The Romance of Modern Chemistry

TWO METALS BETTER THAN ONE These consist of water-pipes led round the upper part of ft room, and at intervals on the pipes there are valves secured by fusible alloy. If a fire should break out in any room fitted with such a sprinkler, the heat will melt the fusible alloy at one or more of the valves, the water will burst out, and there is a fair chance that the fire will be extinguished before it has attained very large proportions. With such examples before us of the way in which the hardness and fusibility of a metal are altered by the addition of another, we are led up to the question—Are these alterations due to the formation of a new substance, a compound of the metals, or are they accounted for by the mere mixture of the constituents ? The difference between a mechanical mixture of two elements and the compound formed by their chemical combination has already been discussed. We must next try to decide whether the features which we generally notice in chemical action are to be observed when we make two metals into an alloy. Now it must be ad- mitted that it is rather difficult to settle the question whether an alloy is a mixture or a compound. In some respects, it is true that the mixing of two metals re- sembles what takes place when two elements combine. Thus we have seen that when iron and sulphur act on each other an enormous amount of heat is liberated, and such liberation of heat very frequently accompanies chemical action. Well, a similar thing occurs when we add sodium to mercury to make an alloy (or an “ amal- gam,” as it is called when mercury is one constituent) ; each addition of sodium is accompanied by a flash of light. So also when a piece of aluminium is added to fused gold, an extraordinary evolution of heat is observed, 77