THE VAPOR FRICTION OF ISOMERIC ETHERS 1 



THE recorded experiments on the friction of vapors, by the 

 transpiration method, having been made with cumbersome 

 apparatus and at the temperature corresponding to the boil- 

 ing points of the substances, it was thought important to 

 devise a method whereby non-saturated vapors could be 

 studied at identical temperatures, for the purpose of ascer- 

 taining whether the constitution as well as the composition 

 of organic compounds influences the molecular volume, of 

 which the vapor-friction is a function. 



The apparatus used consists of a U-tube, one limb of which, 

 about 60 cm. long, has a bore of less than one tenth of a milli- 

 meter, while the bend and the other limb is just wide enough 

 to allow a column of mercury to descend unbroken. A stop- 

 cock and funnel-end are placed on the wider tube, which also 

 bears two marks about 50 cm. apart. The capacity of the tube 

 between these marks is accurately determined. The whole 

 apparatus can be heated uniformly, as it is surrounded by a 

 vapor-jacket. Before heating, the liquid to be studied is 

 poured into the tube and is vaporized as the temperature 

 rises, in such a manner as to expel all air and foreign gases. 

 A short column of mercury, of known length, is introduced 

 by means of the stop-cock, and in its descent forces the vapor 

 through the capillary; the time in which the lower meniscus 

 travels from the upper to the lower mark is ascertained by 

 means of a stop-watch. The method is easy and rapid, and 

 experiments with air gave results agreeing well among them- 

 selves and with the values obtained by the majority of previ- 



1 In collaboration with F. S. M. Peterson. Reprinted from Science, 21, 818 (1905). 



