468 Intelligence and Miscellaneous Articles, 



■which is a gas easily liquefied, has a far greater cohesion than hy- 

 drogen : as regards cohesion, hydrochloric acid is between hydrogen 

 and chlorine, and thus it is more difficult to liquefy than chlorine. 



(2) When the combination of two gases is accompanied by a con- 

 densation, the cohesion of the compound depends on the internal 

 pressure; and as the volume V+V is then greater than V", the 

 cohesion in the case of this gas is much greater than in the prece- 

 ding case. 



In like manner, gaseous combinations formed with condensation 

 of the elements are much more easily liquefied than compounds 

 formed without condensation. Thus it is that protoxide of nitrogen, 

 in which the condensation is equal to a third, could be liquefied ; 

 while binoxide of nitrogen, formed without condensation, has hitherto 

 resisted liquefaction. 



(3) When two compounds C and Q l corresponding to the same 

 volume W are formed of the same elements A and A', and only differ 

 by the volumes V and V of one of the elements A, the volume of 

 the second element being supposed invariable, there is a difference 

 between the cohesions p and p f of the two compounds represented by 

 the relation 



(p'- P )=(R+P)I^. 



In this case the cohesion increases proportionally to the number of 

 volumes of the element A added to the combination, and proportion- 

 ally to the cohesion of the element A increased by the external 

 pressure. 



Thus carbonic acid and carbonic oxide, with the same volume and 

 under the same conditions of temperature and pressure, contain the 

 same quantity of carbon ; carbonic acid contains more oxygen than 

 carbonic oxide. The cohesion of carbonic acid is greater than that 

 of carbonic oxide ; and carbonic acid is the only one of these two gases 

 which has hitherto been liquefied. 



Olefiant gas and marsh-gas present another instance. 



(4) If in a compound C an element A be replaced by another ele- 

 ment Aj which corresponds to the same volume as A, without the 

 volume W of the compound being modified, the element A' being 

 further supposed to be unchanged, a new compound C x is obtained 

 whose cohesion p x is different from p. 



If R x be the cohesion of the element A v we have from formula (2) 



Thus the difference in the cohesions of the two compounds, C x and C, 

 is proportional to the difference of the cohesions in the two elements 

 Aj and A. 



So that, substituting chlorine for hydrogen, bromine for chlorine, 

 iodine for bromine, the compounds obtained by substitution are less 

 volatile. — Comptes Rendu s,M<iYch. 23, 1868. 



