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Synthetic substances with rubber-like properties
I46
CURRENT TOPICS.
[J. F. I.
Synthetic Substances With Rubber-Like Properties.--E. R. BRIDGWATER. (MechanicalEngineering, Vol. 60, No. Io.) Today a great profusion of more or less rubber-like synthetic products is available to the engineering profession--a profusion that must be confusing to engineers who have not had opportunity or occasion to make a careful survey of the field. As a result there may be a tendency to draw broad generalizations in terms that are devoid of exact meaning. It is a fact, however, that the products included in the broad terms "synthetic rubbers" and "synthetic rubber-like materials" have little in common except the ability to stretch to several times their initial length before breaking. In fact, there is less similarity between some of these synthetic products and others than there is between some of them and natural rubber. Moreover the properties of some of these synthetic products may be varied over such a wide range by compounding with other ingredients and vulcanizing under varying conditions that it is unsafe to generalize about any of them. The only way to ascertain whether a rubberlike synthetic product will be suitable for a specific use is to analyze the conditions of service, prepare a composition whose properties approach as closely as possible the ideal revealed by that analysis, and test that composition under conditions related as closely as possible to those that may be encountered in service. It will probably never be possible to tabulate the properties 9 f rubber-like synthetics in so comprehensive a manner that the engineer will be able to select the right product for any particular use by consulting a handbook. Today, at least, it is true that any general tables of properties that may be prepared would be so misleading as to do more harm than good. The engineer who would use rubber or rubber-like synthetics wisely must accept these facts and work within the limitations imposed by them. R. H. O. Erosion Remedies Must Fit Local Conditions.--Rule-of-thumb solutions do not apply to soil erosion problems. A successful soil and water conservation program for any farming section must always be based on local conditions--on existing soil types and topography, on probable climate, and on economic conditions--says H. H. Bennett, Chief of the Soil Conservation Service. Bennett cites the program developed for the wheatlands of the southern Great Plains. In this region where soil blowing is a serious hazard, many erosion control methods successful in humid areas are impracticable. Because of climatic irregularities, systematic crop rotations are undesirable. Soils and seasonal conditions are unfavorable to the growth of legumes. Low rainfall rules out the type of terrace
CURRENT TOPICS.
[J. F. I.
Synthetic Substances With Rubber-Like Properties.--E. R. BRIDGWATER. (MechanicalEngineering, Vol. 60, No. Io.) Today a great profusion of more or less rubber-like synthetic products is available to the engineering profession--a profusion that must be confusing to engineers who have not had opportunity or occasion to make a careful survey of the field. As a result there may be a tendency to draw broad generalizations in terms that are devoid of exact meaning. It is a fact, however, that the products included in the broad terms "synthetic rubbers" and "synthetic rubber-like materials" have little in common except the ability to stretch to several times their initial length before breaking. In fact, there is less similarity between some of these synthetic products and others than there is between some of them and natural rubber. Moreover the properties of some of these synthetic products may be varied over such a wide range by compounding with other ingredients and vulcanizing under varying conditions that it is unsafe to generalize about any of them. The only way to ascertain whether a rubberlike synthetic product will be suitable for a specific use is to analyze the conditions of service, prepare a composition whose properties approach as closely as possible the ideal revealed by that analysis, and test that composition under conditions related as closely as possible to those that may be encountered in service. It will probably never be possible to tabulate the properties 9 f rubber-like synthetics in so comprehensive a manner that the engineer will be able to select the right product for any particular use by consulting a handbook. Today, at least, it is true that any general tables of properties that may be prepared would be so misleading as to do more harm than good. The engineer who would use rubber or rubber-like synthetics wisely must accept these facts and work within the limitations imposed by them. R. H. O. Erosion Remedies Must Fit Local Conditions.--Rule-of-thumb solutions do not apply to soil erosion problems. A successful soil and water conservation program for any farming section must always be based on local conditions--on existing soil types and topography, on probable climate, and on economic conditions--says H. H. Bennett, Chief of the Soil Conservation Service. Bennett cites the program developed for the wheatlands of the southern Great Plains. In this region where soil blowing is a serious hazard, many erosion control methods successful in humid areas are impracticable. Because of climatic irregularities, systematic crop rotations are undesirable. Soils and seasonal conditions are unfavorable to the growth of legumes. Low rainfall rules out the type of terrace