established empirically. It is evident that oxygen or nascent oxygen is not formed by any of these reactions; therefore no accelerated aging can take place by reactions between sulfur and litharge or zinc oxide. One peculiarity is that, although sulfur will react with litharge according to reaction (1), it appears that no oxygen is evolved by reaction (2), one possible reason being that the formation of lead sulfate takes place with a large decrease in free energy and is therefore readily formed. A possible explanation of the reaction between litharge and sulfur is that reaction (2), a possible first stage in reaction (1), is made to proceed to the right by the readiness with which lead sulfate can be formed. With respect to the reactions of zinc oxide, the assumption that zinc sulfide is formed by the action of hydrogen sulfide appears to be true.
Carbon Black in Rubber Compounding
Authors: Parkinson D.
Published: February 2011

The mechanism of filler reinforcement has not yet been fully explained, but there is general agreement that an important, probably the most important, factor is the enormous surface development between the rubber and filler due to the fine particle size of the filler. Explanations have been attempted to show how small particles can cause reinforcement, but a complete theory of the phenomenon which accounts for all the facts is still awaited. Particle size oj carbon blacks.—A knowledge of this property is important in an understanding of the mechanism of reinforcement by carbon black. Because of the difficulty of distinguishing between ultimate particles and compact aggregates, and because the particles themselves are too small to be resolved in an ordinary microscope, the usual microscopical methods of measurement are inapplicable. Ultramicroscopical methods have been used with some success, the results obtained by the method of Gehman and Morris being probably the most reliable. These authors quote an average particle size of 61µµ for a sample of a standard rubber gas black (Micronex). The figures given for P-33 black, Shawinigan acetylene black and Thermatomic black are 159µµ, 130µµ and 1120µµ, respectively.
Report of the Crude Rubber Committee. Presented at the Semi-Annual Meeting of the Division of Rubber Chemistry, September 12, 1940
Authors: Sackett G. A. , McColm E. M. , Nellen A. H. , Oldham E. W. , Parrish W. D. , Schatzel R. A. , Walton J. C.
Published: February 2011

The Crude Rubber Committee is always grateful for comments and suggestions regarding any of its published work or possible lines of investigation, and sincerely requests any member of the Division of Rubber Chemistry to send any ideas or opinions of the tests described here, or of tests in previous reports, to the Chairman of the Committee, so that they may be given consideration in further developments of the work in hand.
The Effect of Rapid Stirring on Latex and on Its Creaming
Authors: Van Dalfsen J. W.
Published: February 2011

1. The paper first discusses the determination of the mechanical stability of latex when stirred in a Hamilton-Beach mixer. Data are given on the stability of fresh latex, ammoniated latex, and concentrated latex. Particular attention is called to the increase in stability of ammoniated latex which takes place during storage, a phenomenon which is probably attributable to the formation of soap and accompanying increase in the charge of the latex particles. Soap added to latex increases considerably its stability and creaming capacity. 2. Fresh latex, stirred rapidly in a Hamilton-Beach mixer, undergoes microflocculation. The rapidly stirred latex coagulates entirely when it is allowed to stand quietly within a period of time which becomes shorter to the extent that stirring causes the mixture to approach more closely the point of actual coagulation in the mixer. This offers the possibility of coagulating fresh latex completely without the use of chemicals, but the method could be applied on a factory scale only with extreme difficulty. 3. When ammoniated latex is stirred rapidly for a time shorter than required for coagulation to become appreciable, microflocculation results. If, after having been stirred, such latex stands quietly, partial coagulation results. In this case the quantity of coagulum is greater, and the time for it to form is shorter, the more closely the mixing period approaches the coagulation point in the mixer.
Influence of the Temperature of Crystallization on the Melting of Crystalline Rubber
Authors: Bekkedahl Norman , Wood Lawrence A.
Published: February 2011

Data presented in this communication show an instance in which melting of a crystalline material is very much dependent on the temperature at which the crystals have been formed. It is well known that many substances in which crystallization is relatively slow can be crystallized at different temperatures in a range below the melting point, but no effect of the crystallization temperature on the temperature of melting seems to have been previously reported. The quantitative results for crystalline rubber, the material under investigation, are shown in Figure 1. The crystallization of unvulcanized rubber in the unstretched state has been found to occur at temperatures between about −40° C and 13° C. The time required for crystallization is about one year at 13° C, about ten days at 0° C, and a few hours at −20° C. Below −40° C the mobility is presumably insufficient for the formation of crystals. Crystallization and fusion are accompanied by changes in volume, heat capacity, light absorption, birefringence, x-ray diffraction, and mechanical properties such as hardness. The volume decreases about 2.5 per cent on crystallization, and the magnitude of the change is little influenced, if at all, by the temperature. Fusion, as measured by the volume increase, is found to be independent of the rate of heating, and to occur over a range of five or ten degrees.
Organic Analysis of Hevea Latex. IV. Amino Acids
Authors: Altman R. F. A.
Published: February 2011

