15 
based on the amount of absolute formaldehyde taken per cubic foot 
of space in charging the room. The weight per cubic foot is 
600 c. c. X 0.3566 
2000 
0.107 gm. TICOH. 
In experiment a the per cent would be 
0.0245 X 100 
0.107 
= 22.9. 
In b it would be 
0.0257 X 100 
0.107 
24.01. 
If a correction were not applied in a the result would be the same 
as in b. 
TEMPERATURE AND HUMIDITY. 
In order to determine the temperature and humidity the sling 
psychrometer was used. 0 This instrument consists of a pair of ther- 
mometers fastened to a piece of stiff sheet metal, provided with a 
handle at the end, by means of which the psychrometer can be rapidly 
whirled in the air. The bulb of one of the thermometers is covered 
with clean muslin, which before using is saturated with clean water. 
These two thermometers are known as the “dry’' and “wet” bulb 
thermometer, respectively. After dampening the wet bulb the psy- 
chrometer is rapidly whirled in the air for a few seconds and then the 
reading of the two thermometers quickly taken. This is repeated 
until the readings are no longer changed b y further whirling. The 
difference between the readings of the dry and wet bulb thermometers 
represents the depression of the wet-bulb thermometer, the degree of 
which is dependent upon the rate of evaporation, which in turn is 
dependent upon the amount of moisture in the atmosphere. The 
dry-bulb thermometer represents the temperature of the air. 
Knowing the temperature of the air and the depression of the wet- 
bulb thermometer, the relative humidity and finally the absolute 
humidity of the air can be ascertained by reference to psychrometric 
tables for obtaining the vapor pressure, relative humidity, and tem- 
perature of the dew-point, prepared by the Weather Bureau, United 
States Department of Agriculture. ° 
On account of the very important part that humidity plays in for- 
maldehyde disinfection the method of calculating this factor in one 
case is here given, e. g. : After whirling the psychrometer the dry-bulb 
thermometer registers 80° F. and the wet-bulb thermometer 73° F. 
The temperature of the dry-bulb thermometer (80° F.) represents the 
temperature of the air, and 7° F. represents the difference between the 
dry and wet bulb thermometers. By referring to the tables for esti- 
mating the relative humidity, we find that this difference of 7° F. at a 
temperature of 80° F. represents a relative humidity of 72 per cent. 
a Marvin, C. F. : Psychrometric tables for obtaining the vapor pressure, relative humidity, 
and temperature of the dew-point. U. S. Weather Bureau, no. 235, Washington, 1900. 
32507— No. 27—06 
•2 
