52 Notices respecting New Books. 



Hence it results that Mariotte's law must not be regarded as a 

 mathematical expression of the perfect gaseous condition, for then 

 hydrogen gas would constitute a more than perfect elastic fluid. 



The elastic resistance which hydrogen presents, probably would 

 not increase indefinitely with the condensation ; a certain state of 

 condensation should exist in the vicinity of which Mariotte's law 

 would be followed quite strictly, then, the condensation increasing, 

 the hydrogen gas would depart again from the law, but in a direction 



contrary to its original aberrations, and the relation '^ would be- 



come greater than unity, and would continue to increase up to the 

 moment of the liquefaction of the gas. 



The temperature necessarily exercises a great influence upon this 

 phaenomenon, for carbonic acid gas, which at 0° departs from Ma- 

 riotte's law, even under pressures less than that of the atmosphere, 

 no longer departs from it at the temperature of 100°. Atmospheric 

 air itself departs from it much less between the same limits of den- 

 sity, at elevated temperatures, than at the ordinary temperature. It 

 is probable that a temperature might easily be obtained, at which 

 the divergences would become insensible, and at a temperature still 

 more elevated atmospheric air would again depart from Mariotte's 

 law, but in the contrary direction, that is, in the direction in which 

 hydrogen gas departs from it at ordinary temperatures. Similar 

 circumstances, but in an inverse order, would, it is not unlikely, pre- 

 sent themselves in hydrogen gas, if it were submitted to lower or 

 higher temperatures. 



It is probable then that Mariotte's law is a law which holds for 

 each gas in a certain state of density and at a definite temperature. 



(^) 



We have then -p^=l. The state of condensation remaining the 



same and the temperature decreasing, the compressibility becomes 

 greater than that which would result from the law, and the relation 

 is >-l. The temperature rising, the gas always taken in the same 

 state of condensation presents a lower degree of compressibility than 

 that which is deduced from the law ; the relation is < 1. Thus, the 



temperature at which the relation ^^~. becomes less than 1, after 



W 

 having been greater, varies necessarily with the density for each gas, 

 and is the more elevated in proportion as the density is more con- 

 siderable. 



It would be very interesting therefore to study the compressibility 

 of gases at elevated temperatures, a study very difficult and almost 



