A 250 cc. cylinder, or other tall vessel deep enough to float the sacchrometer, is suitable for making the measurements. Be sure to have the eye on the level of the liquid when making the readings. If no sugar is in the water, the reading on the hydrometer will be near zero. If there is sugar in the proportion of seven ounces to a gallon of water, the reading will be at the line marked 5.
SYRUPS FOR CANNING
| Berries | —30 degrees, or 3½ pounds of sugar to 1 gallon of water |
| Sweet cherries | —30 degrees |
| Sour cherries | —40 degrees |
| Peaches | —30 to 40 degrees |
| Pears | —20 to 30 degrees |
| Plums | —40 degrees |
Fig. 162. Barometer.
304. Hygroscopes. Hygroscopes are devices for measuring humidity. Forty-five to sixty per cent humidity is desirable in a house. This means forty-five to sixty per cent as much water as the air is capable of taking up at room temperature. Cold air is usually dryer than warmer air because cold air cannot take up as much humidity as warm air. This is analogous to the fact that warm water will dissolve more of some salts or of sugar than cold water.
305. Barometers. Barometers (Fig. 162) are devices which show changes in pressure and currents of air. Changes in the barometer usually indicate changes in the weather, and thus they are of interest to all persons. A decided fall in the mercury of a barometer usually precedes foul weather, while a rise indicates the approach of fair weather. When the pressure is low in any locality, air begins to rush toward that point as it would to fill a vacuum. So a fall in the barometer precedes the coming of a high wind or a rainstorm. A rise in the barometer precedes a calm, and since most rain is accompanied with wind, the calm is a time of fair weather.