bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Sulfur in Rubber Compounds. I. Precipitation of Barium Sulfate in the Presence of Picric Acid
Authors: Lindsly C. Herbert
Published: February 2011

THERE is probably no single operation in analytical chemistry that has received more attention from investigators than that of precipitation of barium sulfate by means of a soluble barium salt for the determination of sulfate or of barium. The literature on this subject is voluminous and the conclusions reached by different investigators as to the proper procedure to employ in order to obtain a precipitate which will be filterable and reasonably pure are highly contradictory. The procedure which seems to be in most general use at present for the determination of sulfate is that of adding the barium chloride solution to the hot sulfate solution very slowly, stirring vigorously meanwhile, then allowing the whole to digest at an elevated temperature for several hours before filtering. The diversity of opinion as to the proper procedure arises, the author believes, from the fact that the barium sulfate precipitate is exceedingly sensitive to its environment and that a very slight change in the amount or kind of impurities present in the solutions during precipitation has a profound effect upon the crystal size and shape of the precipitated particles as well as upon their purity. Kolthoff and Vogelenzang (2) have stated that it is impossible to prescribe a general procedure for the accurate precipitation of sulfate in arbitrary mixtures. In other words, a precipitation procedure which gives satisfactory results in the determination of sulfur in copper ores, for instance, may not yield a satisfactory precipitate when applied to the determination of total sulfur in hard rubber dust, and a study of each type of determination, with due consideration for the amount and kind of impurities present, must be made in order to find the conditions necessary to obtain a precipitate which is pure and easily filterable.
The Coating and Impregnation of Textiles with Latex
Authors: Stevens H. P. , Stevens W. H.
Published: February 2011

Of the various uses to which rubber latex might be expected to be applied, the textile industry is one of the more obvious, yet so far latex has been little used by the manufacturers of textiles, and relatively little work appears to have been done in this field of application. No doubt this arises from the fact that knowledge of the properties and handling of latex is not usually found among textile manufacturers. Where textiles impinge on rubber manufacture the conditions are otherwise, and the earliest application of latex to fibers is to be found in the manufacture of rubber goods. Perhaps the first example of this application consists of the impregnation of tire cords with latex in the place of rubber sols, initiated and developed by the United States Rubber Company (British patent 178,811 (1921); 210,397 (1923)). No information is available as to the extent to which the latex treatment is carried on today, but it does not appear that such has become universal practice in spite of the advantages claimed by the inventors. There are no published data which enable a comparison of the advantages and disadvantages of latex impregnation to be made in comparison with the older process, but it is certain that the impregnation of textile fibers with latex is not as simple an operation as would appear at first sight.
Determination of the Color of Latex
Authors: Cotton F. H.
Published: February 2011

It has long been felt that there is a need for a standard method of measuring the color of latex, a feature of the utmost commercial significance in determining its value and suitability for certain manufacturing processes. The method to be described is the direct outcome of a recent discussion with members of the scientific staff of the London Advisory Committee for Rubber Research. Among the methods hitherto suggested for determining the color of latex are: (1) the use of standard tiles of varying tint with which the latex to be examined may be compared; (2) the use of a standard tintometer, such as that marketed under the trade name “Lovibond”; and (3) the employment of an apparatus embodying a photo-electric cell. Whereas the first of these methods is simple, there is some difficulty in ensuring that the standard color-tiles shall always be of exactly the same tint, and that their density shall undergo no change whatever with time. The color of latex is so largely a neutral gray tint that it hardly seems necessary to employ the wide range of color values incorporated in a tintometer of the Lovibond type. Though a photo-electric cell should be capable of giving an accurate measure of the relative whiteness of different grades of latex, it would not measure differences in tint and its cost would probably prove prohibitive.
Note on the Deterioration of Raw Rubber by Manganese Contamination
Authors: Hastings J. D. , Rhodes E.
Published: February 2011

The presence of excessive amounts of manganese has been found by Bruni and Pelizzola to be associated frequently with tackiness in raw rubber. Bishop and Sekar have described the development of unusual stickiness when rubber prepared from latex to which manganese salts had been added was subjected to a temperature of 50–55° C. for 300 hours. More recently Sackett has found that the use of manganese salts in the manufacture of crude rubber gives a product which becomes tacky and weak on storage, and which, when vulcanized, has a lower tensile strength, a poorer resistance to aging and a poorer abrasion resistance than normal rubber. Bruni and Pelizzola when examining various samples of very tacky estate rubber found amounts of manganese of the order of 0.02 per cent, but were not able to form firm conclusions as to the manner in which such large amounts of manganese find their way into various grades of estate rubber. The present note describes an instance in which it has been possible to trace the cause of serious manganese tackiness in a large consignment of estate rubber.
Rubber Production
Authors: Rhodes Edgar
Published: February 2011

