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[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 quantity of water may be used to dissolve the preparation, when all the excess of water has to be cooled down instead of the substance it is wished to freeze. All the materials used should be pure, and as cool as can be obtained. The ice-pail in which the mixture is made must be of some non-conducting material, as wood--which will prevent the access of warmth from the air; and the ice-pot, in which the liquor to be frozen is placed, should be of pewter, and surrounded nearly to its top by the freezing mixture. Bear in mind that the making of ice-cream, under any circumstances, is an operation requiring considerable dexterity and practice.