The presence of amino acids in fresh latex was reported by Belgrave in 1925. On the basis of certain considerations, he considered it improbable that his experiments involved any profound changes in the original state of the nitrogen compounds. Accordingly the amino acids which he isolated must have been present in the free state in latex. It may be noted here that Belgrave's experiments did not completely exclude either chemical or enzymatic hydrolysis of proteins. Indeed, his amino acids were separated from a serum which was prepared by acidifying fresh latex with acetic acid (20 cc. of 10 per cent acid per liter of latex) and heating gently, with no precautions whatever for inactivating any proteolytic enzymes which may have been present. Aside from Belgrave's paper, there have been only two published references to the presence of amino acids in rubber or latex. Whereas Whitby, Dolid, and Yorston reported the isolation of valine from the acetone extract of crepe rubber, McGavack and Rumbold were able to isolate d-alanine from the serum of old ammoniated latex. There is no reason whatever for assuming from these observations that valine and alanine also occur free in latex. Indeed it would be impossible to give any guaranty that there was no hydrolytic degradation of proteins in the sample. In view of this situation it seemed highly desirable, as part of a systematic organic analysis of latex, to investigate more exactly the free amino acids which are present in latex. In addition to Belgrave's observation a preliminary analysis of fresh bottom latex which had been prepared for other purposes indicated that free amino acids actually do occur in latex. The object of the present paper is to identify the amino acids occurring in latex and, so far as is feasible, to determine the quantity also.
Estimation of Carbon Black in Neoprene Compounds
Authors: Scott J. R. , Willott W. H.
Published: February 2011

During a recent investigation it was necessary to determine the amount of carbon black in a sample of vulcanized Neoprene. The usual method adopted for vulcanized rubber, which consists in dissolving the rubber in nitric acid (British Standard Methods of Testing Vulcanized Rubber, B.S. 903–1940, p. 28), was tried without success, as the Neoprene did not dissolve. No methods for the analysis of Neoprene compounds appear to have been described in the literature; the following method of estimating carbon black, which has been found to work satisfactorily, may therefore prove of interest, especially as it can be used for certain other synthetic rubbers such as Buna. About 1.0 gram of the Neoprene sample is reduced to a fine crumb, such as will pass through a B.S. 10-mesh test sieve, by means of a rapidly rotating rasp. After extraction with acetone and chloroform, the extracted material is dried in a vacuum desiccator, transferred to a 400 cc. beaker, 20 cc. of nitrobenzene added, and the whole heated on a hot plate for a few minutes to allow the Neoprene to swell. 20 cc. of 25 per cent nitric acid (25 volumes of conc. nitric acid and 75 volumes of water) are then added, and the beaker is replaced on the hot plate. The Neoprene disintegrates and dissolves in the nitrobenzene in a few minutes. The beaker is then heated on a steam bath for about an hour, after which 100 cc. of xylene is added and the mixture filtered, while hot, through an alundum crucible or prepared Gooch crucible. The carbon is carefully washed with hot xylene till free from decomposed Neoprene, and finally with acetone. After drying at 150° C, the crucible is weighed, the carbon black then burnt off in a muffle furnace, and the crucible reweighed. The difference between these weights is the amount of carbon black present.
Introduction of the Bending-Strength Test as a Means of Determining the Freezing Point and Changes in Elastic Properties of Soft Rubber at High and Low Temperatures
Authors: Koch E. A.
Published: February 2011

A method for measuring the elastic properties of soft rubber at elevated temperatures and particularly at low temperatures, and for determining its freezing point, is described. This is the first time that a method for testing the flexibility of soft rubber has been used. The special advantages of this method are the small dimensions of the test-specimen and the consequent rapidity with which its temperature can be changed, the small weights with which the test-specimen is loaded, the low heat-capacity of the apparatus, and the ease with which the test-specimen can be made ready for testing. A change of samples can be made within five seconds. The time required for determining the freezing point and hardening point is about one-half hour, after which the apparatus is ready immediately for the next experiment. With a Dewar vessel containing 200–300 grams of solid carbon dioxide, about eight experiments can be carried out without refilling the vessel. Measurements can be reproduced to a fraction of one degree. The factors which, generally speaking, have an influence on the stability of rubber mixtures at low temperatures are discussed. Besides the method for determining freezing points of soft rubber mixtures, a definition of the stiffening point is proposed. Finally the method used for determining the modulus of elasticity of bending is described.
Dynamic Properties of Rubber. Dependence on Pigment Loading
Authors: Gehman S. D. , Woodford D. E. , Stambaugh R. B.
Published: February 2011

