154 Domestic Science 



surface of the mercury, at the various temperatures 

 noted. To obtain the amount of expansion of unit 

 volume corresponding to a change of 1 in temperature, 

 we proceed as follows : 



Suppose that the length of the air-column at 17 is 

 13'8 cm. and that at 39 it measures 14' 8 5 cm. Thus 

 we have that volume of air represented by 13 8 increasing 

 by (14-85 13- 8) = 1'05 when the temperature is raised 

 22. The increase for a rise of 1 is 1'05 ^ 22 = -048 

 (approx.). Each unit volume of air has increased by 

 048 * 13-8 = -0035 of its original volume at 17 for 

 each degree rise of temperature. 



Perform similar calculations to the above for each 

 pair of temperatures registered in your experiment, 

 using the original temperature as one of the pair, and 

 find the mean value of the results. This should be 

 of about the same magnitude as that found in the 

 example given. 



97. By making the original temperature by 

 floating ice in the water till its temperature has fallen 

 to freezing-point, we may find how much unit volume 

 of air expands when its temperature is raised by unit 

 amount. Very careful determinations of this quantity 

 have been made, and its value has been shown to be 

 0' 003665, or, expressed as a vulgar fraction, -%fo. By 

 replacing the air by other gases, it may be shown that 

 the same value is obtained for all of them, with slight 

 variations only. This observation may be put in the 

 form of a general statement : 



All gases expand by 0*003665 of their volumes 

 at C. when their temperatures are raised by 

 1C. 



This statement is true only when the pressure of the 



