The Romance of Modern Chemistry

TWO METALS BETTER THAN ONE and wrought-iron, but with alloys the effects are much more striking. Common solder is a case in point. Soldering consists in joining two metals by an alloy which is more easily melted than either, and which at the same time will coalesce with each metal. Tin and lead, a mixture of which forms ordinary plumber’s solder, melt at 440° and 617° Fahrenheit respectively, while the solder itself melts at 374°. The reader may already have remarked the frequency with which tin is used either to plate or alloy with other metals, and it is in fact very seldom employed by itself. Even the so-called “ tin ” foil in which chocolates are wrapped contains lead, and the utensils which we call “ tins ” are generally iron plated with tin. In the case of solder, as we have seen, the alloy melts at a temperature lower than the melting-point of either constituent. But of the lowering of melting-point pro- duced by mixing far more striking examples are obtained when we take four metals to make an alloy. Lead, tin, bismuth, and cadmium melt at 617°, 440°, 514°, and 608° respectively, and yet by mixing these metals in certain proportions we can prepare an alloy which melts in hot water and is known as “fusible metal.’1 These easily-melted alloys are put to some curious uses ; for example, in connection with fire-alarms. A quantity of fusible metal is arranged in a receptacle in such a way that when a certain temperature has been exceeded the alloy melts, and releases a spring or allows a lever to fall. By this device an electric circuit is closed and a bell is rung. Then, again, fusible alloys play a useful part in the sprinklers which are fitted up in factories and workshops. 76