The institute welcomes contact with users in America. There have been a few occasions when users have approached the institute direct on matters in which it could be of obvious assistance. A notable recent case was that of the manganese deterioration brought by Sackett's organization. In this case the institute was able to be of some assistance and was itself benefited. Such cooperation is excellent, and will be very welcome in Malaya. It would be well also to establish some single committee or organization as a channel through which samples, reports, complaints and suggestions could be circulated freely to American users from Malaya and the London organization, and received in both places from America. If there were a constant contact, for example, between a technical subcommittee of the American Chemical Society's Rubber Division, the technical subcommittee of the London Advisory Committee, and the Board of the Rubber Research Institute, users' requirements would always be known, views could be exchanged, suggestions could be made, word battles fought, and samples and batches of new materials passed forward from Malaya and London for American works test.
Determination of True Free Sulfur in Vulcanized Rubber. A Modification of the Thiocyanate Method
Authors: Minatoya Syukusaburô , Aoe Itirô , Nagai Idumi
Published: February 2011

The limit of quantity of potassium cyanide was determined as regards the interference with the end point of the titration of potassium thiocyanate with silver nitrate solution. Acetone was found to be a suitable solvent for the separation of potassium cyanide from potassium thiocyanate. A new modified method was proposed for the determination of true free sulfur in vulcanized rubber, by the use of acetone to remove the cyanide which renders obscure the end point of the titration of thiocyanate with silver nitrate solution. The proposed method was applied to the analysis of pure sulfur and some rubber goods, and was ascertained to be accurate and easy to carry out, requiring no special apparatus.
Organic Accelerators and Problems Connected with Their Use in the Factory
Authors: Jones Maldwyn
Published: February 2011

It may be said that there are three types of problems to be considered when selecting an accelerator: (1) To determine the approximate limits of curing temperatures and times within which it is desired to work. Questions of skill in handling accelerators and questions of the size and shape of the articles govern this. (2) To determine what are the specific qualities desired in the vulcanizate, and then to select appropriate accelerators coming within the limits specified in (1) above. (3) With the choice narrowed down to one or two products, questions purely of an economic nature will probably determine the final choice. In conclusion the author wishes to express his thanks to the Imperial Chemical Industries Ltd. for permission to publish the results embodied in this paper.
Studies on the Combined Use of Two Different Organic Accelerators. V. Mercaptobenzothiazole and Hexamethylenetetramine
Authors: Aoe Ichiro , Kitayama Hiroshi
Published: February 2011

1. Equal weights of a mixture of hexamethylenetetramine and mercaptobenzothiazole give the optimum accelerating activity and minimized scorching. 2. Scorching tests indicate that there should be no danger of scorching in practice; a comparison of the scorching tendencies of various proportions showed that a ratio of mercaptobenzothiazole 70 and hexamethylenetetramine 30 gives noticeable scorching. 3. The melting point curves, indicate some relation between the above proportion and the scorching phenomenon. 4. The heating curves of two sets of mixtures containing hexamethylenetetramine and sulfur, and hexamethylenetetramine, mercaptobenzothiazole and sulfur, respectively, in an oil bath at 150°, indicate that hexamethylenetetramine and sulfur react exothermically and that this reaction is accelerated by the presence of mercaptobenzothiazole. 5. The products of the reaction between hexamethylenetetramine and sulfur are carbon disulfide, ammonium thiocyanate, hydrogen sulfide, and ammonia. 6. The products of the reaction of two sets of samples heated in an oil bath at 150°, as indicated in 4, were determined quantitatively, and it was found that there was an increase of these products with an increase of time; which was also indicated by the loss of weight during the heating. 7. All of these reaction products had low accelerating power. Thiuram disulfide and ammonium thiocarbamate derived from carbon disulfide and ammonia and ammonium polysulfide derived from hydrogen sulfide, ammonium, and sulfur were tested, since they might have been formed during vulcanization, but they were found to be poor accelerators. 8. A preliminary test of combinations of mercaptobenzothiazole with ammonia, ammonium polysulfide, ammonium thiocyanate, and ammonium dithiocarbamate indicated that ammonia and ammonium polysulfide have some accelerating power, whereas all others are ineffective. 9. The combined use of ammonia and mercaptobenzothiazole forms a molecular compound which is effective as an accelerator, and this is true in an analogous way of the combined use of hexamethylenetetramine and mercaptobenzothiazole. 10. In order to prove experimentally the above theory, an attempt was made to treat a mixture of rubber, mercaptobenzothiazole, zinc oxide and sulfur with ammonia until the latter penetrated throughly the sample, after which the latter was vulcanized. Such treatment gives far better acceleration than does mercaptobenzothiazole without treatment with ammonia. 11. The accelerating power of ammonium polysulfide and mercaptobenzothiazole is attributed to the formation of ammonia from ammonium polysulfide and the reaction of ammonia and mercaptobenzothiazole.
Studies on the Acetone Extraction of Raw Rubber. V. The Influence of Heating at 100° C. and Storage of the Acetone Extract on the Saponification Value
Authors: Endô Hidemaro
Published: February 2011

