2 BULLETIN 494, U. S. DEPARTMENT OF AGRICULTURE. 
The condition of relative humidity in the curing rooms is deter- 
mined by the use of a sling psychrometer. Distilled water at the 
room temperature and clean cloth covers for the wet bulb have been 
used, and the directions recommended by the United States Weather 
Bureau for making accurate use of the sling psychrometer have been 
carefully followed. 
Studies were made to determine the humidity of various parts of 
empty and filled rooms under different conditions of ventilation, in 
order to establish intelligently a practicable and satisfactory method 
for making regular humidity observations. Preliminary determi- 
nations of the humidity outside the curing rooms and inside 
under different conditions of ventilation were made before any con- 
trol measures were attempted. Regular hourly tests of the relative 
humidity were made with the sling psychrometer in several parts of 
the room. In addition to these observations a hygrothermograph 
was placed in each room, in order to keep a continuous record of the 
conditions of temperature and humidity. 
OBJECT OF THE EXPERIMENTS. 
The object of the humidity studies was to determine the effect 
of various percentages of relative humidity in the curing rooms 
upon the curing processes of the lemons and to find out. if possible, 
the condition resulting in the most satisfactory curing, as shown by 
the color and texture of rind, the amount of shrinkage during storage, 
the color and condition of the calyx, or button, as it is commonly 
called, and the commercial quality of the fruits. 
PLAN OF THE WORK. 
Owing to the danger of injury to the lemons in the curing rooms 
and consequent heavy loss to the owners from improper conditions 
of temperature and humidity, it was decided to study the condition 
of relative humidity and its control in empty rooms and with small 
samples of fruit before attempting the control of humidity in rooms 
filled with lemons. 
In the first place, a study was made of the use of ventilation in 
controlling the condition of humidity in the curing rooms. At the 
time these studies were begun, in July, 1914, and during the follow- 
ing four or five months, the relative humidity of the atmosphere at the ^ 
place where these observations were made was normally very low. The 
humidity of the air in the warmest part of the day, usually about 2 
o'clock in the afternoon, sometimes dropped to less than 10 per cent. 
The coolest part of the day during this same season was usually 
about sunrise, and at that time the relative humidity was frequently 
about 90 per cent and often reached 100 per cent. It was decided to 
