ly very general remarks can be made on the subject of cost, as this
item varies greatly in different situations and with the market price of
the materials used. But in England it may be said that for massive work
such as big walls and foundations concrete is nearly always cheaper than
brickwork or masonry. On the other hand, for reasons already given, thin
walls, such as house walls, will cost more in concrete. Steel concrete
is even more difficult to generalize about, as its use is comparatively
new, but even in the matter of first cost it is proving a serious rival
to timber and to plate steel work, in floors, bridges and tanks, and to
brickwork and plain concrete in structures such as culverts and
retaining walls, towers and domes.

_Artificial Stones._--There are many varieties of concrete known as
"artificial stones" which can now be bought ready moulded into the form
of paving slabs, wall blocks and pipes: they are both pleasing in
appearance and very durable, being carefully made by skilled workmen.
Granolithic, globe granite and synthetic stone are examples of these.
Some, such as victoria stone, imperial stone and others, are hardened
and rendered non-porous after manufacture by immersion in a solution of
silicate of soda. Others, like Ford's silicate of limestone, are
practically lime mortars of excellent quality, which can be carved and
cut like a sandstone of fine quality.

_Steel Concrete._--The introduction of steel concrete (also known as
ferroconcrete, armoured concrete, or reinforced concrete) is generally
attributed to Joseph Monier, a French gardener, who about the year 1868
was anxious to build some concrete water basins. In order to reduce the
thickness of the walls and floor he conceived the idea of strengthening
them by building in a network of iron rods. As a matter of fact other
inventors were at work before Monier, but he deserves much credit for
having pushed his invention with vigour, and for having popularized the
use of this invaluable combination. The important point of his idea was
that it combined steel and concrete in such a way that the best
qualities of each material were brought into play. Concrete is readily
procured and easily moulded into shape. It has considerable compressive
or crushing strength, but is somewhat deficient in shearing strength,
and distinctly weak in tensile or pulling strength. Steel, on the other
hand, is easily procurable in simple forms such as long bars, and