106 



ELEMENTS OF LABORATORY WORK 



of a series of observations are recorded by marking along a b 

 the distances corresponding with the volumes, and along a c 

 the distances corresponding with the pressures, in each case 

 according to a given scale, and then erecting at these distances 

 perpendiculars which shall meet in points which mark by their 

 linear distance from a b and a c the condition of the body with 

 regard to volume and pressure at the respective observations. 

 It is obvious that an endless number of observations would 

 yield a continuous line instead of isolated points. Instead of 

 this, a number sufficiently large to detect any irregularity is 

 taken, and then the line joining the points recording these ob- 

 servations becomes the probably true representation of the 

 state at all intermediate stages. 



Such diagrams are given above (figs. 36, 37). 



Table showing Value of Product p v for Air at Various Pressures 

 and at Ordinary Temperatures.^ 



1 From Amagat's observations. 



71. The Measurement of the Change in Volume of a given 

 Mass of Air, when changed from the Temperature of the 

 Room to that of Boiling- Water, while the Pressure remains 

 Unaltered. A round- bottomed flask is tightly fitted with an 

 indiarubber cork, and its position in the welted neck of the 

 flask marked. This cork is to be fitted with a short thermo- 

 meter, and also with a short glass tube, to which is joined an 

 indiarubber tube with a clip, as shown (fig. 38). The glass tube 

 is not to project below the bottom of the cork. The capacity 

 of the flask up to the point marked on the neck, together 



