MATTER FORMED OF SMALL PARTICLES 107 



that of the tubes as far as the clip, is measured by filling 

 with water and then emptying the water into a graduated 

 vessel. 



The flask is thoroughly dried inside, and, with the cork 

 inserted and the clip opened, it is immersed for several minutes 

 in a vessel of boiling water, and the temperature observed. 

 The clip is then tightly closed and the flask quickly removed. 

 The flask is then placed with the mouth of the tube under 

 water of the same temperature as the room, the clip is 

 opened, and the flask is allowed to cool to the temperature of 

 the room. The level of the water outside is made to agree 

 with that of the water inside the flask, and at this point the 

 clip is closed. 



The water which has entered the flask is measured by 

 means of a graduated vessel, and, when its volume is deducted 

 from that of the flask, we obtain the volume of air, at the 

 temperature of the room, which will fill the flask when raised 

 to the temperature indicated by the thermometer. This will 

 be nearly the same as that of boiling 



water (100 C.). That is, we have the <$? CLIP 



means of measuring the change of 

 volume which occurs when a certain 

 volume of air undergoes a certain 



, , r SI V- THERMOMETER. 



change or temperature. The pressure 

 at each temperature is the same, as it 

 is directly exposed to the atmosphere 

 at the higher temperature, and is Fig. 38. 



brought into equilibrium with it, before 



measuring at the lower temperature. If accuracy is not ex- 

 pected, the thermometer may be dispensed with, and the higher 

 temperature taken as 100, but the use of a thermometer is 

 recommended. Suitably short ones may be obtained. 



The same method may be used for other gases. 



72. The Temperature-changes resulting from Changes in 

 the Volume of Gases. When temperature changes in gases are 

 in question, it must be remembered that the quantity of matter 

 constituting a given volume of gas is very small compared 

 with that of the containing vessel. A small change of 



