gullies, pits, and ravines of the iron districts
becoming filled up at no very remote period,
when iron-mastei's would have to go farther
in search of secluded spots whereon rubbish
might be shot.

The philosopher who, by the aid of scientific
observation and research, can point out
to us how to turn all this perplexing mass of
unproductive refuse to good and profitable
account—how, by a simple method, we may
convert this ugly, useless clinker into a
beautiful means of ornamentation, and make it
an indestructible and economical agent in
the construction of public works and dwelling-
houses, surely the man who can accomplish
this deserves some thanks at our
hands.

All this has been accomplished by the
patient research of Dr. W. H. Smith of
Philadelphia, United States, who recently
delivered a lecture on the subject to the members
of our Society of Arts. In this interesting
discourse, the lecturer pointed out the
brittle and useless character of the mineral
refuse of smelting furnaces, as at present
known under the name of slag. A careful
analysis of this hitherto rejected product of
our iron works shows that it is composed, in
the main, of lime, silica, and alumina, with
an occasional admixture of magnesia and
sulphur. In all parts of the world the same
results are arrived at. The slag of France or
Sweden differs in no essentials from that of
Britain or the United States. It is scarcely
necessary to remind the reader of the similarity
in the process of smelting ores, and the
vast operations of nature beneath the crust
of the earth, where, by a like agency of heat,
mountainous deposits of igneous rocks are
constantly being thrown off.

The rocks of this origin are met with in
stupendous masses in most parts of the world.
Whilst Nature, on the one hand, employs
her igneous products in the construction of
gigantic mountain-palaces, man, well aware
of their great value, equally applies those
rocks, under the names of granite, felspar,
basalt, greenstone, syenite, porphyry, serpentine,
&c., in the construction of his most
elaborated architectural edifices. High
geological authorities tell us that if we examine
the composition of the crust of the. globe, we
shall find that of all the earths and earthy
substances therein, three only will be ascertained
to constitute its great bulk, namely
silica, alumina, and lime, precisely those
which mainly compose the slag of the
smelting-house.

The worker in ores when he is occupied
with his blast-furnace is, in fact, but repeating,
on a small scale, the grandest
operations of nature, deep in the bowels of
the earth. Heat is the great first agency
employed by nature and by the philosopher
in the decomposition and re-combination
which produce some of the most beautiful
and useful products with which we are
acquainted.Dr Smith has shown that the
rubbish of the smelting-house is identical in
character, and equally valuable, with most of
the igneous rocky substances.

Like many other valuable discoveries, this
result was arrived at whilst searching
for something else.  It is well to relate how this
truth, so interesting in itself apart from
commercial results, was seized upon by the
American philosopher, since it may tend to
encourage such as may be toiling in other
fields of research.  Impressed with a conviction
of the influence of electricity upon life,
health, and disease, Dr. Smith, at that time a
practitioner in Philadelphia, commenced a
series of experiments in electro-agencies on
the human frame.  Success in that question
induced him to carry his researches to vegetable
life, and from animate he was led to direct
his observations to inanimate objects.  Mineral
matter received attention from him, and,
weighing well the geological facts alluded to
above,  Dr. Smith bent the energies of his
mind to trace the effects of electricity in all
these combinations and reproductions.

Comparing the condition and character of
slag with that of the igneous rocks of nature,
he felt that to electric agency must be attributed
the cause of the great difference existing
between them. In order to test this, he took
a piece of the vitrified mass of slag hot from
the furnace-mouth, and applied to it a metallic
rod. At the point where this electric conductor
came in contact with the substance,
the vitrified mass assumed a pulverulent
character; several rods were employed, and
at each point of contact similar changes in
the condition of the slag were observable.
The electricity rapidly engendered during the
smelting process was parted with as quickly
on the application of the metal conductors,
and hence the sudden and marked change in
the condition of the mineral.

In order more fully to test this theory, the
experimenter threw a quantity of the molten
slag, fresh from the furnace-mouth, into
water. Every atom of the liquid being a
good conductor of electricity rapidly absorbed
it as it lowered the temperature of the mass,
and the immediate consequence was, that the
mineral matter fell into a coarse powder,
entirely deprived of its former cohesion or
solidity.

From these trials Dr. Smith felt convinced
that his electrical theory was correct, and
that it was to the rapid giving forth of its
electricity by sudden cooling in contact with
conducting media that slag owed its brittle
character—in other words, its want of
cohesion and its tendency to pulverise. He
reflected that the great masses of igneous
rocks upheaved from the centre of heat were
in a favourable position for gradually cooling,
their gigantic extent would ensure that
result—hence their extreme hardness and
durability.

With the view of completely testing the