VENTILATING THE HOME 23 



of discomfort, and makes work more difficult. The tem- 

 perature at which one feels comfortable depends on the 

 humidity. With the low degree of humidity usually found 

 in our houses, about 68 degrees is the best temperature. 

 But if enough moisture is added to raise the humidity to 

 50 or 60 per cent, one will feel just as comfortable at 65 

 degrees. The best temperature also depends on the occu- 

 pation and dress of the people living in the room. 



Thermometer. The temperature may be easily watched 

 by means of a thermometer. This consists of a glass tube 

 with a very small bore and a bulb at one end filled with mer- 

 cury, or some colored liquid, usually alcohol, which does 

 not freeze at ordinary temperatures. In making a ther- 

 mometer, the air is removed from the bore above the liquid, 

 so that there is nothing left to interfere with the motion of 

 the liquid. Heat causes the liquid to expand and rise in 

 the bore, which is marked off into degrees. In the common 

 Fahrenheit thermometer, the freezing point of water is 

 marked 32 degrees and the boiling point 212 degrees, and the 

 space between is divided into 180 degrees. In the Centi- 

 grade thermometer the freezing point is marked o, and the 

 boiling point 100 degrees, and the space between is divided 

 into 100 degrees. The Centigrade is much more convenient 

 and is widely used in Europe for general purposes and for 

 scientific work in this country. 



LABORATORY EXERCISE 3 



Purpose. To study and test thermometers. 



Apparatus. Fahrenheit thermometer, Centigrade thermom- 

 eter, beaker or tumbler, ice. 



Directions, i. Make drawings side by side of a Fahrenheit 

 and of a Centigrade thermometer. In each drawing mark the 

 following points : the freezing point of water ; the boiling point 

 of water (this may not appear on some thermometers) ; the 

 temperature of the body (hold finger on bulb or breathe on 



