What is claimed is:1. A reagent composition which is chemically inert when solid and is chemically reactive when molten, comprising(a) a first substance selected from the group consisting of high molecular weight waxes and polymers; and(b) a second substance dissolved, dispersed, or encapsulated in a solid matrix of said first substance, said second substance being highly chemically reactive and selected from the group consisting of strong bases and strong acids,whereby when said reagent composition melts, said second substance is exposed for chemical reaction.2. A reagent composition as defined by claim 1, wherein said first substance is selected from the group of compounds consisting of high molecular weight paraffin waxes, alcohols, diols, polyols, polyglycols and polyglycol ethers.3. A reagent composition as defined by claim 2, wherein the first substance includes up to 25 weight percent of a phase transfer catalyst which is selected from quaternary ammonium and phosphonium salts.4. A reagent composition as defined by claim 1, wherein said first substance has a melting point of from about 30.degree. C. to about 250.degree. C.5. A reagent composition as defined by claim 1, wherein said second substance is an inorganic acid or base.6. A reagent composition as defined by claim 1, wherein said second substance is selected from the group of compounds consisting of the oxides and hydroxides of Li, Na, K, Mg and Ca.7. A reagent composition as defined by claim 1, wherein said second substance is selected from the group of compounds consisting of Li, Na, K, Mg and Ca salts of high molecular weight alcohols, diols, polyols, polyglycols and polyglycol ethers.8. A reagent composition as defined by claim 1, wherein said second substance is selected from the group consisting of oxides, hydroxides and alcoholates of alkali metals and alkaline earth metals.9. A safety device automatically activated in response to an increase in the temperature of a chemical system from a lower normal temperature to a higher abnormal operating temperature, said device being made of a reagent composition as defined in claim 1,whereby when the chemical system temperature increases to the higher abnormal temperature, said reagent composition melts and exposes said second substance for chemical reaction with the chemical system.10. A safety device as defined by claim 9, wherein said first substance is selected from the group of compounds consisting of high molecular weight paraffin waxes, alcohols, diols, polyols, polyglycols and polyglycol ethers.11. A safety device as defined by claim 10, wherein the first substance includes up to 25 weight percent of a phase transfer catalyst which is selected from quaternary ammonium and phosphonium salts.12. A safety device as defined by claim 9, wherein said first substance has a melting point of from about 30.degree. C. to about 250.degree. C.13. A safety device as defined by claim 9, wherein said second substance is an inorganic acid or base.14. A safety device as defined by claim 9, wherein said second substance is selected from the group of compounds consisting of the oxides and hydroxides of Li, Na, K, Mg and Ca.15. A safety device as defined by claim 9, wherein said second substance is selected from the group of compounds consisting of Li, Na, K, Mg and Ca salts of high molecular weight alcohols, diols, polyols, polyglycols and polyglycol ethers.16. A safety device as defined by claim 9, wherein said second substance is selected from the group consisting of oxides, hydroxides and alcoholates of alkali metals and alkaline earth metals.17. A safety device as defined by claim 9, wherein said device is impregnated into a porous material contained in the chemical system.18. A safety device as defined by claim 9, wherein said device is in the form of a coating on at least a portion of the chemical system.19. A safety device as defined by claim 9, wherein said device is arranged adjacent the chemical system.20. A safety device as defined by claim 9, wherein said device is contained within the chemical system.21. A process for automatically discontinuing an abnormal operation of a chemical system in response to an increase in the temperature of the chemical system from a lower normal temperature to a higher abnormal operating temperature, comprising exposing the chemical system to a safety device made of a reagent composition as defined by claim 1, whereby when the chemical system temperature increases to the higher abnormal temperature, said reagent composition melts and exposes said second substance for chemical reaction with the chemical system.22. A process for automatically discontinuing an abnormal operation of a chemical system as defined by claim 21, wherein said first substance is selected from the group of compounds consisting of high molecular weight paraffin waxes, alcohols, diols, polyols, polyglycols and polyglycol ethers.23. A process for automatically discontinuing an abnormal operation of a chemical system as defined by claim 22, wherein the first substance includes up to 25 weight percent of a phase transfer catalyst which is selected from quaternary ammonium and phosphonium salts.24. A process for automatically discontinuing an abnormal operation of a chemical system as defined by claim 21, wherein said first substance has a melting point of from about 30.degree. C. to about 250.degree. C.25. A process for automatically discontinuing an abnormal operation of a chemical system as defined by claim 21, wherein said second substance is an inorganic acid or base.26. A process for automatically discontinuing an abnormal operation of a chemical system as defined by claim 21, wherein said second substance is selected from the group of compounds consisting of the oxides and hydroxides of Li, Na, K, Mg and Ca.27. A process for automaticaly discontinuing an abnormal operation of a chemical system as defined by claim 21, wherein said second substance is selected from the group of compounds consisting of Li, Na, K, Mg and Ca salts of high molecular weight acohols, diols, polyols, polyglycols and polyglycol ethers.28. A process for automatically discontinuing an abnormal operation of a chemical system as defined by claim 21, wherein said second substance is selected from the group consisting of oxides, hydroxides and alcoholates of alkali metals and alkaline earth metals.29. A process for automatically decontaminating toxic products resulting from the abnormal operation of a chemical system in response to an increase in the temperature of the chemical system from a lower normal temperature to a higher abnormal operating temperature, comprising exposing the chemical system to a safety device made of a reagent composition as defined by claim 1,whereby when the chemical system temperature increases to the higher abnormal temperature, said reagent composition melts and exposes said second substance for chemical reaction with the chemical system.30. A process for automatically decontaminating toxic products as defined by claim 29, wherein said first substance is selected from the group of compounds consisting of high molecular weight paraffin waxes, alcohols, diols, polyols, polygycols and polyglycol ethers.31. A process for automatically decontaminating toxic products as defined by claim 30, wherein the first substance includes up to 25 weight percent of a phase transfer catalyst which is selected from quaternary ammonium and phosphonium salts.32. A process for automatically decontaminating toxic products as defined by claim 29, wherein said first substance has a melting point of from about 30.degree. C. to about 250.degree. C.33. A process for automatically decontaminating toxic products as defined by claim 29, wherein said second substance is an inorganic acid or base.34. A process for automatically decontaminating toxic products as defined by claim 29, wherein said second substance is selected from the group of compounds consisting of the oxides and hydroxides of Li, Na, K, Mg and Ca.35. A process for automatically decontaminating toxic products as defined by claim 29, wherein said second substance is selected from the group of compounds consisting of Li, Na, K, Mg and Ca salts of high molecular weight alcohols, diols, polyols, polyglycols and polyglycol ethers.36. A process for automatically decontaminating toxic products as defined by claim 29, wherein said second substance is selected from the group consisting of oxides, hydroxides and alcoholates of alkali metals or alkaline earth metals.