Dynamic properties are specific for different pigments. Curves show the dependence on pigment loading of the dynamic modulus, ratio of dynamic to static modulus, internal friction, dynamic resilience, and calculated relative heat generation at constant force and at constant amplitude. For the same volume loading, the dynamic modulus and internal friction rank in the order: Superspectra, channel black, zinc oxide, clay, blanc fixe, Thermatomic black, i.e., roughly in the order of particle size. The calculated dynamic resilience depends on the ratio of the modulus to the internal friction and increases in the order Superspectra, channel black, clay, Thermatomic black, blanc fixe, zinc oxide. The dynamic modulus shows an almost linear relation with the internal friction for different loadings of the same pigment. The dynamic modulus is independent of the frequency in the range 20–150 cycles per second. It depends on the amplitude, an effect which may be connected with the warming of the test-piece due to the vibration. The amplitude at resonance for the same driving force is approximately constant at all frequencies for a given rubber compound. The results show the wide range of dynamic properties obtainable with different pigments, and bring out the general principles involved in their use for dynamic purposes.
Some Dynamic Properties of Rubber
Authors: Harris C. O.
Published: February 2011

The following conclusions apply to rubber of the stock tested when bonded to steel: 1. For cylinders in compression and specimens in shear, the damping can be expressed in terms of a velocity coefficient. The damping decreases with increase of frequency; it increases with increase of static strain. 2. The dynamic modulus of elasticity is slightly larger than the static modulus and is not affected by change of frequency. It increases with increase of static strain for the cylinders and decreases for the shear specimens. 3. For cylinders in compression, both damping and modulus of elasticity are dependent upon the ratio of diameter to length.
Character of the Thermal Motion of Long Organic Chains, with Reference to the Elastic Properties of Rubber
Authors: Bresler S. E. , Frenkel J. I.
Published: February 2011

1. The theory of Mark and Kuhn, which assumes full freedom of rotation around the bonds of an organic chain, is criticized. Objections are raised as to the mechanism of elasticity of rubber proposed by these two investigators. 2. Based on the findings of Kistiakowsky, Pitzer and others, calculations are made of the elastic forces which hamper free rotation and thereby bring about a ribbonlike structure of the molecule. Calculations show the effect of these elastic forces on the thermal motion of the molecules and on their shape in solution. 3. It is shown that, if care is taken to calculate the modulus of elasticity correctly, the dynamic elasticity assumed by Mark and Kuhn is inadequate to explain the elastic behavior of rubber.
Sunlight and Accelerated Light Aging of Synthetic Rubbers
Authors: Morris Ross E. , James Robert R. , Werkenthin T. A.
Published: February 2011

Recently Werkenthin, Richardson, Thornley and Morris reported on the sunlight and accelerated light aging of various natural and synthetic rubber stocks, and proposed a method for standardizing the accelerated light aging test. The purpose of the present paper is to provide data on the correlation of sunlight aging with accelerated light aging for various synthetic rubber stocks loaded with mineral pigments. FORMULAS AND CURES The formulas and cures for the synthetic rubber stocks are given in Table I. These stocks have a loading corresponding to a good quality, 40 per cent wire insulation compound. Most of the prominent types of synthetic rubber manufactured in this country and one foreign synthetic rubber were included in this study. It was necessary to blend Vistanex Medium with natural rubber, inasmuch as this synthetic rubber cannot be vulcanized.
Nitroparaffins and Derivatives as Heat-Sensitizers for Rubber Latices
Authors: Campbell Arthur William
Published: February 2011

Recent research has made various nitroparaffins and their derivatives available in commercial quantities, and large-scale applications for the materials are rapidly being found. A considerable number of these compounds cause heat sensitization in rubber latices, a phenomenon that has been produced in the past by a number of materials, and is used extensively at present in the manufacture of foamed-rubber products. The use of nitroparaffins in this application is quite new, however, and has recently been the subject of extensive experimentation in this laboratory. In compounded latices it is not unusual to find three or more different materials, each with a definite purpose. In a study such as this, the use of completely compounded latices would unduly complicate the problem; so an effort was made to avoid these complications by running preliminary tests on the individual ingredients alone in a latex-nitroparaffin mix. It was found that gelling could not be produced by a nitroparaffin alone, even though the test mixtures were heated for considerable periods at 80–90° C. However, addition of a small proportion of zinc oxide to these mixes quickly induced gelling. It was also found that the oxides and hydroxides of the elements of Periods 2–6 of the Second Group of the Periodic Table gave results similar to those obtained with zinc oxide:
The Interaction between Rubber and Liquids. III. The Swelling of Vulcanized Rubber in Various Liquids
Authors: Gee G.
Published: February 2011

