331 



With the increase of the temperature of observation, the experimental 

 difficulties of precision-measurements increase very rapidly : measure- 

 ments, which at room-temperature are of the utmost simplicity, are 

 often very difficult at 400° C, and commonly almost impossible 

 above 1000° C. This fact explains, why it has not been possible 

 until now, to communicate the results obtained, because only an 

 extended experience could prove to us the reliability of the method 

 used and the degree of accuracy obtainable. 



^ 2. Of all the methods hithertho described for the determination 

 of surface-tensions, the one most used is the method of measuring 

 the rise of the liquid in capillar}' tubes. Ramsay and Shields and 

 most of the investigators who have followed, have used this method. 

 It can however hardly be denied, that the absolute values A' x, 

 obtained by different observers with the same bquids and at the 

 same temperatures, show discrepancies of considerable magnitude. 

 Commonly this lack of agreement is attributed rather to the unequal 

 degree of chemical purity of the materials studied, than to the methods 

 employed. In many of the cases, however the discrepancies were 

 found with liquids, which can be obtained in a state of complete 

 purity without extraordinary trouble; so that one is easily inclined 

 to the belief that the method of measuring the capillary column 

 includes some sources of error which are not yet sufticiejitly known. 

 Possibly adhesion to the walls of the tubes plays a certain role in 

 it, or perhaps the influence of the angle between liquid and 

 solid material may be not completely negligible, as is ordinarily 

 assumed. 



However there is a decisive argument against the use of the 

 method of capillary ascension in the following investigations; the 

 walls of the capillary tubes used, were always damaged in a greater 

 or less degree by the action of the molten salts. A microscopical 

 examination of the walls of the tubes readily revealed this fact. 

 The method cannot be employed therefore at temperatures, exceeding 

 400^ C, because the liquids will always be contaminated and the results 

 will be almost valueless. Furthermore, the method assumes, that a rather 

 long column of liquid can be held throughout its full length at a 

 constant and uniform temperature. At high temperatures this condi- 

 tion can scarcely be fulfilled. The study of large platinum resistance- 

 furnaces has shown convincingly, that even in a central furnace- 

 tube of about 26 cm. length and 4,5 cm. diameter, with the heating- 

 coil wound inside, the space of really constant temperature is scarcely 



