Abstract
The observations which are recorded in the present paper represent an extension of the single case of litharge which has already been described. They show that, when small percentages of certain substances are added to rubber with a view to protecting the rubber from deterioration by oxygen, these substances are capable of directing the combination of oxygen with the rubber in different ways. This is shown by the fact that, as a result, a given percentage of combined oxygen does not lead to the same deterioration in physical properties. This difference in behavior can be explained logically on the basis of the antioxygenic theory by assuming that some agents act, not by retarding the rate of oxidation, but by deactivating the peroxides as soon as they are formed. By what term are these agents to be designated? First of all it should be recalled how an antioxygenic substance is defined. Every substance is an antioxygenic agent when it has the power, in small percentages, of retarding the rate of absorption of free oxygen by an autoxidizable substance. This definition obviously does not apply to a perfect deactivating agent, since the latter has no effect on the rate of absorption of oxygen, in spite of it too protecting rubber against deterioration by oxygen, and therefore being equally worthy, from the practical point of view, of being called an antioxygenic agent. However, this would only lead to confusion between the phenomenon itself and its effects. Furthermore, since commercial antioxygenic substances appear to show, to a greater or less degree, a combination of the two actions, one might consider designating them by some term which would embody both mechanisms. The word “antiaging agent” is not suitable, for it is too general and applies to cases where, in addition to oxygen, other influences such as light and repeated flexing play a part. There is, then, a problem in terminology to be settled, but this will have to be left unanswered provisionally until sufficient facts which have a more direct bearing on the case are available. Finally attention should be called to the useful effect which may be pictured as a possibility when the two types of protective agents which have been described act jointly. In other words, if the two mechanisms in question were to be superimposed, it would appear to be possible to improve considerably the resistance of rubber to deterioration by oxygen, since any oxygen which escapes the protective action of the true antioxygenic agent has its harmful effect reduced by the deactivating agent. To express it figuratively, it might be said that oxygen which has succeeded in overcoming the first obstacle opposing its action finds itself confronted with a new defense which puts the oxygen partially out of action. As shown by experiments carried out on this subject, which are described in the following paper of this series, this theoretical conclusion is actually borne out by the results of the experiments.
Combined Punctual and Diffused Monitoring of Concrete Structures Based on Dielectric Measurements
