12 EXPANSION OF GASES. 



Dr. Dalton confined a small portion of dry air over mercury 

 in a graduated tube. He marked the quantity by the scale, and 

 the temperature by the thermometer. He then placed the 

 whole in circumstances where it was uniformly heated up to a 

 certain temperature, and observed the expansion. Guy-Lussac's 

 apparatus was more complicated, but calculated to give very 

 precise results. He found that 1000 volumes of air, on being 

 heated from 32 to 212, become 1375, which agreed very 

 closely with the result of Dr. Dalton. Mr. James Crichton, of 

 Glasgow, has lately confirmed this determination, finding that 

 1000 volumes of air become 1374.8. 



It follows consequently that air at the freezing point expands 

 ^-ffth part of its bulk for every added degree of heat on Fah- 

 renheit's scale : that is 



480 cubic inches at 32 become 



481 33 



482 34 &c. 



increasing one cubic inch for every degree. A contraction of 

 one cubic inch occurs for every degree below 32. 

 480 cubic inches at 32 become 



479 31 



478 30 



477 29 &c. 



We can easily deduce, from this law, the expansion which a 

 certain volume of gas at a given temperature will undergo, by 

 heating it up to any particular temperature ; or the contraction 

 that will result from cooling. Air, of the temperature of freezing 

 water, has its volume doubled when heated 480 degrees, and 

 when heated 960 degrees, or twice as intensely, its volume is 

 trebled, which is the effect of a low red heat. 



Hydrogen gas, steam, and the vapour of sulphuric ether were 

 found to expand in the same proportion as air. It has hence 

 been concluded that the rate of expansion is the same in all 

 gaseous fluids. It is to be observed also, that in the same 

 air or gas, the rate of expansion continues uniform at all tem- 

 peratures. 



