The wide range of quality in tho variooa limestonee, whether
we regard their physical character or their value in a che-
mical direction, is very considerable. Glenerally speaking
they may be considered aa too hard or cryBtaUine in texture
for such treatment as that bestowed on the chalks and other
amorphous materials. This obduracy of natural constitution
necessitates the apptication of effective and specially adapted
machinery for its thorough, and as nearly as possible perfect,
redaction. There can be no question that the manntacturer
using such materials is burdened at the initial stage of his
operations with expensive machinery not required by those
engaged in the conversion of chalks and clays. These
unkindly qualities of this class of materials have led to many
Buggestions for their compound and other treatment. The
double-kilning process, as it is sometimes called, destroys
the crystals, and in fact the whole structure of the stone
by its conversion into lime. It is then properly quenched
or slaked, and reduced to a pasty condition, and in this
hydrated form is mixed with the clay sometimes in a finely
powdered state, and also as a semi-fluid. The preferable
method would be to introduce the powdered clay while
the mass is passing through the brick-moulding stage,
not directly into the pag-mill proper of the machine,
bnt after it had traversed a properly defined space, pro-
vided with doable screws, working on two spindles or shafts



3dbvGoOg[e



GBHENT FBOU CABBOKIVEBOUB LmEBXONS. 179

going in a paisllel direction. This would ensore the homo-
geneity of the mass and eecure its perfect amalgamation
in the brick machine. One great advantage in this treat-
ment is the eventual saving in the fuel required for the
kUs. There ia no donbt, however, that, although securing
the most perfect condition for convereioD, it involves an
extra cost in the initial process of decarbonization of the
limestone. Such a cost, however, depends on the locality
in which the process is performed, and most be influenced
entirely by the nearness or remoteness of the fuel. Some
makers have endeavoured to substitute a partial process
of calcination, bat, so far as the author knows, with bnt
little success. If yon adopt this system, either go the whole
length or fall back on the reducing machinery, no middle
conrae can be dealt in with safety.
