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 arc of a circle; the buckets grazed the surface of the bottom and sides of this kettle, the bottom of the latter being immersed in a current of cold water. The hot filtered solution of the crude saltpetre was received into this kettle, and thus kept into a state of rapid agitation, the effect being to produce a wet mass of minute crystals, which, as fast as formed, were taken up by the sharp edged buckets, and lifted sufficiently high to pour into a receiving vat; this permitted the liquid part to flow back into the kettle. By this means in a short time the entire mass of fine deposited crystals from the rapidly cooled liquid, were removed to the vat. When the operation was completed the remaining liquid in the kettle was by the revolutions of the bronze wheel, discharged into one of the eight capacious cisterns below the floor; there were two of these machines employed. The facility for work which this apparatus, with the other mechanical appliances afforded, enabled the refinery to carry the purification of the saltpetre beyond that of the most celebrated powder factories.