The tube or stem contains a paper on which divisions called degrees are marked. The _0_ mark is usually the point reached by the surface of distilled water when the hydrometer is placed in this liquid. The less the density of the liquid, the lower the hydrometer sinks, for it displaces an amount of liquid equal to its own weight. The density of the liquid then can be determined by observing the mark to which it sinks. Specific-gravity hydrometers used in the household show the ratio of the weight of a given volume of liquid to the weight of the same volume of water at a definite temperature. Arbitrary scale hydrometers are used to indicate the concentration or strength of syrup, brines or milk. These are defined as lactometers and Baume hydrometers. A brine hydrometer is called a saltometer, and a syrup gage a sacchrometer. A jellometer, especially for making jelly, is sometimes used instead of a sacchrometer. The scale on this tells how much sugar to use in proportion to the amount of solids in the fruit juice without having to refer to a table. Some hydrometers are constant-volume hydrometers, and on these weights are placed always, to sink the hydrometer to the same depth in the liquid. TABLES FOR BRIX AND BALLING HYDROMETERS WHEN USED AT 20° C.* ==================+========================================= | SUGAR TO A QUART OF FRUIT JUICE TO MAKE READING ON THE | JELLY HYDROMETER +---------------------+------------------- Degrees | Pounds | Ounces ------------------+---------------------+------------------- 5. | | 8. 5.5 | | 9. 6.0 | | 9.6 6.5 | | 10.7 7.0 | | 11.6 7.5 | | 12.4 8.0 | | 13.2 8.5 | | 14.1 9.0 | | 15.0 9.5 | | 15.8 10.0 | 1. | 7.0 ------------------+---------------------+------------------- *When the reading for the fruit juice is determined the table shows how much sugar is used for juice of that specific gravity. TABLE SHOWING AMOUNT OF SUGAR PER GALLON