Two pressure-gauges, one of them fixed on the freezer and the other on
the liquefier, permit of regulating the running of the machine. The
vacuum in the freezer is 0 to 1/2 atmosphere, and the pressure in the
liquefier is 3 to 4 atmospheres. These apparatus make opaque ice, but
will likewise produce transparent, if a pump for injecting air is
adjoined. This, however, doubles the time that it takes to effect the
freezing, and carries with it the necessity of doubling the number of
moulds to have the same quantity of ice.
The cost price of ice made by this system depends evidently on the price
of coal in each country, on the perfection of the boiler and motor, as
well as on the power of the freezing machine. Putting the coal at 20
francs per ton, and the consumption at 2 kilogrammes per horse and
per hour, ice may be obtained at a cost of about half a centime per
kilogramme. The apparatus shown in the accompanying figures have been
constructed according to the following data:
Production of ice per hour............ 25 kilogrammes.
Production of heat units per hour..... 2.5 grammes.
Quantity of ice produced per
kilogramme of coal burned..
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