SECT, ii.] PROPERTIES OF STEAM. 73 



the lower ranges of temperature, and in the same manner as those on the force of 

 the steam of water ; but in describing them it will be some advantage to begin 

 with the experiments of Cagniard de la Tour, on the space alcohol occupies when 

 converted wholly into vapour. To ascertain this point, alcohol of the specific 

 gravity '837 was introduced into small tubes of glass, and hermetically sealed, 

 with a handle of glass attached to each tube. A tube was two-fifths filled with 

 alcohol, and then slowly and carefully heated : as the fluid dilated, its mobility 

 increased ; and when its volume was nearly doubled, it completely disappeared, 

 and became a vapour so transparent, that the tube appeared quite empty. On 

 leaving it to cool for a moment, a very thick cloud formed in its interior, and the 

 liquor returned to its first state. A second tube, nearly half occupied by the 

 same fluid, gave a similar result ; but a third, containing rather more than half, 

 burst. 



A process was next adopted to ascertain the pressure. It consisted in bending 

 a tube into a syphon, one leg to hold the liquid to be tried, and the other leg 

 containing air kept at a constant temperature of 73 by a cooling apparatus, and 

 separated from the fluid by mercury : both legs being sealed, the end containing 

 the liquid was heated, and when the liquid became vapour the diminution in the 

 bulk of the air was marked. 



Alcohol of the specific gravity '837 was reduced into vapour at a temperature of 

 497 in a space a little less than 3 times its original bulk; and 476 parts of 

 air were reduced to 4 ; indicating a pressure, according to M. Cagniard de la 

 Tour, of 119 atmospheres, or 3570 inches of mercury. 1 



105. The experiments on alcohol vapour at lower temperatures are collected 

 in the following table. 



1 By the same process as was adopted in finding the constants for calculating the force of the 

 steam of water (art. 86.) the formula for the vapour of alcohol of sufficient purity to boil at 

 173 is 



f- (* + 100 \ 6 

 " V 154-9 ) ' 



or, in logarithms, 



log./ = 6 (log. (t + 100) - 2-1900o) 5 



where t is the temperature of the vapour, and/ its force in inches of mercury. By this rule the 

 force for a temperature of 497 is 3280 inches : the experiment of M. Cagniard de la Tour 

 gives 3570 inches. 