(1) When the acetone extract was heated at 100° C., the saponification value (AT) first diminished and then increased. (2) When the acetone extract was stored, the saponification value (AT) first increased and then diminished and returned to the original value. (3) The determination of the saponification value was carried out as follows: The sample was extracted for the required time, the acetone was evaporated off as rapidly as possible and the flask was dried in a steam bath for as short a time as possible. The drying time must not be over 15 minutes, and usually 5 minutes is sufficient. The dried flask was cooled and weighed, after which 20 cc. of 0.2 N alcoholic KOH was added and the flask heated on a water bath for 60 minutes. The excess alkali was titrated with 0.1 N HCl solution, using phenolphthalein as indicator.
Thixotropy and Plasticity in the Rubber Industry
Authors: Freundlich H.
Published: February 2011

Sole and gels are characteristic colloidal systems. In sole the continuous phase or dispersion medium is a liquid and is in excess; the disperse phase is distributed in this medium in the form of small particles invisible in the ordinary microscope, and having diameters below 0.5 µ. The particles may be liquid or solid or have a more complicated structure. The term colloidal may be used in a somewhat broader sense, to include for instance, latex which contains a certain percentage of larger particles visible in an ordinary microscope, and with diameters up to about 5 µ. It is arbitrary to draw the line of demarcation between colloidal and non-colloidal systems at 0.5 µ most properties of colloidal systems may be found in systems containing larger particles (up to about 6–7 µ) and most methods used in colloid science may be applied to them. The term gel is not so easy to define. The conception favored in the earlier days of colloid chemistry that gels are the counterpart to sols, having a solid medium of dispersion and a disperse phase consisting of small drops of liquid, is not now popular and does not seem probable. It is assumed by many investigators that gels have a structure similar to that of foams or concentrated emulsions, the disperse phase consisting of small solid particles and the dispersion medium being liquid as in the case of sole; but it is present in very thin layers, generally only a few mµ thick, separating the solid particles from each other.
The Oil Resistance of Rubber. I Study of the Swelling of Vulcanized Rubber
Authors: Tanaka Yoshio , Kambara Shû , Noto Jirô
Published: February 2011

To study the effect of solvents on the elastic properties of vulcanized rubber, the following three points were investigated. 1. The swelling maximum obtained by various mixed solvents. 2. The stress-strain curves of rubber swollen to different degrees. 3. Time-swelling and time-deswelling curves. The spiral theory of molecular structure of rubber proposed by Fikentscher and Mark is utilized to explain the experimental results.
The Influence of Mastication on the Oxido-Aging of Rubber. A Comparison with the Influence of Heating
Authors: Dufraisse Charles , Vieillefosse Roger
Published: February 2011

It may rightly be said that vulcanization improves all the properties of rubber except its tendency to deteriorate. We have undertaken a systematic study with a view to ascertaining why raw rubber, which shows so little tendency to oxidize and is so stable, loses its resistance upon being vulcanized and becomes both more easily oxidized and more easily altered. To this end, we have studied successively each of the factors which may have an influence on its oxidizability. In a previous article we settled the question of metallic impurities, particularly iron, which ordinarily is introduced into rubber either by means of the ingredients added or by removal from the steel rolls during the mechanical action. Under ordinary conditions the deleterious effect of iron, without being zero, is not great; it simply merits attention. In any case, it is not sufficient to explain the undesirable change in stability which is found after vulcanization. Taking the factors in order, mastication was next studied. This treatment, which is almost always necessary and the discovery of which has made possible the development of the rubber industry, would seem, a priori, to be rather dangerous from the point of view with which we are concerned. In the first place, it disrupts the substance, a condition which cannot be favorable to its subsequent equilibrium. But above all there is the danger that it may be an “inductor” of autoöxidation.
Heat Capacity, Entropy, and Free Energy of Rubber Hydrocarbon
Authors: Bekkedahl Norman , Matheson Harry
Published: February 2011

The best method for obtaining the free energy of formation of rubber is by making use of the third law of thermodynamics. This makes necessary the determination of heat-capacity values of rubber from room temperature down to temperatures sufficiently low to apply an empirical formula for obtaining the values below this lower temperature. From these heat-capacity values the entropy may be obtained. Then from this latter value, along with the entropy values of carbon (graphite) and gaseous hydrogen and the heat of formation of rubber, a reliable value for the free energy of formation of rubber may be calculated. Several investigators have previously determined the heat capacities of rubber, but their observations were not made at temperatures sufficiently low to permit accurate extrapolation to the absolute zero in order to apply the third law. Furthermore, in the previous work the possibility that rubber at low temperatures might exist either as a metastable amorphous form or as a crystalline form was not clearly recognized. In the present investigation the aim was not only to extend the temperature range but also to obtain data of a higher order of accuracy than that previously reported.
Corrosive Action of Sulfur against Metallic Copper during Vulcanization
Authors: Satake Shozo
Published: February 2011

