Experimental cookery

crystallization." The rate of crystal growth is retarded because of adsorp- tion of the foreign substance by the crystals. If the substance is strongly adsorbed, crystallization may be retarded to such a rate that it is practically abolished, even though the solution is very supersaturated with the crystal- lizing substance. Since the adsorption prevents crystal growth, if a pre- cipitate is formed in the presence of a substance strongly adsorbed by the precipitate, it will crystallize in a much finer state of subdivision. Some- times the substance is more strongly adsorbed at one face than at another, so that this face grows more slowly than is customary and thus becomes comparatively larger in relation to other faces. This explains why crystals from pure solutions may have different shapes from those obtained from impure solutions. Speaking of sugar manufacture and crystallization of sucrose, Zitkowski says, "If the content of non-sugars in the solution is high enough crystallization may be prevented even though evaporation is carried to the point of dryness." The addition of other carbohydrates, such as dextrose, levulose, and starch, to sucrose solutions retards the crystal- lization of the sucrose. The extent to which they delay crystallization depends upon how strongly they are adsorbed and the proportion added. Other substances strongly adsorbed by sucrose crystals are fat and proteins. Hence, the use of butter, milk, and egg white all retard crystal growth. Crystallization o£ sucrose in sugar manufacture. In sugar manu- facture, when it is time to start crystallization in the mass of boiling sirup, the sugar boiler may lower the pressure, w^hich causes violent boiling or agitation, or he may add a sirup or water to change the concentration or temperature. He may also seed the sirup by adding a sufficient amount of small sugar crj^stals. The crystals when first formed are too small to be visible in the sirup but grow to visible size. This may be in a few moments. The sugar boiler controls the temperature, pressure, and density to bring the crystals to the desired size. If they are too small when finished, too much sugar is lost in washing the liquid from the crystals. If they are too large, the public does not care for them. Grades of sugar. Rice states that there is a surprising lack of informa- tion about the various grades of sucrose sugar produced and their specific uses, probably because the information has not been given general circula- tion. He lists 36 grades of sucrose, to which may be added many more grades made for a specific use with a particular equipment. The following classifications are those given by Rice. The refined sugar distributed for household use is somewhat smaller in grain size than that found some years ago, because the general demand has been for a more rapidly dissolving sugar. As the finer grain gives a whiter appearance, the tendency has been to produce a finer sugar. Fine Granulated is produced in the largest quantity of any grade. In the same class, each with increasingly finer grain or crystal size, are Extra-fine Granulated, Berry or Fruit or Fruit Powdered (it is designated by all GRADES OF SUGAR 53 these names), and Coating. Rice states the name Fruit Powdered has nothing to do with fruit nor is the sugar powdered. The "Coating" is used where unusually fine crystals are desired.