We will suppose we want a lemon-water ice, _i.e._, we have made some very strong and sweet lemonade, and we want to freeze it.

It is well known that water will freeze at a certain temperature, called freezing-point.

By mixing chopped ice and salt and a very little water together, a far greater degree of cold can be immediately produced, viz., a thermometer would stand at 32 degrees below freezing-point were it to be plunged into this mixture.

An ice machine is a metal pail placed in another pail much larger than itself.
The "sweet lemonade" is placed in the middle pail, and chopped ice and salt placed outside it.

The proportion of ice to salt should be double the weight of the former to the latter.