94 



decrease of volume of about 2.5 percent, the capillary tube is sealed 

 at the bulb. After having been filled up with rock oil (by means 

 of an air pump) the instrument is ready for use. It may be pointed 

 out that only a few cc. of rock oil were used (comp. § 2. c). 



4. The petroleum used was prepared as follows: After having 

 been heated for 24 hours at 100° in contact with sodium, it was 

 distilled off from the metal. The part distilling below 175° was 

 not used; the remaining liquid was kept in contact with sodium 

 and used for the experiments. 



5. In order to get the metal free from oxide the method described 

 by v. Rossen Hoogendijk v. Bi.eiswijk ') may be followed. Small 

 pieces of the metal are put into benzene to which small portions 

 of amylalcohol are cautiously added. When the metal has become 

 bright it is put into the rock oil prepared as described above. 



6. We were not able to detect any impurity in 10 grams of the 

 metal. 



7. We used the (electric) thermostat described by Ernst Cohen 

 and Helderman in their investigations on cadmium'), which enabled 

 us to keep the temperature constant within some thousandths of a 

 degree. The thermometers used were compared with two instruments 

 checked by the Pliys. Techn. Reichsanstalt at Charlottenburg-Berlin. 



8. Before describing the measurements some remarks may be 

 made concerning the melting point of the metal experimented with. 



As is generally known, metals show, even if they are pure, a range 

 of fusion. This can be determined here very exactly by dilatometric 

 measurements as the process of melting is accompanied by a marked 

 change of volume (about 2.5 per cent). 



While the level of the meniscus remained constant at 97°. 12 

 during 17 hours, there occurred a strong dilatation at 97°. 22. 



The beginning of solidification of the molten metal was determined 

 in the following way : We put 25 cc. of sodium into a wide glass 

 tube which contained some rock oil in order to prevent the metal 

 from oxidation. A Beckmann thermometer (graduated to hundredths 

 of a degree) and a glass stirrer pass through a cork in the neck of 

 the tube. The whole was placed into an oil thermostat the temperature 



1) Zeitsclir. f. anorg. Chemie 74, 152 (1912). 



2) Zeitschr. f. physik. Chemie 87, 409 (1914). 



