554 
ON ALLOYS AND THEIR USES. 
efficacy and any other advantages resulting from its application as steam fuel. Such an 
application might therefore be a great advantage to gas companies. 
Unfortunately the quantity of this oil which is available is very small as compared 
with the requirements of steam navigation, probably not amounting to 100,000 tons a 
year in the whole country, and therefore its application must be very limited. 
(To be continued.) 
ON ALLOYS AND THEIR USES. 
(.Abst 'act of a Lecture delivered at the Royal Institution by Professor Augustus 
Matthiessen , F.R.S.) 
The object of this discourse was to show experimentally why alloys are used in pre¬ 
ference to their component metals. 
Alloys may be, chemically considered, divided into three classes:— 
1 . Chemical combinations. 
2 . Mechanical mixtures. 
3. Solutions of the one metal in’ the other which has become solid, or, for shortness’ 
sake, solidified solutions of the one metal in the other. 
Under the term chemical combination such alloys may be considered which are the 
result of the combination of two metals when these unite together with great energy 
and evolution of heat, producing an alloy the physical and chemical properties of which 
we cannot foresee. As an example of such alloys those of gold, with tin, lead, or zinc 
may be quoted; for if to melted tin, lead, or zinc, gold be added, the two metals unite 
together with great energy, and produce an alloy which is exceedingly brittle and 
totally unfit for practical purposes. 
It is for this reason that the more expensive metals, silver and copper, are used for 
alloying gold for the purposes of coinage, etc. 
With regard to such alloys as may be looked upon as mechanical mixtures, like oil 
and water, or rather as ether and water,—for no two metals are known which, like oil 
and water, do not dissolve at all in one another; but a few metals are known which, like 
ether and water, dissolve slightly in one another, for ether will dissolve a certain amount 
of water, and water a certain amount of ether. If ether and water be mixed together, 
say in equal parts, two layers will be formed, the top one being ether containing a little 
water, the lower one water containing a little ether. Two metals, for instance, which 
behave in exactly a similar manner to ether and water are lead and zinc, for lead when 
fused with zinc will dissolve 1*6 per cent, zinc, and zinc in its turn will take up 1*2 per 
cent. lead. 
If these two metals be fused together, say in equal parts, they will separate into two 
layers, like ether and water, the top one, being the specifically lighter, zinc, with a small 
percentage of lead, the lower one lead, with a small percentage of zinc. If such an 
alloy be made and cast in a mould, the difference in the behaviour of the two ends may 
be easily shown ; for the top one is so brittle that it cannot be bent without breaking, 
whereas the lower one may be bent with ease. 
Such chemical combinations and mechanical mixtures are, however, comparatively 
rare; and for alloys in common use, practice has almost invariably chosen such alloys 
as may be considered as belonging to the third class, rejecting those of the first and 
second as worthless for practical purposes. 
Under the term solidified solutions of the one metal in the other, such alloys may be 
considered, which, like the chlorides of potassium and sodium when fused together, pro¬ 
duce a mass having some of the physical properties totally different from those of the 
component salts. It cannot be assumed that the chloride of sodium enters into chemical 
combination with the chloride of potassium. One important property of a solidified 
solution is, that the components are homogeneously diffused in one another, so that even 
under the most powerful microscope they can no longer be distinguished from one another. 
Alloys are used because they possess certain physical properties to a far greater extent 
than their component metals. The physical properties may be divided into two classes. 
1 . Those which in all cases are imparted to the alloy, approximately in the ratio in 
w T hich they are possessed by the component metals. 
