Cork insulation; a complete illustrated textbook on cork insulation ...

CORKBOARD ICE CREAM CABINET 391
ing to the <strong>insulation</strong> of walls and structures to be subjected
to low temperatures, as previously elaborated in this text,
to the end that ice cream cabinets may contain adequate insu-
lation installed so as to insure permanent cabinet efficiency.
160.—Mechanical Ice Cream Cabinets.—The trend in the
development and applications of mechanical refrigerating- ma-
chinery was slowly but constantly from large many-ton plants
toward smaller units, much as in the development of electric
power the large-motor main-shaft drive gave way a little at
a time to individual drive by small motors. But the high
pressures at which ammonia compression refrigerating ma-
chines operate, placed restrictions on the smallness, the light-
ness, and the cost of production of the ammonia units of
fractional-ton capacity, past which it was not practical for
the manufacturer to go. And that minimum cost was too
high for general application to small refrigeration duty, such
as the cooling of household refrigerators and retail ice cream
cabinets, when in competition with ice, and ice and salt
mixtures.
The use of a refrigerant that could be effectively operated
at relatively low pressures, such as sulphur dioxide, proved
to be the solution of the problem, which development estab-
lished the small fractional-ton refrigerating machine as a
practical and economical refrigerating unit through much
lighter and simpler construction and greatly reduced cost.
However, in the practical application of such household refrigerating
units, as they quickly came to be known, it was
determined that their successful operation, as well as their
low manufacturing cost, depended on a certain restriction of
the unit refrigerating capacity.
Thus the efforts to reduce the cost of production of the
fractional-ton ammonia compression machine to the point of
successful competition with ice and salt mixtures were, m
general, unsuccessful; while the efforts to economically raise
the unit refrigerating capacity of the sulphur dioxide type of
machine enough to handle the heavier duty cabinets were, in
general, unavailing. But virtually by the simple expedient
of increasing the thickness of the corkboard <strong>insulation</strong> in ice
cream cabinets to be mechanically cooled, and by so setting