USES OF PLATINUM
In past discussion of the uses of platinum some confusion has resulted from the lack of appreciation that all commercial platinum is not the pure metal. The pure metal is required for chemical work of all sorts, but for other uses the iridium alloys are used. Electrical platinum contains 15 to 50 per cent. iridium, but averages 25 per cent., and jeweler’s platinum carries about 10 per cent. iridium. Palladium, another of the platinum group metals, is also of importance, chiefly in the form of palladium-gold alloys, which can be used to replace platinum in the dental and jewelry industries. Rhodium, one of the rarer elements of crude platinum, has a limited use in electrical pyrometers. Osmium and ruthenium, the remaining members of the platinum group, appear to have little use, though osmium, when properly used, can be employed as a substitute of iridium to harden platinum alloys.
The essential uses of platinum metals are in the chemical and electrical industries, and probably the dental industry should be classed as essential. Pure platinum is required in the chemical industry for catalysers in the manufacture of sulphuric acid (about 75,000 ounces now in use in the United States) and in the manufacture of nitric acid from ammonia. For the sulphuric-acid industry, platinum chloride is the primary material containing platinum. Asbestos or anhydrous magnesium sulphate soaked in platinum chloride, and then baked to drive off the chlorine, forms what is known as “contact mass,” which is charged into the chambers of contact acid plants. Very fine-mesh platinum gauze is used for the catalyser in nitric-acid plants. Some gauze used for this purpose has a reinforcing edge of platinum-iridium wire. Pure platinum utensils of various kinds, including crucibles, dishes, tongs, and triangles, are required in every chemical laboratory. It is possible to substitute palladium-gold alloys, or even gold, nickel, nichrome, and silica, for some utensils, but no substitutes have yet been found which will entirely replace platinum chemical ware.
Platinum-iridium alloys have been used extensively by the electrical industry, but substitutes are constantly being developed. Tungsten, molybdenum, and nickel-chrome alloys are the principal substitutes used so far, but their use has not done away with the necessity of platinum in the industry. The principal use of platinum-iridium alloys in electrical work is in contact points, and the proportion of iridium necessary in the alloys is directly dependent on the intensity of the current passing through the contacts and the speed at which the contacts move. Probably the largest consumption of platinum alloy is in the manufacture of telephone and telegraph equipment, including sending and receiving instruments, switch boards and relays. There is also a large consumption of platinum for contacts in magnetos used for various kinds of internal-combustion engines. Automobile makers are, however, developing starting systems that do not require platinum, so we can hope for a lessening future demand from that quarter.
Platinum has an important use in dentistry, though in emergencies palladium-gold alloys have been used as substitutes. Seemingly, however, the substitutes are not entirely satisfactory, and it may be necessary to go back to platinum for certain dental uses. The chief uses are for pins for crown work, pins for fastening artificial teeth to plates, and foil for making molds of cavities in which to bake porcelain fillings. For the time being, the palladium-gold substitutes can be used and perhaps they will be developed so that the use of pure platinum in the future may not be necessary.
The non-essential use of platinum metals is in jewelry, and it seems certain that this misuse of platinum metals must be stopped in order that industrial development may continue. It is estimated that for a number of years 50 per cent. of the platinum consumed in the world went into jewelry. A large part of platinum-mounted jewelry is in private ownership, and as the value of the metal in a jewel is approximately 35 per cent. of the total cost, it is evident that it would be difficult, if not impossible, in case of necessity to recover more than a small proportion of the large quantity of platinum that is in the form of jewelry.