The cheapest, and perhaps the
best, of these for ordinary use, is one which is frequently employed
in France, both for making dessert ices, and cooling wines, &c. It
consists of coarsely powdered Glauber salt (sulphate of sodium), on
which is poured about two-thirds its weight of spirit of salts
(hydrochloric acid).

The mixture should be made in a wooden vessel, as that is preferable
to one made of metal, which conducts the external heat to the
materials with great rapidity; and when the substance to be cooled is
placed in the mixture, the whole should be covered with a blanket, a
piece of old woollen carpet doubled or some other non-conducting
material, to prevent the access of the external warmth; the vessel
used for icing wines should not be too large, that there may be no
waste of the freezing mixture. This combination produces a degree of
cold thirty degrees below freezing; and if the materials are bought of
any of the wholesale druggists or dry salters, it is exceedingly
economical. It is open, however, to the very great objection, that the
spirit of salt is an exceedingly corrosive liquid, and of a pungent,
disagreeable odour: this almost precludes its use for any purpose
except that of icing wines.

[FAIR AND SOFTLY GO SURE AND FAR.]

2143. Further Directions.

Actual quanties--one pound of chloride of ammonium, or sal ammoniac,
finely powdered, is to be _intimately_ mixed with two pounds of
nitrate of potasium or saltpetre, also in powder; this mixture we may
call No. 1. No. 2 is formed by crushing three pounds of the best
Scotch soda. In use, an equal bulk of both No. 1 and No. 2 is to be
taken, stirred together, placed in the ice-pail, surrounding the
ice-pot, and rather less cold water poured on than will dissolve the
whole; if one quart of No. 1, and the same bulk of No. 2 are taken, it
will require about one quart of water to dissolve them, and the
temperature will fall, if the materials used are cool, to nearly
thirty degrees below freezing. Those who fail, may trace their want of
success to one or other of the following points:--the use of too small
a quantity of the preparation,--the employment of a few ounces;
whereas, in freezing ices, the ice-pot must be entirely surrounded
with the freezing material: no one would attempt to freeze with four
ounces of ice and salt. Again, too large a qu