THREE STATES OF MATTER 



51 



There are two kinds of thermometer scales commonly 

 used. In one, the point to which the mercury column 

 sinks when submerged in melting ice is marked 

 32, and the point to which it rises at sea level 

 when immersed in unconfined steam, the boiling 

 point, is 212. The distance between the boil- 

 ing and freezing points is divided into 180 

 equal parts. Each one of these parts measures 

 a Fahrenheit degree of temperature: This is 

 the common household thermometer of this 

 country and England. 



Another kind of thermometer scale, which 

 is used almost exclusively in scientific work 

 and in those countries where the metric system 

 of weights and measures has been adopted, 

 is called the Centigrade. In this scale, the 

 point at which ice and snow melt is marked 

 and the point at which water boils, 100. A 

 degree Centigrade then is ^^ the distance the 

 column expands when heated from freezing 



Fig. 26. 



to boiling, instead of 

 -j-J^j- of this distance as 

 in the Fahrenheit scale. 

 There are a number of 

 different designs of 

 thermometers. Some 

 are for measuring very 

 high, others for measur- 

 ing very low, tempera- 

 tures. Thermometers 

 are also constructed so 

 as to be self-recording. 

 26. The Three States of Matter. There are three states 

 or conditions in which substances exist : solid, liquid and 



THERMOGRAPH. 



This device makes a continuous record of 

 the temperature for a week at a time. 