The entropy of swelling of vulcanized rubber is estimated, and assumed independent of the nature of the swelling liquid. The heat of swelling is related to the cohesive energy of the liquid, and a value of 66 calories per cc. deduced for the cohesive energy density of rubber. The swelling power of a liquid can be calculated approximately if its cohesive energy and molecular volume are known. Substantial agreement with theory is found in most cases, although it is necessary to consider aliphatic and aromatic liquids separately. The anomalously high swelling power of acids and alcohols arises from their association.
Equation of State of Some Synthetic Rubbers
Authors: Peterson L. E. , Anthony H. L. , Guth Eugene
Published: February 2011

The synthetic rubbers thus far developed bid fair to replace rubber permanently in hundreds of its varied uses. Though no one synthetic can, as yet, replace rubber in all of its applications, there are several synthetics available, each one of which excels rubber in one particular property. For example, some synthetics are oil- and gasoline-resistant, others resist the aging effects of heat, light, and oxygen, while still others surpass rubber in their resistance to flexing and abrasion.
Importance of Acidic Components in Compounding Ammonia-Preserved Latex with Zinc Oxide
Authors: Wren W. G.
Published: February 2011

In view of the experimental work described above, it appears that changes in viscosity of zinc oxide-compounded latex are due largely to the presence of ammonium salts of naturally occurring acids. These salts enable zinc to pass into solution, and to be absorbed by the latex globules, thus giving rise to the thickening commonly experienced. The amount of zinc passing into solution is directly proportional to the amount of acid present, and it is therefore suggested that determination of the acids by either of the methods described (viz., titration to pH 11 with caustic alkali, or from pH 7 to the end-point with hydrochloric acid), would form a sound basis for the classification of latices in regard to their behavior on compounding with zinc oxide. The investigations thus indicate that the variability of latex is due, in part at least, to the presence of acidic substances and may, therefore, be controlled by preventing the formation of the acids, or by their removal. Summary.—It is demonstrated that naturally occurring acidic substances control the solubility of zinc oxide in ammonia-preserved latex, and it is concluded that they are probably the controlling factor in determining the increase in viscosity which occurs in latex compounded with zinc oxide. In support of this view, it has been shown that the addition of various types of acid to ammonia-preserved latex markedly increases thickening after mixing with zinc oxide, and that the removal of naturally occurring acids reduces the thickening. It is suggested that titration of the acids in latex by the methods described forms a sound basis for the classification of latices in regard to their behavior on compounding with zinc oxide.
Effect of Temperature and Pressure on Oxygen Pressure Aging
Authors: Neal A. M. , Bimmerman H. G. , Vincent J. R.
Published: February 2011

An increase in the temperature of the oxygen pressure test from 70° to 80° C greatly increases the rate of aging of rubber vulcanizates. The temperature coefficients of aging rate for the six stocks tested vary between 1.63 and 3.48. The state of cure markedly affects the temperature coefficient of some stocks. It is obvious that no change in the specification from 70° to 80° C should be made without first determining the temperature coefficient of the stock involved. A decrease in the pressure of the oxygen pressure test decreases the rate of aging, but the rate is not proportional to pressure. The relative rates of aging between 0.5 and 300 pounds oxygen pressure for the stocks tested vary between 1.09 and 4.87 for the normal cures, and between 1.50 and 6.74 for the longer cures. The state of cure markedly affects the change in rate of aging with change in pressure. The data show that changes in the pressure of the oxygen pressure test must be accompanied by a revision of all aging specifications, which will involve an individual study of each stock and every cure of each stock, since no correlation between stocks seems to exist for the changes in rate of aging that occur with changes in pressure.
Rubber, Polyisoprenes and Allied Compounds. II. The Molecule-Linking Capacity of Free Radicals and Its Bearing on the Mechanism of Vulcanization and Photo-Gelling Reactions
Authors: Farmer Ernest Harold , Michael Stephen E.
Published: February 2011

