Platinum is a strange, silvery-looking metal which expands when heated at almost the same rate as glass. Platinum wire can, therefore, be melted into glass without the danger of the glass cracking when both cool, hence its use in the glass bulbs of electric lamps.

It is heavy, can be beaten out or drawn out readily ; but it is almost unacted upon by air or acids. It has the strange property of absorbing considerable quantities of gases like hydrogen; and, besides its use for incandescent bulbs, it is turned into jewellery, and is used in photography and for the manufacture of chemical apparatus. One of its uses belongs to an obscure chemical operation known as catalysis. Sir Humphry Davy, just a century ago, exhibited what he called a “lamp without flame.” He suspended a spiral of platinum in ether whose vapours joined on the platinum with the oxygen of the air causing the metal to glow. The point of this and similar experiments is that the ether might be left in contact with the iron for ages without any change taking place. We mav keep a mixture of oxygen with double the amount of hydrogen in a closed vessel almost as long as we like without any action taking place.

We know that these are the ingredients of water, and that if we brought a flame near or introduced an electric spark there would be a flash and an almost instantaneous chemical change. But we can produce the same result if we introduce a clean strip of platinum foil. The combination takes place. Water is produced; and sometimes the platinum begins to glow and the last of the gases explode. If the platinum be examined afterwards it is no lighter in weight and no change can be found in it. If it be kept quite clean and not fingered it can be used for the same mysterious operation again.

There are a number of other instances of catalysis in which platinum has been used. Some of them have not as yet been applied industrially, though students have seen the method employed in the laboratory. Such an experiment is the passing of air or oxygen into a flask containing a solution of ammonia and a spiral of platinum wire. At first the flask is filled with dense white fumes of ammonia compounds ; but later, when the oxygen is passed in quickly, orange fumes of nitro¬gen peroxide appear, and the explosive gases at length take fire from- the glowing platinum. The nitrogen peroxide being of the greatest value for the production of nitric acid some use has been made of the process in Germany.