The use of copper wire electroplated with tin for insulated electric wires was originated by Siemens eighty-five years ago (through Saito, J. Soc. Chem. Ind. Japan, 18, 248 (1915)), and its merits lie in the fact that it prevents a lowering of the electrical conductivity and mechanical strength from corrosion of copper by the sulfur in the rubber, and also prevents the rubber from deteriorating abnormally fast by contact with the copper. The manufacture of rubber for coating wire has improved rapidly since the appearance of organic accelerators and combined accelerating and vulcanizing agents, such as the polynitrobenzenes and benzoyl peroxide of Ostromislensky, the selenium of Boggs and tetramethylthiuram tetrasulfide and tetramethylthiuram disulfide. Recently, it was reported (India Rubber World, 87, 38 (1933)) that rubber compounded with 2 per cent of 1,3,5-trinitrobenzene as vulcanizer does not corrode wire conductors and does not deteriorate abnormally fast when the rubber mixture is covered directly on the wire and vulcanized. The prediction was also made that tin-coated copper wire will disappear entirely from the cable world. As a matter of fact, marine cables have for a long time been covered with an insulator consisting chiefly of gutta-percha or balata hydrocarbon, in direct contact with the copper conductor, and have given good service. The para-gutta insulation of marine cables, recently developed by the Western Electric Company, U. S. A., is composed partly of rubber, with no tin coating on the copper conductor. Nevertheless, the principal factor which decides the “electrical life” of rubber submerged in water is, according to Curtis (J. Res. Natl. Bur. Standards, 5, 539 (1930)) the deterioration of the rubber by copper salts, and Asano (J. Soc. Chem. Ind. Japan, 24, 336 (1921)) reported that smoked sheet became so sticky that it required considerable strength to separate after it had been held between two copper plates for six months. The status of the electric insulating wire industry today is such that a thorough investigation of the tin coating of copper wire and the methods of tin coating in connection with the deterioration of rubber by the copper wire is desirable. The investigation described in the present paper was carried on with this object, and it deals with experiments on the corrosion of metallic copper by sulfur during vulcanization, and shows the formation of copper sulfides as corrosion products.
The Formation of High Polymers by Condensation between Metallic Polysulfides and Dihalogenated Hydrocarbons and Ethers
Authors: Patrick J. C.
Published: February 2011

The general theory of formation of high molecular weight linear polymers by condensation between bifunctional compounds of low molecular weight to form products of large molecular mass has been so thoroughly reported in the literature that no extensive citation is believed to be advisable here. A very thorough study of this type of reaction has been made by Carothers and his co-workers on the formation of polyesters, the reaction being of the general type: One can, without taxing the imagination, conceive of the polymerization of isoprene or butadiene as belonging to the same general type of phenomenon, differing only in the fact that the reacting molecules are alike instead of different and that the “condensate” is one double bond per molecule. Therefore, no attempt will be made in this paper to distinguish between condensation and polymerization. When organic dihalides having CH2X terminals, in which “X” denotes a halogen, are caused to react with metallic polysulfides, MSxM, there usually results a linear polymer of high molecular weight.
Investigation of the Structure of Rubber by Means of Electron Diffraction
Authors: Kruilov K. I.
Published: February 2011

1. Irradiation of unstretched rubber with an electron beam gives electronograms in the form of three amorphous rings with identity periods of 4.15, 2.05, 1.25 A. U. The third identity period closely approaches the distance between the carbon atoms of the carbon chain of a rubber molecule. 2. An electronogram obtained by the irradiation of stretched rubber with an electron beam discloses interference points, and the whole pattern has the character of a fiber diagram. 3. An electronogram contains more details (rings, points) than the corresponding x-ray diagram. Thus electron analysis makes it possible to obtain more information relating to the structure of rubber, and in this respect has an advantage over x-ray analysis. 4. Calculation of the electronograms shows that the elementary cell of rubber has orthorhombic symmetry with edge dimensions of a=12.3, b=8.3, c=8.1 A. U. These results agree with the model of the elementary cell of rubber constructed by von Susich, Mark, and Meyer on the basis of x-ray analysis. 5. Highly oriented rubber preparations give in addition to a large number of points, a certain number of spots which do not fit into the scheme of points of oriented rubber. This phenomenon requires a further study. 6. Spot interference appears, as a rule, only with stretched films. The localized maxima on the interference rings of irradiated unstretched films observed in some cases are explained by a partial orientation formed in the process of drying the film.
Inorganic Substances with Rubber-like Properties
Authors: Meyer Kurt H.
Published: February 2011

Two inorganic substances with elasticity similar to that of rubber are described in the literature of the subject, viz., elastic sulfur and polyphosphonitrilic chloride. In this paper we shall deal with investigations of both. It is common knowledge that sulfur heated to 170° becomes highly viscous; if then cooled, e. g., by plunging into water, it yields an amorphous elastic product. If threads of this amorphous product are stretched, they show a double refraction, and, as Trilat has found, develop a fiber-diagram. With Go the author has examined this diagram, and deduced from it the following arrangement of the sulfur atoms: long chains of sulfur atoms, linked by strong homeopolar valences, are arranged parallel to the direction of stretching. Their special position in the elementary cell is shown in Fig. 1. In a recent publication, Warren has made it clear that ordinary sulfur is made up of 8-atom rings. The molecular weight of the elastic form Sn is not known, but seems to be very high. We know from earlier work that the melting of sulfur produces an equilibrium between the two forms, and this shifts, at higher temperatures, in favor of the chain-sulfur. About 1000 calories per gram atom S are consumed in the transformation of S8 into Sn.
Plasticization of Rubber
Authors: Garner T. L. , Blow C. M.
Published: February 2011

