becomes the Portland cement of commerce.

This process of manufacture is almost identical in principle and in
practice with that described and patented by Mr. Joseph Aspden in the
year 1824; and though various methods have been patented for utilizing
the waste heat of the kilns in drying the slurry previous to
calcination, still the main feature of burning the material in mass in
large and expensive kilns remained the same, and is continued in
practice to the present day. The attention of the author was directed
to this subject some time since in consequence of the failure of a
structure in which Portland cement formed an essential element, and he
had not proceeded far in his investigation of the cause of the failure
when he was struck with what appeared to him to be the unscientific
method adopted in its manufacture, and the uncertain results that must
necessarily accrue therefrom. Admitting, in the first place, that the
materials employed were considered the best and most economical for
the purpose readily accessible, viz., chalk and an alluvial deposit
found in abundance on the banks of the Thames and the Medway, and
being intimately mixed together in suitable proportions, was it
necessary, in order to effect the chemical combination of the
ingredients at an intense heat, to employ such massive and expensive
structures of masonry, occupying such an enormous space of valuable
ground, with tall chimney stacks for the purpose of discharging the
objectionable gases, etc., at such a height, in order to reduce the
nuisance to the surrounding neighborhood? Again, was it possible to
effect the perfect calcination of the interior of the lumps alluded to
without bestowing upon the outer portions a greater heat than was
necessary for the purpose, causing a wasteful expenditure of both
time and fuel? And further, as cement is required to be used in the
state of powder, could not the mixture of the raw materials be