S9« TEE SCIENTIFIC MONTHLY
all our iron and steel objects. To ayoid rost has been the aim of man ever since he discovered iron and its nses. When qnite pure^ the rust- ing of iron is greatly retarded, but it is scarcely possible to indefinitely defend even pure iron against rust. Fire, sea-water, and ice, as well as the weather, could destroy a structure of iron in the course of time, and even in much less time than it would take the same agents to de- stroy a structure of stone. When properly imbedded in concrete, how- ever, iron or steel not only adds greatly to the strength of the concrete, but is very much less liable to rust, owing to the protective effect of the cement.
If iron is of doubtful permanence, will other metals or alloys serve better? Undoubtedly some of them might, to a certain degree. Bronze is surely very resistant to the weather, as are its components, copper and tin. These, however, could be readily melted in a fire, as could zinc, aluminum and lead. Gold and silver are even more resistant to corrosion and high temperatures, but their cost prevents their extenave use. The same is true of platinum, tungsten, vanadium and still rarer metals. We can scarcely choose a single metal that will serve as an ideally resistant agent or material and at the same time be of prac- tical use.
Clay products often appeal to us as having singular powers of re- sistance to certain destructive agents, but in all cases such products are found to have some fatal weakness. While quite resistant to the weather, and to a certain degree of heat, yet severe weather conditions or intense heat may destroy them. In most cases the practicable forms of these products are brittle, and for that reason are readily damaged. Ancient inscriptions in clay have been preserved for a very long time, and are of great interest and importance in archeology, but we should remember that the destructive agents directed against them did not include severe weather conditions nor high temperatures.
Possibly the most resistant mineral substances that appeal to modern man are asbestos and its allied minerals, talc, steatite and serpentine. These lend themselves readily to the shaping of numerous articles* Asbestos in particular is very familiar to us in its uses as a fire-proofing material and non-conductor of heat. Softness and brittleness, however, are objectionable properties of most products from these minerals, just as brittleness is a characteristic weakness of kaolinite or clay products.
Glass, while hard and resistant to the weather, is too readily injured by high temperatures, and is too brittle to give us much hope in our search for an ideally resistant material. While glass is of enormous importance in our modern civilization, it seems probable that most of it will remain in its present forms only under quite favorable conditions.
If the substances so far discussed are unsuitable for the purpose of perpetuating or safeguarding our records and relics of ancient and
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