The effect of oxygen in the mastication process of raw rubber has been demonstrated by Cotton (Trans. Inst. Rubber Ind., 6, 487 (1931) and Busse (Ind. Eng. Chem., 24, 140–146 (1932), who obtained a considerable reduction in the rate of plasticization of raw rubber when milled in the absence of oxygen. In a recent paper (Blow and Garner, Trans. Inst. Rubber Ind., 10, 465 (1935)) it was suggested that work on similar lines with rubber-carbon black stocks and rubber-softener mixtures might yield interesting results. The opportunity to carry out some experiments presented itself, and the results form the subject of this note. Experimental.—A small Werner-Pfleiderer enclosed mixer, suitably modified to render it as gas-tight as possible, was employed. The weight of rubber taken for each test was 14 ounces. This was fed into the mixer piece by piece, over a period of two minutes, and milled for a further 5 1/2 minutes; the atmosphere in the mixer was in one series nitrogen, freed from oxygen by passing through pyrogallol, and in another series oxygen. Sufficient gas was supplied to the mixer to maintain a pressure of about 5 cm. of water. The conditions of temperature, time, etc., were as accurately controlled as possible. Plasticity measurements were made 30 hours after the milling process, the plasticity figure being the time in seconds taken to compress a pellet (1 sq. cm. in cross-section and 1 cm. long) between platens 1 sq. cm. cross-section from a thickness of 7.5 to a thickness of 5 mm. under a load of 1000 gms. at 100° C.
Rubber Solvents and Substances Which Lower the Viscosity of Rubber Cements
Authors: Fabritziev B. V. , Buĭko G. N. , Pakhomova E. A.
Published: February 2011

1. The greatest effect in reducing the viscosity of rubber solutions is produced by alcohols. This effectiveness increases in the following order: isopropyl, butyl, ethyl propyl, isoamyl, and methyl alcohol. Of these the most active is methyl alcohol and the least active isopropyl alcohol; all other alcohols are closely similar in action. Acetophenol, pyridine, and acetone also reduce considerably the viscosity of rubber solutions, but are greatly inferior in their effectiveness to the alcohols. Ethyleneglycol and dichloroethane reduce the viscosity very little. The addition of 1 to 5 per cent of water greatly increases the viscosity, which contradicts the observations of Messenger and Porritt. However the concentration of water in our experiments was considerably higher than that used by these authors. 2. With higher concentrations of active liquids, the degree of reduction of viscosity increases, but there is a definite limit of concentration above which further reduction of viscosity is very small. With alcohols this limiting concentration is at 2–3 per cent. 3. The effect of active substances in the reduction of viscosity depends on the concentration of the cement and on the preliminary mechanical treatment of the rubber, i. e., the greater the concentration of cement and the less the rubber is subjected to preliminary mechanical treatment, the greater the reduction of the viscosity; in other words the higher the original viscosity the greater is the reduction in the viscosity by active substances. 4. The viscosity of a rubber cement increases during storage, regardless of the presence of an alcohol. During short periods of storage (up to 1 day) the effectiveness of time alcohol is maintained, but during prolonged storage its action decreases and with methyl alcohol the viscosity actually increases. 5. The rate of gelation of a self-curing cement depends on the nature of the viscosity-reducing agent. Methyl alcohol causes more rapid gelation than ethyl alcohol. In conclusion, for reducing the viscosity of self-curing cements the addition of 3 parts of ethyl alcohol to 100 parts by weight of a cement it is recommended as the lest procedure for industrial requirements.
The Effect of Addition of Colloids on the Coagulation of Latex
Authors: Tanaka Yoshio , Kuwata Tsutomu , Noguchi Takashi
Published: February 2011

1. A known proportion of colloid was added to dilute, dialyzed latex (rubber content 3.5 per cent) to determine the effect of colloids on the coagulation of latex. Various proportions of 0.2 N acids were added; the mixtures were then left for 24 hours. The relations between the state of coagulation of latex and the proportion of acid are shown graphically. 2. The coagulation curves of acetic, hydrochloric, sulfuric, and nitric acids show that latex is coagulated by a definite quantity of acid, above which proportion the coagulation disappears and then reappears by further addition of acid. The first coagulation is apparently governed by the p H value of the dispersed medium, and the charge on the surface of the rubber particles is opposite to that of rubber dispersed in an alkaline medium. The second coagulation is governed by the concentration of cations. 3. Gum arabic, casein, saponin, gum tragacanth, glue, “funori,” or hemoglobin were added to latex and coagulation obtained by the addition of 0.2 N acetic acid or hydrochloric acid. Each gave the characteristic curve of a protective colloid; dextrin, however, had no influence on the coagulation curve. 4. The influence of the colloids on the coagulation curve is of particular interest in studying further the properties of colloids and rubber particles, and this will be discussed in detail in connection with further investigations.
Effect of Pressure on the Dielectric Constant, Power Factor, and Conductivity of Rubber-Sulfur Compounds
Authors: Scott Arnold H.
Published: February 2011