Ostromislensky discovered that benzoyl peroxide when heated with rubber to 140° brought about a species of vulcanization of the rubber, the chemical nature of which has been the subject of much conjecture and experimental investigation. It was thought at first that the process was essentially one of oxidation and, indeed, free benzoic acid derived from the peroxide was isolated by Ostromislensky from the reaction product; but van Rossem, Dekker, and Prawirodipoero found that, although much benzoic acid was liberated during the reaction, some became united with the rubber, and could afterwards be freed by saponification. Van Rossem and his collaborators, however, were unable to correlate the accumulated observations with the previously published generalizations of Gelissen and Hermans concerning the nature of the reactions between benzoyl peroxide on the one hand and numerous substances, including alcohols, organic acids, and saturated and benzenoid hydrocarbons, on the other; nevertheless, they agreed with Gelissen and Hermans on one point, viz., that to some extent cleavage of the peroxide with formation of benzoic acid probably occurred, and they suggested that the concomitant reaction was a dehydrogenation of the rubber, the latter possibly becoming cross-linked as a result (2C5H8+PhCO·O·O·COPh→—C5H7·C5·H7—+2PhCO2H). Subsequently, Ostromislensky, following useful observations by Bock, made a new examination of the reaction, and concluded that it proceeded according to the equation:
The Crystal Structure of Rubber Hydrochloride
Authors: Bunn C. W. , Garner E. V.
Published: February 2011

“Rubber hydrochloride”, the crystalline substances made by addition of hydrogen chloride to rubber, is of interest for two reasons. First, the periodicity along the fibre axis of drawn specimens indicates that the carbon chain has not the simple plane zigzag form found in paraffin hydrocarbons, but is somewhat shortened by folding. There is similar evidence that several other chain polymers also have folded chains; the elucidation of the geometry of such molecules would form a useful contribution to our knowledge of the stereochemistry of carbon compounds in general and chain polymers in particular. Rubber hydrochloride appeared to be a suitable substance for crystallographic investigation from this point of view: it gives a well-defined x-ray diffraction pattern. Moreover, a prediction of the chain form has been made on the basis of a knowledge of the periodicity and the use of a hypothesis which has been called the principle of staggered bonds. The determination of the structure by x-ray methods forms the first test of the validity and usefulness of this hypothesis. Secondly, rubber hydrochloride is interesting on account of its physical properties. Unlike rubber itself, it is crystalline at room temperature, “melting” at about 115° C. The present work on its crystal structure forms part of a program of research being carried out in this laboratory, and is a contribution to the attempt to understand the physical properties of chain polymers in terms of molecular structure.
Some Observations on the Flex-Cracking Characteristics of GR-S (BUNA-S) Compounds
Authors: Breckley Joseph
Published: February 2011

Probably the most serious defect of GR-S rubber is its poor resistance to flex-cracking, and much research has been conducted in an effort to improve this characteristic. Among the many tests employed in the study of rubber is the bend-flexing method, using the De Mattia apparatus, as described in A.S.T.M. Method D430-35T. However, when GR-S vulcanizates were flexed according to the standard procedure, erratic results were obtained. In an effort to secure more reproducible test data, a study was made of the crack growth that proceeded from small nicks made initially in the surface of the sample. Some difficulty was encountered in making a nick of uniform dimensions until a procedure was developed whereby a pinhole about 0.025 inch in diameter and approximately 0.05 inch deep was made in the center of the grooved surface of the test-piece. The hole was made by a pointed piece of steel, shielded so that it could penetrate the sample only to a constant depth. When the samples were prepared in this manner, the crack growth which extended from the hole during flexing was fairly uniform, and the results were reproducible within rather close limits.
The Influence of Chemical Structure on the Imbibition of Liquids by Rubber. I
Authors: Whitby G. S. , Evans A. B. A. , Pasternack D. S.
Published: February 2011

Studies of the swelling of rubber which had been carried out up to 1924 were reviewed by one of the authors in an earlier publication. A review of subsequent studies is to be found in a paper by Scott, who himself has contributed some data on the subject. These prior studies were not, however, concerned primarily to secure systematic information on the influence of the chemical structure of liquids on their imbibition by rubber, and they involved only a relatively small number of liquids, except for the study by Lee, in which the behavior of raw rubber in sixty-nine liquids was observed only qualitatively. Further, a good many of the earlier observers used material of unknown history and composition, such as “black rubber tubing”, and often assuming the swelling to reach a maximum in twenty-four hours. In the present study the course of the swelling of rubber, both raw and vulcanized, has been followed, quantitatively, at intervals over long periods, and a very large number of liquids have been examined. The present installment deals largely with classes of liquids (acids, alcohols, aldehydes, ketones, etc.) containing the more highly polar groups. A collection of hydrocarbons is, however, included, because hydrocarbons are in general good swelling agents, and data on them will serve for comparison with that on other classes of compounds.