provisions in the reign of Henry VIII.

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.

[3] Arnott's Elements of Physics.

Lord Brougham, in his Introduction to the _Library of Useful
Knowledge_, characterizes this as a process, by which more money has
been made in a shorter time, and with less risk and trouble, than was
ever perhaps gained from an invention; and as "the fruit of a long
course of experiments, in the progress of which known philosophical
principles were constantly applied, and one or two new principles
ascertained."[4]