This paper reports the results of a study on the effect of pressure on the dielectric constant, power factor, and conductivity of rubber-sulfur compounds, and is the third paper of a series dealing with the electrical properties of rubber-sulfur compounds. The previous papers dealt with the effect of sulfur content, temperature, and current frequency on these electrical properties. The results reported in the present paper have been corrected for changes in the dimensions of specimens caused by changes in pressure. The required data for making these corrections were obtained from a detailed study of the compressibility of rubber-sulfur compounds which has recently been completed.
Semi-Ebonite. Part 2
Authors: Gibbons P. A. , Cotton F. H.
Published: February 2011

In Part 1 (Rubber Chem. and Tech., 8, 554 (1935)) frequent reference was made to the volatile products emitted during the aging of semi-ebonite under different conditions. In this section an experiment is described wherein the various products were detected and some attempt made to estimate the relative amounts of each. The experiment in its original form presented considerable difficulty, and many disappointments were experienced before a modified apparatus was finally adopted. Experimental Method.—Eight test-pieces, one from each of the accelerated cures (see Part 1), were cut to a convenient size, six inches by one inch. The test-pieces were carefully weighed and their thickness determined as the average of several readings on the micrometer. The strips were suspended from a bent glass rod projecting from a cork-bearing inlet and outlet tubes (see Fig. 5). The cork was then inserted in a clean conical flask and the latter sealed with wax until it withstood a considerable vacuum. The flask was placed in a Geer oven automatically maintained at 70° C. The outlet tube was attached to an absorption train and the inlet tube to a purifying train.
Determination of Free Sulfur in Rubber Containing Mercaptobenzothiazole and Tetramethylthiuram Disulfide
Authors: Kheraskova E. , Korsunskaya E.
Published: February 2011

Free sulfur in a given vulcanizate is a definite and constant quantity. It can be extracted from rubber with acetone and various other sulfur solvents, and can be reduced directly in the rubber to hydrogen sulfide. The claim of Teny, supported by experimental evidence, that acetone extracts the entire sulfur in rubber has not been confirmed by other investigators. Several methods for the determination of free sulfur in rubber are known. The classic method, adopted by the U. S. National Bureau of Standards, involves the extraction of sulfur with acetone and subsequent oxidation of the sulfur with bromine to sulfuric acid. The extraction consumes from 4 to 6 hours. This method gives excellent results with rubber mixtures containing no sulfur-bearing accelerators. When sulfur-bearing accelerators are present in a rubber mixture, they are dissolved by acetone and may be oxidized together with the extracted sulfur by bromine. To investigate the possible effect of accelerators (mercaptobenzothiazole and tetramethylthiuram disulfide) in a rubber mixture on the determination of free sulfur by the classic method, a series of experiments on the determination of sulfur in these accelerators under the conditions of analysis of free sulfur was undertaken.
Sulfuric Acid as a Latex Coagulant
Authors: Wiltshire J. L.
Published: February 2011

The replacement of formic or acetic acid by sulfuric acid for coagulating has the obvious attraction of saving money, but this acid undoubtedly has a bad reputation among planters, and the published literature on the subject is not encouraging. Several authors of standard books on estate practice have emphasized the results of Martin, who observed that the addition of one-eighth of one per cent of sulfuric acid to dry rubber caused a very marked retarding effect on the rate of vulcanization. As, however, the total amount of acid used for coagulation is approximately one-half of one per cent, and by far the greatest proportion of this will be removed in the serum and in the wash-water, it seems unlikely that any quantity approaching Martin's figure would be allowed to remain in the rubber. Martin's results can be regarded as nothing more than a warning, and certainly do not constitute any real evidence of the unsuitability of sulfuric acid.
Studies on the Nature of the Action of Organic Accelerators for Rubber Vulcanization. IV. The Detection and Analysis of Organic Accelerators. Systematic Identification of Organic Accelerators
Authors: Shimada Keiichi
Published: February 2011

Though much work has been carried out and recorded on the comparative vulcanizing power of various organic accelerators, yet so far as the author is aware, there is very little published work on the detection of commercial organic accelerators; probably a few laboratories have some special test of their own, but as yet no one has seriously taken up this field. The present investigation was carried out with a view to devise a simple but satisfactory systematic method of identifying general organic accelerators now used in the rubber industry.
The Determination of Free Sulfur by a Volumetric Method Part II
Authors: Guppy W. D.
Published: February 2011

