Note (return) — Spirit of Discovery.

The process of refining sugar in vacuo is the most useful application of "the fact that liquids are driven off, or made to boil at lower degrees of heat when the atmospheric pressure is lessened or removed."3 The first part of the process is to dissolve impure sugar in water, and after clarifying the solution, to boil off or evaporate the water again, that the dry crystallized mass may remain. Formerly this evaporation was performed under the atmospheric pressure, and a heat of 218° or 220° was required to make the syrup boil; by which degree of heat, however, a portion of the sugar was discoloured and spoiled, and the whole produce was deteriorated. The valuable thought occurred to Mr. Howard, that the water might be dissipated by boiling the syrup in a vacuum or place from which air was excluded, and therefore at a low temperature. This was done accordingly; and the saving of sugar and the improvement of quality were such as to make the patent right, which secured the emoluments of the process to him and other parties, worth many thousand pounds a-year. The syrup, during this process, is not more heated than it would be in a vessel merely exposed to a summer sun.