DIVISIBILITY. 



25 



100 



o 



FIG. 3. 



~-BP 



212 



ception, expand or contract alike, when the temperature is 

 raised or lowered an equal number of degrees. 



Melting and boiling 1 . The temperature at which a solid sub- 

 stance is converted into a liquid and this into a gas, is of a 

 certain fixed degree or point for every substance, and the tem- 

 peratures at which this conversion takes place are known as 

 melting- (fusing-) and boiling-points. 



Not all matter is capable of existing in the three states of 

 aggregation, like water. Thus we know carbon in the solid 

 state only. 



Other substances, again, may assume two, but not the third 

 state. Some substances pass from the 

 solid directly into the gaseous state 

 (ammonic chloride, calomel), and the 

 process of converting a solid into a gas 

 directly, and this back again into a solid, 

 is called sublimation. 



Distillation is the conversion of a liquid 

 into a gas, and the recondensation of 

 the gas into a liquid. 



Thermometers are instruments indi- 

 cating different temperatures. Use is 

 made in their construction of the change 

 in volume of different substances by 

 the action of heat. The most common 

 thermometer is the mercury thermom- 

 eter. This instrument may be easily 

 constructed by filling with mercury a 

 glass tube, having a bulb at the lower 

 end, and placing it into boiling water. 

 The point to which the mercury rises 

 is marked B. P. (boiling-point), and 

 the tube sealed by fusion of the glass. 

 It is then placed in melting ice, and the 

 point to which the mercury sinks is 

 marked F. P. (freezing-point). The distance between the boil- 

 ing- and freezing-points is then divided into 100 degrees in the 

 so-called centigrade thermometer, or into 180 degrees in the 



FR~~. 



.32' 





Centigrade. Fahrenheit. 

 Thermometric scales. 



