But the oxyhydrogen jet is now employed in many factories for the welding of metals. This is known as fusion welding, since the two parts are actually reduced to liquid. The usual way to go about this work is to bevel off the ends or edges to be joined. Suppose, for instance, that we wanted to weld two pieces of brass pipe together. We should first file or otherwise trim the edges to be joined until when put together they form a groove practically as deep as the metal is thick. Then with a stick of brass wire in the left hand, and an oxyhydrogen blowpipe in the right, we should direct the flame from the pipe on to the metal until, at one point, the sides of the groove were beginning to melt. Then, inserting the point of the wire into the groove, we should melt a little off it. Thus we should work all round the joint, melting the sides of the groove and filling in with melted metal from the wire, until the whole groove had been filled up and the metal added had been thoroughly amalgamated with that on either side. As a matter of fact, if it were brass which we were working on we should probably use the cheaper though less pure form of hydrogen--coal-gas--so that it would really be "oxycoal-gas" that we should use and not oxyhydrogen. The latter is used, however, notably for the fusion-welding of lead, or "lead-burning," as it is termed. The blowpipe is a brass tube about a foot or eighteen inches long, with two passages in it, one for the oxygen and the other for the other gas. The gases are brought to one end of it through rubber pipes, while at the other end there is a nozzle in which the gases mingle and from which they emerge in a fine jet. The oxyhydrogen flame has a temperature of about 2000° C., hot enough to melt fire-clay. That does not matter in the case of welding, however, since the molten metal is very small in quantity at any given moment, and is allowed to cool before it can run away. It would be an awkward temperature to deal with, nevertheless, in a furnace. It seems strange that it does not burn the nozzle of the blowpipe, but the fact that it does not is, it is believed, explained by the fact that the expansion of the gas, as soon as it emerges from the hole out of which it shoots, causes a comparatively cool space just there, shielding it from the intense heat farther on. An exceedingly interesting use of the oxyhydrogen flame is in the manufacture of artificial rubies. These stones are made in Paris by a very simple means. The necessary chemicals are prepared and ground to an exceedingly fine powder. This is then allowed to fall through an oxyhydrogen flame. Thus there is no need for a crucible capable of withstanding this high temperature, since the melting takes place as the particles are in the act of falling. When they reach the support prepared to catch them they have cooled somewhat. Stones so called are real rubies--artificial, but not shams. They possess every property of the ruby from the mine.