﻿Mr. F. Burden on the Boiling-points of Organic Bodies. 529 



is increased by ^3 of the velocity at 0° C. for each degree the 

 vapour is raised above this point. Therefore the velocity of 

 the molecules of any vapour at its boiling-point may be calcu- 

 lated by dividing the number in the fourth column by 273, mul- 

 tiplying the quotient by the number which indicates the boiling- 

 point, and adding the result to the number in the fourth column. 

 By this means were obtained the numbers in the sixth column 

 of the Tables. 



A comparison of the Tables for paraffins, olefines, aromatic 

 and other hydrocarbons, and the ethers (simple, mixed, and com- 

 pound) shows such a uniformity as clearly indicates a law. The 

 very small difference is less than might have been expected from 

 the difficulties in the way of obtaining the exact boiling-points. 



The law which I would deduce from these results may be ex- 

 pressed thus : — When any hydrocarbon or oxygen ether in a 

 state of vapour, under a barometric pressure of 760 millims., is 

 gradually cooled until the velocity of its molecules is reduced to 

 1140 feet per second, then, and not till then, has the force of 

 cohesion power to condense it into a liquid. 



It is an easy algebraical deduction from this that the boiling- 

 point of any of these bodies may be found by multiplying the 

 square root of the specific gravity by a constant which I have 

 calculated at 51*5, and deducting 273°; and whatever may be 

 thought of the hypothesis by which I have endeavoured to con- 

 nect the facts with molecular theories, the fact remains that by 

 this formula a Table of boiling-points for these bodies may be 

 constructed which will not differ from the results of experiment 

 more than these differ from one another. As a proof of this, I 

 have added a number of supplemental Tables, in which the cal- 

 culated boiling-points are compared with those observed by the 

 experimenter whose name follows. 



The remaining Tables show a considerable difference from 

 these results. The alcohols and acids especially give a much 

 higher velocity at their boiling-points. There are grounds for 

 believing, however, that these series are not so exceptional as 

 they at first appear. M. Bineau, in a paper in the Comptes 

 Rendus, states that the acids belonging to the series H OH (2/l-1) O 2 

 exhibit a remarkable variation in the volume of vapour which 

 they furnish at different temperatures. Thus formic acid at its 

 boiling-point has a specific gravity of 46 in place of 23, and re- 

 gains its proper bulk only at a temperature of 213°. Acetic 

 acid at its boiling-point has a specific gravity of 57 instead of 30. 

 If we make the alteration required by these facts in the Table for 

 acids, formic acid will show at its boiling-point a velocity of 

 1160 feet, and acetic acid a velocity of 1134 feet per second. 

 The experiments of M. H. Herwig show that ethyl alcohol 