1. The method previously described for the volumetric determination of free sulfur in vulcanized rubber has been compared with the older gravimetric methods in cases where other organic compounds containing sulfur are present in the vulcanizate. 2. The volumetric method gave lower results than the methods involving oxidation of the acetone extract in the case of vulcanized rubber containing aldehydeamine condensation products of thiouram disulfide compounds. This indicated that the sulfur combined with some organic compounds was not reduced by the reagents used. 3. The results with the accelerator tetraethylthiouram disulfide showed that in some cases part of the sulfur in organic compounds was reduced under the conditions of the reaction. 4. The acetone-soluble and the acetone-insoluble portions of brown substitute contain organic sulfur compounds. Part of the sulfur in these compounds was reduced to hydrogen sulfide by the action of nascent hydrogen. 5. The sulfur compounds present in white substitute were stable toward the reducing agents used in the estimation of free sulfur. 6. The sulfur compounds formed by the vulcanization of ebonite were in part reduced to hydrogen sulfide with tin and acid. Variations in the composition of the mixing and in the vulcanizing conditions altered the amount of these reducible compounds. 7. The volumetric method previously described cannot be used for the determination of the free sulfur in ebonite, brown substitute or in vulcanized rubber containing brown substitute. In the case of vulcanized rubber containing brown substitute or of ebonite the method can be used to determine the amount of sulfur in the acetone extract. 8. The volumetric method can be employed for the determination of the free sulfur in soft vulcanized rubber containing white substitute and in reclaimed rubber.
The T-50 Test for State of Cure
Authors: Gibbons W. A. , Gerke R. H. , Tingey H. C.
Published: February 2011

In tires, machine supports, conveyor bells, hose, waterproof clothing and footwear, and other rubber articles, the state of vulcanization of the rubber in the rubber compound is important for best results in service. A simple, rapid, and accurate physical test for state of cure is described, which is independent of the composition of the rubber compound. The test depends upon the observation that for a specific rubber compound the greater the state of cure the lower is the temperature at which chilled stretched rubber will spontaneously retract.
Anode Process for Rubber Articles and Coatings
Authors: Beal C. L.
Published: February 2011

THE term “anode process” has been chosen and used widely in the trade to designate a fundamental method for the production, directly from rubber latex, rapidly, and in one application, of articles and coatings of the highest grade of unmasticated rubber. Rubber latex, a milky exudation from the bark of rubber trees, is composed chiefly of tiny particles of rubber suspended in a water phase or serum, not unlike globules of butter fat in milk. Rubber latex contains small amounts of many organic compounds and inorganic salts. Some of these non-rubber materials, such as the proteins and resins, are considered to be adsorbed on the surfaces of the rubber particles and to be responsible for many of the colloidal characteristics of latex. As it comes from the tree, the latex is unstable and coagulates easily, but, when stabilized with ammonia, it can be safely shipped and stored for long periods. Like most colloidal particles in suspension in an alkaline medium, the rubber particles of ammoniated latex are negatively charged through the adsorption of hydroxyl anions. The particles, many as small as 1/25,000 inch in diameter, are in constant oscillation (Brownian movement) and are kept from hitting one another and sticking together (coagulating) by the repulsion of their electric charges. When the hydroxyl ions are neutralized or otherwise removed from the particles, the electric repulsion between particles disappears and coagulation results.
Tensile Tests of Vulcanized Rubber at High Speed
Authors: van Rossem A. , Beverdam H. B.
Published: February 2011

The types of apparatus most frequently used for elongation tests of rubber have only a slow speed. Thus the maximum rate of elongation of the Schopper dynamometer is 120 cm. per minute and in ordinary practice 60 cm. per minute is the speed used. The normal rate ordinarily used in America with the Scott apparatus is 20 in. per minute. On the other hand, it has been found by experience that slightly vulcanized rubber which, on the Schopper machine, gives very good values of tensile strength and resilient energy at rupture, even excellent values, is on the contrary brittle when stretched very rapidly by hand and breaks with a very low elongation. Consequently it is of interest, chiefly from the point of view of a study of rubber, to carry out elongation tests at high speed. As is easily seen from the technical literature, this problem has been neglected. At the Bureau of Standards the influence of the rate of elongation on the results of tensile tests has already been studied, but the rate varied only between five and forty-five inches per minute. Briefly, the results of this study seem to indicate a general tendency for the elongation and resistance to extension to increase with increase in speed of elongation. Hauser and Rosbaud have also made tests on the influence of the speed of elongation, but their tests were on raw rubber and at extremely slow speeds. As for the brittleness which appears at high rates of elongation, only very casual references are to be found in the literature. By a study of gas black Park has proved that the maximum physical properties found by hand-testing do not agree with the maximum obtained with the Scott dynamometer. Recently Wright5 has also pointed out the “shortness” of vulcanized rubber and has emphasized the importance of tensile tests at high speed. Unfortunately, we did not have at our disposal any apparatus which permitted recording the stress-strain curve at high speed and reading the ultimate elongation and tensile strength. Accordingly, we used in our tests a Charpy ram pendulum, belonging to the section of metallography of the Polytechnical School of Delft. It is known that this apparatus as well as others similar to it are used in determining the energy necessary to rupture various materials. This apparatus was changed and on the two supporting surfaces were attached two pins in such a way that a rubber ring could be placed there without elongation as seen in Fig. 1. This ring was then broken with the ram pendulum. The greater the energy expended in breaking the ring, the less the pendulum rises. As is known, the energy expended in breaking the ring is calculated by the aid of a numerical table by comparison with an oscillation without rupture of the ring. For each type of vulcanizate, at least six rings were tested by this pendulum method. In addition some rings from the same vulcanizates were given the usual tensile test on the Schopper dynamometer. From the resulting curve the energy of rupture can be determined in kilograms in the usual manner by the aid of a planimeter.
The Kinetics of the Vulcanization of Rubber
Authors: Nordlander Birger W.
Published: February 2011

