372 Dr. T. Carrielley on the 



tuent elements ; (2) On the position or arrangement of these 

 elements in the molecule. The first of these is more especially 

 rendered evident in homologous series, and the second in 

 isomeric compounds. Of the latter, however, we shall have 

 little or nothing to say in the present communication, as it is 

 intended, if opportunity admits, to refer to it at length in a 

 subsequent paper. 



The connexion between the boiling-points and composition 

 of organic compounds as pointed out by Kopp (Ann. Chem. 

 Pharm. xcvi. pp. 2, 230, xcviii. pp. 267, 367) is so well known 

 that it will be unnecessary to go into detail with regard to it. 

 It will be sufficient to mention his more important conclu- 

 sions : — (1) Analogous compounds presenting the same differ- 

 ence of composition very frequently differ by the same amount 

 in their boiling-points. A compound containing xG more or 

 less than another compound of analogous function generally 

 boils at a temperature 2 9x degrees higher or lower than the 

 latter ; and if it contains xH more or less, it generally boils 

 at 5x degrees lower or higher. These rules are best applied 

 in the case of compounds belonging to the same homologous 

 series. In the fatty acids C n H 2W , 2 and corresponding alco- 

 hols and compound ethers each addition of CH 2 raises the 

 boiling-point, on an average, by (29 — 2 x 5) = 19°, thus 

 agreeing with the above rule. (2) An acid CJE[ 2n 2 boils 40° 

 above the corresponding alcohol C n H 2w+2 0. (3) A compound 

 ether C w H 2ra 2 boils 82° below the acid isomeric with it. In 

 other series of compounds the difference in boiling-point cor- 

 responding to a difference of CH 2 is mostly regular ; but it is 

 sometimes more and sometimes less than 19. As a rule, the 

 greater the quantity of in a compound, the smaller is the 

 effect on the boiling-point of an increase of CH 2 in the com- 

 position. In the halogen compounds of the alcohol radicals 

 C n H 2n +i, a difference of CH 2 corresponds to a difference of 24 

 to 31 degrees in the boiling-point. As an instance of boiling- 

 points calculated in this way being subsequently verified by 

 experiment, I give the following : — 



Calculated. Found. 



Heptyl chloride 158 159-2"" 



„ bromide 179 178-5 



„ iodide 202 201*0 



„ acetate 189 191*5_ 



Notwithstanding, however, the near agreement of many of 

 the calculated with the experimental boiling-points, Linne- 

 mann (Ann. Ch. Pharm. clxii. p. 39), who has carefully de- 

 * C. F. Cross (Chem. Soc. Journ. 1877, ii. p. 128). 



