THE USES OF PLATINUM AND ITS ALLIES _Platinum._—In the chemical industry platinum is largely used for catalyzers in the manufacture of sulphuric, acetic and nitric acids; for stills for the final concentration of sulphuric acid; and in the electro-chemical industry. In the making of “contact” sulphuric acid a “contact mass” is charged into the chambers of the plant. This is formed by soaking asbestos, or anhydrous magnesium sulphate, with platinic chloride solution, and baking the mass to drive off the chlorine. The contact mass usually contains from 7 to 8 per cent. platinum, in a very finely-divided state. In the making of acetic acid from a mixture of air and alcohol vapour, platinized asbestos is used. For the catalyzer used in the conversion of ammonia into nitric acid a very fine-meshed platinum gauze is used; this is strengthened at its edges with platinum-iridium wire. One ounce of platinum is required for the production per annum of 25 tons of catalytic acid, or of 40 tons of nitric acid from ammonia. In the finely-divided state all the other metals of the platinum group, especially palladium, have also the facility of absorbing great quantities of certain gases, and can be used as catalysts. Owing to its high melting-point, and to the resistance to the action of acids at high temperatures, platinum is largely used for chemical ware in the form of crucibles, dishes, etc. Platinum crucibles are indispensable in the chemical analysis of rocks. In the electrical industry platinum is largely used for contact points, in telegraph and telephone apparatus, in magneto-contacts, and in the construction of the thermo-couples of pyrometers. In the manufacture of jewellery, especially in the crown-setting of diamonds, platinum has been much used in the place of gold: alloyed with a little iridium it can be worked into delicate designs, which are durable. During the war, however, when platinum was largely wanted in the making of munitions, its use in jewellery manufacture was much restricted. Platinum was formerly largely used in dentistry. In photography potassium platino-chloride is required for producing platinotype prints. In the form of barium platino-cyanide it is used in X-ray photography as a coating for the projecting screen. Platinum is required in the manufacture of certain parts of chronometers, theodolites and watches; also for standard weights and measures, and for various types of self-lighting lamps[4] p. 561. _Palladium_ has its chief value as a substitute for platinum, in palladium-gold alloys, which are used extensively in dentistry, for jewellery and for chemical ware. It is also utilized in the manufacture of astronomical instruments and watches, also for plating metal ware[1] p. 1002. The use of palladium as a catalyzer is well known.