While engaged in the development of a sensitive test for mercury vapor, the writer made the observation that if sulfur were melted and then allowed to cool, a surface was formed that at first was very reactive to mercury vapor, as evidenced by the rapid formation of black mercuric sulfide. However, a day or so after preparation, the surface had lost its reactivity entirely, since even exposure to mercury vapor of high concentration at an elevated temperature failed to produce any blackening at all. It appeared as though an active but unstable form of sulfur had been produced when the sulfur was melted, which in short time had changed over into a non-reactive form. This curious behavior of sulfur seemed interesting enough to warrant a separate investigation, and a study was, therefore, made of the activity of various forms of sulfur toward mercury vapor, the details of which will be published in a separate paper. However, before stating the results that were obtained, a brief review of our present knowledge of the various allotropic modifications of sulfur will be included. The most common form of sulfur is the rhombic, or Sα, modification which is stable up to 95° C. At this temperature it changes over into the monoclinic, or Sβ, form, which is stable in the region between 95° C. and the melting point, 114.5° C. When melted, the sulfur forms a pale yellow fluid liquid which, when heated further, goes over into a brownish, very viscous state with a maximum of viscosity at 160°–170° C. Above this temperature the melt becomes more and more fluid and boils at 444.5° C. From the classical work by Smith and co-workers it is known that there are two forms of sulfur in the melt, called Sλ and Sμ, the former of which is soluble in CS2, and on freezing out yields the two crystalline forms of sulfur. The latter is insoluble in CS2, is amorphous, and will, on rapid freezing out, retain the amorphous state which, however, at room temperature gradually is converted into Sα, especially in the presence of crystalline sulfur. The amount of Sμ present in the liquid at the melting point is very small, but increases rapidly with the temperature, especially around 160°–170° C., causing the highly viscous state of sulfur at these temperatures.
Isoprene and Rubber. Part 23. Cryoscopic Measurements of Rubber Solutions
Authors: Staudinger H. , Bondy H. F.
Published: February 2011

Pummerer, Andriessen, and Gündel published a work with this title which contains a number of remarks about the communication of Staudinger, Asano, Bondy, and Signer. The following discussion deals with this subject. 1. Molecular Weight Determinations of Rubber in Camphor according to East Determinations of the molecular weight of rubber in camphor cannot explain the constitution of rubber because, as has been explained before, when rubber is heated in melted camphor, at 170°-180°, a very pronounced decomposition of the rubber to semi-colloidal cleavage products takes place. The rubber molecule is very unstable as a consequence of the peculiar position of the double bonds in the chain; cleavage takes place with extraordinary ease, and attention has already been called to the fact that the cleavage of hexaphenylethane into triphenylmethyl, of dicyclopentadiene into cyclopentadiene, as well as the migration of the ally group, e. g., in phenylallyl ethers, the mobility of the substituents in allyl residues and finally the extremely easy depolymerization of rubber, all have one and the same cause: namely, that a substituent in the ally! group is very loosely combined. These facts, which are of such importance in the chemistry of rubber, should not be ignored as happens in most works on rubber. In order to study the decomposition, we carried out viscosity determinations. As the following experiments show, the viscosity of rubber is much less after melting in camphor than before. There occurred a very great decomposition at 170°, as was to be expected, and the relation t1/t2 which characterizes the decomposition is about 15. If pure rubber is decomposed in boiling tetralin the relation t1/t2 = 6.2. The decomposition in camphor is, therefore, surprisingly great, possibly because of the greater concentration of the dissolved rubber. The camphor solution used was 10 per cent, that of tetralin on the contrary was only 1 per cent.
The Long Spacings of Rubber and Cellulose
Authors: Clark George L. , Corrigan Kenneth E.
Published: February 2011

1. A new method for the examination of highly polymerized compounds is proposed. This consists in the direct measurement from diffraction interferences of colloidal micelle dimensions. 2. The construction of an instrument consisting of an x-ray tube with magnesium target and vacuum camera without intervening window or air space is described. 3. The major spacing of unstretched vulcanized rubber is found to be 99.3 A˚. U. 4. The number of isoprene molecules per unit cell is estimated to be of the order of eight thousand. 5. Three measurements of the long spacings of cellulose are recorded.
The Action of Solvents with Rubber
Authors: Stamberger P. , Blow C. M.
Published: February 2011

1. Methods and results of measurements of the swelling pressure and osmotic pressure of rubber jellies and solutions are described. 2. Within the range of concentrations which was measured, no differences were found between the rubber jellies and the solutions. 3. Rubber of various origins gave the same values. 4. A few influences which bring about changes in viscosity have been discussed.