﻿606 



Dr. A. Ferguson on the Boiling- Points and 



equation proposed by the present writer, agree still more 

 exactly with the observed values. Making due reservation 

 for the paucity of the experimental data, it would seem that 

 (xvi.) can be used with some confidence to calculate the 

 critical temperatures of the higher members of the series oE 

 normal paraffins. 



Proceeding on similar lines to those followed in deducing 

 boiling-point formulae for the paraffins, it would be possible 

 to obtain empirical equations for other homologous series. 

 But it is perhaps of more interest to consider certain of these 

 series as derived from the paraffins by substitution, thus 

 obtaining some insight into the question of replacement 

 values. Taking the primary alkyl bromides as an example, 

 defining the term " replacement value " as meaning the 

 difference between the boiling-point of the paraffin and that 

 of the corresponding bromide,, and denoting it by p, we find 

 that the graph between log p and log n is very closely linear. 

 This leads at once to the relation 



or since 



we may write 



^36=187-5, 



B = 6/ P -r-T^ 



• • (xvii.) 



where n as usual is the number of carbon atoms in the mole- 

 cule (the numerical values of the constants were read off 

 directly from the graph). From (xvii.), therefore, we may 

 calculate at once the boiling point of a given primary alkyl 

 bromide, if we know that of the corresponding paraffin. 

 The agreement between the observed and calculated values 

 is shown in Table IV. below. 



Table TV. 



Bromide. 



0p obs. 



6 b obs. 



0b calc. 



Difference. 



















C 3 H 7 Br 



228-0 



343-8 



3441 



+0-3 



C 4 H 9 Br 



2740 



3740 



376-0 



4-20 



C 5 H n Br 



3093 



4025 



402-2 



-0-3 



C G H 13 Br 



3420 



429 



427 8 



-1-2 



C-H 15 Br 



371-4 



452-0 



4517 



-0-3 



C 8 H 17 Br 



3986 



4740 



474-3 



4-0-3 



Average difference regardless of sign =0 o, 73. 

 * Observed values from Young, Phil. Mag. I. c. 



