102 On Relations of Liquids and their Saturated Vapours. 



shows cohesion of a molecule as the potential antecedent of the 

 inclination of its thermomolecular line. 



§ 53. M. Pierre has subjected four liquids to examination 

 which are closely related to each other by chemical substitution. 

 These are the Dutch liquid H 2 C CI and H^Cl^C, HC CI 2 , 

 H*'C'C1 B *. The boiling-points are 85°, 1 L4°2, 138°'5, and 

 153°-5; and if their lines issue from the ether-node, therespec- 



p 

 tive values of h are 187, 198, 212, 220; and -r is constant for 



all, being the same as in line No. 16 of the above Table; so it is 

 satisfactory evidence of their belonging to the ether-node. But 



- varies from 4*4 to 3*1; so there is no relation between mole- 



cular volume and slope of their lines. They are, however, con- 

 nected by the proportion which holds good between their tan- 

 gents h and their proportionate dilatations at the respective r 



temperatures. This ratio, -=— • -7 (of line No. 19, Table), is the 



same in all, and equal to 4*00 very nearly. If — is constant, 



as in line 12 of Table, then -7- • 77— is also constant ; so that 



dv Leo 



in these substitutional liquids the proportionate expansion for 

 increments of temperature respectively proportional to h or Co> 

 is the same in all. Thus, while the integral cohesion of a 

 molecule determines h as usual, the proportionate expansion 

 for intervals of t temperature is the same in all, although 

 there is no apparent relation between their absolute molecular 

 volumes. 



§ 54. In employing chemical symbols in this inquiry, it is 

 necessary to express the molecule of a compound in terms 

 of the molecules of its constituents, not of the atoms. This 

 is done by simply dividing the usual atomic formulae by 2, 

 unless when arsenic, phosphorus, selenium, or sulphur is in- 

 volved — the divisors being then 4 for the first three, and 6 

 for the last. 



It would be a boon to molecular physics if chemists could do 

 without the word atom, and substitute in its place molecule, half- 

 molecule, quarter-molecule, &c. Thus an atom of mercurv is a 

 molecule ; an atom of cadmium is a molecule ; an atom of oxygen 

 is half a molecule; an atom of phosphorus is one-fourth of a 

 molecule, &c. An atom of ether is a molecule, which denote by 

 the letter E. An atom of sulphurous acid is a molecule, which 

 denote by the letter U. An atom of sulphurous ether is a mo- 

 lecule, which denote by the letter Q. 



