376 Dr. T. Garnelley on the 



in support of his view. The following are the mean veloci- 

 ties calculated by him for several series of compounds : — 



Paraffins 1138 feet per second. 



Olefines 1155 „ „ 



Other hydrocarbons 1182 „ „ 



Aromatic hydrocarbons... 1243 „ „ 



Simple ethers 1131 „ „ 



Methvlic salts ... 1185 „ „ 



Ethylic salts 1140 „ „ 



Other ethereal salts 1125 „ „ 



• Anhydrides 1167 „ „ 



The alcohols and acids, however, give a much higher velo- 

 city (1300-1800 feet per second) at their boiling-points than 

 the above. But it is probable that these compounds are not 

 so exceptional as might at first sight appear ; for the acids of 

 the series C» H 2 « 2 exhibit a remarkable variation in the 

 volume-vapour which they furnish at different temperatures 

 (Bineau). Thus, formic acid at its boiling-point (101°) has a 

 vapour-density of 46 in place of 23, and gains its proper bulk 

 only at 213°. A similar thing also applies to acetic acid. If, 

 therefore, these facts be taken into consideration, formic acid 

 will show at its boiling-point a velocity of 1160 feet, and 

 acetic acid a velocity of 1134 feet per second. Herwig has 

 shown that ethyl-alcohol also possesses an exceptional vapour- 

 density at or near its boiling-point. 



Pictet has recently pointed out (Compt. Rend, lxxxviii. 

 pp. 855, 1315), as already stated, that there exists a simple 

 relation between the atomic weight, coefficient of expansion, 

 and melting-point of a solid body*. He also finds that a similar 

 relation (Corrupt. Rend, lxxxviii. p. 1315) exists between the 

 atomic weight, coefficient of expansion, and boiling-point of 

 a liquid ; thus : — 



(1) The length of oscillation of liquid molecules at the 



V p 



(2)*T=Kn; 



where a = mean coefficient of expansion between the melting- 

 arid boiling-points, d= density, k — constant, T = boiling-point 

 reckoned from —273° C, p = the physical molecular weight, 

 i. e. those weights of different liquids which absorb equal 

 quantities of heat on their temperature being raised from 0° 

 to 1° 0. ; and this, being inversely as the specific heat, is a 



* See also a paper by Wiebe on this subject in the Chemical News for 

 September 26, 1879, p. 154 



