96 CHEESE MAKING. 
197. Moisture in the Curing Room. 
A matter that has not received proper attention in curing 
American Cheddar cheese is the humidity of the air in the 
curing room. There are two instruments for measuring the 
humidity—the hygroscope and psychrometer. 
198. The Hygroscope. 
The hygroscope is an instrument consisting of a coil of ma- 
terial very sensitive to moisture. As it takes up from or gives 
off water to the atmosphere the coil moves a hand around a dial 
which shows the per cent of humidity. 
Fig. 49.—Hygrometer or Hygroscope. 
199. The Psychrometer. 
The psychrometer consists of two accurate thermometers. 
On the bulb of one is a wick which dips in a cup of distilled 
water. When the air is saturated it has all the water it will 
hold. If the air is not saturated, water will evaporate from the 
wick, and the dryer the air the greater the evaporation. As 
the water passes from around the bulb into the air it lowers the 
temperature. 
The thermometer should be fanned briskly with a good fan 
for three minutes, and then the reading taken quickly. First 
find the dry-bulb reading on the chart and then the wet-bulb 
reading in the next column; in the third column, opposite the 
