In modern ice cream factories _Brine Freezers_ are generally used. In a _Refrigerator Plant_ intensely low temperatures are produced by the vaporizing of compressed ammonia or carbonic acid in an ice machine, and brine circulating in iron pipes is cooled by such medium and may, in turn, cool the air in the _Cold Storage_ room, or the cream in the freezer, or pure water in metal boxes for the manufacture of _Artificial Ice._ It has been attempted to make the brine freezers _continuous_, the cream mixture being fed into the machine at one end and discharged frozen at the other. But this system has not so far been successful, and intermittent or batch freezers are most practical yet both for hand and for power. [Illustration: Power brine freezer ] Rich material, frozen in a good machine, whether intermittent or continuous, will expand from 50% to 100%, and the original material should not fill the freezer can more than half full. The manufacture of ice cream has been the subject of study and experiments for years in the Dairy Department of the Agricultural College at Ames, Iowa, where Professor M. Mortensen has worked out a comprehensive classification from which any manufacturer may readily choose his formulas, modifying them to suit his local conditions and special problems. The outline kindly furnished the author by Professor Mortensen is so interesting and instructive as to be well worth copying substantially in full, leaving out the “Ices” in which no milk or cream is used and which are therefore not of special interest in connection with the purpose of this book—the use of more and better milk. [Illustration: Ice cream factory ] CLASSIFICATION ADOPTED AT IOWA EXPERIMENT STATION Considering the work of former writers as well as names used by business men, the following classification was worked out by the station: I. Plain Ice Creams. II. Nut Ice Creams. III. Fruit Ice Creams. IV. Bisque Ice Creams. V. Parfaits. VI. Mousses. VII. Puddings. VIII. Aufaits. IX. Lactos. Explanation and Formulas I. _Plain Ice Cream_ is a frozen product made from cream and sugar with or without a natural flavoring. Formulas are given for making ten gallons of finished ice cream. _Vanilla Ice Cream_: 5 gallons 25% cream 8 lbs. sugar 4 oz. vanilla extract _Chocolate Ice Cream_: 5 gallons cream 10 lbs. sugar 1½ lbs. bitter chocolate 4 oz. vanilla extract _Maple Ice Cream_: 5 gallons 25% cream 6 lbs. cane sugar 2 lbs. maple sugar 2 oz. caramel 4 oz. vanilla extract _Caramel Ice Cream_: 5 gallons 25% cream 8 lbs. sugar 12 oz. caramel 4 oz. vanilla extract _Coffee Ice Cream_: