rear of
the building. Thus the refining room was entirely free from ashes, dust
and smoke.

The centre space of the floor, about thirty-six feet square, was sunk
four feet to allow water from the canal to pass around the bottoms of
two of the large evaporating pans, which were placed therein near the
centre of this area, and nine feet apart; these were used for a special
purpose.

The best quality of gunpowder can only be made from the purest
saltpetre; the impurities of the crude material are mainly deliquescent
salts, which rapidly deteriorate the strength of the powder by the
moisture absorbed. To refine more or less the rough saltpetre of
commerce is then a necessity even in producing an inferior article.

To carry the refining process to the extent of nearly absolute purity,
required several successive crystallizations and washings, involving a
large amount of manual labor in the manipulation, and consuming much
time. This was particularly the case in the very large amount of
saltpetre, eight to ten thousand pounds per day, used by the Works, the
refining of which would demand extended buildings and apparatus, as well
as requiring a large number of operatives. Hence, it became desirable to
devise methods by which hand labor could be superseded by motive power
and machinery; in this I was entirely successful. Thus, in the
operations of filling the various boiling pans with water or
mother-liquor; the transference of the boiling solution of saltpetre to
the draining trough, and thence to the crystallizing machines; the
cooling down of the solutions, and their constant agitation to break up
the forming crystals into fine particles, and transferring of these to
an adjoining tank; the washing of the crystallized mass, and the
subsequent removal of the mother-liquor and wash-waters, were all
accomplished by machinery, with the assistance of two or three workmen
only.

The saving of time and labor was thus manifest, and the rapidity with
which these operations were performed, permitted a double and triple
process in a single day; thus allowing a degree of purity in the product
of refined saltpetre not attained in any other refinery. Its purity was
such generally, that there was not the one-hundred-thousandth part of
chlorides left in the salt.

Of the machinery used, the most important was a bronze revolving wheel
with buckets attached to the periphery, which worked into an iron pan or
kettle, whose section was an